Background spike activity of cerebellar nucleus interpositus neurons in rats

Using computer analysis of the background spike activity recorded from cell units of the cerebellar nucleus interpositus, it was possible to distinguish several dynamic types and regularity gradings that specifically characterize these neurons, and to correlate these characteristics with the statistical parameters of their activity.Translated from Neirofiziologiya, Vol. 25, No. 2, pp. 98–100, March–April, 1993.     

Plastic synaptic reorganization in the sensorimotor cortex of adult cats after lesioning of the contralateral cerebellar nucleus interpositus

Intact cats and animals undergoing lesioning of the contralateral cerebellar nucleus interpositus between one and six months previously were used in this research, employing intracellular recording techniques and investigating the response of corticospinal neurons (CSN) to stimulating the aforementioned nucleus, the ipsilateral cerebellar nucleus interpositus, and the ventrolateral thalamic nucleus. A reduction was found in the stage of rise to peak in monosynaptic thalamocortical EPSP in CSN of operated animals, with a low axonal conduction velocity, pointing to distant terminal dendrosomatic sprouting and formation of new synapses at proximal sections of the CSN somatodendritic membrane. Findings are presented on formation of ipsilateral interpositothalamocortical projections duplicating similar contralateral projections in intact animals. Contralateral cortico-interposital collaterals were found in intact animals and similar sprouting of ipsilateral origin in those which had undergone surgery.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 761–771, November–December, 1990.     

Influences of cerebellar interpositus nucleus and fastigial nucleus on neuronal activity of lateral hypothalamic area

Stimulation of cerebellar interpositus nucleus and (astigial nucleus could influence the neuronal activi-ty of lateral hypothalamic area in the cat, and some of the neurons which respond to the cerebellar stimulations are glucose-sensitive neurons. These results suggest that the cerebellum is involved not only in motor control, but also in the regulation of non-somatic functions through the cerebello-hypothalamic pathways.     

Responses of the red nucleus neurons to stimulation of the paw pads of forelimbs before and after cerebellar lesions.

Cerebellar cortex ablation releases deep cerebellar nuclei of monosynaptic inhibition from Purkinje cells. Therefore, it strengthens excitatory influence from Interpositus Nucleus (IN) upon Red Nucleus (RN), which results in much higher facilitation of the rubro-spinal neurons. This causes a big increase of spontaneous discharge rate, and eliminates brakes of discharges from responses generated by somatosensory stimuli. These two changes destroy content and timing of feedback information flowing through the spino-cerebello-rubro-spinal loop. This false bias of the feedback information, very important for fast postural adjustment and coordination of ongoing movements executed by central motor program, may at least in part be responsible for abnormal motor behavior evoked by cerebellar damage. Hemicerebellectomy resulted in dramatically reduced spontaneous activity and responses to limb stimulation because of severing a major input to the red nucleus from deep cerebellar nuclei. Due to direct somatosensory input to magnocellular Red Nucleus (mcRN) from the spinal cord that bypassed the cerebellum, the latency of response to limb stimulation was not changed and the narrower receptive fields were still present.     

Analysis of evoked potentials of the cerebellar cortex

Evoked potentials (EP) of the cerebellar cortex in response to stimulation of peripheral nerves are characterized by a two-phase positive-negative oscillation of the potential having a latent period of 10–25 msec. The electropositive phase can contain up to three components. The latent period of component I comprises 3–9 msec. The latent period and amplitude of this component are distinguished by considerable stability, which indicates the predominant significance of presynaptic processes in its formation. The sign of component II changes at a depth of 500 µ (and more), which corresponds to the position of the granular cell layer. At this level there arises in the neurons a response with a latent period of 4–10 msec in the form of a group (3–10) of impulses with a frequency of up to 200 per sec. It is concluded that the granular cells participate in the formation of component II and partially participate in the formation of components I and III of the EP. Responses to stimulation of the nerves appear synchronously with the EP in 24% of responding Purkinje cells; they fall on the maximum electropositive deviation or component III of the EP. Microinjections of 1% strychnine into the cerebellar cortex cause an increase of EP amplitude; impulse activity of the neurons is intensified. This indicates participation of postsynaptic processes in the formation of EP. No shifts in the EP of the cerebellar cortex were observed after intracortical injection of 0.1% atropine.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 429–433, July–August, 1970.     

Functional relations between neighboring neurons of nucleus interpositus of the cat cerebellum

In the nucleus interpositus (IP) of the cat cerebellum the response patterns to peripheral stimulation were recorded, and the interactions between electrophysiologically identified neurons were studied with cross correlation techniques. The response patterns were composed of excitation appearing with latencies of about 8 to 22 ms., separated and succeeded by phases of inhibitions. Four basic types of interneuronal connectivities were observed: 1) intranuclear excitation, 2) shared input from a common source, 3) intranuclear inhibition, and 4) stimulus coordinated firing. Shared input appeared in all combinations of paired neurons and extended for a distance from 300 microns up to 1000 microns. Intranuclear excitation as well as inhibitory synaptic connection occurred mainly in combinations between interneurons and efferent neurons. Stimulus coordinated firing of paired neurons was found in almost the entire extent of the nucleus interpositus.     

Restoration of evoked responses in the rat dorsomedial thalamic nucleus after amygdaloid lesion

The changing pattern of focal potentials in the thalamic dorsomedial nucleus, produced by stimulating the periamygdaloid cortex between 2 and 90 days after unilateral destruction of the basolateral amygdaloid nuclei, was investigated during semichronic experiments on anesthetized rats. A comparison was made between the parameters and spatio-temporal characteristics of potentials, as revealed at different stages of functional reorganization of thalamo-limbic interaction. The biggest increase in latency to peak of the principal positive-negative component is seen during the first two months after amygdaloid lesion. The original pattern and numerical features of focal potentials are restored in 2.5 months. The potentials formed during the course of the compensatory process differed from those of animals with an intact CNS, however, the amplitude of their test response to paired stimuli being incompletely restored, especially at interstimulus intervals of 40–150 msec. Findings indicate the high functional plasticity of the neural fibers mediating afferents at the level of the above thalamic association nucleus.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 153–161, March–April, 1986.     

Spontaneous activity and evoked responses of cerebellar cortical neurons to vagal and limb nerve stimulation in pigeons

Spontaneous activity and evoked reponses of the cerebellar cortical neurons of decerebrate pigeons to stimulation of the vagus nerve and nerves of the limbs were investigated. The cell responses were uniform in type regardless of the character of stimulation. Phasic and tonic responses, predominantly of excitatory type, were recorded. The phasic responses had both short (10–20 msec) and long (up to 80 msec) latent periods. The latter predominated. Features distinguishing the unit responses to vagal stimulation of the limb nerves included: a smaller number of activated cells, longer latent period of the responses, absence of activation of Purkinje cells through the climbing fibers, and lower capacity for rhythm binding.     

Aftereffect phenomena in neurons of the cerebellar cortex

The reactions of Purkinje cells (PC) of the cerebellar cortex during electrocutaneous stimulation of one of the extremities with different frequencies (from one stimulus in 10 sec to one to five stimuli per sec) were studied in experiments on cats. It was shown that the reactions to the first and subsequent stimuli were different. This indicates the presence of an aftereffect from the first stimulus. It is assumed that the variability of the responses of PC to infrequent stimuli is connected with changes in their functional state which develop in response to "spontaneous" cerebellopetal impulses, as well as to circulation of excitation in intracerebellar circuits. With an increase in the frequency of the stimuli, the changes in excitability induced by previous peripheral stimuli, not only in the reacting PC, but also in the whole neuronal network of the corresponding cerebellopetal pathway, evidently acquire paramount importance. The absence of a direct relationship between strong peripheral stimulation and the degree of the reactions of the PC may be due to the involvement of intermediate neurons both of the exciting and inhibitory type in the transmission of impulses at the level of the cerebellar cortex.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 573–580, November–December, 1970.     

Features of evoked potentials in the cerebellar cortex of rabbits

We investigated evoked responses of the cerebellar cortex of rabbits under Nembutal or chloralose anesthesia to stimulation of the sciatic, brachial, and vagus nerves. The parameters of evoked potentials (E Ps), together with features of their distribution throughout the cerebellar cortex, enabled us to divide them provisionally into three types. Evoked potentials of the first type have a latent period of 5–10 msec and a two-phase or more complex shape. Evoked potentials of the second type have a latent period of 10–23 msec and include from one to four components. Evoked potentials of the third type are discharges with long latent periods (20–50 msec) and consist of a series of slow sinusoidal oscillations. Appearance of an initial electronegative component is characteristic of EPs of the cerebellar cortex of rabbits, especially those of the second and third types. Evoked potentials of the first type are local.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 73–80, July–August, 1969.     

The polypeptide PEP-19 is a marker for Purkinje neurons in cerebellar cortex and cartwheel neurons in the dorsal cochlear nucleus

This light and electron microscopic immunocytochemical study shows that the polypeptide PEP-19, a presumptive calcium binding protein specific to the nervous system, represents an excellent marker for cerebellar Purkinje cells and dorsal cochlear nucleus (DCoN) cartwheel cells. The polypeptide clearly reveals the entire populations of both types of neurons, including their complete dendritic and axonal arborizations. Other PEP-19 containing neurons in the two regions display weak immunoreactivity restricted to the cell body or to cell body and principal dendrites. Electron microscopic localization of PEP-19-like immunoreactivity reveals similarities between this polypeptide, parvalbumin, and a 28K vitamin D-dependent calcium binding protein. However, calmodulin, which is expressed in both Purkinje and granule cells, may differ from PEP-19. Similarities between the organization of the cerebellar cortex and the DCoN superficial layers have been known for some time, with several types of neurons in one system having their presumed homologue in the other. These data provide further support for the proposed structural and functional homology between Purkinje and cartwheel neurons, and establishes PEP-19 as a useful marker for examining degeneration of these two neuronal populations in murine cerebellar mutants.     

Directional tuning of visual cortex neurons in the cat before and after nembutal injection

Directional tuning was investigated in 40 neurons of the primary visual cortex (area 17) before and after Nembutal injection during acute experiments on immobilized cats. Preferred orientation (PO) in 50% of neurons was found to be stable after the drug, while the remainder showed a consistent shift in PO (averaging 53.6±8.0°) for a number of hours. Neurons with consistent PO more frequently showed a preference for horizontal and vertical stimulus orientation; cells with unstable tuning had a wider PO distribution. More refined directional detection (i.e., finer tuning) was noted in "stable" rather than in "unstable" neurons both before and after administering the drug. Under narcosis, directional tuning altered in 50% of cells — an effect more marked in "unstable" than in "stable" cells (68% as against 38%). Mean background discharge rate also fell by an average of 5.5-fold and induced firing rate declined 1.5-fold during narcosis, moreover.Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 669–676, November–December, 1991.     

Neurons in the rat lateral hypothalamic area integrate information from the gastric vagal nerves and the cerebellar interpositus nucleus

Previous investigations have demonstrated that the neuronal activity in the lateral hypothalamic area (LHA) is respectively modulated by afferent inputs from the gastric vagal nerves innervating the upper gastrointestinal tract, as well as the cerebellar interpositus nucleus (IN). The aim of this study was to examine whether the gastric vagal and cerebellar IN inputs converge onto single LHA neurons in rats, especially those sensitive to glycemia. Of the 114 LHA neurons recorded, 60 (52.6%) and 51 (44.7%) responded to gastric vagal and cerebellar IN stimulation, respectively. Of the 60 LHA neurons responsive to gastric vagal stimulation, 30 also responded to the cerebellar IN stimulus, indicating a convergence of gastric vagal and cerebellar inputs onto single hypothalamic cells. When the gastric vagal nerves and cerebellar IN were stimulated simultaneously, a summation of the responses was observed in all 6 neurons tested. Moreover, of 24 neurons that responded to both the gastric vagal and cerebellar IN stimuli, 15 (62.5%) were identified as glycemia-sensitive. These results demonstrate that the visceral information transmitted by the gastric vagal nerves and the somatic information forwarded by the cerebellar IN converge onto single LHA neurons, especially those sensitive to glycemia. The findings also suggest that integration of somatic-visceral responses related to short-term feeding regulation may take place in the LHA.     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Retrograde degeneration of the neurons of the cerebellar nuclei after partial removal of the associative cerebral cortex

Retrograde degeneration of the cerebellar nuclei cells has been studied after partial ablation of the associative parietal cerebral cortex in the cat. The material is stained after Nissl. Retrogradely degenerated and normal cells are counted. The "ghost-cells" in the cerebellar nuclei indicate that a direct axonal connection exists between some neurons and the cerebral cortex operated, while the cells that are at other stages of degeneration are, perhaps, connected with this part of the cortex by means of axonal collaterals.     

Non-traditional large neurons in the granular layer of the cerebellar cortex

The granular layer of the cerebellar cortex is composed of two groups of neurons, the granule neurons and the so-called large neurons. These latter include the neuron of Golgi and a number of other, lesser known neuron types, generically indicated as non-traditional large neurons. In the last few years, owing to the development of improved histological and histochemical techniques for studying morphological and chemical features of these neurons, some non-traditional large neurons have been morphologically well characterized, namely the neuron of Lugaro, the synarmotic neuron, the unipolar brush neuron, the candelabrum neuron and the perivascular neuron. Some types of non-traditional large neurons may be involved in the modulation of cortical intrinsic circuits, establishing connections among neurons distributed throughout the cortex, and acting as inhibitory interneurons (i.e., Lugaro and candelabrum neurons) or as excitatory ones (i.e., unipolar brush neuron). On the other hand, the synarmotic neuron could be involved in extrinsic circuits, projecting to deep cerebellar nuclei or to another cortex regions in the same or in a different folium. Finally, the perivascular neuron may intervene in the intrinsic regulation of the cortex microcirculation.