Akio Samejima

Postnatal development of the geniculocortical projection in the cat: Electrophysiological and morphological studies

SummaryUsing laminar field potential analysis, we examined responses elicited by both photic and optic nerve stimulations in 30 kittens of 0–65 days of age and in three adult cats. In adult cats, the response in the visual cortex on optic nerve stimulation is a wave complex which consists mainly of surface positive-depth negative (sP-dN) potentials. By contrast, the response in neonates consists of two surface negative — depth positive (sN-dP) waves. In 2 weeks, preceding the sN-dP waves, an sP-dN wave appears. As age increases, the sP-dN wave becomes of higher voltage and the sN-dP waves become of lower voltage. Thus, the configuration of the response resembles that of adult cats in 3–4 weeks. Both photic and optic nerve stimulations elicit responses of the same configuration in the same area. The extent of the responsive area is exactly the same at any age as in adult cats.Using the orthograde HRP method, we examined terminals of the geniculocortical afferent in 23 kittens of 0–43 days of age. The density of labeled terminals in layer I is much higher in kittens before 1 week of age (n = 8) than in kittens after 1 month of age (n = 5), whereas the density of labeled terminals in layer IV is higher in the older kittens than in the younger kittens. These electrophysiological and morphological changes are correlated in reference to the maturation of the neuronal circuit in the visual cortex.

Electrophysiological evidence for axonal sprouting of cerebellothalamic neurons in kittens after neonatal hemicerebellectomy

SummaryChanges in cerebellothalamic projections in kittens after neonatal hemicerebellectomy were studied by the retrograde and anterograde horseradish peroxidase (HRP)-tract-tracing methods. The number of cerebellar nuclear neurons labeled retrogradely with HRP injected into the ipsilateral VA-VL complex of the thalamus was much more numerous in neonatally hemicerebellectomized kittens than in intact kittens. Presumed terminals of ipsilateral cerebellothalamic fibers labeled anterogradely with HRP injected into the cerebellar nuclei were also distributed more densely and extensively in the thalamic areas, especially in the VA-VL complex, of hemicerebellectomized kittens than in the thalamic areas of the control kittens. These results are in good accordance with those obtained from the previous electrophysiological study (Kawaguchi et al., 1979) and offer corroborating evidence for axonal sprouting of cerebellothalamic neurons after neonatal hemicerebellectomy.

The mode of synaptic activation of pyramidal neurons in the cat primary somatosensory cortex: an intracellular HRP study.

SummaryA total of 141 pyramidal neurons in the cat primary somatosensory cortex (SI) were recorded intracellularly under Nembutal anesthesia (7 in layer II, 43 in layer III, 8 in layer IV, 58 in layer V and 25 in layer VI). Most neurons were identified by intracellular staining with HRP, though some layer V pyramidal neurons were identified only electrophysiologically with antidromic activation of medullary pyramid (PT) or pontine nuclear (PN) stimulation. Excitatory synaptic potentials (EPSPs) were analyzed with stimulation of the superficial radial nerve (SR), the ventral posterolateral nucleus (VPL) in the thalamus and the thalamic radiation (WM). The pyramidal neurons in layers III and IV received EPSPs at the shortest latency: 9.1±2.1 ms (Mean+S.D.) for SR and 1.6±0.7 ms for VPL stimulation. Layer II pyramidal neurons also responded at a short latency to VPL stimulation (1.7±0.5 ms), though their mean latencies for SR-induced EPSPs were relatively longer (10.6±1.9 ms). The mean latencies were much longer in layers V and VI pyramidal neurons (10.2±2.4 ms and 2.9±1.5 ms in layer V pyramidal neurons and 9.9±2.5 ms and 2.8±1.6 ms in layer VI pyramidal ones, respectively for SR and VPL stimulation). The comparison of the latencies between VPL and WM stimulation indicates that most layer III–IV pyramidal neurons and some pyramidal cells in layers II, V and VI received monosynaptic inputs from VPL. These findings are consistent with morphological data on the laminar distribution of thalamocortical fibers, i.e., thalamocortical fibers terminate mainly in the deeper part of layers III and IV with some collaterals in layers V, VI and II-I. The time-sequences of the latencies of VPL-EPSPs indicate that corticocortical and/or transcallosal neurons (pyramidal neurons in layers II and III) fire first and are followed by firing of the output neurons projecting to the subcortical structures (pyramidal neurons in layers V and VI).

Short latency activation of local circuit neurons in the cat somatosensory cortex

Intracellular horseradish peroxidase (HRP) study was performed in the cat primary somatosensory cortex (SI) under Nembutal anesthesia. Response properties of neurons were analysed with stimulation of the peripheral nerve (superficial radial nerve; SR) and thalamic ventrobasal nucleus (VB). A total number of 23 cells (15 in layers III and IV, 6 in layer V and 2 in layer VI) were identified morphologically as local circuit neurons with intracellular HRP staining. The latencies of SR-induced (7.7-8.5 ms) as well as VB-induced excitatory postsynaptic potentials (EPSPs) (1.3-1.5 ms) were significantly shorter than those of pyramidal neurons (9.1-10.6 ms for SR and 1.6-2.8 ms VB EPSPs). Morphological features of identified local circuit neurons are all, except one in layer VI, aspiny and presumed to be inhibitory in nature. The present study indicates that presumed inhibitory interneurons in the cat SI could be activated first by thalamic inputs among cortical neurons and set to inhibit the output cells for the sharp contrast in the sensory processing.

Morphology of layer V pyramidal neurons in the cat somatosensory cortex: an intracellular HRP study ☆

Pyramidal tract (PT) or corticopontine neurons of the cat somatosensory cortex (SI) were identified with antidromic activation on stimulation of the bulbar pyramid or pontine nuclei (PN) and stained intracellularly with HRP after examining the electrophysiological properties. Comparison of the conduction velocity of the stem axons and the soma-dendritic morphology revealed that in the cat SI, there exists two types of layer V pyramidal neurons, i.e. one has smooth apical dendrites with larger soma (51.6 +/- 9.5 x 22.7 +/- 2.8 micron) and the other has richly spinous apical dendrites with smaller soma (34.0 +/- 8.8 x 15.3 +/- 3.3 micron). The former group responded antidromically at latencies shorter than 1 ms by PT stimulation or 1.5 ms by PN stimulation, respectively. These values were consistent with the borderline latencies between two similar groups of layer V pyramidal neurons in the motor (fast and slow PTNs) and parietal (aspiny and spiny layer V corticopontine neurons) cortices in the cat.

Organization of afferent connections to the lateral and interpositus cerebellar nuclei from the brainstem relay nuclei: a horseradish peroxidase study in the cat

Afferent projections to the lateral (dentate) and interpositus cerebellar nuclei from the brainstem relay nuclei were studied in cats using the horseradish peroxidase (HRP) method. In the first series of experiments, HRP was injected into the brachium pontis. Mossy fiber terminals were anterogradely labeled, predominantly in the lateral (hemispherical) part, moderately in the intermediate part, and slightly in the vermal part of the cerebellum. Besides these terminals in the cerebellar cortex, axon terminals labeled anterogradely were also found in the cerebellar nuclei. The labeled terminals appeared almost exclusively in the lateral nucleus and rarely in the interpositus nucleus. Cells labeled retrogradely were found both in the pontine nuclei and the tegmental reticular nucleus, but not in other brainstem nuclei. In the second series of experiments, HRP was injected into the lateral and interpositus nuclei, and retrograde labeling was examined in the brainstem relay nuclei. After HRP injection into the lateral nucleus, the number of labeled cells was significantly large in the pontine nuclei, but fairly small in the reticular or vestibular nuclei. The number of labeled cells was generally large in the inferior olive, mainly in the principal olive. After HRP injection into the interpositus nucleus, the number of labeled cells was moderate in the reticular or vestibular nuclei, but small in the pontine nuclei. The number of labeled cells in the inferior olive was also large, being distributed mainly in the accessory olives. These results indicate that the pontine nuclei and the principal olive provide major afferent inputs to the lateral nucleus, whereas the reticular nuclei, the vestibular nuclei and the accessory olives are the major afferent sources to the interpositus nucleus.

Electrophysiological studies on the cerebellocerebral projection in the rat

Abstract Cerebellocerebral responses in the rat were investigated by laminar field potential analysis in the cerebral cortex under Nembutal anesthesia. Stimulation of the three cerebellar nuclei induced conspicuous responses in the sensory-motor cortex only on the contralateral side, particularly in the forelimb and vibrissae areas of the motor cortex. Laminar field potential analysis and unitary recordings performed extra- and intracellularly from pyramidal tract neurons revealed that the evoked potential was composed of two kinds of responses. One was due to the deep thalamocortical (TC) response (superficial positive-deep negative potentials) which was ascribed to excitatory postsynaptic potentials (EPSPs) generated in the deep cortical layers (somata and dendrites near the somata of pyramidal neurons), and the other was due to the superficial TC response (superficial negative-deep positive potentials) which was ascribed to EPSPs in the superficial cortical layers (upper parts of apical dendrites of pyramidal neurons). Comparison of the responses in the cortex induced by stimulation of the cerebellar and thalamic nuclei confirmed that the ventrolateral complex of the thalamus is the relay portion of the cerebellocerebral responses in the rat. The results of the present study are compared with those of the cat and monkey.

Changes in the cerebello-cerebral response in the parietal cortex following ablation of the motor cortex in the cat: early occurrence and persistence

To elucidate the compensatory mechanism which begins to work soon after damage to the brain, changes in the cerebellar-induced cerebral cortical response in the parietal association cortex after ablation of the frontal motor cortex were studied in the cat. Stimulation of the interpositus or the lateral nucleus of the cerebellum before decortication, as reported in intact animals, induced two distinct types of response in the frontal motor and parietal association cortices respectively. The response in the frontal cortex was a sequential occurrence of a surface positive-depth negative (sP-dN) wave and a surface negative-depth positive (sN-dP) wave, and the response in the parietal cortex was mainly an sN-dP wave. In a small proportion of animals, the latter wave was preceded by a small sP-dN wave or a small dN wave without an sP wave. Ablation of the frontal motor cortex induced in the majority of animals a marked change in the cerebello-parietal cortical response, i.e. the occurrence of a new sP-dN wave preceding the sN-dP wave or enhancement of the pre-existing small dN wave, resulting in the parietal cortical response similar to the frontal cortical response of intact animals. The earliest post-lesion time observed for the occurrence of change was less than 1 hour, whereas its persistence was confirmed up to 213 days post-lesion.

An intracellular analysis of the entopeduncular inputs on the centrum medianum-parafascicular nuclear complex in cats

Intracellular recording from the CM-PF neurons was performed by stimulation of the EN, the caudate nucleus (Cd), the cerebellar nuclei (CN) and the motor cortex in the cat under Nembutal anesthesia. Twenty-seven neurons in the CM-PF nuclear complex and two neurons near the habenular nucleus received monosynaptic inhibitory postsynaptic potentials (IPSPs; latency of 1.0-4.0 ms, mean 2.3 ms) by EN stimulation. Cd stimulation evoked excitatory postsynaptic potentials (EPSPs) followed by long hyperpolarizations in most of the CM-PF neurons and produced antidromic activation in 7 neurons. Six neurons received EPSPs (latencies of 4-7 ms) by cortical stimulation. CN stimulation affected only two neurons in the present study. Intracellular HRP staining revealed that some CM-PF neurons have polygonal or spindle-shaped somata with fine, long and sparsely spinous dendrites.

Two groups of corticofugal neurons identified with the pontine stimulation in the cat parietal association cortex: an intracellular HRP study

A classification of the parietal corticofugal neurons was performed in cats under Nembutal anesthesia. Eighty-eight neurons were identified with antidromic activation by the pontine stimulation. Thirteen neurons were furthermore identified with intracellular HRP staining. In these neurons, we found the close correlation between morphological features and conduction velocities. The faster conducting group of the neurons had relatively large somata, sparsely spinous apical dendrites, tap root basal dendrites and wide apical dendritic fields. The slower group had small somata and numerous dendritic spines.