Pathways mediating descending control of spinal nociceptive transmission from the nuclei locus coeruleus (LC) and raphe magnus (NRM) in the cat

Summary We have previously reported that electrical stimulation in LC or NRM when tested on the activity of a multireceptive neurone in the spinal cord produced similar inhibitory actions. The present study aimed to define the pathways that mediate this descending inhibitory action in the spinal cord by pharmacological means and by making surgical lesions in the spinal cord or NRM. Attempts to differentiate pathways pharmacologically did not succeed since the i.v. administration of the 5-HT antagonists, methysergide and cinnanserin failed to antagonise descending inhibition evoked from either NRM or LC. Lesions involving a part or whole of the ipsilateral ventral quadrant reduced the inhibition produced from LC to a greater extent than that from NRM in 24 multireceptive neurones. In seven of these neurones stimulation in LC was without any effect after the lesion. In 23 multireceptive neurones recorded after making lesions that spared the ipsilateral ventral quadrant the effects of LC stimulation were unchanged. NRM effectiveness was reduced by an ipsilateral dorsolateral funiculus (DLF) lesion but required a bilateral DLF lesion for an almost complete abolition. Similar results were obtained when the effect of the various lesions were studied on the dorsal root potentials (DRPs) generated from LC or NRM. Lesions in the midline raphe complex, that included NRM, did not block the inhibitory action of LC stimulation. The inhibition produced from both these nuclei was additive whereas excitation was not. We conclude that LC actions in the spinal cord are mediated primarily through a pathway in the ipsilateral ventral quadrant whereas those from NRM are mediated through bilateral projections in DLF. Furthermore, although NRM plays no part in mediating LC actions and separate and independent pathways mediate their spinal action yet these apparently independent pathways have plenty of scope for interaction in the dorsal horn of the spinal cord itself.     

Mechanisms mediating the brain stem control of somatosensory transmission in the dorsal horn of the cat's spinal cord: an intracellular analysis

Summary The effect of brainstem stimulation was studied on neurones recorded intracellularly in the superficial and deeper laminae of the lumbosacral dorsal horn of the spinal cord in anaesthetised cats. Stimulation in the nucleus locus coeruleus (LC) produced a hyperpolarisation in 4/13 multireceptive neurones and produced a biphasic action consisting of a hyperpolarisation which was followed by a depolarisation in 3/13 neurones. These actions were produced irrespective of whether the multireceptive neurone was located in the superficial or deeper laminae of the dorsal horn. Stimulation failed to produce postsynaptic potentials in the remaining 6/13 multireceptive neurones. The amplitude of hyperpolarisation was increased by the passage of depolarising pulses through the recording microelectrode and decreased by hyperpolarising pulses. Stimulation in other brainstem areas such as, the lateral (FTL), paralemniscal (FTP) and central (FTC) divisions of the tegmental field and the nuclei raphe magnus (NRM) and reticularis magnocellularis (RMc) also hyperpolarised neurones in the dorsal horn. The polarity of hyperpolarisation evoked from some brainstem areas (FTP, FTC, RMc) could be reversed to depolarisation by the passive diffusion of ions from the recording microelectrode containing 3M-KCl. Brainstem (LC, NRM, FTP, FTL) stimulation generated long lasting (700 ms) hyperpolarisation on 4/4 selectively nocireceptive neurones of lamina I. There was, however, no effect on the activity of 5/5 neurones recorded in laminae I/II which in addition to receiving excitatory cutaneous inputs were inhibited by heat stimuli. Stimulation in LC also produced dorsal root potentials (DRPs) and reduced the amplitude of simultaneously recorded excitatory postsynaptic potentials (EPSPs) generated by the activation of primary afferent fibres in 3 multireceptive neurones. It is concluded that inhibition of nociceptive transmission in the spinal cord from LC and other brainstem areas may involve both pre- and postsynaptic mechanisms.     

Hypothalamic control of nocireceptive and other neurones in the marginal layer of the dorsal horn of the medulla (trigeminal nucleus caudalis) in the rat

Summary The effect of electrical stimulation of the preoptic area of the hypothalamus on the discharge of neurones in the marginal layer (lamina I) of the trigeminal nucleus caudalis was studied in the anaesthetised rat. There was a powerful suppression of the discharge evoked by noxious thermal stimuli in 49/49 specific nociceptor driven (nocireceptive) neurones. The inhibitory effect increased with graded increases in the intensity of preoptic stimulation. Stimulation, however, produced only a small reduction in the discharge of 14/17 cold receptive neurones. Thresholds for producing suppression of cold receptive neurones were generally higher than those for nocireceptive neurones. There was no effect on the activity of 12/12 low threshold mechanoreceptive neurones. The inhibitory action generated on the activity of nocireceptive neurones was reduced by electrolytic lesions in the nucleus raphe magnus (NRM) or the nucleus paragigantocellularis lateralis (PGCL) or the dorsolateral and ventrolateral periaqueductal gray matter (PAG). Lesions made in the ventral or dorsal aspect of PAG were, however, ineffective in reducing the suppression. It is suggested that the powerful descending inhibitory control of nociceptive transmission in the trigeminal nucleus caudalis is one of the neuronal mechanisms mediating analgesia from the preoptic area of the hypothalamus.     

Bulbar neurones with axonal projections to the trigeminal motor nucleus in the cat

Summary The location of bulbar neurones with axons projecting to the ipsi- and contralateral trigeminal motor nucleus were investigated in cats anaesthetized with sodium pentobarbital. Wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected in amounts of 5–24 nl. A volume-calibrated microelectrode was used for recording of evoked potentials and pressure injection of WGA-HRP. The injection site was guided by the position where a maximal antidromic response was evoked by electrical stimulation of the masseteric nerve. The survival time was 19–22 h. In preparations with the depot located in the masseteric subnucleus retrogradely stained neurones were found bilaterally in the borderzone of the trigeminal motor nucleus. Dense populations of stained neurones were observed ipsi- and contralaterally in the dorsal division of the main sensory trigeminal nucleus and the subnucleus- of the oral nucleus of the spinal trigeminal tract. Clusters of WGA-HRP-neurones were observed bilaterally in the lateral tegmental field at the level of the subnucleus- of the oral nucleus of the spinal trigeminal tract, bilaterally dorsal to the facial nucleus and contralaterally adjacent to the hypoglossal nucleus. No stained neurones were found in the gigantocellular reticular nucleus. A group of stained neurones was located in the marginal nucleus of brachium conjunctivum and some were found in the raphé nuclei near obex. Cell profiles were of two types: medium-sized neurones with a triangular profile and 30–40 m diameter, and fusiform neurones 10×50–70 m. Convergence of descending cortical and trigeminal afferent inputs on interneurones located in the lateral borderzone of the trigeminal motor nucleus, i.e. the intertrigeminal area, is reported in the preceding paper.List of Abbreviations BCM Marginal nucleus of the brachium conjunctivum - CAE Nucleus caeruleus - CI Inferior central nucleus - Cu Cuneate nucleus - Cux External cuneate nucleus - DMV Dorsal motor nucleus of the vagus - FTG Gigantocellular tegmental field - FTL Lateral tegmental field - FTP Paralemniscal tegmental field - Gr Gracile nucleus - Mb Medial borderzone of NVmt - NintV Intertrigeminal area - NsV Supratrigeminal nucleus (area) - NVmes Mesencephalic trigeminal nucleus - NVmt Trigeminal motor nucleus - NVsnpr Main sensory trigeminal nucleus - NVsnpr-d Main sensory trigeminal nucleus, dorsal division - NVsnpr-v Main sensory trigeminal nucleus, ventral division - NVspc Caudal nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - NVspo- Subnucleus- of the oral nucleus of the spinal trigeminal tract - V Spinal trigeminal tract - NVII Facial nucleus - VII Facial nerve - NXII Hypoglossal nucleus - XII Hypoglossal nerve - Ols Superior olive - Rb Rostral borderzone of NVmt - Vb Ventral borderzone of NVmt - VIN Inferior vestibular nucleus - VSL Superior vestibular nucleus, lateral division     

刺激猫红核对三叉神经脊束核尾侧亚核诱发放电的抑制作用及其途径

电刺激猫对侧或同侧红核对大多数三叉神经脊束核尾侧亚核神经元由刺激下齿槽神经引起的诱发放电有抑制作用,其中包括由伤害性刺激引起的诱发放电。向中缝大核内注射微量利多卡因后,红核的抑制时程明显缩短,甚至抑制作用完全消失。结果提示红核对三叉神经脊束核尾侧亚核的抑制作用主要是通过中缝大核实现的。     

Ascending projections from the nucleus of the brachium of the inferior colliculus in the cat

Summary Ascending projections from the nucleus of the brachium of the inferior colliculus (NBIC) in the cat were studied by the autoradiographic tracing method. Many fibers from the NBIC ascend ipsilaterally in the lateral tegmentum along the medial border of the brachium of the inferior colliculus. At midbrain levels, fibers from the NBIC end in the superior colliculus, the pretectum, the central gray and the peripeduncular tegmental region bilaterally with ipsilateral predominance. NBIC fibers to the superior colliculus are distributed densely to laminae VI an III throughout the whole rostrocaudal extent of the colliculus. In the pretectum, NBIC fibers terminate in the anterior and medial nuclei and the nucleus of the posterior commissure. NBIC fibers to the dorsal thalamus are distributed largely ipsilaterally. Many NBIC fibers end in the dorsal and medial divisions of the medial geniculate body, but few in the ventral division. The NBIC also sends fibers to the suprageniculate, limitans and lateralis posterior nuclei and the lateral portion of the posterior nuclear complex; these regions of termination of NBIC fibers constitute, as a whole, a single NBIC recipient sector. Additionally, the NBIC sends fibers to the centralis lateralis, medialis dorsalis, paraventricular and subparafascicular nuclei of the thalamus.Abbreviations APtC Pars compacta of anterior pretectal nucleus - APtR Pars reticulata of anterior pretectal nucleus - BIC Brachium of infertior colliculus - CG Central gray - CL Nucleus centralis lateralis - CP Cerebral peduncle - D Dorsal division of medial geniculate body - IC Inferior colliculus - LG Lateral geniculate body - LP Nucleus lateralis posterior - Lim Nucleus limitans - M Medial division of medial geniculate body - MD Nucleus medialis dorsalis - ML Medial lemniscus - NBIC Nucleus of brachium of inferior colliculus - NPC Nucleus of posterior commissure - PN Pontine nuclei - Ppr Peripeduncular region - Pt Pretectum - Pbg Parabigeminal nucleus - Pol Lateral portion of posterior nuclear complex - Pom Medial portion of posterior nuclear complex - Pul Pulvinar - Pv Nucleus paraventricularis - R Red nucleus - SC Superior colliculus - Sg Nucleus suprageniculatus - Spf Nucleus subparafascicularis - V Ventral division of medial geniculate body - VPL Nucleus ventralis posterolateralis - VPM Nucleus ventralis posteromedialis - II,III,IV,VI Tectal laminae     

A ventral lateral geniculate nucleus projection to the dorsal thalamus and the midbrain in the cat

Summary Retrograde tracing experiments using horseradish peroxidase (HRP) have been utilized for demonstrating the origin of efferent projections of the ventral lateral geniculate nucleus (LGNv) in the cat. HRP-positive cells identifiable as origins of thalamic projections were found in LGNv after injections of HRP into the lateral central intralaminar nucleus. The labeled cells appeared concentrated in the medial part of the internal division of LGNv, consisting of medium-sized multipolar cells. Contralaterally, fewer labeled cells were present in the corresponding part of LGNv. In the case of injections of HRP into the midbrain (pretectum and superior colliculus), labeled cells in LGNv were distributed almost exclusively in its external division, composed of mainly small cells. Little overlap of the distribution of HRP-positive cells was seen in LGNv between the thalamic and midbrain injection cases.Abbreviations Ad Dorsal anterior nucleus - Am Medial anterior nucleus - Av Ventral anterior nucleus - BSC Brachium of superior colliculus - Cg Central gray - Cl Lateral central nucleus - Ld Dorsal lateral nucleus - LGNd Dorsal lateral geniculate nucleus - LGNv Ventral lateral geniculate nucleus - Lp Posterior lateral nucleus - Md Dorsal medial nucleus - NIII Oculomotor complex - NOT Nucleus of the optio tract - NPC Nucleus of posterior commissure - OT Optic tract - P Posterior nucleus (Rioch 1929) - Pc Paracentral nucleus - Po Posterior group of thalamic nuclei - Pt Parataenial nucleus - PTa Anterior pretectal nucleus - PTm Medial pretectal nucleus - PTp Posterior pretectal nucleus - Pul Pulvinar - R Red nucleus - Rt Thalamic reticular nucleus - Sg Suprageniculate nucleus - Va Anterior ventral nucleus - VI Lateral ventral nucleus - Vm Medial ventral nucleus - Vpl Posterolateral ventral nucleus - Vpm Posteromedial ventral nucleus - Zi Zona incerta - II Layer of superior colliculus - III Layer of superior colliculus - IV (Kanaseki and Sprague, 1974)     

The cerebellotectal pathway in the grey squirrel

Summary In the well laminated superior colliculus of the grey squirrel the cells of origin of the crossed descending pathway to the brainstem gaze centers are contained within the inner sublamina of the intermediate grey layer. The technique of anterograde transport of horseradish peroxidase was used to determine whether the pathway from the cerebellum to the superior colliculus terminates in this region. The technique of retrograde transport of horseradish peroxidase was used to localize the source of this pathway within the cerebellum and to determine the morphology of the cerebellotectal neurons. The grey squirrel cerebellotectal pathway provides two terminal fields to the superior colliculus: a diffuse projection into the deep grey layer and a more concentrated, interrupted projection into the inner sublamina of the intermediate grey layer. The more concentrated projection overlies precisely the tectal sublamina that contains the cells of origin of the predorsal bundle. In contrast to animals with frontal eyes, the cerebellotectal pathway in the grey squirrel was found to project almost entirely contralaterally and the vast majority of the cells of origin for the pathway were distributed ventrally, in the caudal pole of the posterior interpositus nucleus and the adjacent region of the dentate. The labelled cells in both cerebellar nuclei were large and displayed similar morphologies.Abbreviations BC Brachium conjunctivum - BP Brachium pontis - CN Cochlear nuclei - D Dentate nucleus of the cerebellum - DLG Dorsal lateral geniculate nucleus - DLPG Dorsal lateral pontine grey - I Interpositus nucleus of the cerebellum - IC Inferior colliculus - III Oculomotor nucleus - IO Inferior olive - ITB Ipsilateral tectobulbar pathway - F Fastigial nucleus of the cerebellum - MG Medial geniculate nucleus - NRTP Nucleus reticularis tegmenti pontis - OPT Stratum opticum - PAG Periaqueductal grey - PDB Predorsal bundle - PB Parabigeminal nucleus - PH Prepositus hypoglossi - PUL Pulvinar nucleus - PT Pretectum - RN Red nucleus - SAI Stratum album intermediale (intermediate white layer) - SAP Stratum album profundum (deep white layer) - SGI Stratum griseum intermediale (intermediate grey layer) - SGP Stratum griseum profundum (deep grey layer) - SGS Stratum griseum superficiale (superficial grey layer) - SN Substantia nigra - sV Sensory division of the trigeminal complex - Ve Vestibular nuclei - VII Facial nucleus - VLG Ventral lateral geniculate nucleus     

GABAergic neurons comprise a major cell type in rodent visual relay nuclei: an immunocytochemical study of pretectal and accessory optic nuclei

Summary The enzyme glutamic acid decarboxylase (GAD) has been localized in sections of rodent brains (gerbil, rat) using conventional immunocytochemical techniques. Our findings demonstrate that large numbers of GAD-positive neurons and axon terminals (puncta) are present in the visual relay nuclei of the pretectum and the accessory optic system. The areas of highest density of these neurons are in the nucleus of the optic tract (NOT) of the pretectum, the dorsal and lateral terminal accessory optic nuclei (DTN, LTN), the ventral and dorsal subdivisions of the medial terminal accessory optic nucleus (MTNv, MTNd), and the interstitial nucleus of the posterior fibers of the superior fasciculus (inSFp). The findings indicate that 27% of the NOT neurons are GAD-positive and that these neurons are distributed over all of the NOT except the most superficial portion of the NOT caudally. The GAD-positive neurons of the NOT are statistically smaller (65.9 m²) than the total population of neurons of the NOT (84.3 [j,m2) but are otherwise indistinguishable in shape from the total neuron population. The other visual relay nuclei that have been analyzed (DTN, LTN, MTNv, MTNd, inSFp) are similar in that from 21% to 31% of their neurons are GAD-positive; these neurons are smaller in diameter and are more spherical than the total populations of neurons. The data further show that a large proportion of the neurons in these visual relay nuclei are contacted by GAD-positive axon terminals. It is estimated that approximately one-half of the neurons of the NOT and the terminal accessory optic nuclei receive a strong GABAergic input and have been called GAD-recipient neurons. Further, the morphology of the GAD-positive neurons combined with their similar distribution to the GAD-recipient neurons suggest that many of these neurons are acting as GABAergic, local circuit neurons. On the other hand, the large number of GAD-positive neurons in the NOT and MTN (20–30%) in relation to estimates of projection neurons (75%) presents the possibility that some may in fact be projection neurons. The overall findings provide morphological evidence which supports the general conclusion that GABAergic neurons play a significant role in modulating the output of the visually related NOT and terminal accessory optic nuclei.Abbreviations to Figures A Cerebral aqueduct - CP Posterior commissure - DK Nucleus of Darkschewitsch - DMN Deep mesencephalic nucleus - DTN Dorsal terminal nucleus, accessory optic system - HITr Habenulointerpeduncular tract - IGL Intergeniculate leaflet - INC Interstitial nucleus of Cajal - inSFp Interstitial nucleus, superior fasciculus, posterior fibers - LGNd Dorsal lateral geniculate nucleus - LGNv Ventral posterior nucleus - LP Lateral posterior nucleus - LTN Lateral terminal nucleus, accessory optic system - MB Mammillary body - MGN Medial geniculate nucleus - ML Medial lemniscus - MTNd Medial terminal nucleus, dorsal subdivision, accessory optic system - MTNv Medial terminal nucleus, ventral subdivision, accessory optic system - NOT Nucleus of the optic tract - NPC Nucleus of posterior commissure - OT Optic tract - PA Anterior pretectal nucleus - PAG Periaqueductal gray - pbp Nucleus parabrachialis pigmentosus - pC Cerebral peduncle - PM Medial pretectal nucleus - pn Nucleus paranigralis - PO Pretectal olivary nucleus - pp Posterior pretectal nucleus - PPN Peripeduncular nucleus - RNm Magnocellular division, red nucleus - RNp Parvocellular division, red nucleus - SC Superior colliculus - SGP Stratum griseum profundus, superior colliculus - SGS Stratum griseum superficiale, superior colliculus - SGM Stratum griseum medium, superior colliculus - SNc Substantia nigra, pars compacta - SNr Substantia nigra, pars reticulata - SO Stratum opticum, superior colliculus - VB Ventrobasal complex - ZI Zona incerta - 3N Oculomotor nerve, root fibers - 3V Third ventricle Supported by USPHS grants EY03642, NS15669, NS20228, EY03018, and NS15321. C.E.R. is the recipient of a Klingenstein Fellowship in the Neurosciences; R.H.I.B. is a Research Career Development Fellow of the National Eye Institute; and J.H.F. is a Research Career Development Fellow of the National Institutes of Health     

Nociceptive neurones in the superficial dorsal horn of cat lumbar spinal cord and their primary afferent inputs

Summary The morphology, background activity and responses to stimulation of primary afferent inputs of small neurones in the superficial dorsal horn which could only be excited from the skin by noxious stimulation were investigated by intracellular recording and ionophoresis of HRP. Neurones which gave similar responses to afferent stimulation were morphologically heterogeneous with respect to dendritic tree geometry and axonal projection, but were located around the lamina I/II border. Cutaneous excitatory receptive fields responding to noxious stimulation were generally small; most neurones had more extensive inhibitory fields responding to innocuous mechanical stimulation, in many cases overlapping the excitatory fields. Generally, stimulation of the excitatory field resulted in depolarization of the neurone and increased action potential firing, and stimulation of the inhibitory field resulted in hyperpolarization. Electrical stimulation of peripheral nerves revealed the existence of converging excitatory inputs carried by different fibre groups, and all neurones received an inhibitory input activated at low threshold. Excitatory responses were short-lived and occurred consistently in response to repeated stimulation. Central delay measurements gave evidence of a number of A monosynaptic inputs but only one A monosynaptic input; inhibitory inputs along A fibres were polysynaptic. The constant latency and regularity of the C response suggested monosynaptic connections. Low intensity stimulation of inhibitory inputs elicited a short-lived i.p.s.p. which increased in amplitude with increasing stimulus strength until it disappeared into a more prolonged hyperpolarization. This was associated with inhibition of background action potentials, and increased in duration with increasing stimulus strength up to C levels, indicating an A and C component. It is suggested that the level of excitability of these neurones depends on the relative amounts of concurrent noxious and innocuous stimulation, and that the resultant output, which is conveyed mainly to other neurones within the spinal cord, could modulate reflex action at the spinal level as well as affecting components of ascending sensory pathways.Supported by grant no. 11853/1.5 from the Wellcome Trust     

Organization of projections from the principal sensory trigeminal nucleus to the hypoglossal nucleus in the rat: an experimental light and electron microscopic study with axonal tracer techniques

Summary The organization of projections from the principal sensory trigeminal nucleus (PSN) to the hypoglossal nucleus (XII) in the rat was investigated at the light and electron microscopic level with retrograde and anterograde axonal tracer techniques. Microiontophoretic injection of horseradish peroxidase (HRP) into XII resulted in retrograde labeling of neurons confined to the dorsal one-third of the PSN. Labeled neurons were found bilaterally, although a clear preponderance for ipsilateral distribution was evident. Most labeled neurons were found in the medial one-third and caudal two-thirds of the PSN. Labeled neurons were large (30–50 m), round-to-pear shaped multipolar cells with dendrites oriented primarily in the mediolateral direction. At the electron microscopic level, HRP reaction product was found throughout the cytoplasm of soma and processes of PSN projection neurons. The ultrastructural characteristics of these cells included a round, centrally placed nucleus and invaginated nuclear envelope, sparse Nissl bodies, numerous free ribosomes, mitochondria, lysosomes and Golgi complexes. Three to four main stem dendrites gradually tapered from the cell body and numerous synaptic terminals impinged upon soma and dendrites of labeled PSN neurons. Microiontophoretic injection of tritiated amino acids or HRP into the dorsal one-third of the PSN resulted in moderately dense terminal labeling in XII bilaterally, although mainly ipsilaterally. Terminal labeling was found diffusely throughout all regions of XII. Fibers descended the brainstem in the dorsolateral reticular formation and entered XII ventrolaterally. At the electron microscopic level, boutons containing HRP reaction product were found to synapse on dendritic processes in XII. Labeled boutons were characterized by clear, spherical vesicles and an asymmetrical postsynaptic density. The significance of these results are discussed in relation to oro-lingual motor behavior.Abbreviations used in Figures Am Nucleus ambiguus - Ax Axon - Den Dendrite - dlRF dorsolateral reticular formation - G Golgi apparatus - IO Inferior olive - ITR Intertrigeminal region - IV Fourth ventricle - Lf Lipofuscin - LRN Lateral reticular nucleus - mRF Medial reticular formation - mPB Medial parabrachial nucleus - MV Motor trigeminal nucleus - MVN Medial vestibular nucleus - Nu Nucleus - PSN Principal sensory trigeminal nucleus - Py Pyramid - R Ribosomes - RF Reticular formation - SC Subnucleus caudalis - SI Subnucleus interpolaris - SO Subnucleus oralis - SOL Solitary tract nucleus - STR Supratrigeminal region - T Terminal - TB Trapezoid body - VII Facial nucleus - VIIn Facial nerve - X Dorsal vagal nucleus - XII Hypoglossal nucleus     

Influence of peripheral nerve injury on response properties of locus coeruleus neurons and coeruleospinal antinociception in the rat

Noradrenergic locus coeruleus (LC) is involved in pain regulation. We studied whether response properties of LC neurons or coeruleospinal antinociception are changed 10-14 days following development of experimental neuropathy. Experiments were performed in spinal nerve-ligated, sham-operated and unoperated male rats under sodium pentobarbital anesthesia. Recordings of LC neurons indicated that responses evoked by noxious somatic stimulation were enhanced in nerve-injured animals, while the effects of nerve injury on spontaneous activity or the response to noxious visceral stimulation were not significant. Microinjection of glutamate into the central nucleus of the amygdala produced a dose-related inhibition of the discharge rate of LC neurons in nerve-injured animals but no significant effect on discharge rates in control groups. Assessment of the heat-induced hind limb withdrawal latency indicated that spinal antinociception induced by electrical stimulation of the LC was significantly weaker in nerve-injured than control animals. The results indicate that peripheral neuropathy induces bidirectional changes in coeruleospinal inhibition of pain. Increased responses of LC neurons to noxious somatic stimulation are likely to promote feedback inhibition of neuropathic hypersensitivity, while the enhanced inhibition of the LC from the amygdala is likely to suppress noradrenergic pain inhibition and promote neuropathic pain. It is proposed that the decreased spinal antinociception induced by direct stimulation of the LC may be explained by pronociceptive changes in the non-noradrenergic systems previously described in peripheral neuropathy. Furthermore, we propose the hypothesis that emotions processed by the amygdala enhance pain due to increased inhibition of the LC in peripheral neuropathy.     

Contralateral corticofugal projections from the lateral,suprasylvian and ectosylvian gyri in the cat

Summary Contralateral corticofugal projections were investigated following multiple injections of a mixture of tritiated leucine and proline into the lateral, postlateral, suprasylvian and ectosylvian gyri of adult cats. Transported label was found in several Contralateral subcortical regions. These included the claustrum, caudate-putamen, thalamic intralaminar nuclei, pretectum, and the superior and inferior colliculi. These results show that the crossed corticofugal projections are common in the cat and are more extensive than has been previously reported.Abbreviations AC Anterior Commissure - AM Anteromedial Nucleus - AV Anteroventral Nucleus - Cd Caudate - CeM Central Medial Nucleus - CL Central Lateral Nucleus - Cl Claustrum - CM Centromedian Nucleus - GP Globus Pallidus - IC Inferior Colliculus - LD Laterodorsal Nucleus - LGd Dorsal Nucleus of the Lateral Geniculate complex - LP Lateral Posterior Nucleus - MD Mediodorsal Nucleus - MG Principal Nucleus of the Medial Geniculate complex - OT Optic Tract - Pa Anterior Pretectal Nucleus - Pl Pulvinar Nucleus - Put Putamen - Re Reuniens Nucleus - RN Red Nucleus - SC Superior Colliculus - SN Substantia Nigra - TRC Tegmental Reticular Nucleus, central division - VA Ventral Anterior Nucleus of thalamus - VB Ventrobasal Complex of thalamus - 3 Oculomotor Nucleus     

Histochemical mapping of succinic dehydrogenase and cytochrome oxidase in the pons and mesencephalon of squirrel monkey (Saimiri sciureus)

Summary The distribution of succinic dehydrogenase (SDA) and cytochrome oxidase (Cy. O) has been investigated in a series of sections through the pons and mesencephalon of the squirrel monkey brain. The localization of the two enzymes is very similar in the various regions and shows only slight differences. The epiphysis, however, shows moderately strong SDA and very mild Cy. O activity. Particularly strong SDA and Cy. O activity has been observed in the cell bodies of the various cranial nerve nuclei, nucleus colliculi inferioris, colliculi superioris, nuclei griseum pontis, reticularis tegmenti pontis, lemnisci lateralis pars dorsalis, geniculatum laterale and mediale, and pulvinaris. The enzyme content of the neurons and cell bodies is generally stronger compared to the neuropil which often occurs in smooth, loose, compact and reticulated forms. Any special relationship between the neurons and neuropil with regard to their enzyme content has, however, not been observed. The cranial nerves, and fibers of the brachium conjunctivum, corpus callosum, and fornix show very mild enzyme activity except those of the trapezoid complex which show moderate enzyme activity.Abbreviations Ann Nucleus annularis - APT Area praetectalis - AS Aquaeductus Sylvii - BC Brachium conjunctivum - BCI Brachium colliculi inferioris - BCS Brachium colliouli superioris - BP Brachium pontis - Cb Cerebellum - CC Corpus callosum - CCI Commissura colliculi inferioris - CCS Commissura colliculi superioris - Cd Nucleus caudatus - CHD Commissura hippocampi —parsdorsalis - CoI Colliculus inferior - CoP Commissura posterior - CoR Corona radiata - CoS Colliculus superior - CPf Cortex piriformis - CR Cortex retrosplenialis - DBC Decussatio brachii conjunctivi - DG Nucleus dorsalis tegmentalis(Gudden) - DR Nucleus dorsalis raphes - EP Epiphysis - F Fornix - FH Fimbria hippocampi - FLM Fasciculus longitudinalis medialis - FRPC Formatio reticularis pontis, parscaudalis - FRPO Formatio reticularis pontis, parsoralis - FRTM Formatio reticularis tegmentimesencephali - GC Substantia grisea centralis - GCd Substantia grisea centralis, parsdorsalis - GCv Substantia grisea centralis, parsventralis - GL Corpus geniculatum laterale - GM Corpus geniculatum mediate - GPO Griseum pontis - Hipp Hippocampus - HL Nucleus habenulae lateralis - HM Nucleus habenulae medialis - IP Nucleus interpeduncularis - LC Nucleus locus coeruleus - LCb Lingula cerebelli - Lim Nucleus limitans thalami - LL Lemniscus lateralis - LLD Nucleus lemnisci lateralis —parsdorsalis - LM Lemniscus medialis - LP Nucleus lateralis posterior thalami - MD Nucleus medialis dorsalis thalami - Mv Nucleus motorius n. trigemini - NCI Nucleus colliculi inferioris - NCS Nucleus centralis superior tegmenti - NCT Nucleus trapezoideum - NMv Nucleus tractus mesencephalicus n.trigemini - NR Nucleus ruber - NST Nucleus supratrochlearis - NSv Nucleus tractus spinalis n. trigemini - NiiiC Nucleus centralis n. oculomotorii - NiiiD Nucleus n. oculomotorii — pars dor-salis - NiiiV Nucleus n. oculomotorii — pars ven-tralis - Niv Nucleus n. troehlearis - nvm Nervus trigeminus, portio major - niv Nervus trochlearis - nvi Nervus abducens - OS Nucleus olivaris superior - P Nucleus posterior thalami - PbL Nucleus parabrachialis lateralis - PbM Nucleus parabrachialis medialis - PC Pedunculus cerebri - Pg Nucleus parabigeminalis - PUI Nucleus pulvinaris inferior thalami - PUL Nucleus pulvinaris lateralis thalami - PUM Nucleus pulvinaris medialis thalami - Py Tractus pyramidalis - Pv Nucleus principalis n. trigemini - R Nucleus reticularis thalami - RTP Nucleus reticularis tegmenti pontis - SNc Substantia nigra — pars compacta - SNd Substantia nigra — pars diffusa - Sub Subiculum - TCT Tractus corticotectalis - VR Nucleus ventralis raphes - III Ventriculus tertius - IV Ventriculus quartus     

Pontine neurones: Electrophysiological evidence of mediating carotid baroreceptor inputs to supraoptic neurones in rats

Summary Effects of pressure stimulation of the isolated carotid sinus, of occlusion of the common carotid artery and of tail pinching on the discharge activity of dorsal pontine area neurones and antidromically identified supraoptic neurosecretory neurones were studied in male rats anaesthetized with urethane. Electrical stimulation of the supraoptic nucleus (SON) produced antidromically conducted action potentials in a small number (24/384) of the units recorded in the dorsal pontine area. Pressure pulse stimulation of the isolated carotid sinus inhibited and carotid occlusion facilitated discharge activity in some of the tested dorsal pontine area neurones. In these responsive pontine neurones a transient excitation of grouped discharges was occasionally observed to concur with a small, spontaneous depression of the arterial blood pressure. Tail pinching excited some of these pontine neurones. Histological examination revealed that these responsive neurones were located in the dorsal pontine area close, but ventral and lateral, to the locus coeruleus. Electrical stimulation of the dorsal pons evoked a synaptically mediated excitation in 20 and inhibition in the other seven of the 52 SON units which were identified antidromically after stimulation of the pituitary stalk. Pressure stimulation of the isolated carotid sinus evoked an inhibition of discharge activity in some of the SON units which were excited by dorsal pontine area stimulation. All of the six tested units which showed inhibition after dorsal pontine area stimulation were unresponsive to pressure stimulation. Based on these data, it was concluded that at least some of the neurones which mediate carotid baroreceptor inputs to SON neurosecretory neurones are located in the dorsal pontine area close, but ventral and lateral, to the locus coeruleus and that these dorsal pontine area neurones also mediate converging synaptic inputs originating from somatic pain receptors.Supported by the grants Nos. 277035 and 410809 from the Ministry of Education, Science, and Culture, Japan     

Some electrophysiological properties of neurones of rat locus coeruleus.

1. Electrical activity of neurones of the locus coeruleus (LC) was studied in rats anaesthetized with urethane. By stimulating the dorsal pathway (DP) of axons of LC neurones in the mid=brain and observing field responses in the dorsolateral tegmentum of the pons, micro-electrodes were oriented to record unit discharges of LC neurones. They were evoked by DP stimulation mainly during the negative wave of the field response. 2. In the extraceullar records of spike discharges of LC meurones A and B spikes were distinguished. Very often the third component (C spike) was observed to ride on the descending stroke of the B spike. When present in the evoked discharge, it was also seen in the spontaneous discharge. 3. The DP-elicited unit discharges of LC neurones were classified into three types. The type 1 response had a fixed latency and a distinct A-B step. In the type 2 response the A spike occurred with a fixed latency, but the B spike followed it with variable delays, sometimes exceeding 5 msec. Being supported by the data of the collision test with spontaneous discharges, the type 1 and 2 responses were assumed to be due to antidromic excitation. The type 3 response whose characteristic was a wide variation of the latency from stimulation to stimulation was categorized as orthodromic excitation. Among seventy-four responses, forty-four were type 1, eight type 2 and twenty-two type 3. The conduction velocities of axons of LC neurones, determined from the latencies of the A spike of the type 1 and 2 responses, ranged from 0-3 to 1-4 m/sec with a mean of 0-69 m/sec. 4. Delay of the B spike in antidromic excitation was observed as a unique property of LC neurones. It was seen in the response to a single shock of DP (type 2 response) or in the response to the second shock of DP following the first one shortly (type 1 response). Since delay of the B spike in the type 2 response could not be ascribed to refractoriness, it was suggested that DP stimulation produced an inhibitory effect upon LC neurones. 5. LC neurones were invaded antidromically from the frontal or visual cortex, hippocampus, cerebellum or from varied combinations of them. About 70% of LC neurones were activated antidromically from the frontal cortex. The antidromic latencies ranged from 15 to 90 msec. 6. Some LC neurones were activated trans-synaptically by stimulation of those forebrain sites which received axonal projections from LC. All LC neurones examined were excited trans-synaptically by eletrical stimulation of the skin and the optic nerve. The sensory inputs arising from a vast area of the skin or those from the skin and the optic nerve were proved to converge on to the same LC neurones.     

刺激和损毁蓝斑核对网状巨细胞核神经元放电的影响

对水合氯醛浅麻醉的大鼠观察了电刺激或损毁蓝脏核(LC)对延髓网状巨细胞(NGC)神经元自发放电及伤害性反应的影响。结果如下:1)在143个NGC神经元中有63个伤害性神经元,12个会聚神经元,68个非伤害性神经元。在伤害性神经元中,伤害兴奋性的占2/3,伤害抑制性的占1/3。2)电刺激同侧及对侧LC可分别抑制64％及68％的伤害性神经元的伤害性反应,对大部分非伤害性神经元及会聚神经元无影响。3)损毁LC后,有45％(5/11个)伤害性神经元自发放电增加,67％(4/6个)伤害性神经元伤害性反应强度增加,且电刺激原LC位点的抑制作用减弱或消失。本工作说明,NGC伤害性神经元接受LC抑制性影响,对NGC及LC在抗伤害中的作用进行了讨论。     

The dendritic architecture of the medial terminal nucleus of the accessory optic system in the rat,rabbit, and cat

Summary The neurons of the medial terminal nucleus (MTN) of the accessory optic system (AOS) have been studied in the rat, rabbit and cat in Golgi-Cox and Golgi-Kopsch impregnated brain sections. The present anatomical findings permit a division of the MTN of these species into dorsal and ventral components (MTNd, MTNv), in agreement with other investigations. The MTNd contains predominantly linear-bipolar and linear-multipolar shaped neurons with cell bodies that measure in the range of 25–50 m. These neurons have 2 to 4 primary dendrites which, along with their smaller dendritic branches, are oriented in the plane of the long axis of the MTN (i.e. from ventromedial to dorsolateral). These linear-bipolar and linear-multipolar cells represent 70–80% of the neurons of the MTNd as seen in the Golgi impregnated sections. The remaining 20–30% of the MTNd neurons are nearly all multipolar in shape with somata measuring in the range of 15–25 m. An occasional multipolar neuron is larger, has a soma that measures around 30–60 m and has dendrites which extend outward from the cell body to cover large areas of the MTNd. There was considerable extension of the dendrites of MTNd neurons into the MTNv; however, the dendrites of MTNd neurons were not observed extending into the adjacent substantia nigra (SN) or ventral tegmental area (VTA) of Tsai (1925). Conversely, the dendrites of neurons in the neighboring SN and VTA course along the borders of the MTN but only occasionally extend into the MTN. The neuron population of the MTNv consists almost entirely of small-multipolar shaped cells with somata measuring from 15–25 m and dendritic trees resembling those described for multipolar cells of the MTNd. A small number of neurons of the ventral division are medium-multipolar in shape with cell bodies that measure approximately 30–60 m. Typically, these cells have several dendrites which extend ventrally within the MTNv and one or more dendrites that extend either across the MTNv or dorsally into the MTNd. Only a few linear-bipolar and linear-multipolar neurons were observed in the MTNv. The present findings are discussed in relation to anatomical, physiological, and histochemical studies on the MTN.Abbreviations to Figures CP Cerebral Peduncle - DTN Dorsal Terminal Nucleus - LG Lateral Geniculate Nucleus - LP Lateral Posterior Nucleus - MG Medial Geniculate Nucleus - ML Medial Lemniscus - MTNd Medial Terminal Nucleus, dorsal division - MTNv Medial Terminal Nucleus, ventral division - NTO Nucleus of the Optic Tract - PA Anterior Pretectal Nucleus - pn Nucleus Paranigralis - PP Posterior Pretectal Nucleus - Pul Pulvinar - PO Olivary Pretectal Nucleus - RN Red Nucleus - SGS Stratum Griseum Superficiale, Superior Colliculus - SN Substantia Nigra Supported by USPHS research grant EYO3642 from the National Eye Institute     

Direct projections from brainstem to telencephalon

Summary Ascending anterograde degeneration, as identified by the NautaGygax and Fink-Heimer methods, was traced following massive unilateral lesions placed at various levels of the brainstem reticular formation. Degenerating axons were traced through the subthalamus into the striatal complex with a few fibers reaching the deep layers of the frontal poles. In general, the distribution of this ascending tract is in agreement with results obtained with histochemical methods.Abbreviations AC Anterior commissure - BC Brachium conjunctivum - C Cerebellum - CG Central gray - C/P Caudate/Putamen - DBC Decussation of the Brachium conjunctivum - F Fornix - GP Globus pallidus - H Hippocampus - HI Habenulo-interpeduncular tract - IC Internal capsule - IP Interpeduncular nucleus - MB Mammillary body - MF Medial longitudinal fasciculus - ML Medial lemniscus - OB Olfactory bulb - OT Optic tract - P Pons - PC Posterior commissure - RN Red nucleus - S Septum - SC Superior colliculus - SN Substantia nigra - ST Subthalamus - ZI Zona incerta Research supported by grants #MH-19793-02 and MH-22095-01 from the National Institutes of Mental Health.     

The organization of descending tectofugal pathways underlying orienting in the frog,Rana pipiens

Summary In the frog, identical orienting deficits, involving a failure to turn toward stimuli in the ipsilateral hemifield, can be produced by small white matter lesions either in the caudal mesencephalon (Kostyk and Grobstein, 1987a) or in the caudal medulla (Masino and Grobstein, 1989). These findings suggest that descending turn signals may run uninterrupted from the midbrain to the spinal cord, and that something other than tectospinal axons may carry such signals. We here report studies to determine whether there is a tecto-recipient structure whose axons pass through the known critical lesion sites in the caudal mesencephalon and medulla, and whether damage to such a structure, sparing tectospinal pathways, produces an orienting deficit. Horseradish peroxidase (HRP) was applied to behaviorally effective lesions in the caudal medulla and the resulting labelling patterns compared with those resulting from application of HRP to nearby but behaviorally ineffective lesions at the same rostrocaudal level. A column of large cells in the ventrolateral midbrain tegmentum (including nMLF as well as parts of AV and PV) was robustly labelled in all effective lesion cases, and less frequently labelled in ineffective cases. A quantitative analysis showed labelling in this region to be more highly correlated with the existence of a behavioral deficit than that in any other brain region. Reconstructions of single retrogradely labelled cells in the rostral part of the column (nMLF) showed that they have dendrites in a position to receive tectal input and axons which pass through the critical lesion sites in both the caudal mesencephalon and the caudal medulla. Tegmental lesions, sparing the tectospinal tracts, produced ipsilateral turning deficits in cases where the large cell column was completely removed but did not when the column was spared. The findings support the hypothesis that tectofugal signals involved in orienting turns descend uninterrupted to the spinal cord on something other than tectospinal axons, and suggest that the critical projections derive from the large cell column of the ventral tegmentum.Abbreviations A Anterior Thalamic nucleus - AD Anterodorsal nucleus - AV Anteroventral nucleus - B Neuropil Bellonci - BO Basal Optic nucleus - CbN Cerebellar nucleus - Cb Cerebellum - CG Central Grey - CPG Corpus Geniculatum Thalamicum - DH Dorsal Horn - Ent Entopeduncular nucleus - Hb Habenular nucleus - IP Interpeduncular nucleus - LA Lateral Anterior Thalamic nucleus - LCC Tegmental Large Cell Column - LP nucleus Lateralis Profundus - LPD Lateral Posterodorsal nucleus - LPV Lateral Posteroventral nucleus - Mg Magnocellular Thalamic nucleus - NB Nucleus Bellonci - nMLF Nu. Medial Longitudinal Fasciculus - NLM Nu. Lentiformis Mesencephalicus - NPC Nucleus of the Posterior Commissure - OT Optic Tectum - PD Posterodorsal Tegmental nucleus - P Posterior Thalamic nucleus - PTG Pretectal Grey - PV Posteroventral Tegmental nucleus - Ris Isthmic Reticular nucleus - Rinf Inferior Reticular nucleus - Rmed Medial Reticular nucleus - Rsup Superior Reticular nucleus - SC Suprachiasmatic nucleus - SF Solitary fasciculus - SO Superior olivary nucleus - SV Secondary visceral nucleus - T6 Tectal layer 6 - T8 Tectal layer 8 - Tel Telencephalon - TP Posterior tubercle - TSL Torus semicircularis laminaris - TSmg Torus semicircularis magnocellular - TSp Torus semicircularis principalis - VH Ventral horn - VLD Ventrolateral dorsal nucleus - VLV Ventrolateral ventral nucleus - VM Ventromedial nucleus - 2V Secondary visceral nucleus - 3 Oculomotor nucleus - 4 Trochlear nucleus - 5me Mesencephalic trigeminal nucleus - 5m Trigeminal motor nucleus - 7m Facial motor nucleus - 8V Ventral vestibular nucleus - 8d Dorsal vestibular nucleus - n8 Vestibular nerve - 9m Glossopharyngeal motor nucleus