Effect of visual deprivation on evoked potentials in the visual cortex and superior colliculus in rabbits

Evoked potentials arising in the visual cortex and superior colliculus to stimulation of the collateral eye by single, paired, and repetitive flashes were recorded in rabbits reared in darkness or in normal illumination. The absence of significant change in the latent period and amplitudes of the first two components of the collicular responses and of the recovery cycle and response to repetitive stimulation in the light-deprived animals suggest that photic stimulation does not affect the normal functional development of the rabbit retinotectal system. However, functional deafferentation in the early postnatal period gives rise to serious disturbances of visual cortical function, as reflected in a marked decrease in amplitude of the primary response, lengthening of the recovery cycle, and narrowing of the range of rhythm-binding frequencies of flashes. These disturbances were reversible. The period of maximal sensitivity of the rabbit retinocortical system to visual deprivation begins at the end of the first month of postnatal life. The possible mechanisms lying at the basis of these functional disturbances in light-deprived animals are discussed.     

Interactions between electrical activities of the sensomotor cortex and the hippocampus during 'animal hypnosis' in rabbits

The electrical activity of the left and right sensorimotor cortex and left and right dorsal hippocampus (CA3 fields) was recorded during "animal hypnosis" in rabbits. The "animal hypnosis" produced asymmetry in the spectral power of the hippocampal electrical activity due to an increase in the power of delta 1, delta 2, and theta 1 components in the left-hippocampus and decrease in the spectral power in the same ranges in the right-hippocampus. Hemispheric asymmetry in the electrical activity during the "animal hypnosis" was also expressed in the indices of coherence between the sensorimotor cortex and hippocampus. EEG coherence between the left sensorimotor cortex and left hippocampus in the delta 1, theta 1, and theta 2 ranges was higher than that between the right-side structures.     

The mechanism of interaction between the thalamic posterior lateral nucleus and the sensomotor cortex in rabbits

The thalamic posterior lateral nucleus was shown to exert phasic and tonic effects on the function of sensomotor cortex: the former in the form of pulvinar-cortical responses, and the latter in the form of foci of increased or decreased excitability. The findings suggest an inhibitory tonic effect of the sensomotor cortex on neuronal network of the posterior lateral nucleus.     

Control of the superior colliculus by the lateral prefrontal cortex

Several decades of patient, functional imaging and neurophysiological studies have supported a model in which the lateral prefrontal cortex (PFC) acts to suppress unwanted saccades by inhibiting activity in the oculomotor system. However, recent results from combined PFC deactivation and neural recordings of the superior colliculus in monkeys demonstrate that the primary influence of the PFC on the oculomotor system is excitatory, and stands in direct contradiction to the inhibitory model of PFC function. Although erroneous saccades towards a visual stimulus are commonly labelled reflexive in patients with PFC damage or dysfunction, the latencies of most of these saccades are outside of the range of express saccades, which are triggered directly by the visual stimulus. Deactivation and pharmacological manipulation studies in monkeys suggest that response errors following PFC damage or dysfunction are not the result of a failure in response suppression but can best be understood in the context of a failure to maintain and implement the proper task set.     

Amino acid profiles in long-evans rat superior colliculus,visual cortex,and inferior colliculus

An ultransensitive triple-column ion-exchange/fluorometric method was utilized to measure the levels of over 30 amino acids and related primary amino compounds in Long-Evans rat superior colliculus (SC), visual cortex (VC) and inferior colliculus (IC). Comparison of levels of amino compounds revealed distinctly different profiles for each region. Major constituents were the neurotransmitters and related compounds glutamate, glutamine, GABA, taurine, aspartate and glycine. Glutathione levels were also relatively high in all three regions. SC exhibited a significantly higher level of GABA and -alanine compared to both VC and IC. VC had significantly higher levels of glutamate and taurine. VC exhibited the lowest level of glycine and IC the highest. A time-course experiment using SC documented that levels of eleven of thirty-four compounds, including GABA, were subject to significant postmortem alteration in vitro. SC GABA stability experiments indicated that significant in vitro increases of free GABA levels between 1 and 4 min postmortem were associated with equimolar decreases of conjugated GABA levels.     

Physiological properties of neurons in superficial layers of superior colliculus of rabbits

Neurons in superficial layers of the superior colliculus of the rabbit are classified into three types by their electrophysiological properties. Among them, two types belong to projecting neurons which send axons to the thalamic pulvinar (N=52) and dorsal lateral geniculate nucleus (N = 54) respectively. All other neurons are pooled into the third type (N=99). Projecting neurons of both types receive monosynaptic visual inputs via optic tract fibers of similar conduction velocity, indicating that in the superior colliculus of the rabbit, there is no difference in conduction velocity between the two pathways. They also receive trisynaptic inhibitory inputs, most likely via recurrent inhibitory circuits. The third type of neurons receives disynaptic optic and trisynaptic inhibitory inputs. The function of neurons of the third type is studied.     

Cortico-cortical connections between the auditory fields and the sensomotor area of the cortex]

In 18 cats by means of two methods--anterograde degeneration and retrograde transport of exogenic horseradish peroxidase--cortico-cortical connections of the auditory fields to the cortical sensomotor area have been studied. These connections have been stated to terminate in layers V-III of certain parts of the sensomotor area corresponding to the projections of the foreleg and the head. Initial neurons of the connections studied are pyramidal cells in layers III and II. They are situated in rostral and caudal parts of the fields AI and AII, but within these levels they occur in different areas of the auditory fields.     

Gap-like junctions between neurons and glia in the superior colliculus of mammals

The neuron cell bodies and glia cells are separated by a narrow intercellular cleft of 200 A. We present here evidence that perikarya neuronal and perineuronal glia of the superior colliculus of the Oryctolagus Cuniculus communicate through gap-like junctions according to ultrastructural parameters. These junctions would mean some degree of electronic coupling between neuron cell bodies and perineuronal glia cells.     

Morphologic changes in the sensomotor cortex in experimental neurosis

Disturbances of higher nervous activity (experimental neurosis) are attended with morphological changes of blood circulation in the sensorimotor area of the cerebral cortex, corresponding to distonic vascular disorders, as well as with hypoxic and neuroglial changes. Observed changes in the nervous tissue also reflect adaptive and defensive mechanisms of the brain (in rabbits).     

Electrophysiological relations between the superior colliculus and the red nucleus in the cat.

The electrical activity of single units located in the parvicellular part of the red nucleus (pRP) was recorded extracellularly in nitrous oxide anesthetized and C1-transected adult cats. In this area, neurons were found to respond to electrical stimulation applied to intermediate and deep layers of the right superior colliculus (SC). Forty neurons located in the pRN of both sides were studied. Three neurons out of 18 (16.6%) located in the contralateral pRN and six neurons out of 22 (27.3%) located in the ipsilateral pRN were driven by the right SC stimulation. The pRN neurons were separated into four groups according to the latency response to the SC stimulation: 1) 0.6-1.9 ms, 2) 2-4 ms, 3) 4-6 ms, 4) variable latency responses. Each of these four groups of neurons showed a particular pattern of discharge, even though their discharge frequency showed a strong consistency. Four pRN neurons, which responded to SC stimulation, showed a significant correlation with spontaneous horizontal eye movements of saccadic type. It is known that the SC represents one of the main outputs of the striato-nigral motor system. The relation between the SC and the pRN described in the present study suggest that connections exist between the cortico-rubral and the striato-nigral systems, since both have the SC as a common output structure. It is likely, therefore, that the cortico-rubral-SC system is involved in the control of oculomotor functions, and that the SC may serve to establish interactions between systems concerned with eye movements.     

Intrinsic processing in the mammalian superior colliculus

The mammalian superior colliculus receives visual inputs from the retina and primary visual cortex in its superficial layers and sends descending motor commands from its deeper layers. It is now becoming clear that a connection exists between these layers, but the signal transmission through it is not robust. The induction of burst discharges in the deeper layer neurons by direct visual inputs from the superficial layers may lead to 'express' saccadic eye movements with extremely short reaction times in behaving animals.     

Excitability of the sensomotor cortex and red nucleus of rabbits at different levels of spatial synchronization of cortical potentials

To determine the excitability of the rabbit sensomotor cortex and red nucleus the animal's motor response to electrical stimulation of these structures at threshold strength was investigated. In computerized experiments the excitability of these structures was compared in situations characterized by different degrees of correlation of cortical potentials. An increase in the level of spatial synchronization of cortical potentials was shown to be accompanied by an increase in the excitability of the sensomotor cortex and red nucleus. This increase in excitability is evidently a neurophysiological mechanism of the increase in probability of appearance of an effector response to sensory stimulation when the level of spatial synchronization of cortical potentials is raised.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 19–24, January–February, 1977.     

Elementary transcallosal connections of the rabbit sensomotor cortex]

Antidromic responses of two callosal neurones to a local electrical stimulation of the rabbit sensorimotor cortex may be recorded simultaneously with one microelectrode in the homotopic cortical area. In such recording conditions the relative amplitude of extracellularly recorded action potentials of the two neurones is determined primarily by the distance between these neurones and the electrode's tip. In response to the stimulation of the symmetrical area transcallosal monosynaptic excitation of the callosal neurone may occur; two callosal neurones may exite monosynaptically one and the same recorded neurone. The results suggest the existence of clusters or columns, formed jointly by the bodies and terminals of callosal neurones; a functional interconnection between symmetrical clusters or columns may exist, in particular a positive feedback.     

Hypothalamic influences on unit activity in the cat sensomotor cortex

Experiments on unanesthetized, immobilized cats showed different effects of individual hypothalamic nuclei on spontaneous unit activity in the sensomotor cortex. Compared with the posterior hypothalamic nucleus (PHN) and its anteromedial region (AMH), in response to stimulation of the lateral hypothalamic nucleus (LHN) changes in spontaneous activity were more frequently found. The ratio between activation and inhibitory responses was 36 and 36% for AMH, 51 and 30% for LHN, and 47 and 28% for PHN. An approximately equal number of sensomotor neurons (27–34%) gave tonic responses. Phasic changes in spontaneous activity were observed more often in response to stimulation of LHN, less frequently to stimulation of AMH and PHN. Responses of "nonpyramidal" neurons to stimulation of AMH and LHN were identical. "Pyramidal" units were more sensitive to LHN stimulation. Variations in hypothalamic effects depending on the type of response of sensomotor neurons to sensory stimuli were detected. Cells with tonic responses were more susceptible to influences of LHN and AMH than cells which responded by phasic changes in spontaneous activity to sensory stimuli. Fewer still positive responses were recorded in areactive neurons.Medical Institute, Chita. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 115–122, March–April, 1972.