The influence of naloxone on the C fiber response of dorsal horn neurons and their inhibitory control by raphe magnus stimulation

In intact rats anesthetized with chloralose, the effects of naloxone were studied on the responses of spinal cord dorsal horn neurons to C fiber stimulation and upon the inhibition induced on these responses by stimulation of the nucleus raphé magnus (NRM). (1) A mean 44% facilitatory effect on responses to C fibers was observed for 12/19 units. (2) A mean 30% reduction of the inhibitory effects of NRM was found for 14/29 units. (3) However there is no clear relationship between these facilitatory effects and the diminution of the efficiency of NRM stimulation. These results demonstrate a facilitatory effect of naloxone upon the transmission of noxious messages at the spinal level and confirm that opiate endogenous substances are implicated in the inhibitory mechanisms activated by stimulation of NRM.     

Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. II. projections from the dorsolateral pontine tegmentum and raphe nuclei

The descending projections to the spinal cord arising from the dorsolateral pontine tegmentum and brain stem raphe nuclei have been investigated by means of the horseradish peroxidase (HRP) technique. Particular attention was taken to clarify the cells of origin and the funicular trajectory of these spinal projections.After injections of HRP into the spinal cord, a significant number of HRP labeled neurons were observed in the following dorsolateral pontine tegmental structures: (1) an area ventral to the nucleous cuneiformis; (2) principal locus coeruleus; (3) locus coeruleus α; (4) locus subcoeruleus; (5) Kölliker-Fuse nucleus; and (6) nucleus parabrachialis lateralis. As a rule, the projections are ipsilateral and the descending fibers course in the ventral part of the lateral funiculus.As concerns the raphe-spinal projections, we have demonstrated that the nucleus raphe dorsalis also sends axons to the cervical segment of the spinal cord. Furthermore, in accord with previous reports, HRP labeled cells were also identified in the nucleus raphe magnus, pallidus and obscurus, but not in the nucleus raphe centralis superior and pontis.On the whole the present study further clarified the organization of spinal projections from the dorsolateral pons and raphe nuclei and provided some additional anatomical data for the physiology of the tegmentospinal and raphe-spinal projections.     

A reaction time paradigm can simultaneously index spatial compatibility and neural pathway effects: A reply to Levy

Levy (Neuropsychologia22, 95–97, 1984, argues that our earlier study [Bradshawet al., Neuropsychologia20, 605–609, 1982] generated massive spatial compatibility effects, and that our inferences regarding neural pathway effects have neither empirical nor theoretical support and are predicated upon an unverified and unlikely assumption. We discuss in detail the nature of the interactions of stimulus position, response position, responding hand and field of stimulation (all left/right), and the differential contributions of spatial compatibility, anatomical connectivity and the arm position effect. Levy's arguments are found to be totally incorrect, and based upon a series of serious misconceptions.     

The postnatal development of functional properties of central vestibular neurons in the rat

The postnatal development of the responses of rat central vestibular neurons to horizontal angular acceleration was studied in the time and frequency domain. The resting discharge was very low and irregular during the first postnatal days, increased gradually and became more regular throughout the first month and reached adult values approximately by the end of the first month. The relative distribution of type I and type II units was the same in all age groups. Threshold for frequency increase to angular acceleration and sensitivity of unit responses became lower and higher, respectively, as time elapsed after birth. Adult values were reached approximately by the end of the first month. There was a slight tendency towards shorter time constants and smaller phase lags in one-month-old animals when compared with the younger animals. The results are discussed in conjunction with similar work performed in vestibular afferents and correlated with known morphological and behavioral studies.     

Discharge patterns of cat raphe neurons during sleep and waking

Discharge patterns of 21 single neurons of median and magnus raphe have been chronically recorded with tungsten microelectrodes stereotaxically placed in freely behaving unrestrained, unanesthetized cats. These neurons in the median and magnus raphe fired slowly during slow-wave sleep (SWS, 5.66 ± 4.24/sec), faster during awake (AWA, 11.11 ± 7.56/sec) and fastest during paradoxical sleep (PS, 15.87 ± 8.46/sec). Student'st-test (single-tailed) indicated that differences between SWS and AWA, SWS and PS were highly significant, and was significant between AWA and PS. The ratio of the firing rate of PS to SWS varied from 1.4 to 5 for the entire group. During PS the raphe units had a tendency to fire in burst. Interspike interval and joint interval distribution histograms (JIDH) also showed pronounced differences between the patterns of raphe activity during PS and SWS. Twelve units recorded from raphe magnus began to discharge more rapidly about 10–20 sec before the onset of the hippocampal theta rhythm characteristic of PS. This enhanced unit activity decreased concomitantly with the cessation of theta activity. These data indicate that neurons in raphe magnus might participate in the generation and maintenance of theta activity in dorsal hippocampus (DH) during PS. The lower single unit activity during SWS in comparison to AWA seems to disagree with Jouvet's ‘active serotonergic control of the SWS’; the increased raphe magnus activity prior to and during theta rhythm in DH gives some support to his ‘possible participation of the serotonergic caudal raphe system in PS genesis’.     

The dorsal and medial raphe projections to the substantia nigra in the rat: Electrophysiological, biochemical and behavioural observations

Electrophysiological experiments have been performed in urethane anaesthetized rats to investigate the projections from the dorsal (DRN) and medial raphe nuclei (MRN) to the substantia nigra. The biochemical and behavioural effects following discrete electrolytic lesions in the dorsal and medial raphe have also been investigated.Stimulation of the DRN produced predominantly inhibition of spontaneous activity of single neurones in the substantia nigra though some neurones were also excited. Bilateral stimulation of the substantia nigra produced antidromic spikes in DRN and MRN neurones.Lesions of the DRN and MRN produced a significant reduction in substantia nigra 5-HT concentration. Additionally, DRN lesions reduced striatal 5-HT, while MRN lesions reduced hippocampal 5-HT. Both lesions increased substantia nigra HVA concentration but did not affect DA concentration. Neither DRN nor MRN lesions affected striatal HVA, although DA levels were significantly elevated after 14 days.Animals with DRN lesions explored more than controls or MRN-lesioned animals. However, this behaviour was transient and was not observed after 14 days. On the other hand, MRN-lesioned animals were significantly hyperactive.These observations suggest that the substantia nigra receives a direct monosynaptic inhibitory input from the DRN and MRN and that these pathways use 5-HT as a neurotransmitter serving to tonically inhibit dopaminergic neurones. While 5-HT and dopamine appear to be involved in the control of motor behaviour, the precise relationship between these serotoninergic and dopaminergic systems in this respect is unclear.     

Early stages in the acquisition of a bimanual motor skill

Children and adults were trained and tested on a coordinated bimanual task that required them to rotate both hands either at the same or at different angular velocities in order to move the pen of an X-Y recorder along three angles of slant (45, 67 and 22 degrees), and to rotate both hands in the same clockwise direction rather than as mirror image movements. Initially both groups exhibited a tendency to rotate both hands at the same angular velocity even when the task required differential motor output from the two hands. With visual feedback, the tendency toward synchronization, such that both hands moved at the same angular velocity, was asymmetrically distributed, but under blindfolded conditions such asymmetries disappeared. Accuracy of performance increased with practice; and visual feedback enhanced accuracy of performance. The findings suggest that during early stages in the acquisition of a bimanual skill, unintended bilateral coactivation occurs at multiple levels of motor organization; mirror associated movements are only one simple subset of unintentional intermanual synergies.     

Head and body space to left and right,front and rear—I. Unidirectional competitive auditory stimulation

Very substantial right ear advantages (REAs) and right side advantages (RSAs) are reported for vocal shadowing latencies to laterally presented competitive verbal stimuli from a single earphone or loudspeaker. When head and body hemispace were dissociated by inducing a 90° head turn, with presentations either lateral or front-back with respect to the body, RSAs and REAs vanished, indicating that stimuli neither in the head nor in the body hemispace alone appear capable of generating any lateral asymmetries. However, a front-of-body (but not front-of-head) superiority compared with the rear was obtained. Most importantly, a powerful ventriloquism effect was obtained whereby a laterally placed dummy loudspeaker produced “pseudo”-RSAs with anterior-posterior-located sound sources. This suggests that it is the perceived position of a sound source rather than its actual position or ear of entry which determines asymmetries.     

Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. I. Origins of the reticulospinal tracts and their funicular trajectories

Using a retrograde tracer technique with horseradish peroxidase (HRP) attempts were made to determine the origins of reticulospinal tracts and their funicular trajectories. Reticulospinal tracts originating from the mesencephalic reticular formation (RF) were composed of: (1) descending projections arising from the cluster of cells located just lateral to the periaqueductal gray that course in the anterior funiculus (AF) and ventral part of the lateral funiculus (LF) with ipsilateral predominance; and (2) projections from the cluster of cells located dorsal to the brachium conjunctivum that course in the ipsilateral LF. Origins of the pontine reticulospinal tracts arising from the n. reticularis pontis oralis (Poo) have been divided qnto three parts: (1) medial one-third; (2) middle; and (3) ventrolateral. The axons from the medial part descend ipsilaterally via the medial part of the AF, while the axons from the ventrolateral part of the Poo give rise to diffuse descending projections in the AF and LF. The middle part of the Poo has been further subdivided into: (1) dorsal part that gives rise to spinal projections ipsilaterally in the ventrolateral funiculus (VLF); and (2) ventral, particularly its upper part, whose axons descend bilaterally via the DLF. Origins of reticulospinal tracts from the n. reticularis pontis caudalis (Poc) could be divided into three parts: (1) medial; (2) dorsolateral; and (3) ventrolateral. The medial part of the Poc is a source of axons via the medial part of the ipsilateral AF, while the ventrolateral part of the nucleus is a source of axons via the contralateral LF. The spinal projections from the dorsolateral part of the Poc appears to course diffusely in the AF and LF, but with DLF predominance. The n. reticularis gigantocellularis (Gc) was found to be a main medullary source of the spinal projections in the ipsilateral AF, while n. reticularis magnocellularis (Mc) is the major source of the fibers coursing ipsilaterally in the VLF. The most medial part of the Mc descends ipsilaterally via the medial part of the AF, while the ventrolateral part of the nucleus together with the n. reticularis lateralis of Meesen and Olszewski descends ipsilaterally via the DLF. It has also been found that the axons from the n. reticularis paramedianus pass via both the AF and LF with ipsilateral predominance, while the n. reticularis dorsalis and ventralis course via the LF with ipsilateral predominance.     

Facilitation of memory consolidation by vasopressin: Mediation by terminals of the dorsal noradrenergic bundle?

Administration of arginine-vasopressin (AVP, 5 micrograms, s.c.) immediately after the learning trial results in a long-term facilitation of a one-trial learning passive avoidance response. This effect of AVP is absent in animals with prior destruction of the ascending dorsal noradrenergic bundle by bilateral microinjection of 6-hydroxydopamine (6-OHDA). Postlearning local microinjection of a minute amount of AVP via chronically implanted cannulae into the locus coeruleus did not influence passive avoidance behavior. Upon injection into the midbrain dorsal raphe nucleus, however AVP facilitated passive avoidance behavior. This effect, however, was absent in rats receiving previous microinjection of 5,6-dihydroxytryptamine (5,6-DHT) or of 6-OHDA into the dorsal raphe nucleus. Bilateral 6-OHDA-induced lesions of the nucleus accumbens or 5,6-DHT-induced destruction of the dorsal raphe nucleus did not prevent the effect of AVP administered subcutaneously. The data suggest that vasopressin facilitates memory consolidation processes by modulating noradrenergic neurotransmission in terminals of the dorsal noradrenergic bundle. The serotoninergic neuronal network originating from the dorsal raphe nucleus has a secondary--norepinephrine-mediated--influence upon these processes.     

Selective amplitude histograms: a statistical approach to EEG-single unit relationships in generalized epilepsy.

Statistical analysis techniques that permit detection and quantification of EEG-single unit correlations were employed in a study of generalized penicillin epilepsy in the cat. Single unit activity was recorded in cerebral and cerebellar cortices and compared to the locally recorded EEG. It was found that during generalized paroxysmal activity the background EEG was significantly related to the time of occurrence of unit discharge. The degree of synchrony of various units differed but tended to increase as the duration and extent of paroxysmal activity increased. These relationships were usually not evident upon visual inspection of the original unprocessed data but were consistently detected by the analysis techniques described here. The results demonstrate the usefulness of a statistical approach to the analysis of single unit data and suggest that, not only is there a significant relationship between paroxysmal events and neuronal activity in generalized penicillin epilepsy, but also an overall trend to closer synchronization of EEG and single unit discharges during nonparoxysmal periods.     

Mnoaminergic reinnervation of the transected spinal cord by homologous fetal brain grafts.

It was shown that immature noradrenaline (NA) containing cells from locus coeruleus and 5-hydroxytryptamine (5-HT) containing cells from the raphé nuclei could survive homologous transplantation to adult spinal cords that were adrenergically denervated by a transverse lesion. Fully viable transplants were found at all postoperative time studied (0.5-4 months) and both NA and 5-HT cell bodies were found to produce a network of nerve terminals in the gray matter and axons in the white matter that reached cranially and caudally at least 10 mm from the cell bodies. The nerve fibers had a normal varicose appearance. It was concluded that NA and 5-HT axons can grow in adult lesioned white matter.     

Bisecting rods and lines: effects of horizontal and vertical posture on left-side underestimation by normal subjects

In Experiment I normal subjects performed the classical clinical line-bisection task, and demonstrated a left-side underestimation. In Experiment II subjects maintained fixation upon a central position and adjusted a rod passing through this fixation point so that both extremities were judged equal. The left-side underestimation was very much greater under these conditions, but was considerably reduced when retinal and gravitational coordinates were dissociated by making the subjects lie horizontally on one or other side. Subjects then demonstrated greater left-side and top-half underestimation when lying on the left than on the right side. Gravitational coordinates and the apparent locus of events in extrapersonal space are determinants of perceptual asymmetries at least as important as anatomical connectivities.     

Influence of midbrain stimulation on the excitability of neurons in the medial hypothalamus of the rat

Extracellular action potentials were recorded from 1098 neurons in the medial hypothalamus of pentobarbital anesthetized male rats. Their excitability was analyzed after single 1 Hz stimulation of the midbrain periaqueductal gray (PAG) or adjacent reticular formation. Cells were also examined for their response to median eminence (ME), amygdala, lateral septum (LS) or anterior hypothalamic/preoptic area (AHA/POA) stimulation. Antidromic invasion from midbrain stimulation was recorded from 110 neurons. Eight of these neurons showed features of axon branching and displayed antidromic invasion from both midbrain and amygdala (2 cells) or AHA/POA (6 cells). Many neurons with midbrain projections displayed orthodromic responses to stimulation in the amygdala, but few responded to AHA/POA or LS stimulation. Midbrain stimulation evoked orthodromic responses from 99 medial hypothalamic neurons. Many of these cells also displayed orthodromic responses to amygdala or AHA/POA stimulation, whereas a small number were activated antidromically by stimulation in these sites. None of 42 neurons activated antidromically from median eminence stimulation were responsive to midbrain stimulation. These results provide electrophysiological evidence of reciprocal connections between medial hypothalamic and medial midbrain areas, and indicate that medial hypothalamic neurons with midbrain connections are subject to influences from other extrahypothalamic areas.     

Neurohypophyseal peptides in the developing rat fetus

The quantitative changes in the content of the neurohypophyseal peptides, neurophysins, oxytocin, and vasopressin, were determined in the developing rat fetus. No neurohypophyseal peptides were found in 12-day fetuses. Neurophysins were first detected at day 13 and increased dramatically on day 14. The hormones vasopressin and oxytocin were not detected at day 13 and were measured at low levels at day 14. A 350-fold molar excess of neurophysin to hormones existed at day 14. From day 14 to day 19 the total content of neurophysin decreased while the content of vasopressin and oxytocin slowly increased. At day 19 there was a near molar equivalency between the content of neurophysin and that of the neurohypophyseal hormones. From day 18 to day 22 there was a sharp increase in the content of vasopressin while the content of neurophysin and oxytocin increased less dramatically. At term there was a molar excess of vasopressin, and the molar ratio of neurophysin to hormone at the time of delivery was 0.12. Measurement of vasopressin by different radioimmunoassays and by bioassay indicated no contribution of arginine-vasotocin to the measured vasopressin.     

Cross-cultural differences in hemisphericity: EEG asymmetry discriminates between Japanese and Westerners

This study was designed to test the hypothesis that Japanese subjects exhibit different patterns of resting EEG asymmetry compared with Westerners. EEG was recorded from the left and right temporal and parietal scalp regions in bilingual Japanese and Western subjects during eyes-open and eyes-closed rest periods before and after the performance of a series of cognitive tasks. Alpha activity was integrated and digitized. Japanese subjects were found to exhibit greater relative right-sided parietal activation during the eyes closed condition. This difference was found to be a function of greater left hemisphere activation among the Westerners. Various possible contributors to this cross-cultural differences are discussed.