Response of caudate nucleus neurons to acoustic stimulation during functional blockade of the thalamic centrum medianum in the cat

The response of caudate nucleus neurons to acoustic stimulation (a click at 0.5 Hz) was investigated during chronic experimentation in cats using intracellular techniques and reversible blockage of the thalamic centrum medianum produced by anode polarization. Having analyzed poststimulus histograms it was found that the response of phasic activation to an acoustic signal decreased, and disappeared in 52% of neurons. A reduction in the level of spontaneous activity was also observed in neurons of the caudate nucleus. The significance of a direct pathway from the thalamic centrum medianum to the caudate nucleus is discussed from the viewpoint of acoustic signal transmission to caudate nucleus neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 92–99, January–February, 1986.     

Efferent connections of the centrum medianum of the cat thalamus revealed by autoradiography

Efferent connections of the centrum medianum and parafascicular nucleus of the thalamus (CM-Pf complex) in cats were studied by the method of anterograde axonal transport of tritiated amino acids followed by autoradiography. Projections from CM-Pf ascend to nuclei of the ventral group and nonspecific nuclei of the thalamus, preoptic, dorsal, lateral, and posterior areas of the hypothalamus, and also into the subthalamic region. Descending pathways are formed only by neurons of the caudomedial part of CM-Pf. They project into the pretectal region, superior colliculus, reticular formation, locus coeruleus, region of the ramus communicans, and substantia grisea centralis of the mesencephalon and pons, and also into the nuclei raphe, magnocellular reticular area, and inferior olivary nucleus of the medulla. In agreement with previous observations it was found that the caudomedial part of CM-Pf does not send direct projections into the cortex and striatum.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 224–230, March–April, 1984.     

Sources of ascending afferent projections to the midbrain central tegmental area and centrum medianum thalami in cats

After microinjections of horseradish peroxidase into the central tegmental area of the midbrain and centrum medianum thalami in cats, labeled neurons were found in the nucleus of the tractus solitarius, gracile and cuneate nuclei, spinal nuclei of the trigeminal nerve, the external nucleus and nucleus of the brachium of the inferior colliculus, the medial pretectal region, nucleus of the posterior commissure and stratum intermediale of the superior colliculus, and reticular structures of the medulla and pons. Comparison of the location of the sources of ascending afferent projections in the central tegmental area of the midbrain and centrum medianum thalami showed that the reticular formation receives mainly visceral projections through the nucleus of the tractus solitarius, whereas the centrum medianum thalami is innervated mainly by the system of sensory somatic nuclei.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 172–178, March–April, 1982.     

Vestibular projections in the cat temporal cortex

Boundaries of vestibular projections in the temporal cortex during stimulation of the vestibular nerve were studied in cats anesthetized with pentobarbital and chloralose or chloralose alone. The caudal boundary of the vestibular zone was shown to run along the anterior ectosylvian gyrus. A focus of evoked activity was found in the suprasylvian sulcus or 1–2 mm rostrally to it. All short-latency evoked potentials recorded during vestibular nerve stimulation in the temporal region caudally to the zone mentioned above were connected with the spread of current to auditory structures. To verify the extent of spread of the stimulating current, focal potentials were recorded in the vestibular and superior olivary groups of nuclei. Special experiments were carried out to study the topography of these potentials at the level of bulbar structures during stimulation of vestibular and auditory nerves. According to the results, there is no second vestibular area in the temporal cortex in cats. Vestibular afferentation is projected mainly into the contralateral hemisphere, and the response latency is 5.2±0.7 msec. The ipsilateral evoked potentials had a long latent period (8.4±1.3 msec), and their amplitude depended on the type of anesthesia; it was accordingly postulated that additional synaptic relays exist in this vestibulocortical pathway.     

Organization of the thalamic and cortical projections of the cat neostriatum]

The investigation has demonstrated that in the cat the nucleus caudatus and the putamen are projected on the cortex and thalamic nuclei of the ipsilateral hemisphere according to a certain topical principle characterized by both similarity in localization of projections of these two structures of the neostriatum and their difference. On the one hand, to the same fields of the cortex and the thalamic nuclei fibres from both structures of the neostriatum go, and on the other hand--a number of cortical zones and thalamic nuclei get projections either from the nucleus caudatus or from the putamen only. Owing to a certain organization of the connections studied, it is possible to consider them as the base of functional heterogeneity of the basal ganglia. Over-lapping of the cortical and thalamic projections of the nucleus caudatus and the putamen might explain common striatal effects on behavioral reactions.     

Relationship between thalamic projections and different areas of the parietal association cortex in cats

Thalamic neuronal projections to the parietal association cortex were investigated in cats applying techniques of retrograde axonal transport of two fluorescent dyes (primuline and fast blue). The dorsal thalamic pulvinar (PL) as well as the dorsal and caudal lateral posterior nucleus (LP) were found to project mainly to the central suprasylvian gyrus (CSSG), while the ventral PL and the ventrorostral LP send out projections to rostral sites of the same gyrus (RSSG). Neurons with dual labeling were found in the PL, LP, suprageniculate, anteroventral, and ventrolateral thalamic nuclei following a single injection of two different markers into the RSSG and CSSG, as well as the centrolateral, paracentral, and centromedial nuclei. Topical organization of sources of cortical projections within the PL-LP complex can apparently provide a high level of discrimination of visual signals by individual cortical units. At the same time, the RSSG and CSSG appear to function in harmony to a considerable extent during integration of information of differing cortical origin; this could point to a lack of differentiation on the part of the RSSG and CSSG, corresponding to feline cortical areas 5 and 7 approximately.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 135–142, March–April, 1991.