红核在大脑皮质下行调控脊髓伤害感受性传递中的作用

以电刺激外周感受野诱发的大鼠脊髓背角WDR和NS神经元的晚串放电（C-反应）为指标，以串脉中刺激对侧大脑脚（CP）作为条件刺激，在C-反应受到明显抑制的神经元。分别观察了电解损毁红核（RN）和RN内注射兴奋性氨基酸的受体拮抗剂对刺激CP的下行抑制作用的影响。结果发现：损毁同侧RN后，刺激CP对C反应的抑制作用明显减弱，而损毁同侧RN背侧结构，对侧RN及假损毁RN均无此效应；RN内微量注射兴奋性氨基酸受体拮抗剂AP5和DNQX均可减弱刺激CP对C-反应的抑制。提示RN至少部分参与大脑皮质对脊髓伤害感受性传递的下行抑制作用。且以同侧RN为主；在与痛觉调制有关的皮质-RN通路中既有NMDA受体又有非NMDA受体的参与。     

Physiological properties of the output neurons in the deep layers of the superior colliculus of the rabbit

Using antidromic and orthodromic stimulation techniques, we studied physiological properties of the output neurons in the deep layers of the superior colliculus (SC) of 34 New Zealand rabbits. SC cells antidromicaly activated from the contralateral predorsal bundle (PDB) could also be activated by stimulation of the contralateral SC and ipsilateral central lateral nucleus of the thalamus (CL). The majority of these output neurons responded predominantly to the stimulation of the optic nerve, and only a small proportion of the output neurons were responsive to the stimulation of somatosensory and auditory (and/or vestibular) nerves. These results suggest that the orienting reflex might be elicited mainly by visual afferents in the rabbit The output SC neurons were subject to a 70 ms inhibition after antidromic stimulation of the PDB and a 40 ms inhibition after transsynaptic (orthodromic) stimulation of the optic chiasm (OX), indicating that the output neurons in the deep layers of the SC might be subject to at least two inhibitory circuits. These results are discussed in the context of a putative saccadic suppression circuitry model.     

Functional changes in thalamic relay neurons after focal cerebral infarct: a study of unit recordings from VPL neurons after MCA occlusion in rats.

We evaluated neuronal and histological changes of thalamic neurons 1, 4, 7, and 14 days after middle cerebral artery (MCA) occlusion in rats. After the somatosensory evoked potentials (SEPs) were measured from the cerebral cortex, the thalamic relay neuronal activities were recorded with a glass microelectrode following repetitive electrical stimulation of the contralateral forepaw at frequencies ranging from 1 to 50 Hz. In approximately 95% of the occluded rats, the ipsilateral somatosensory cortex and/or the subcortical somatosensory pathway developed infarct, resulting in SEP loss. We evaluated unit data from rats with abolished SEPs. The average firing rate of the nucleus ventralis posterolateralis (VPL) neurons in response to 25 stimulations at 30 Hz was significantly reduced to 0.1 spike/stimulus 1 day after MCA occlusion. In sham-operated rats, the same stimulation produced 0.7 spike/stimulus. The firing rate recovered to 0.4 spike/stimulus at 30-Hz stimulation 4 and 7 days after occlusion. This was followed by resuppression (0.1 spike/stimulus) 14 days after occlusion. Histological study revealed some abnormal neurons in the ipsilateral thalamus 7 days after occlusion. We were unable to find normal-shaped neurons in the VPL 14 days after occlusion. The present study demonstrates that cortical infarct produces functional and morphologic changes that gradually and progressively affect the ipsilateral thalamus, although incomplete transient recovery of somatosensory transmission may occur.     

Interactions between nucleus centrum medianum and gigantocellular nociceptive neurons

Cells in nucleus reticularis gigantocellularis (NGC) and nucleus centrum medianum (CM) are known to respond to tooth pulp stimulation, which is a nociceptive trigeminal stimulus. We examined the effect of stimulation of CM on this class of neurons in NGC. Thirty-nine percent of the 57 neurons tested were antidromically activated by stimulation of the ipsilateral CM, while 28% of the 40 neurons tested were antidromically activated from the contralateral CM. In addition, the spontaneous activity of seven NGC neurons was altered by stimulation of the ipsilateral CM, while five cells were affected by stimulation of the contralateral CM. These data suggest a complex and reciprocal interaction between neurons in NGC and CM.     

Acetylcholinesterase activity and acetylcholine effects in the cerebello-rubro-thalamic pathway of the cat

Unilateral transections of the brachium conjunctivum (BC) of cats resulted, after 2–3 weeks, in marked loss of acetylcholinesterase (AChE) activity from the contralateral red nucleus (RN) and ventral tier nuclei of the thalamus (VA-VL). Significant changes in activity were not observed in other locations. Sensitivity of RN neurons to iontophoretically applied acetylcholine (ACh) was studied under conditions which should maximize ACh sensitivity, including AChE inhibition, but ACh was found to have only a weak depressant effect on excitability or no effect at all. Intravenous physostigmine usually increased spontaneous activity of RN neurons, and sometimes increased potentials evoked by electrical stimulation of cerebellar nuclei, to a small extent. Anticholinergic drugs were found not to influence such evoked responses, except to reverse the effects of physostigmine. It is concluded that ACh is not a major transmitter in the excitatory cerebello-rubral tract in spite of the relationship of AChE to this pathway.     

Differential effect of thalamic and subthalamic lesions on early and late components of the somatic evoked potentials in man.

The effect of thalamic (Vo), subthalamic (Raprl) and combined (Vo-Raprl) unilateral lesions on early and late components of the somatic evoked potentials (SEPs) was investigated in a group of 16 cases operated on for the treatment of contralateral dyskinetic movements. In these cases, SEPs were independently produced by stimulation of the left and right median nerves and recorded at the corresponding somatosensory scalp regions. In addition, EEG frequencies and reaction time (RT) were independently and bilaterally determined. These tests were performed before and after operation and changes in SEP, EEG and RT were quantitatively evaluated in relation to both ipsilateral preoperative and contralateral postoperative controls. 1. All cases with either thalamic or combined lesions involving Vo nucleus showed an ipsilateral reduction in amplitude of late SEP components and EEG frequency and a contralateral increase RT. A peculiar form of "inattention" to the contralateral hand was also found. Quantitative evaluation of the total group showed significant amplitude reduction in late SEP components in relation to both ipsilateral preoperative and contralateral postoperative controls. Changes in EEG and RT were only significant in relation to their preoperative ipsilateral controls. 2. Two cases with subthalamic lesions and quick postoperative recovery showed no apparent change in SEP, EEG and RT. Three cases with similar lesions and slow postoperative recovery showed bilateral decrease in amplitude of late SEP components, EEG frequency and increase in RT. Clinical inattention to contralateral hand was also found in all these cases. Quantitative evaluation of the total group showed no significant changes in these parameters in relation to preoperative controls. 3. None of these lesions produced changes in early SEP components or somatosensory deficits at the contralateral hand.     

Morphology and synaptic connections of crossed corticostriatal neurons in the rat

The neurons of origin of the bilateral corticostriatal projection arising from the medial agranular cortical field in rats were identified by antidromic activation from contralateral neostriatal stimulation. The same cells were tested for antidromic activation from the contralateral neocortex and for orthodromic responses to stimulation of neocortex of the contralateral hemisphere or ipsilateral rostral thalamus. The neurons were then stained by intracellular injection of horseradish peroxidase. The laminar distribution of these neurons was compared to that of cortical cells stained retrogradely after injection of wheat germ agglutinin/HRP in the ipsilateral or contralateral neostriatum. The morphological features of physiologically identified corticostriatal neurons, their laminar organization, and their responses to stimulation were examined and compared with crossed corticocortical and brainstem-projecting cells. Crossed corticostriatal cells of the medial agranular cortical field were medium-sized pyramidal neurons found in the superficial part of layer V and in the deep part of layer III. Their basilar dendritic fields and initial intracortical axon collateral arborizations were coextensive with the layer defined by the distribution of corticostriatal neurons. The apical dendrites were thin and sparsely branched but consistently reached layer I, where they made a small arborization. These morphological features were shared by cortical neurons projecting to contralateral neocortex but not responding antidromically to stimulation of contralateral neostriatum, but they were not shared by brainstem-projecting cortical cells. Orthodromic responses to contralateral cortical stimulation consisted of brief excitatory postsynaptic potentials that were followed by powerful and longer-lasting inhibitory postsynaptic potentials. Corticostriatal cells also exhibited small excitatory postsynaptic potentials in response to thalamic stimulation. Many crossed corticostriatal neurons were also commissural corticocortical neurons. The results of reciprocal collision tests showed that this was due to the existence of two separate axonal branches, one projecting to contralateral neocortex and one to contralateral neostriatum. Intracellular staining of these neurons revealed ipsilateral axonal projections to the neostriatum and cortex.     

Brainstem influences on transmission of somatosensory information in the spinocervicothalamic pathway

The inhibition of somatosensory responses of lateral cervical nucleus neurons resulting from stimulation of the brainstem has been investigated. Single unit extracellular recordings were obtained from neurons in the lateral cervical nucleus of chloralose-anesthetized cats. Electrical stimulation of the periaqueductal gray, nucleus raphe magnus, nucleus cuneiformis, and nuclei reticularis gigantocellularis and magnocellularis was found to be very effective in inhibiting the responses of lateral cervical nucleus neurons evoked by electrical or tactile stimulation of the skin. Additional experiments were performed to determine whether the inhibitory effects were mediated in the spinal cord dorsal horn or in the lateral cervical nucleus. These experiments which examined the effect of brainstem stimulation on the responses induced by stimulation of the dorsolateral funiculus or on the antidromic latency of activation of lateral cervical nucleus neurons from thalamus, revealed that most and possibly all the inhibition could be accounted for by an action on the spinal cord. These results are consistent with other studies showing that spinocervical tract cells in the spinal cord can be inhibited by stimulation of the same brainstem regions.     

Synaptic pharmacology of the superior olivary complex studied in mouse brain slice.

The synaptic pharmacology of the lateral superior olive (LSO) and medial nucleus of the trapezoid body (MNTB) was examined in a brain slice preparation of the mouse superior olivary complex (SOC). Physiological responses in SOC were elicited by electrical stimulation of the trapezoid body ipsilateral or contralateral to the recording site, and bilateral interactions were investigated by combined ipsilateral and contralateral stimulation. Pharmacological effects were tested by bath application of amino acid agonists and antagonists. Neurons in MNTB were excited by contralateral stimulation and unaffected by ipsilateral stimulation. Excitatory amino acid (EAA) agonists--kainic acid (KA), quisqualic acid (QA), or L-glutamate--caused spontaneous firing at low concentrations and eliminated responses at higher concentrations in MNTB. The EAA agonist NMDA had relatively little effect at comparable concentrations. Stimulus-elicited responses were blocked by non-NMDA antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6,7-dinitro-quinoxaline-2,3-dione (DNQX) and by the nonspecific EAA antagonist kynurenic acid, but were unaffected by the NMDA antagonist D,L-2-amino-5-phosphonovaleric acid (APV). LSO neurons were typically excited by ipsilateral stimulation and inhibited by contralateral stimulation. In LSO, KA, QA, and L-glutamate caused spontaneous firing at low concentrations and eliminated responses at higher concentrations, and NMDA had relatively little effect. Excitatory responses in the vast majority of LSO neurons were blocked by CNQX, DNQX, or kynurenic acid. Some responses were also blocked by APV. LSO neurons were affected by glycine, and contralateral inhibition in LSO was completely blocked by strychnine. NMDA also blocked inhibition in LSO. These results indicate that excitation of both MNTB and LSO neurons is mediated primarily by an EAA neurotransmitter through non-NMDA receptors and that contralateral inhibition of LSO cells is mediated through strychnine-dependent glycine receptors. NMDA receptors may play a role in binaural processing by modulating contralateral inhibitory input to LSO.     

Cortical and spinal somatosensory input to the superior colliculus in the golden hamster: An anatomical and electrophysiological study

The horseradish peroxidase technique was used to identify the sources of somatosensory afferent fibers to the hamster's superior colliculus. These experiments demonstrated that the tectum receives axons from pyramidal cells in layer V of the ipsilateral sensorimotor cortex, contralateral lamina IV of all levels of the spinal cord, the contralateral dorsal column nuclei, lateral cervical nucleus, internal basilar nucleus, and nucleus of the spinal trigeminal tract. Electrical stimulation of the spinal cord coupled with extracellular single unit recordings concentrated, for the most part, in the posterior portion of the tectum revealed that such stimuli activated approximately 40% of the cells tested. Almost of these units were isolated ventral to the stratum opticum and 86% were responsive only to somatosensory stimulation. Analysis of the latencies of collicular responses obtained with two point spinal stimulation in intact hamsters and in animals subjected to somatosensory cortical and/or spinal damage indicated that the initial impulse elicited from most collicular cells was mediated by a polysynaptic pathways(s) which probably synapses in the dorsal column, lateral cervical, and/or internal basilar nuclei. Damage to the dorsal spinal cord and/or somatosensory cortex altered neither the incidence nor the response characteristics of spinally driven collicular neurons. This indicated that most somatosensory collicular cells also received input from the spinotectal fibers which travel in the ventrolateral quadrant. Electrical stimulation of somatosensory cortex activated about 20% of the cells tested in the ipsilateral superior colliculus. If cortical and spinal stimulation were delivered with an interstimulus interval ranging between 50 and 80 msec the response of the tectal neuron to the latter stimulus was suppressed in most cases. This was true regardless of the order of the stimulus pairing. Concurrent somato-sensory cortical shocks also suppressed responses to tactile stimuli for 21% of the cells tested.     

Excitation of wide-field ventralis posterolateralis neurons by contralateral thalamic stimulation

Interconnections between the nuclei ventralis posterolateralis (VPL) of the thalamus were studied using single-unit recordings from chloralose-anesthetized cats. Responses to stimulation of the contralateral VPL (cVPL) were evoked in 28.9% of the 218 neurons sampled. Those neurons responsive to cVPL stimulation were almost exclusively those with an ipsilateral component to their receptive fields, i.e., sb (receptive fields on both fore- or hind limbs) and m neurons (receptive fields on all four limbs), but not all neurons of either of these sets responded. Only 2 of 127 neurons with receptive fields on either the contralateral fore- or hind limb, sa neurons, responded to cVPL stimulation. cVPL-Responsive and -unresponsive m neurons differed little in the properties of their responses to skin stimulation and no differences were found in their distribution within the nucleus. Corticopetal neurons were found among both cVPL-responsive and -unresponsive neurons. VPL neurons were shown to exhibit coadunate behavior, like cortical neurons, but no evidence was found of modulation of m neuron excitability by local sa neurons. Responsiveness of m neurons to cVPL stimulation was blocked by application of ice or KCl crystals to the contralateral, but not the ipsilateral cortex. The possibility is considered that some responses to cVPL stimulation are antidromically conducted.     

Tonotopic and somatotopic representation in the nucleus basalis of the barn owl, Tyto alba

We have investigated the somatosensory and auditory representations in the nucleus basalis of the barn owl. In pigeons and finches, the nucleus basalis contains a representation of the beak and an auditory area. In the barn owl, the nucleus basalis also contains a complete somatotopic map of the head and body (as in the budgerigar), with a tonotopically organized auditory area in close proximity to the representation of the facial ruff and the preaural area. Recordings within and around the nucleus basalis revealed predominantly (about 80%) contralateral responses to somatic stimulation. The somatotopic map was oriented with the head down and rostral. Penetrations revealed an over-representation of the feet in dorsal basalis, followed by the rest of the body and wings more ventrally. Towards more rostral positions in nucleus basalis, responses from the head and beak predominated ventrally. The auditory response area was encountered below the region that responded to stimulation of the facial ruff and preaural flap regions and above a region responsive to beak stimulation. Auditory responses were tonotopically organized, with low best frequencies dorsal. Some penetrations yielded predominantly monaural responses with a fairly broad dynamic range, similar to those recorded from the ventral nucleus of the lateral lemniscus (LLV) and the cochlear nucleus angularis, whereas other penetrations contained predominantly binaural responses sensitive to interaural time differences (ITD). The physiological responses could be predicted on the basis of auditory projections to the nucleus basalis. An injection of biotinylated dextran amine (BDA) in the auditory region of nucleus basalis retrogradely labeled cells in both the caudal and rostral parts of the intermediate lateral lemniscal nucleus (LLIc and LLIr), and a few cells in the anterior part of the dorsal lateral lemniscal nucleus (LLDa, previously known as nucleus ventralis lemnisci lateralis, pars anterior, or VLVa) and in the posterior part of the dorsal lateral lemniscal nucleus (LLDp, previously known as nucleus ventralis lemnisci lateralis, pars posterior, or VLVp). A large injection of cholera toxin B-chain (CTB) into the nucleus basalis also produced dense retrograde labeling of a previously unidentified nucleus on the lateral aspect of the rostral pons, that we here call nucleus pontis externus (PE). An injection of CTB into PE produced dense retrograde labeling of the contralateral dorsal column nuclei and anterograde labeling of the ipsilateral lateral and dorsolateral nucleus basalis. Together these results define major somatosensory and auditory projections to the owl telencephalon that bypass the thalamus.     

Nitric oxide synthase/nicotinamide adenine dinucleotide phosphate-diaphorase in the brainstem trigeminal nuclei after transection of the masseteric nerve in rats.

In this study, the responses of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and neuronal nitric oxide synthase (nNOS) activities were quantitatively analyzed at different times in both ipsilateral and contralateral sides of trigeminal nuclei, after unilateral trigeminal muscle nerve transection, in Sprague Dawley rats. In the control animals, both NADPH-d- and nNOS-positive neurons were constitutively distributed in the rostrolateral solitary tract nucleus, dorsomedial part of trigeminal nucleus oralis (Vo/Sn), and superficial layers (VcI/II) of the trigeminal nucleus caudalis (Vc). NADPH-d-positive neurons appeared in the trigeminal mesencephalic nucleus ipsilaterally at 5 days (mean +/- SEM: 30.5 +/- 5.6) and were maintained until 8 weeks (33 +/- 10.6) after the denervation. In the trigeminal motor nucleus, NADPH-d-positive neurons appeared transiently and bilaterally, peaking at 1 week (663.5 +/- 156.2, ipsilateral side; 687.5 +/- 118.6, contralateral side) after unilateral denervation of the masseteric nerve. In both Vo/Sn and Vc, the number of NADPH-d-positive neurons in the control animals showed a decrease at 3 days but significantly increased from 5 days to 1 week and gradually fell to the control values by 8 weeks after the denervation. There were no significant differences observed between the two sides in either Vo/Sn or Vc. nNOS-positive neurons were similarly distributed and the numbers of labeled neurons were similar to those of NADPH-d-positive neurons after the denervation, although the changes were delayed by approximately 1 week. In conclusion, after unilateral nerve transection, the peak NADPH-d activity occurs 1 week prior to nNOS activity.     

Acute thrombotic infarction suppresses metabolic activation of ipsilateral somatosensory cortex: evidence for functional diaschisis

To study the effects of focal infarction on the capacity for functional activation of an ipsilateral somatosensory system remote from the lesion, we produced a small thrombotic infarct in the left frontal pole of male Wistar rats by a photochemical method. Five days later, the awake, restrained rats received tactile stimulation of the large whiskers (vibrissae) of the right side of the face, while a double-label 14C-autoradiographic study of local CMRglc (lCMRglc) and local CBF (lCBF) was performed. Unlesioned and unstimulated animals served as controls. In rats without frontal infarct, vibrissae stimulation led to activation of lCMRglc in the three synaptic relay stations of the barrel-field pathway (ipsilateral trigeminal medullary nucleus, contralateral ventrobasal thalamus, and contralateral barrel-field cortex). The mean increment in lCMRglc was 42% in lamina IV of barrel-field cortex and 49% in ventrobasal thalamus. Normalized lCBF tended to increase in superficial cortical laminae. In unstimulated animals with frontal infarct, lCMRglc was reduced by 20-30% throughout the ipsilateral barrel-field cortex as well as other ipsilateral cortical regions, but not in ventrobasal thalamus or other subcortical areas. In animals with frontal infarct subjected to contralateral vibrissae stimulation, a remarkable suppression of activation was observed throughout the barrel-field cortex so that left-less-than-right hemispheral lCMRglc asymmetry persisted despite stimulation. The ventrobasal thalamus, similarly, failed to increment its lCMRglc with vibrissae stimulation, whereas activation of the trigeminal nucleus was not suppressed. Similar trends were observed in the normalized lCBF data. These observations, which establish that a small frontal infarct is capable of suppressing normal physiological activation in remote ipsilateral brain structures, may have important implications with respect to suppression and recovery of function in human ischemic stroke.     

Characteristics of the human contra- versus ipsilateral SII cortex.

OBJECTIVES: In order to study the interaction between left- and right-sided stimuli on the activation of cortical somatosensory areas, we recorded somatosensory evoked magnetic fields (SEFs) from 8 healthy subjects with a 122 channel whole-scalp SQUID gradiometer. METHODS: Right and left median nerves were stimulated either alternately within the same run, with interstimulus intervals (ISIs) of 1.5 and 3 s, or separately in different runs with a 3 s ISI. In all conditions 4 cortical source areas were activated: the contralateral primary somatosensory cortex (SI), the contra- and ipsilateral secondary somatosensory cortices (SII) and the contralateral posterior parietal cortex (PPC). RESULTS: The earliest activity starting at 20 ms was generated solely in the SI cortex, whereas longer-latency activity was detected from all 4 source areas. The mean peak latencies for SII responses were 86-96 ms for contralateral and 94-97 ms for ipsilateral stimuli. However, the activation of right and left SII areas started at 61+/-3 and 62+/-3 ms to contralateral stimuli and at 66+/-2 and 63+/-2 ms to ipsilateral stimuli, suggesting a simultaneous commencing of activation of the SII areas. PPC sources were activated between 70 and 110 ms in different subjects. The 1.5 s ISI alternating stimuli elicited smaller SII responses than the 3 s ISI non-alternating stimuli, suggesting that a considerable part of the neural population in SII responds both to contra- and ipsilateral stimuli. The earliest SI responses did not differ between the two conditions. There were no significant differences in source locations of SII responses to ipsi- and contralateral stimuli in either hemisphere. Subaverages of the responses in sets of 30 responses revealed that amplitudes of the SII responses gradually attenuated during repetitive stimulation, whereas the amplitudes of the SI responses were not changed. CONCLUSIONS: The present results implicate that ipsi- and contralateral SII receive simultaneous input, and that a large part of SII neurons responds both to contra- and ipsilateral stimulation. The present data also highlight the different behavior of SI and SII cortices to repetitive stimuli.     

Anatomical and physiological properties of ipsilaterally projecting spinothalamic neurons in the second cervical segment of the cat's spinal cord

Anatomical and electrophysiological methods were used to investigate the projections and response properties of neurons in the second cervical (C2) spinal segment of the cat giving origin to a previously undescribed projection to the ipsilateral thalamus. The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify neurons in C2 giving rise to thalamic projections. Following large (3.0 μl) thalamic HRP injections, a large numbers of labeled neurons was observed in lateral laminae VII–VIII of C2 ipsilateral to the injections. They occurred as small clusters of cells along the longitudinal axis of C2. Labeled neurons were also observed contralaterally in the lateral cervical nucleus, dorsal horn (especially medial lamina VI), and loosely distributed in the ventral horn. The ipsilaterally projecting neurons were also labeled following small (0.2–0.5 μl) HRP injections restricted to individual spinothalamic terminal zones (intralaminar nuclei, ventrobasal complex-nucleus ventralis lateralis border zone, medial division of the posterior nuclei), indicating that as a group they project widely throughout the thalamus. Single unit recording methods were used to obtain complementary information on the functional properties of these neurons. The antidromic stimulation method was applied to identify units in C2 projecting to the ipsilateral thalamus in anesthetized, paralyzed cats. Three categories of ipsilaterally projecting C2 units were identified: (i) units not driven by any type of natural stimulation; (2) units having large cutaneous receptive fields (RFs) and wide dynamic response ranges (“widefield”), and (3) units with smaller RFs and varied properties (“other”). Widefield units with bilaterally symmetrical and asymmetrical RFs were observed. Co-stimulation of different portions of an excitatory RF produced summation of the unit response. Inhibitory RF components were identified in one third of the widefield units. Unit recordings after spinal tract lesions revealed that the afferent input passed via the ipsilateral lateral and/or ventral funiculi. Widefield unit responses to somatosensory stimuli could be inhibited by dorsal column conditioning stimulation. Several “other” units resembled widefield units, while a second group had small RFs restricted to the C2 dermatome. Possible functional roles of the projecting C2 neurons in somatosensory and non-specific systems are discussed.     

A first-order synaptic relay for taste fibers in the pontine brain stem of the cat

Microelectrode recordings were used to locate taste responsive neurons in a recently discovered area of termination of facial nerve afferents in the pontine brain stem of the cat. The neurons were activated by electrical stimulation of the chorda tympani nerve, followed by stimulation of the tongue with standard taste of solutions. Electrolytic lesions were made to mark the depth of active sites and electrode penetrations were reconstructed from frozen serial sections.

The taste neurons were found in a group of cells lying outside and dorsomedial to the main body of the principal sensory trigeminal nucleus. The small size of the taste responsive area and its relationship to typical trigeminal responses lend weight to the existence of a morphologically distinct nucleus intertrigeminails reported elsewhere.

The report of an uncrossed dorsal trigeminal tract linking this area to the thalamus would explain the ipsilateral taste projection found in the thalamus of cat and monkey. The contralateral taste projection in the rat would be consistent with the absence of a pontine termination for the facial afferents in that species. The existence of a taste are in the bulbar solitary nucleus of the cat was confirmed and its possible role in taste function is discussed.     

Independent efferent populations in the nucleus of the optic tract: An anatomical and physiological study in rat and cat

The efferent projections of the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic system (DTN) to the contralateral NOT-DTN, ipsilateral inferior olive (IO), ipsilateral nucleus prepositus hypoglossi (NPH), and ipsilateral dorsal lateral geniculate. nucleus (LGNd) were examined in pigmented rats and in cats by using anterograde and retrograde tract tracing, as well as extracellular recording and electrical stimulation. Anterograde tracing in the rat revealed a dense termination field of NOT-DTN efferents throughout the homologous contralateral territory. In both species three different cell populations, projecting to the contralateral NOT-DTN, ipsilateral IO, and ipsilateral LGNd, respectively, were distinguished by means of multiple retrograde tracing. No clear topographical segregation of the different NOT-DTN relay cell populations was observed. On the other hand, a large proportion (at least 60%) of NOT-DTN neurons projecting to the ipsilateral NPH were found to bifurcate upon the IO in the rat. Electrophysiologically, NOT-DTN neurons projecting to the IO were identified by their directionally selective responses. Such neurons were never activated by electrical stimulation of either the contralateral NOT-DTN or the ipsilateral LGNd. Neurons antidromically activated from the contralateral NOT-DTN could not be activated from the ipsilateral LGNd. Thus, in both cat and rat the NOT-DTN includes at least three independent relay cell populations. As a consequence, the NOT-DTN must serve functions additional to the generation of eye movements during optokinetic nystagnus, a function subserved by the directionally selective NOT-DTN cells. © 1995 Wiley-Liss, Inc.     

Effects of contralateral superior laryngeal nerve stimulation on dorsal medullary inspiratory neurons

The effects of superior laryngeal nerve (SLN) stimulation on phrenic (PHR) nerve activity and on activity of dorsal respiratory group (DRG) inspiratory (I) neurons contralateral to the stimulus were examined in decerebrate, paralyzed cats. Stimulation caused bilateral PHR suppression followed by recovery at ca. 30 ms. Most DRG neurons (70%) contralateral to the stimulus were inhibited, but average onset of inhibition lagged that of PHR suppression. This contrasts sharply with the observation in an earlier study that inhibition of ipsilateral I neurons on the average preceded PHR suppression. The remaining neurons (30%) were not inhibited. Only 22% of contralateral neurons were excited by SLN stimulation, in contrast to 52% of ipsilateral neurons. Thus, contralateral DRG I neurons do not mediate the onset of bilateral PHR suppression by SLN stimulation and are probably inhibited through a longer pathway than that for the ipsilateral unit responses.     

Red nucleus neurons actively contribute to the acquisition of classically conditioned eyelid responses in rabbits

The red nucleus (RN) is a midbrain premotor center that has been suggested as being involved in the acquisition and/or performance of classically conditioned nictitating membrane/eyelid responses. We recorded in rabbits the activity of RN and pararubral neurons during classical eyeblink conditioning using a delay paradigm. Neurons were identified by their antidromic activation from contralateral facial and accessory abducens nuclei and by their synaptic activation from the ipsilateral motor cortex (MC) and the contralateral cerebellar interpositus (IP) nucleus. For conditioning, we used a tone as a conditioned stimulus (CS) followed 250 ms later by a 100 ms air puff as an unconditioned stimulus (US) coterminating with it. Conditioned responses (CRs) were determined from the evoked changes in the electromyographic activity of the orbicularis oculi (OO) muscle. Recorded neurons were classified by their antidromic activation and by their changes in firing rate during the CS-US interval. Identified neurons increased their firing rates in relation to the successive conditioning sessions, but their discharge rates were related more to the EMG activity of the OO muscle than to the learning curves. Reversible inactivation of the IP nucleus with lidocaine during conditioning evoked a complete disappearance of both conditioned and unconditioned eyelid responses, and a progressive decrease in CR-related activity of RN neurons. In contrast, MC inactivation evoked a decrease in the acquisition process and an initial disfacilitation of neuronal firing (which was later recovered), together with the late appearance of CRs. Thus, RN neurons presented learning-dependent changes in activity following MC inactivation.