The corticothalamic projection from the second somatosensory cortical area in the cat an experimental study with silver impregnation methods

Summary The corticothalamic projection from the anterior ectosylvian gyrus in the cat has been studied with the silver impregnation method of Nauta. The second somatosensory cortical area (SII) projects upon the ipsilateral nucleus ventralis posterolateralis (VPL), nucleus ventralis posteromedialis (VPM), the posterior thalamic region (PO) and to a slight extent upon the reticular nucleus of the thalamus (R), the centrum medianum (CM), the parvocellular part of VPM (VPMpc) and the nucleus ventralis posterior inferior (VPI). A somatotopical arrangement in the projection upon the ventro-basal (VB) complex has been demonstrated and a topical arrangement in the corticothalamic fibers from SII to PO is also evident. The transitional area between SII and the second auditory cortex sends fibers mainly to the entire magnocellular part of the medial geniculate body (MGmc) and to a lesser degree to the principal division of this nucleus (MGp). The corticofugal fibers from SII follow various and rather complicated circuitous routes before they end in the different thalamic nuclei. The experimental findings are discussed in the light of recent anatomical and physiological observations. It is shown that zones B and C of SII which have been shown by Carreras and Andersson (1963) to possess a large number of place and modality specific neurons project upon the VB-complex. On the other hand, zone A which contains a majority of place and modality unspecific neurons sends its fibers exclusively to PO. Finally the problem of thalamocortical projections to SII is briefly discussed. Addendum: After the present paper had been submitted for publication the work of DeVito (1967) came to the author's knowledge. Several of the findings made by DeVito have been confirmed in the present study. On the other hand, DeVito has not considered Carreras and Andersson's zones A, B and C in SII and she does not describe a somatotopical arrangement in the projection from SII upon the VB complex and PO.     

The termination of the spinothalamic tract in the cat an experimental study with silver impregnation methods

Summary The termination of the spinothalamic tract (STT) in the cat has been studied light microscopically in Fink-Heimer and Nauta impregnated sections. Following lesions of the STT at various rostrocaudal levels of the spinal cord the degenerating fibres in the thalamus and subthalamus were mapped, mainly in transverse sections. The cervicothalamic tract was not injured by the lesions.The spinothalamic fibres enter the diencephalon through the mesencephalic reticular formation and terminate in the following regions: the medial portion of the magnocellular part of the medial geniculate body (MGmc), the ventrolateral portion of the medial part of the posterior nuclear complex (PO_m), the caudolateral and medial parts of the zona incerta (ZI), the nucleus centralis medialis (CeM), the nucleus parafascicularis (Pf), the lateral part of the nucleus centralis lateralis (CL), the medial and rostrolateral parts of the nucleus ventralis lateralis (VL). To reach these regions the fibres pass through the nucleus centrum medianum (CM), the nucleus subparafascicularis (SPf) and the nucleus paracentralis (Pc). The fibres that terminate in the VL pass through Forel's field H₁ and the external medullated lamina (EML). Conclusive results were not obtained concerning a termination in the CM. The spinothalamic fibres do not pass through nor terminate in the nucleus ventralis posterolateralis (VPL) and the nucleus reticularis (R). The VPL, defined as that portion of the ventral thalamus that receives terminal fibres from the dorsal column nuclei, has been found to extend rostrally only as far as Horsley-Clarke level anterior 10.5. The results strongly support the view that all the spinothalamic fibres terminate ipsilateral to their course in the ventral quadrant of the spinal cord. No signs of a somatotopical organization of the termination of the STT were found.List of Abbreviations Cd nucleus caudatus - CeM nucleus centralis medialis - CG circumaqueductal gray substance - CL nucleus centralis lateralis thalami - CM nucleus centrum medianum thalami - CP commissura posterior - CTT cervicothalamic tract - EML external medullated lamina - H₁ Forel's field H₁ - HP tractus habenulopeduncularis - LCN nucleus cervicalis lateralis - LG corpus geniculatum laterale - LP nucleus lateralis posterior thalami - MD nucleus medialis dorsalis thalami - MG corpus geniculatum mediale - MGmc corpus geniculatum mediale, pars magnocellularis - MGp corpus geniculatum mediale, pars principalis - ML medial lemniscus - MRF mesencephalic reticular formation - OT optic tract - Pc nucleus paracentralis thalami - Pf nucleus parafascicularis thalami - PO posterior group of thalamic nuclei - PO₁ lateral part of PO - PO_m medial part of PO - R nucleus reticularis thalami - SG nucleus suprageniculatus - STT spinothalamic tract - VA nucleus ventralis anterior - VL nucleus ventralis lateralis thalami - VM nucleus ventralis medialis thalami - VPI nucleus ventralis posterior inferior - VPL nucleus ventralis posterior lateralis thalami (VPL₁ + VPL_m) - VPL₁ lateral part of VPL - VPL_m medial part of VPL - VPM nucleus ventralis posterior medialis thalami - VPMpc parvocellular part of VPM - ZI zona incerta     

Dorsal column input to thalamic VL neurons: an intracellular study in the cat

Summary This study investigated the role of the ventral lateral (VL) nucleus of the thalamus as a lemniscal relay to motor cortex. Intracellular recordings were obtained from thalamic VL relay neurons in cats anesthetized with chloralose, following stimulation of the dorsal column nuclei. VL neurons were identified by their short-latency input from the cerebellar nuclei, their antidromic activation from motor cortex and their anatomical location. A total of 105 neurons was studied. The occurence of temporal facilitation to double volleys was also examined. It was found that 80/105 (75%) neurons responded with excitation and/or inhibition to stimulation of the dorsal column nuclei. The latencies of the postsynaptic responses ranged from 2.0 to 20 ms (median 10.0 ms). The latencies of nearly all responses (79/80) were > 3 ms and nearly all responses (45/47) which were tested for it, displayed temporal facilitation to double shock stimulation, consistent with polysynaptic transmission. Effective stimulation sites were found in the gracile and cuneate nuclei. Recording sites were located throughout VL, including the border region with the ventral posterior lateral nucleus (VPL). There was no obvious topographic relationship between location of recording site and latency or polarity (excitation versus inhibition) of the synaptic responses. This is consistent with dorsal column input diffusely distributed over VL. When the recording electrodes penetrated VPL, characteristics of the EPSPs were indicative of monosynaptic transmission (short latency, no temporal facilitation). This clear transition from VL to VPL suggests that it is not necessary to define, on physiological grounds, a separate border region between these two nuclei. The data provide evidence that dorsal column information reaches VL neurons polysynaptically, not monosynaptically. This indicates that VL is part of a long-latency, not short-latency path through the dorsal column nuclei to motor cortex.     

Electrophysiological evidence for a projection from medial prefrontal and anterior limbic cortex toward the medial preoptic area in the cat

Summary Neurons in cat medial prefrontal cortex, anterior limbic cortex and possibly the indusium griseum were identified by antidromic invasion as having axonal projections towards the medial preoptic region, using both macro- and microstimulation techniques. These projecting axons were found to be of slow conduction velocity (0.2–4.8 m/s) and to in some cases also send branches towards the anteromedial thalamus, mediodorsal thalamus, ventromedial tegmentum, basolateral amygdala or medial forebrain bundle. Threshold-depth curves for axons excited by microstimulation in the medial preoptic region were very steep, with proportionality constants of 0.3–7.1 m/A. Calculations based on the threshold-depth curves confirmed that microstimulation was most probably only activating axons within the MPO, and current spread to lateral fibers of passage following macrostimulation in the MPO was not detected in the branching studies.     

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique

Summary Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex.Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14–26 m in diameter (mean 19.4±4.5 m SD). Small (10–20 m) and medium (20–40 m) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells.Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20–27 h), the number of labeled neurons was very small.The relative paucity of labeled Corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.Abbreviations AL gyrus lateralis anterior - ASigm gyrus sigmoideus anterior - ASup gyrus suprasylvius anterior - Br.p. brachium pontis - Cor gyrus coronalis - L left - L.m. lemniscus medialis - MEct gyrus ectosylvius medius - MSup gyrus suprasylvius medius - N.dl. nucleus dorsolateralis - N.l. nucleus lateralis - N.m. nucleus medianus - N.p. nucleus peduncularis - N.pm. nucleus paramedianus - N.r.t. nucleus reticularis tegmenti pontis - N.v. nucleus ventralis - Ped corticospinal and corticopontine fibers in cerebral peduncle - PSigm gyrus sigmoideus posterior - R right     

Two modes of cerebellar input to the parietal cortex in the cat

Summary The characteristics of cerebellar input to the parietal cortex through the ventroanterior-ventrolateral (VA-VL) complex of the thalamus were investigated in the adult cat by using combined electrophysiological and anatomical methods. Two distinct parietal regions were activated by stimulation of the cerebellar nuclei (CN). In the first region located in the depth of the bank of the ansate sulcus, stimulation of the CN induced early surface positive-deep negative potentials and late surface negative-deep positive potentials. In this cortical area, potentials of similar shape and time course were evoked at a shorter latency by stimulation of the ventrolateral part of the VA-VL complex where large negative field potentials were evoked by stimulation of the CN. After injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in this part of the VA-VL complex, axon terminals of thalamocortical (TC) fibers were found in layers I, III and IV in the depth of the bank of the ansate sulcus and layers I and III in the motor cortex. In the second region located in the suprasylvian gyrus, late surface negative-deep positive potentials were evoked by stimulation of the CN and similar potentials were evoked at a shorter latency from the dorsomedial part of the VA-VL complex where large cerebellar-evoked potentials could be recorded. PHA-L injection in this thalamic region stained TC fibers and their terminals in layer I of the suprasylvian gyrus, and in layers I and III of the motor cortex. The laminar distribution of TC axon terminals in two different regions of the parietal cortex could account for the depth profiles of the cerebellar- and the thalamic-evoked potentials in each region. These results show that cerebellar information is conveyed to two separate areas in the parietal cortex by two different TC pathways.     

A cerebellar projection onto the pontine nuclei an experimental anatomical study in the cat

Summary Fibres passing from the intracerebellar nuclei to the pontine nuclei proper have been noted only by few students. In the present study this projection is analysed by mapping with the Nauta (1957) and Fink and Heimer (1967) methods the degeneration which occurs in the pontine nuclei following stereotactically placed electrolytic lesions in different parts of the intracerebellar nuclei in the cat. Cerebellopontine fibres come from the lateral cerebellar nucleus (NL) except its ventralmost part, and from the rostral but probably not from the caudal part of the interpositus anterior (NIA) and the interpositus posterior.The fibres end in three fairly well circumscribed regions of the pontine nuclei: a longitudinal column in the paramedian pontine nucleus, a column in the dorsolateral nucleus and one in the dorsal peduncular nucleus. Fibres from the NL as well as the NIA appear to end in all three regions, but the possibility of a more specific distribution cannot be excluded. Parts of the projection areas in the pons appear to be specific to cerebellar afferents, while other parts overlap with terminations of cerebropontine fibres, especially from SmI and SmII.The findings support the conclusions arrived at in recent studies of the cerebral corticopontine projections by P. Brodal (1968a, 1968b, 1971a, 1971 b) that the pontine nuclei are very precisely organized. The general principles in the organization of the corticopontine and cerebellopontine projections appear to be similar.Working in the Anatomical Institute, University of Oslo, with leave of absence from the Laboratory of Normal Anatomy, University of Coimbra, Portugal, with a grant from the Portugese Institute for Higher Culture.     

Corticospinal projections from the medial wall of the hemisphere

Summary We injected wheat germ agglutinin conjugated to horseradish peroxidase into different segments of the spinal cord in order to examine the topographic organization of corticospinal projections from the medial wall of the hemisphere. We observed that substantial projections to the spinal cord originate not only from the supplementary motor area (SMA) in area 6, but also from 2 regions within the cingulate sulcus. The distribution of labeled neurons following tracer injections into different spinal cord segments indicates that corticospinal projections from the SMA and from the 2 cingulate regions are somatotopically organized. These findings together with other recent anatomical observations suggest that the corticospinal projections from the medial wall of the hemisphere provide the basal ganglia and limbic system with a somatotopically organized access to spinal cord mechanisms.     

Identification of the projection from the visual cortex to the claustrum by anterograde axonal transport in the cat

Summary Visual cortex, including areas 17, 18, and sometimes 19, was injected with tritiated leucine. Terminal labelling could be detected by autoradiography in the dorsocaudal part of the ipsilateral claustrum in all cases.     

Cerebellar projections from the cervical enlargement: an experimental study with silver impregnation and autoradiographic techniques in the cat

Summary The cerebellar projection of neurons in the cervical enlargement was investigated in cats using two neuroanatomical methods, the successive degeneration method (Sherrington and Laslett 1903) and the autoradiographic tracing technique (³H-leucine). With both methods projections were found to the anterior lobe, posterior vermis and paramedian lobule. In the anterior lobe the projection was bilateral mainly to the vermal part of lobules I–V and the adjoining part of lobule VI, although some projection was also observed bilaterally to lobules I–VI lateral to the vermis. In the posterior vermis projection was found bilaterally to lobule VIII and in neighboring parts of lobule VII B. In the paramedian lobule the projection was mainly ipsilateral to the lesions/injections to the pars copularis and the adjoining part of the pars posterior. Only minor differences between the two methods were noted. In conclusion, spinocerebellar neurons project mainly to the vermal area of the anterior lobe (including the most anterior part of lobule VI), to lobules VII B and VIII and to the ipsilateral paramedian lobule.     

An experimental electron microscopic study on the striatonigral projection in the cat

Summary The ultrastructure of the cat's substantia nigra was investigated from 2–21 days following large lesions of the caudate nucleus and the putamen. From 4 days on a large number of degenerating boutons and degenerating unmyelinated fibers are seen in the substantia nigra, in the pars compacta as well as the pars reticulata. Both parts, mainly the latter, receive striatal afferents. The degeneration in the substantia nigra following striatal lesions is of the dark type. Most of the degenerating boutons apparently are of the type I (see Rinvik and Grofová, 1970) and end on all parts of the nigral cell surface, including the dendritic spines. One instance of a degenerating presynaptic bouton in an axo-axonic synapse has been found. Some degenerating boutons also probably belong to the type II bouton, while degenerating boutons of type III were never seen following the striatal lesions. The electron microscopic identification of early axonal degeneration in the central nervous system, is discussed with reference to the paper of Cohen and Pappas (1969). Problems concerning the pars compacta versus the pars reticulata of the substantia nigra are taken up. The possible sources of origin of the different types of boutons in the cat's substantia nigra, is discussed.On leave of absence from the Anatomical Institute of the Medical Faculty, Charles' University in Prague, with an IBRO grant nr. E. 29.99-1.A preliminary report of some of the observations was presented at the XIIth Congress for Morphologists in Prague, October '69.We gratefully acknowledge the valuable technical assistance of Mrs. J. L. Vaaland and the skilful help by Mrs. B.E. Branil in the preparation of the microphotographs.     

Properties of single neurons in the cat midsuprasylvian gyrus

Summary Responses of cells in the midsuprasylvian gyrus (MSSG) of cats were investigated following electrical stimulation of the central lateral nucleus (CL) of the thalamus and tooth pulp, low-threshold cutaneous or visual afferents. Electrical stimulation in CL induced excitation in many cells located in cortical areas 5 and 7. Cells in these areas also received input from somato-sensory and visual afferents. Cells in MSSG showed a wide convergence from tooth pulp, low-threshold cutaneous afferents and from the CL. The majority of wide convergent cells in area 5 were found in layers IV and V, while cells excited by CL and tooth pulp were found in layers II and III. Similarities were found between CL and tooth pulp evoked responses with regard to the excitation-inhibition pattern. The excitation evoked from CL and tooth pulp was less often followed by a hyperpolarizing potential compared to that seen after low-threshold lip, paw and visual afferent stimulation. Stimulation sites in the lateral parts of CL-evoked responses with the shortest latencies in area 5. In this part of the cortex, short latency synaptic potentials were found in cells in superficial layers. In the same area, synaptic potentials of short latency were also evoked by electrical stimulation of tooth pulp, lip and paw. Light-flash stimulation evoked responses with the shortest latencies in area 7. The results of this study demonstrate that putative nociceptive information reaches the parietal association cortex and that part of this input may be relayed via CL. We suggest that the excitatory influences of nociceptive and CL stimulation is related to behavioral arousal and attention mechanisms.Abbreviations AV anteroventral nucleus - CL central lateral nucleus - CM centre median nucleus - GL lateral geniculate nucleus - LD lateral dorsal nucleus - LP lateral posterior complex - MD mediodorsal nucleus - MSSG midsuprasylvian gyrus - OT optic tract - PAC paracentral nucleus - PF parafascicular nucleus - Po posterior thalamic nuclei - PP pes pedunculi - STT spinothalamic tract - VB ventrobasal complex - VA ventroanterior nucleus - VL ventrolateral complex - VMB basal ventromedial nucleus - VMH ventromedial hypothalamic nucleus - VPL ventroposterolateral nucleus - VPM ventroposteromedial nucleus - C.Max contralateral maxillary canine tooth - I.Max ipsilateral maxillary canine tooth - C.Mand contralateral mandibular canine tooth - I.Mand ipsilateral mandibular canine tooth - C.Lip contralateral upper lip - I.Lip ipsilateral upper lip - C.F.Paw contralateral forepaw - I.F.Paw ipsilateral forepaw - C.H.Paw contralateral hindpaw - I.H.Paw ipsilateral hindpaw - AP anteroposterior plane (in mm anterior to the interauricular plane) - ML mediolateral plane (in mm lateral to the midline)     

Somatotopical organization of the projection from the nucleus interpositus anterior of the cerebellum to the red nucleus. An experimental study in the cat with silver impregnation methods

Summary Small lesions were done in various areas of the nucleus interpositus anterior (NIA) of the cerebellum, and the distribution of terminal degeneration was studied in the red nucleus with the methods of Nauta and Glees. The NIA projects to the contralateral red nucleus. Two principles of organization can be demonstrated in the projection: a caudorostral arrangement in the red nucleus corresponds to a mediolateral organization in the NIA and a mediolateral arrangement in the red nucleus corresponds to a caudorostral organization of the NIA. The latter distribution coincides with the somatotopical areas of the red nucleus defined by Pompeiano and Brodal (1957). Special attention has been paid to the questions of the subdivision of the cerebellar nuclei and of the course of the fibres issuing from the nuclei in the cerebellar hilus. The present findings on the projection of the NIA to the red nucleus have been correlated with recent anatomical and physiological data on the cerebellum and the red nucleus.Abbreviations BC brachium conjunctivum - c caudal - d dorsal - Ext extensor effects - Flex flexor effects - forel forelimb area - HB hook-bundle - Hb. P habenulo-peduncular tract - hindl hindlimb area - I lateral - m medial - NF nucleus fastigii or medialis - NIA nucleus interpositus anterior - NIP nucleus interpositus posterior - NL nucleus lateralis - r rostral - v ventral - III root fibres of the third nerve - IV fourth ventricle Fellow of the Canadian Medical Research Council.     

Corticospinal fibres from the medial aspect of the cerebral hemisphere in the cat an experimental study with the nauta method

Summary Using the silver impregnation method of Nauta (1957), corticospinal fibres have been shown to take origin from the cerebral cortex of the medial aspect of the hemisphere in the cat. From the medial wall of the anterior sigmoid gyrus and the anterior cingulate area of the cingulate gyrus corticospinal fibres descend in both lateral funiculi of the cord to sacral cord segments. The fibres in the contralateral lateral funiculus are more numerous than those in the ipsilateral. The ipsilateral component is relatively much greater in the projection from the medial wall of the anterior sigmoid gyrus than in the projection from the primary sensorimotor cortex (Nyberg-Hansen and Brodal 1963). The corticospinal fibres demonstrated in the present study terminate within Rexed's laminae IV–VII as do those from the latter cortical region.The findings are discussed in relation to relevant fibre connections of the supplementary motor area and the anterior cingulate area, and to physiological stimulation and ablation experiments on the medial cerebral cortex. Special emphasis is put on the probability that the supplementary motor area in the cat is localized to the medial wall of the anterior sigmoid gyrus.     

Dendrodendritic synapses of cells that have axons: The fine structure of the Golgi type II cell in the medial geniculate body of the cat

Summary This study provides a combined analysis with the Golgi method and electron microscopy of the Golgi type II cells of the thalamus in the cat. In the ventral nucleus of the medial geniculate body these cells constitute a large, morphologically homogeneous population of neurons. They are clearly distinguished from the thalamo-cortical neurons by their size, shape, kinds of dendritic appendages, and cytoplasmic structure. The axon of the Golgi type II cell is exceptionally short and forms a small number of lumpy endings in the vicinity of its origin. The dendrites are often longer and much more elaborately branched than the axon. The shafts of these dendrites bear spiculated appendages, while the distal ends of the dendrites form clusters of very large endings. The appendages and terminal clusters participate in the nests of axonal endings formed by the afferent auditory axons and the dendritic branches of thalamo-cortical neurons. These axonal nests are the synaptic nests observed in electron micrographs. Within the synaptic nests the endings of Golgi type II neurons form dendrodendritic synapses on the dendrites of the thalamocortical neurons. The dendritic endings of Golgi type II neurons also receive synapses from the afferent axons. The dendrodendritic synapses may involve the Golgi type II neurons in an inhibitory role in the thalamo-cortical transformation of auditory signals. The dendrodendritic endings of the Golgi type II neurons continue to grow in the adult cat. Possibly these cells are involved in the evolution of cortical functions and in the plastic changes of neural activities that modify behavior.Supported by U. S. Public Health Service Research Grant NS 06115 and GRS Grant 5S01FR05381-08 to Harvard University.     

Topographical projections from the cerebral cortex to the nucleus of the solitary tract in the cat

Summary The distribution of cerebral cortical neurons sending projection fibers to the nucleus of the solitary tract (NST), and the topographical distribution of axon terminals of cortico-NST fibers within the NST were examined in the cat by two sets of experiments with horseradish peroxidase (HRP) and HRP conjugated with wheat germ agglutinin (WGA-HRP). First, HRP was injected into the NST. In the cerebral cortex of these cats, neuronal cell bodies were labeled retrogradely in the deep pyramidal cell layer (layer V): After HRP injection centered on the rostral or middle part of the NST, HRP-labeled neuronal cell bodies were distributed mainly in the orbital gyrus and caudal part of the infralimbic cortex, and additionally in the rostral part of the anterior sylvian gyrus. After HRP injection centered on the caudal part of the NST, labeled neuronal cell bodies were seen mainly in the caudoventral part of the infralimbic cortex, and additionally in the orbital gyrus, posterior sigmoid gyrus and rostral part of the anterior sylvian gyrus. The labeling in the infralimbic cortex, orbital gyrus and anterior sylvian gyrus was bilateral with a predominantly ipsilateral distribution, while that in the posterior sigmoid gyrus was bilateral with a clear-cut contralateral dominance. In the second set of experiments, WGA-HRP was injected into the cerebral cortical regions where neuronal cell bodies had been retrogradely labeled with HRP injected into the NST: After WGA-HRP injection into the orbital gyrus, presumed axon terminals in the NST were labeled in the rostral two thirds of the nucleus bilaterally with an ipsilateral predominance. After WGA-HRP injection into the rostral part of the anterior sylvian gyrus, a moderate number of presumed axon terminals were labeled throughout the whole rostrocaudal extent of the NST bilaterally with a slight ipsilateral dominance. After WGA-HRP injection into the middle and caudal parts of the anterior sylvian gyrus, no labeling was found in the NST. After WGA-HRP injection into the caudal part of the infralimbic cortex, presumed terminal labeling in the NST was seen throughout the whole rostrocaudal extent of the nucleus bilaterally with a dominant ipsilateral distribution. After WGA-HRP injection into the posterior sigmoid gyrus, however, no terminal labeling was found in the NST. The results indicate that cortico-NST fibers from the orbital gyrus terminate in the rostral two thirds of the NST, while those from the infralimbic cortex and the rostral part of the anterior sylvian gyrus project to the whole rostrocaudal extent of the NST.     

Short latency inputs to phrenic motoneurones from the sensorimotor cortex in the cat

Summary Short latency responses were recorded from C₅ phrenic roots and intracellularly from phrenic motoneurones following stimulation of the pericruciate cortex or medullary pyramids in cats anaesthetized with Nembutal or chloralose-urethane. Focal stimulation of the cortical surface (single pulses, 0.5–2 ms, 0.3–8 mA) during inspiration evoked EPSPs (latency 4.7 ± 1.7 ms, rise time 1.9 ± 1.1 ms, amplitude 0.22 to 3.94 mV) in 42% of motoneurones studied (n = 107). The EPSPs were absent, or on average 60% smaller, following stimulation during expiration. In all but two motoneurones, during both inspiration and expiration, hyperpolarizing potentials were observed either following the initial depolarization or alone. They could be reversed by hyperpolarizing current or chloride injection. Stimulation of the pyramidal tract at mid medullary level (1 to 3 pulses, 0.2 ms) evoked short latency excitation in phrenic motoneurones only with currents of more than 200 A. Smaller stimuli applied to the medial reticular formation above the pyramidal tract evoked excitation (onset latency 1.5–3.2 ms) in which the earliest part was probably monosynaptic. These results show that the corticospinal responses in phrenic motoneurones are both excitatory and inhibitory. They are not transmitted through the pyramidal tract and are at least disynaptic. Excitation evoked from the medullary pyramidal tract can be explained by current spread beyond the pyramidal tract fibres.     

Responses of cat preoptic neurons to stimulation of the medial frontal cortex and the medial basal hypothalamus

Summary Responses of single preoptic neurons to electrical stimulation of the medial frontal cortex, the mediobasal hypothalamus (MBH) and the medial forebrain bundle (MFB) were recorded in anaesthetised cats. Single pulse stimulation of the medial frontal cortex orthodromically drove 96 otherwise quiescent preoptic neurons, which were found more frequently in the dorsal preoptic region, inhibited 53% of the spontaneously active preoptic neurons and excited 16%. Testing of cortically influenced preoptic neurons with MBH or MFB stimulation resulted in antidromic invasion of 6% (MBH) and 9% (MFB). Convergence of orthodromic inputs from medial frontal cortex and MBH was detected in 78% of spontaneously active preoptic neurons, and three-way convergence including input from MFB was noted in 17% of neurons tested with all stimulators. Some cortex-responsive neurons were found to also respond to vaginal or anal probing, paw squeezing and haemorrhage. The role of this input to the preoptic region from medial frontal cortex remains to be elucidated, but may include neuroendocrine, behavioural and homeostatic functions.     

The thalamo-caudate versus thalamo-cortical projections as studied in the cat with fluorescent retrograde double labeling

Summary The distribution of thalamic cells projecting to the head of the caudate and their interrelations with thalamo-cortical cells were studied in the cat with different combinations of fluorescent tracers. Injections in the head of the caudate were combined with the injections in the pericruciate, proreal, suprasylvian, anterior cingulate, occipital and ectosylvian cortices. The following results were obtained: (i) Injections in the head of the caudate resulted in retrograde labeling of thalamic cells medially and laterally to the anteromedial (AM) nucleus, and in the medioventral part of the ventral anterior (VA) nucleus. Further, labeled cells were distributed throughout the anterior intralaminar central medial (CeM), paracentral (Pc) and central lateral (CL) nuclei, and the posterior intralaminar center median-parafascicular complex (CM-Pf). Labeled cells were mainly grouped in the mediodorsal parts of the anterior intralaminar nuclei; they were also found in the more dorsal part of the mediodorsal (MD) nucleus, ventral to the thalamic paraventricular (Pv) nucleus and to the habenular complex, (ii) Thalamo-cortical and thalamo-caudate cells overlapped in the medial part of the VA; in the anterior intralaminar nuclei they were either intermingled or were distributed in separate clusters or longitudinal bands. The two cell populations also overlapped in the posterior intralaminar complex. The greatest overlap occurred with the thalamic cell population projecting to the pericruciate cortex. (iii) Thalamic cells bifurcating to the head of the caudate and to the pericruciate cortex were found lateral to the AM, within the VA, and throughout the anterior intralaminar nuclei, especially in the CeM and in the posterior part of the CL; a few branched cells were also found in the CM. Thalamic cells bifurcating to caudate and anterior suprasylvian cortex were also found in the VA. Very few cells (scattered in the anterior thalamus lateral to the AM, as well as in the CeM, Pc and CL) were found to bifurcate to the head of the caudate and the other cortical fields here examined.Supported in part by grants CNR 80.00515.04, 81.00283.04