Cerebellar Input Research Articles

Selforganization and information processing of neural networks

To investigate whether corticothalamic (CT) neurons in the motor cortex (Mx) receive cerebellar input via the ventroanterior–ventrolateral nucleus of the thalamus (VA–VL), we recorded intracellular potentials from neurons in the Mx of anesthetized cats and examined effects of stimulation of the VA–VL and the brachium conjunctivum on them. After this electrophysiological identification, horseradish peroxide (HRP) was injected iontophoretically into the recorded neurons for morphological analysis. We identified 34 neurons as CT neurons by their antidromic response to stimulation of the VA–VL, of which 13 were layer VI CT neurons and 21 were layer V CT neurons. A majority of the CT neurons of both layers VI and V received monosynaptic excitatory postsynaptic potentials (EPSPs) from the VA–VL and di- or polysynaptic EPSPs from the cerebellum. The laminar distribution and morphological characteristics of single CT neurons receiving cerebellar input were analyzed on 19 HRP-labeled CT neurons. Eight layer V and six layer VI CT neurons were reconstructed from serial sections. All the reconstructed layer VI CT neurons were modified pyramidal neurons whose apical dendrites ended in layer III or V, and all the stained layer V CT neurons were typical pyramidal neurons, although the laminar and tangential distribution of recurrent collaterals of these neurons varied from neuron to neuron.

Evidence for reactive synaptogenesis in the ventrolateral thalamus and red nucleus of the rat: changes in high affinity glutamate uptake and numbers of corticofugal fiber terminals.

High affinity glutamate uptake into corticofugal fiber terminals was measured in the ventrolateral thalamus and red nucleus at varying time intervals after lesions were made by kainic acid in the contralateral interpositus nucleus of the cerebellum in rats. Under similar conditions the density of cortical fiber terminals was estimated using the Fink-Heimer impregnation technique. 1. Glutamate uptake steadily increased in the ventrolateral thalamus up to 60 days after lesions in the contralateral cerebellum. 2. Similar changes were noted in the red nucleus. 3. The changes were dependent on the integrity of corticofugal fibers to the thalamus and red nucleus. 4. No changes in uptake of gamma-aminobutyric acid were noted. 5. Saturation curves for glutamate uptake suggested a change in the maximal number of transport sites. 6. Fink-Heimer degeneration studies showed an increase in cortical terminals in the ipsilateral ventrolateral thalamus and in both rostral and caudal regions of the red nucleus following lesions in the contralateral interpositus nucleus. The data are consistent with an increase in the number of cortical fiber terminals in reaction to loss of cerebellar input to the ventrolateral thalamus and red nucleus. This study correlates anatomical and biochemical evidence for collateral sprouting in a model based on electrophysiologic data in the red nucleus and extends the model to include the thalamus.

Morphological features of layer V pyramidal neurons in the cat parietal cortex: an intracellular HRP study.

Layer V pyramidal neurons in the cat parietal cortex (areas 5 and 7) were investigated with intracellular HRP staining. Antidromic responses were recorded intracellularly as well as extracellularly with pontine stimulation under Nembutal anesthesia. The relationship between the latency of antidromic responses and the morphology of HRP-stained neurons was analyzed. A total of 65 neurons were stained with HRP, and sixteen of these neurons were activated antidromically with pontine stimulation. Two distinct groups of layer V pyramidal neurons were detected morphologically by intracellular HRP staining; i.e., one (F type) consisted of neurons with relatively large somata (58.4 +/- 8.1 micron X 24.5 +/- 5.1 micron, N = 11) and aspiny or sparsely spinous apical dendrites, and the other (S type) consisted of neurons with smaller somata (44.6 +/- 7.6 micron X 19.3 +/- 3.9 micron, N = 22) and richly spinous apical dendrites. These two groups showed different electrophysiological properties; i.e., the former responded antidromically to pontine stimulation at a latency shorter than 1.5 ms (namely, with a conduction velocity faster than 18 m/second) and the latter responded at a latency longer than 1.5 ms. The two neuronal types in the parietal cortex corresponded respectively to fast and slow pyramidal tract neurons (PTNs) investigated in the sensorimotor cortex. Although their morphological features were almost similar to those of PTNs, the branching pattern of apical dendrites of the F-type pyramidal neuron seemed to be different from that of fast PTNs. In the parietal cortex, apical dendrites of F-type neurons showed rather frequent branching in layer I. This was similar to the pattern of branching in slow PTNs. Such a characteristic branching pattern suggested that, in the cat parietal cortex, layer V pyramidal neurons of both types are adapted to receive cerebellar inputs through the ventroanterior (VA) thalamic nucleus to the superficial cortical layers.

An analysis of potentially converging inputs to the rostral ventral thalamic nuclei of the cat.

Potentially convergent inputs to cerebellar-receiving and basal ganglia-receiving areas of the thalamus were identified using horseradish peroxidase (HRP) retrograde tracing techniques. HRP was deposited iontophoretically into the ventroanterior (VA), ventromedial (VM), and ventrolateral (VL) thalamic nuclei in the cat. The relative numbers of labeled neurons in the basal ganglia and the cerebellar nuclei were used to assess the extent to which the injection was in cerebellar-receiving or basal ganglia-receiving portions of thalamus. The rostral pole of VA showed reciprocal connections with prefrontal portions of the cerebral cortex. Only the basal ganglia and the hypothalamus provided non-thalamic input to modulate these cortico-thalamo-cortical loops. In VM, there were reciprocal connections with prefrontal, premotor, and insular areas of the cerebral cortex. The basal ganglia (especially the substantia nigra), and to a lesser extent, the posterior and ventral portions of the deep cerebellar nuclei, provided input to VM and may modulate these cortico-thalamo-cortical loops. The premotor cortical areas connected to VM include those associated with eye movements, and afferents from the superior colliculus, a region of documented importance in oculomotor control, also were labeled by injections into VM. The dorsolateral portion of the VA-VL complex primarily showed reciprocal connections with the medial premotor (area 6) cortex. Basal ganglia and cerebellar afferents both may modulate this cortico-thalamo-cortical loop, although they do not necessarily converge on the same thalamic neurons. The cerebellar input to dorsolateral VA-VL was from posterior and ventral portions of the cerebellar nuclei, and the major potential brainstem afferents to this region of thalamus were from the pretectum. Mid- and caudo-lateral portions of VL had reciprocal connections with primary motor cortex (area 4). The dorsal and anterior portions of the cerebellar nuclei had a dominant input to this cortico-thalamo-cortical loop. Potentially converging brainstem afferents to this portion of VL were from the pretectum, especially pretectal areas to which somatosensory afferents project.

Comparative analysis of cerebellar unit discharge patterns in the decerebrate cat during passive movements.

1) The present experiments were undertaken to study how information about the parameters of a passive movement is processed at different neuronal levels of the cat cerebellar cortex. The analysis has been performed by recording extracellularly in the intermediate part of the cerebellar anterior lobe from presumed mossy fibres, presumed granule cells, and Purkinje cells with simple spikes and complex spikes. 2) The discharge patterns obtained during passive movements of the cat's forepaw were characterized by components which could be related to dynamic or static parameters of the movement. With respect to the occurrence of dynamic responses, patterns were classified according to a statistically derived measure in three different types. By using the same statistical measure, discharge patterns were additionally classified into two subgroups according to their response components reflecting static parameters. Within the patterns a clearcut relationship between dynamic and static components was observed. The corresponding distributions are shown and discussed. 3) A very interesting result of the classification of cerebellar discharge patterns is that the distribution of the different types depended on the level of integration within the cerebellar cortex. Patterns of the low scale integrated cerebellar input (mossy fibre-system), as well as those of granule cells (the first cerebellar computational niveau), reflected both static and dynamic movement parameters. At the Purkinje cell level (a level with a high degree of convergence) the discharge patterns are characterized predominantly by dynamic responses. 4) The interrelationship between complex- and simple spikes of Purkinje cells was tested by different methods: a) By analyzing the paired values of the mean complex-(CS) and simple spike (SS) discharge probabilities of 110 Purkinje cells a scatter was obtained, indicating an underlying hyperbolic relation (prob(CS) = a/(prob(SS]b). Thus, a high CS discharge probability is accompanied by a low SS probability and vice versa. b) The timelocked complex- and simple spike responses were studied by comparing the similarity of their responses. All combinations of complex- and simple spike patterns were observed, ranging from a sign correct similarity to a mirror image similarity. The distribution of the measure for similarity shows that the mirror image predominated. c) The individual simple spike discharge probability is characterized by a pause evoked by the occurrence of a complex spike event. The simple spike discharge probabilities during an interval preceding and following a complex spike event were compared.(ABSTRACT TRUNCATED AT 400 WORDS)

Converging cerebellofugal inputs to the thalamus. II. Analysis and topography of thalamic EPSPs induced by convergent monosynaptic interpositus and dentate inputs.

A large number of projections from cerebellar nuclei converge onto individual neurones in the thalamic relay to the motor cortex. Among the thalamic cells receiving cerebellar inputs, 75 out of 153 (50%) were found to be influenced by monosynaptic inputs from at least two cerebellar nuclei and 2 (1.5%) from three nuclei (the interpositus, dentate and fastigial nuclei). The pathways of the inputs converging on the same unit were found to be monosynaptic in 67 thalamic neurons, and disynaptic in the eight others. The monosynaptic nature of the majority of the pathways was proved by analysing the synaptic delay and the spatial and temporal summation. The 67 thalamic neurons receiving direct convergent influences were found to be distributed within the central portion of the VL. Forty-four of them give off projections to all the cortical areas, although a slightly higher proportion is to be found within the motor cortex shoulder area than elsewhere (medial part of area 4). Consequently, the specific function of the neurons receiving direct, convergent cerebellar inputs is not to control one particular part of the musculature but on the contrary, to transmit reciprocal facilitatory effects between the interpositus and dentate nuclei to all the cortical motor subdivisions. Maps summarizing monosynaptic responses obtained with semi-chronic preparations were drawn at thalamic and cortical levels. Each VL neuron was found to be a point where the two cerebellar circuits converge and may interact: the cerebrocerebellar circuit, which passes through the dentate nucleus, generates a feedward motor command: this can either modify or be modified by the feedback peripheral loop, which passes through the interpositus nucleus.

Dendritic and somatic appendages of identified rubrospinal neurons of the cat

Giant neurons of the red nucleus of the cat were stained intracellularly with horseradish peroxidase and examined using light microscopy, electron microscopy of thin sections, and high voltage electron microscopy of thick sections (2–5 μm). Special attention was paid to the arrangement of dendritic spines and other appendages relative to the distribution of synaptic contacts from known sources. In the region of the neuron known to receive synaptic contacts from the nucleus interpositus of the cerebellum (soma and proximal 200–300μm of dendrites), the dendrites were relatively unbranched, and free of long spines or complex appendages. The surface of the neurons in this region was covered with a dense layer of short thin appendages that invaginated or penetrated between the synaptic terminals that cover this part of the cells. The small spines received synapses of the types associated both with the cerebellar afferent fibers and with the local inhibitory interneurons. These same terminals made synaptic contacts directly onto the surface of the neurons and onto the lateral surfaces of the spines, suggesting that the spines may serve primarily to increase the available synaptic surface area. The more distal portion of the dendritic field, where cerebellar afferents do not make synaptic contacts, exhibited a dramatically different appearance. The dendrites were much more branched, and exhibited many and varied dendritic appendages. The appendages were of three general types. One was a large protrusion with a cup-shaped head that formed the principal postsynaptic component of a glomerular arrangement also involving an axon terminal and usually a presynaptic dendrite. A second was a long thin filiform process that usually occurred around the glomeruli. This appendage was occasionally postsynaptic. The third was a spherical appendage containing many lysosomal organelles resembling residual bodies. The glomerular dendritic protrusions were very common in the distal portion of the dendritic field, numbering at least 1000 per cell. At least some of the glomeruli are specialized for receipt of synaptic input from the corticorubral pathway, since lesions of sensorimotor cortex resulted in degeneration of the central synaptic terminal in some glomeruli on horseradish peroxidase-injected rubrospinal neurons. These specializations of dendritic structure may contribute to the differences in excitatory postsynaptic potential wave shape between cortical and cerebellar inputs, and they may play a role in the changes in the cortical excitatory postsynaptic potential that develop after lesions of cerebellar inputs. In addition, they suggest a difference in the way that inhibitory inputs from intrinsic GABAergic neurons may interact with excitatory input from cerebellum and cerebral cortex.

In vivo electrochemical demonstration of potassium-evoked monoamine release from rat cerebellum

In vivo electrochemical methods were employed to study the potassium (K +-evoked release of monoamines from the cerebellum of the chloral hydrate anesthetized rat. K +-evoked releases were elicited using micropipette-Nafion-coated graphite epoxy electrode arrays in the granule/Purkenje cell layer, molecular layer, and white matter. These recorded releases were generally found to be reversible, moderately dose-dependent, and reproducible. However, the temporal dynamics of the releases were different for the cell layer versus molecular layer records. Releases were infrequently observed in cerebellar white matter, an area which is relatively devoid of monoamine containing terminals. The signals recorded from the cell and molecular layers were significantly attenuated by pretreatment with nomifensine, a potent catecholamine reuptake blocker, significantly prolonged the K +-evoked signals observed in both the granule/Purkenje cell and molecular layers. These data, taken together with earlier reports on the electrophysiological responses to activation of cerebellar noradrenergic inputs, support the conjecture that in vivo electrochemical recording methods have the sensitivity and spatial resolution for studies of functional monoamine release from brain regions that have a diffuse or laminated monoamine innervation.

Anatomical evidence of a reciprocal connection between the posterior thalamic nucleus and the parvocellular division of the red nucleus in the rat. A combined retrograde and anterograde study

The functional and anatomical organizations of the magnocellular part of the red nucleus are now well established. Our knowledge of the parvocellular part is, however, more limited. Using both anterograde and retrograde tracing methods, the present study suggests in the rat the existence of a large projection from the posterior thalamic nucleus to the parvocellular part of the red nucleus. In turn, the parvocellular part of the red nucleus sends a weaker projection to the posterior thalamic nucleus. Three different tracers were utilized (horseradish peroxidase alone, horseradish peroxidase conjugated to wheat germ agglutinin and Phaseolus vulgaris leucoagglutinin), all of which gave similar results. The posterior thalamic nucleus is known to receive a large proportion of somatosensory afferents. It is suggested, therefore, that in addition to receiving cerebellar and cortical inputs, the parvocellular part of the red nucleus has access to highly integrated somatosensory and/or nociceptive information delivered by the posterior thalamic nucleus.

The role of the monkey sensory cortex in the recovery from cerebellar injury.

The aim of the study was to investigate the contribution of the primary sensory cortex in the compensation of cerebellar deficits during self-paced movements. For this purpose, monkeys were trained on motor tasks which required goal-reaching and independent finger movements. The intermediate and lateral deep cerebellar nuclei and the sensory cortex were lesioned in isolation and in sequence and the course of motor recovery was studied on the test performances. The deep nuclei were lesioned by kainic acid injections, the sensory cortex was removed by ablation. Cerebellar lesions in isolation produced obvious deficits at proximal and distal joints, affecting both slow and fast motor adjustments. Only lesions of the anterior portions of the intermediate and lateral deep nuclear complexes produced deficiencies in voluntary movements. Lesions of the posterior portions produced postural disturbances. The process of recovery following cerebellar lesions was slow and, depending on the nature of the task, was found to be differentially disruptive for motor performances requiring fast and slow motor adjustments. The deficits at distal joints appeared to be more enduring than those at proximal joints. Sensory cortical lesions in isolation produced much less severe and more transient motor deficits. They consisted of hand clumsiness and their recovery was fast and reached higher levels of performance than following cerebellar lesions. When the sensory cortex was removed secondarily to a cerebellar lesion and after recovery from the cerebellar deficits, the initially recovered motor performance became much worse again (decompensation). Removal of the sensory cortex prior to a cerebellar lesion exaggerated the cerebellar deficits and severely limited their recovery. Slow and fast motor performances were completely abolished for three weeks following sequential lesions. Signs of recovery subsequently appeared and stabilized at low levels of performance by five to seven weeks. The effects of combined, sequential cerebellar and sensory cortical lesions were much worse than expected if the effects from the two lesions were merely additive. This indicates that there is some functional interrelationship between the sensory cortex and the cerebellum, which promotes compensation. The somatosensory cortex appears to play a crucial role in the process of recovery from cerebellar motor deficits and it is likely that sensation is an important component in the process of recovery. It is suggested that the sensory cortex exerts its compensatory actions via a structure or structures which receives convergent cerebellar and sensory cortical inputs.

Afferent connections of the nuclei reticularis pontis oralis and caudalis: A horseradish peroxidase study in the rat

The afferent connections of the nuclei reticularis pontis oralis and caudalis were studied experimentally in the rat by the aid of either free horseradish peroxidase or horseradish peroxidase conjugated with wheat germ agglutinin used as retrograde tracers. The results suggest that the nucleus reticularis pontis oralis receives its main input from the zona incerta and field H 1, of Forel, the superior colliculus, the central gray substance, and the mesencephalic and magnocellular pontomedullary districts of the reticular formation. Many other structures seem to represent modest additional sources of projections to the nucleus reticularis pontis oralis; these structures include numerous cortical territories, the nucleus basalis, the central amygdaloid nucleus, hypothalamic districts, the anterior pretectal nucleus, the substantia nigra, the cuneiform, the accessory oculomotor and the deep cerebellar nuclei, trigeminal, parabrachial and vestibular sensory cell groups, the nuclei raphe dorsalis and magnus, the locus coeruleus, the dorsolateral tegmental nucleus, and the spinal cord. While the afferentation of the rostral portion of the nucleus reticularis pontis caudalis appears to conform to the general pattern outlined above, some deviations from that pattern emerge when the innervation of the caudal district of the nucleus reticularis pontis caudalis is considered; the most striking of these differences is the fact that both spinal and cerebellar inputs seem to distribute much more heavily to the referred caudal district than to the remaining magnocellular pontine reticular formation. The present results may contribute to the elucidation of the anatomical substrate of the functionally demonstrated involvement of the nuclei reticularis pontis oralis and caudalis in several domains that include the regulation of the sleep-waking cycle and cortical arousal, somatic motor mechanisms and nociceptive behavior.

Projection on the motor cortex of thalamic neurons with pallidal input in the monkey

The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.

Synaptic responses of red nucleus neurons in the alert cat to cortical and cerebellar inputs

Postsynaptic potentials of neurons of the red nucleus (RN), evoked to stimulation of the sensorimotor region of the cerebral cortex and cerebellar nucleus interpositus, were studied in chronic experiments on alert cats by means of an intracellular recording technique. Movements of the animals were restricted by rigid fixation (through a special device previously attached to the head) of the animal's head on the frame of the stereotaxic apparatus. Rubrospinal neurons were identified according to their antidromic activation in response to stimulation of the rubrospinal tract at the decussation level. A decrease in the critical level of depolarization necessary for spike generation was shown to be a characteristic peculiarity for mono-and polysynaptic reaction of the RN neurons in the alert animals. A rare possibility of recording separate EPSPs, the presence of burst discharges of rubrospinal neurons as well as a higher activity of RN interneurons was observed.

Nigral modulation of cerebello-thalamo-cortical transmission in the ventral medial thalamic nucleus.

In the rat, the highly active GABAergic neurons of the substantia nigra pars reticulata (SNR) are known to exert a tonic inhibitory influence on cells in the ventral medial thalamic nucleus (VM). Considering that this nucleus is involved in the transfer of cerebellar signals towards motor cortex, we investigated the role played by SNR in that transmission. For this purpose we examined how changes in nigral background activity are reflected in the reactivity of VM cells to their cerebellar input. We report here that a GABA induced nigral pause increases the efficacy of cerebellar afferent volleys in VM, whereas an increase of nigral background by bicuculline, interrupts cerebello-thalamo-cortical transmission. It is concluded that nigrothalamic neurons subserve a permanent gating of cerebello-thalamo-cortical transmission in VM.

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. III. Cerebellar input to corticofugal neurons destined for different subcortical nuclei in areas 4 and 6

To analyze the cerebellar effects on corticofugal neurons destined for different subcortical nuclei, intracellular recordings were made from corticofugal neurons in areas 4 and 6 of the cat. Corticonuclear neurons to the red nucleus (RN) and the pontine nucleus (PN), and pyramidal tract neurons (PTNs) with collaterals to these nuclei were identified by their antidromic responses to the stimulation of these nuclei and the pyramid. Three types of RN-projecting neurons (corticorubral neurons (CRNs), corticopontine neurons (CPNs) with a collateral to the RN and PTNs with a collateral to the RN) and two types of PN-projecting neurons (CPNs and PTNs with a collateral to the PN) were differentiated. Furthermore, these corticofugal neurons were classified as fast and slow neurons on the basis of a critical axonal conduction velocity of 20 m/s. About 80% of 98 RN-projecting neurons in area 4 were PTNs, and among the rest, CPNs were more common than CRNs. A similar tendency of the frequency distribution of 37 RN-projecting neurons was also observed in area 6. In area 4, about 70% of 158 PN-projecting neurons were PTNs (80 fast and 30 slow PTNs) and the rest were CPNs, while in area 6, only 35% of 99 PN-projecting neurons were PTNs (10 fast and 25 slow PTNs). Among the CPNs in areas 4 and 6, slow CPNs were more frequently encountered. Cerebellar effects on these identified corticofugal neurons were investigated, using electrical stimulation of the brachium conjunctivum (BC). In both areas 4 and 6, a substantial number of fast conducting CRNs, CPNs and PTNs projecting to the RN or the PN received short-latency (pre-dominantly disynaptic), large-amplitude EPSPs from the BC, and a considerable number of slow conducting neurons to the RN and/or the PN received longer-latency, smaller-amplitude EPSPs from the BC.

Interaction of norepinephrine with purkinje cell responses to cerebellar afferent inputs in aged rats

—Age-related differences in the modulatory actions of NE on the evoked activity of cerebellar Purkinje cells were examined in young (3 month) and old (18–20 month) Fischer 344 rats. We have previously shown that NE is more potent in young than in old rats, in terms of its ability to inhibit spontaneous activity. In this investigation complex spike excitation, simple spike excitation, and inhibition of Purkinje cell discharge were elicited by stimulation of climbing fibers, mossy fibers, and cerebellar parallel fibers, and quantified by computing post-stimulus time histograms of the neuronal response, recorded extracellularly. Histograms were compared before, during and after local ejection of NE from multibarreled micropipettes. In young rats NE preferentially inhibits spontaneous discharge more than evoked excitations. The inhibitory response of the Purkinje cell to activation of basket and stellate cell afferents is potentiated by NE with respect to the inhibition of spontaneous discharge. In old rats the NE-induced potentiation of both excitatory and inhibitory responses was significantly diminished. The loss of noradrenergic enhancement of the relative responsiveness of Purkinje neurons to afferent inputs in senescent animals may relate to behavioral deficits seen in aging.

The Cerebellum and Neural Control

Masao Ito is responsible for the remarkable discovery 20 years ago that the action of Purkinje's cells on their target neurons is uniformly inhibitory or disfacilitatory. This finding contributed greatly to our understanding of cerebellar function. Since that time, he and his colleagues in Tokyo have worked intensely upon the physiologic functions of the floccular lobe with respect to the vestibulo-ocular system. In this work he has systematically tested a hypothesis originally proposed by Marr and later modified by Albus that plastic interactions between climbing fibers and parallel fibers upon Purkinje's cells are responsible for aspects of motor learning. Ito's work has allowed theoretical constructs to be made concerning cerebellar input to adaptive and predictive control, multivariate control, motor learning, and motor programming. This work provides the underpinnings of the present book. The book presents a detailed review of cerebellar anatomy, physiology, and pharmacology. The text is divided into four

Morphological characteristics of serotonin nerve fibers in the mammalian hypothalamic nuclei

The efferent connections of the thalamic nucleus dorsointermedius posterior were studied in the pigeon. In pigeons, this thalamic nucleus receives both paleostriatal (basal ganglia) and cerebellar input and has been compared to nuclei of the mammalian thalamic ventral tier on this basis. The present results show that neurons of nucleus dorsointermedius posterior project upon a crescent-shaped neuronal field within the neostriatum intermedium as well as upon the ventral paleostriatum and nucleus intrapeduncularis. The relationship of the neostriatum intermedium field to avian motor pathways is discussed and it is suggested that nucleus dorsointermedius posterior thalami of birds may play a role comparable to that of the mammalian ventral tier nuclei in the neural control of motor functions.The efferent projections of dorsointermedius posterior were contrasted with those of adjacent structures within the avian posterior thalamic complex. Neurons within nucleus dorsomedialis posterior appear to be related to the avian limbic system and project to a neuronal field within the rostromedial portion of the neostriatum intermedium. Neurons in nucleus dorsolateralis posterior have been shown to receive input from the optic tectum;12 efferents from dorsolateralis posterior were traced to a small triangular wedged-shaped field within the ventromedial portion of the periectostriatal belt.

High affinity glutamate uptake in the red nucleus and ventrolateral thalamus after lesion of the cerebellum in the adult cat: biochemical evidence for functional changes in the deafferented structures.

High affinity glutamate uptake (HAGU) was measured within the red nucleus (RN) and the ventrolateral thalamic area in intact adult cats and in animals which had undergone a large hemicerebellectomy 8 to 21 days before. In the side contralateral to the lesion, results show two types of changes in HAGU: 1. In the caudal parts of the RN and the ventrolateral thalamic nucleus (VL), a strong HAGU decrease was demonstrated suggesting some cerebellorubral and cerebellothalamic fibres use glutamate (Glu) as their neurotransmitter. 2. In the rostral parts of the RN and the VL, an increase in HAGU was detected. This increase was particularly large at thalamic level, which led us to perform a kinetic analysis of the uptake system. Results show that the increase observed in HAGU is related in the thalamic area to an increased affinity of the transport sites for Glu. The mechanism of the HAGU increase measured in the rostral VL after cerebellectomy was further investigated in the presence of acetylcholine (ACh) which we have previously shown to be possibly involved in the neurotransmission of some cerebellothalamic and cerebellorubral fibres. ACh was shown to exert an inhibitory effect on HAGU in the control situation. Decrease in affinity of the transport sites for Glu induced by ACh was more pronounced when HAGU was enhanced as a consequence of the cerebellar lesion. We hypothesized that the cerebellectomy enhances the activity of nerve terminals which take up Glu in the VL and that we have shown to be mainly related to corticothalamic neurons. The basic mechanism involved in this activation could be the withdrawal of presynaptic inhibitory controls on corticothalamic fibres due to the removal of the putative cholinergic cerebellar input. This hypothesis was extended to the RN where previous electrophysiological and anatomical studies have suggested that the cerebellar lesion induces a sprouting of corticorubral nerve terminals. The increase in HAGU in response to the cerebellar lesion could constitute an adaptive mechanism by which the CNS may compensate for the loss of the excitatory cerebellar input to the RN and thalamic neurons by increasing the corticofugal transmission.

Electrophysiological and morphological studies on thalamic neurons receiving entopedunculo- and cerebello-thalamic projections in the cat

Electrophysiological studies on the entopedunculo- and cerebello-thalamic projections were performed by intracellular recordings in the thalamic VA, VL and VM nuclei of cats under sodium pentobarbital anesthesia. Identification of the thalamic neurons was performed electrophysiologically by antidromic activation on stimulation of the precruciate cortex (areas 4 and 6) and the caudate nucleus, and morphologically by intracellular staining with HRP through recording microelectrodes. One hundred and sixty-three neurons were collected in the VA, VL and VM nuclei. In 79 neurons penetrated in the medial and ventral parts of the VA and VL nuclei, stimulation of the entopeduncular nucleus induced monosynaptic IPSPs (latency of 1.1–3.5 ms, mean 2.07 ms). Sixteen neurons were identified as thalamo-cortical relay neurons and 3 were activated only orthodromically by precruciate stimulation. Seventy-eight neurons located dorsolaterally to the entopeduncular-influenced neurons received only cerebellar EPSPs. Only 6 neurons showed convergence of entopeduncular and cerebellar inputs. They were scattered around the border between the entopeduncular and cerebellar projection areas. Sixteen neurons could be stained intracellularly by HRP injection. From the pattern of dendritic arborization, two types of neurons can be distinguished: neurons whose dendrites spread radially in all directions and neurons whose dendrites extend mainly along the long axis of the soma for a long distance in the frontal plane, respectively. The former are relay cells to the cerebral cortex or the caudate nucleus (i.e. projection neurons) and the latter appear to be interneurons in the thalamus.