Visual thalamic afferents to area 29 of the rat limbic cortex

Afferent connections of the retrosplenial area of the rat limbic cortex were investigated by the retrograde horseradish peroxidase axon transport method. After injection of horseradish peroxidase (HRP) into area 29 of the cortex, HRP-labeled cells were found in the dorsal part of the lateral geniculate body and the posterolateral, pretectal, and anterior dorsal thalamic nuclei. Connections were found between cortical area 29 and visual projection areas (areas 17 and 18a) and with area 29 on the contralateral side of the brain. The results are evidence that all the principal visual structures of the thalamus and the visual cortical projection area form direct projections to the retrosplenial cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 135–139, March–April, 1982.     

Early lesion of the reticular thalamic nucleus disrupts the structure and function of the mediodorsal thalamus and prefrontal cortex

The thalamic reticular nucleus (TRN), part of the thalamus, is a thin GABAergic cell layer adjacent to the relay nuclei of the dorsal thalamus. It receives input from the cortex and other thalamic nuclei and provides major inhibitory input to each thalamic nucleus, particularly the mediodorsal nucleus (MD). As the MD is important for supporting optimal cortico–thalamo–cortical interactions during brain maturation, we hypothesized that that early damage to the TRN will cause major disturbances to the development and the functioning of the prefrontal cortex (PFC) and the MD. Rat pups at P4 were randomized in three groups: electrolytic lesion of TRN, TRN‐sham‐lesion group, and the classical control group. Seven weeks later, all rats were tested with several behavioral and cognitive paradigms, and then perfused for histological and immunohistochemical studies. Results showed that TRN lesion rats exhibited reduced spontaneous activity, high level of anxiety, learning and recognition memory impairments. Besides the behavioral effects observed after early TRN lesions, our study showed significant cytoarchitectural and functional changes in the cingulate cortex, the dorsolateral and prelimbic subdivisions of the PFC, as well as in the MD. The assessment of the basal levels of neuronal activity revealed a significant reduction of the basal expression of C‐Fos levels in the PFC. These experiments, which are the first to highlight the effects of early TRN lesions, provided evidence that early damage of the anterior part of the TRN leads to alterations that may control the development of the thalamocortical–corticothalamic pathways.     

Projections of the central cerebellar nuclei to the intralaminar thalamic nuclei in cats

Projections of the central cerebellar nuclei to the intralaminar thalamic nuclei were studied in cats with the use of light and electron microscopy. Almost all intralaminar nuclei were shown to obtain cerebello-thalamic projections. The entire complex of the central cerebellar nuclei serves as a source of such projections; yet, involvement of different nuclei is dissimilar. Destruction of the central and, especially, caudal regions of the fastigial nucleus evoked in the intralaminar thalamic nuclei degenerative changes in the nerve fibers (from swelling and development of varicosities up to total fragmentation). Pathological phenomena could be noticed in the most caudal regions of the above thalamic nuclear group, including the medial dorsal nucleus. Projections of the cerebellar interpositus nucleus were directed toward nearly the same regions of the intralaminar nuclei; degeneration was more intensive (covered thecentrum medianum) when posterior regions of the interpositus nucleus were destroyed. Destruction of the lateral cerebellar nucleus evoked a similar pattern of pathological changes, but degeneration was also observed in some structures of the ventral and anterior nuclear groups of the thalamus. Electron microscopic examination showed that degeneration of dark and light types developed in the fiber preterminals and terminals. It can be concluded that the central cerebellar nuclei project not only to the ventral complex of the thalamic nuclei, but also to the anterior, medial, and intralaminar nuclear groups (rostral and caudal portions).     

Connections between the anterior thalamic nuclei in turtles (data of the peroxidase method)

It turtles, Testudo horsfieldi (Gray) connections of anterior dorsomedial and dorsolateral thalamic nuclei have been investigated by means of horseradish peroxidase, injected ionophoretically. Retrogradely labelled neurons are predominantly revealed ipsilaterally in the cerebral structures belonging to the limbic system: in the forebrain--basal parts of the hemisphere, septum, adjoining nucleus, nuclei of the anterior and hippocampal commissures, hippocampal cortex, preoptic area; in the diencephalon--in the subthalamus (suprapeduncular nucleus), in some hypothalamic structures (para- and periventricular nuclei, posterior nucleus, lateral hypothalamic area, mamillary complex); in the brain stem--ventral tegmental area, superior nucleus of the suture. Less vast connections are with nonlimbic cerebral formations: projections to the striatum, afferents from the laminar nucleus of the acoustic torus, nuclei of the posterior commissure. Similarity and difference of the nuclei investigated in the turtles with the thalamic anterior nuclei in lizards, with the anterior and intralaminar nuclei in Mammalia are discussed. An idea is suggested on functional heterogeneity of the anterior nuclei in reptiles and on their role for ensuring limbic functions at the thalamic level.     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 μm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V–VI; some were also present in layers I–III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

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.     

A horseradish peroxidase study on the mammillothalamic tract in the rat

The mammillary projections to the anterior thalamic nuclei were investigated in the rat, using the horseradish peroxidase (HRP) method. Pars centralis of the medial mammillary nucleus projects to the medial portion of the ateromedial nucleus (AM). Pars medialis (Mm) of the medial mammillary nucleus sends fibers to the ipsilateral AM and sparsely to the medial portion of the contralateral side. The ventral and dorsal portions of Mm project to the anterior and posterior portions of AM, respectively. The pars latralis (Ml) and pars posterior (Mp) of the medial mammillary nucleus send fibers predominantly to the ipsilateral anteroventral nucleus and sparsely to the contralateral side. A slight difference between Ml and Mp projections was observed. The lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus.     

Afferent connections of the basolateral division of the amygdaloid complex of the cat brain

Injection of horseradish peroxidase into the basal macrocellular and lateral nuclei of the amygdaloid complex (BLAC) in the cat brain has revealed their rich thalamic afferentation. On the BLAC there are massive projections of: a) nuclei of the middle line of the precommissural pole of the dorsal thalamus (anterior parts of the paratenial, interanteromedial and reunial nuclei), as well as the whole anterior paraventricular nucleus, medial part of the ventral posteromedial nucleus; b) postcommissural nuclei of the dorsal thalamus; some "nonacustical" nuclei of the internal geniculate body (ventrolateral nucleus, medial and macrocellular parts and the most caudal end of the internal geniculate body). Rather essential are projections of the "posterior group nuclei", those of the suprageniculate nucleus, of some parts of the ventral thalamus (subparafascicular nucleus, marginal and peripeduncular nuclei) and parabrachial nucleus. Scattered single projections are obtained from all hypothalamic parts (most of all the ventromedial nucleus), reticular nuclei of the septum, substantia innominata, substantia nigra, truncal nuclei of the raphe. Variety of the dorsal thalamic nuclei, sending their fibers to the BLAC reflects variety of sensory information, that gets here, according to its modality, degree of its differentiation and integrity. A number of the dorsal thalamus nuclei, owing to abundance of labelled neurons, can be considered as special relay thalamic nuclei for the BLAC resembling corresponding relay nuclei for the new cortex.     

Thalamic relay of somatic and visceral signals to the orbital cortex

We investigated the role of different thalamic nuclei in the relaying of afferent signals into the anterior section of the coronary gyrus and into the orbital gyrus, using the evoked-potentials method, in delicate experiments on cats under Nembutal or Nembutal-chloralose narcosis, and also in experiments on cats not anesthetized but immobilized by injection of succinyl choline. Specific projection zones of the lingual, vagus, and glosso-pharyngeal nerves have been charted in the anterior coronary gyrus. The thalamic relay for that region is the medial pole of the ventral posterior nucleus. The orbital gyrus contains associative projections of both somatic and visceral nature. The relay for signal transmission in this region is also located in the ventral posterior nucleus. Relaying takes place, however, not in the central parts of the nucleus, where projections of the corresponding receptor zones have been charted, but nearer its lower medial surface. There is also an indirect route for associative projections, passing through the medial center and the intralaminar nuclei. That route emerges into the cortex through the ventral anterior and reticular nuclei. A feature of the projections of the vagus nerve in the orbital cortex is the existence of a supplementary region that exhibits responses, lying along the sulcus rhinalis. It was found that relaying for that region takes place in the ventral medial and submedial nuclei of the thalamus.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 65–72, July–August, 1969.     

Projections of different areas of the putamen on tha thalamic nuclei]

In the work presented the projections of rostral and caudal areas of the putamen on the thalamic nuclei were studied. The analysis of the frontal serial sections from the cat brains impregnated according to the methods of Nauta-Gygax, Finck-Haimer, Wiitanen made it possible to state that all the areas of the putamen radiate a great number of axons to the lateral thalamic nuclei--ventro-anterior, ventro-lateral, lateral-posterior, and ventro-posterior-medial. Only the rostral area of the putamen sends a mass of fibres to the nuclei of the median thalamus--medial-dorsal, central, central-lateral and ventro-posterior-lateral. On the other hand, in the posterior thalamic nucleus a great number of axons only from caudal area of the putamen have their terminals.     

Properties of monosynaptic connections between callosal neurons and specific thalamic nuclei

A comparative analysis of monosynaptic afferent and efferent connections of callosal neurons and target neurons of transcallosal fibers with neurons of the specific ipsilateral thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral, and anteroventral) was undertaken on the sensomotor cortex of unanesthetized rabbits, using an electrophysiological method. Differences were demonstrated between callosal neurons and target neurons of transcallosal fibers with respect to monosynaptic inputs from the thalamic nuclei and pathways proceeding toward these structures and (or) entering the pyramidal tract. Among target neurons, compared with callosal neurons, more cells had descending projections (54 and 14%, respectively). Monosynaptic action potentials arose in 22% of target neurons in response to stimulation of specific thalamic nuclei, whereas no such responses occurred in callosal neurons. Projections of target neurons into thalamic nuclei were shown to be formed both by independent fibers and by axon collaterals of the pyramidal tract. It is postulated that the distinctive properties thus discovered indicate significantly greater convergence of influence of thalamic relay neurons on the target neurons; this determines differences known to exist in characteristics of receptive fields and spontaneous and evoked activity of callosal neurons, on the one hand, and of neurons excited synaptically by transcallosal stimulation, on the other hand.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 305–314, May–June, 1985.     

Projections from lamina V of the cerebral cortex to the dorsomedial thalamic nucleus and neighboring nuclei]

The laminar projections from the cerebral cortex to the mediodorsal thalamic nucleus and adjacent thalamic nuclei were studied by means of the horseradish peroxidase (HRP) retrograde axonal transport method. A possible correlation was found between the connectivity arising from layer V of the cerebral cortex, and the rich-acetylcholinesterase (AChE) regions within the subcortical structures under study. This suggests the possibility that layer V of the cerebral cortex in Alzheimer's disease is initially affected and subsequently those rich-AChE subcortical regions with which it is connected.     

The structural-functional characteristics of the rostral sections of the neocortex in Chiroptera]

Studies have been made on the connections of rostral neocortex in bats in order to reveal connections with the structures of the auditory sensory system the existence of which is indicated by evident specific responses to ultrasound in the form of synchronization reaction. It was shown that dorsolateral parts of the rostral neocortex receive topically organized projections from the thalamic nuclei VPL and VL. Connections with the auditory cortex and suprageniculate nucleus are not evident. Afferents of the medial wall of the rostral cortex originate from the thalamic nuclei MD and AM. Possible pathways of auditory afferentation to the dorso-lateral part of rostral neocortex are discussed.     

Extrinsic cells, immunoreactive to Ca-binding protein, as sources of thalamic visual centres in tortoises

Extrinsic sources of calcium-binding proteins involved in immunoreactive innervation of the visual thalamic nuclei Rot and GLd in turtles (Testudo horsfieldi and Emys orbicularis) were studied using HRP tracing method and immunohistochemistry. In 1.5-4.5 months after monocular enucleation calbindin (Calb)-, parvalbumin (Parv)- and calretinin (Calr)-labeling was found in fragments of degenerated retinal fibers in the contralateral optic tract and in some retinorecipient structures (optic tectum, GLd and GLv). Changes in GLd were detected in its neuropil part. in 2.0-3.5 months after unilateral ablation of tectum and pretectum, the densities of Parv-, Calb- and Aclr-immunoreactivity terminals and fibers were diminisched in the ipsilateral n. Rot, with the maximum effect seen in Parv. Following HRP injection into the visual thalamus (Rot and GLd), retrogradely labeled cells with Parv label only, were revealed in the ventrothalamic nucleus Enta, pretectal nucleus Ptv, and in all types of Ca-binding proteins (CaBPr) in separately labeled cells of the optic tectum. Thus, it has been shown that thalamic visual centers in turtles have multiple extrinsic cells, which serve as sources of CaBPr projections. The present data suggest that organization of CaBPr inputs to visual thalamus in reptiles (turtle) and higher amniotes are fundamentally similar.     

Control of absence seizures induced by the pathways connected to SRN in corticothalamic system

The cerebral cortex, thalamus and basal ganglia together form an important network in the brain, which is closely related to several nerve diseases, such as parkinson disease, epilepsy seizure and so on. Absence seizure can be characterized by 2–4 Hz oscillatory activity, and it can be induced by abnormal interactions between the cerebral cortex and thalamus. Many experimental results have also shown that basal ganglia are a key neural structure, which closely links the corticothalamic system in the brain. Presently, we use a corticothalamic-basal ganglia model to study which pathways in corticothalamic system can induce absence seizures and how these oscillatory activities can be controlled by projections from the substantia nigra pars reticulata (SNr) to the thalamic reticular nucleus (TRN) or the specific relay nuclei (SRN) of the thalamus. By tuning the projection strength of the pathway “Excitatory pyramidal cortex-SRN”, ”SRN-Excitatory pyramidal cortex” and “SRN–TRN” respectively, different firing states including absence seizures can appear. This indicates that absence seizures can be induced by tuning the connection strength of the considered pathway. In addition, typical absence epilepsy seizure state “spike-and-slow wave discharges” can be controlled by adjusting the activation level of the SNr as the pathways SNr–SRN and SNr–TRN open independently or together. Our results emphasize the importance of basal ganglia in controlling absence seizures in the corticothalamic system, and can provide a potential idea for the clinical treatment.     

Convergence between projections from different thalamic nuclei to columns of the rat somatosensory cortex

Primuline fluorochrome retrograde transport technique was used to investigate sources of thalamocortical projections to a single rat somatosensory cortex column connected with the projection of the C₃ vibrissa. Labeled cells were identified in eight different thalamic nuclei: two specific, five nonspecific, and one association nucleus. Labeled neurons differed in the degree of stain accumulated as well as cell numbers and density of distribution from one nucleus to another, indicative of the different arborization patterns of their axons within the cortex. Highest numbers of heavily stained cells as well as highest density of distribution were observed in the ventral thalamic nucleus. The convergence seen between different thalamocortical inputs on to a single somatosensory cortex column explains the functional differences observed between neurons belonging to the same column and makes the formation of functionally distinct neuronal groupings appear possible on this structural basis.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 168–174, March–April, 1989.     

Horseradish peroxidase-positive neurons of nonspecific thalamic nuclei projecting to the primary somatosensory cortex in cats

The morphology and topography of neurons whose axons form the nonspecific thalamic input in the primary somatosensory area were studied in the cat forebrain by the retrograde axonal horseradish peroxidase transport method. Stained cells were found in the dorsolateral part of the nucleus ventralis anterior, and were diffusely distributed in the nucleus centralis, lateralis, the lateral part of the nucleus dorsalis medialis, and the dorsal part of the centrum medianum. In the nucleus paracentralis only solitary, palely stained neurons were detected. Cells stained with horse-radish peroxidase were multipolar, triangular, or fusiform. The results are evidence that besides the ventrobasal complex, the nonspecific nuclei of the diencephalon also project into the somatosensory cortex. This indicates the existence of multiple afferent thalamic inputs into the somatic cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 435–440, September–October, 1979.     

Localization of sources of thalamic inputs into the sensorimotor cortex in the rabbit using retrograde axonal transport technique

It was shown that the rabbit sensorimotor cortex received afferent fibers from neurons located in the specific, nonspecific, and association thalamic nuclei using the retrograde axonal transport technique. The distribution, dimensions, and shape of the somata of relay neurons spread through the thalamic nuclei were analyzed. The total number of neurons sending out thalamo-sensorimotor-cortical fibers was calculated and the coordinates of loci with the highest density of these cells in each thalamic nucleus were identified. Multipolar and stellate cells with somata measuring 12–20 µm and 10–15 µm in diameter, respectively, prevailed amongst relay neurons. Amongst the specific nuclei, the majority of afferent fibers are sent out by the ventrolateral, ventral anterior, and anterior ventral nuclei. A comparable number of afferent fibers are sent out by the mediodorsal and paracentral nuclei; these split up among the association nuclei and paracentral nuclei, respectively. It is suggested that afferents from many different groups of thalamic nuclei are essential for the sensorimotor cortex to participate in thalamocortical interaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 87–94, January–February, 1987.     

Differences in the sensory support of the anterior and posterior sections of the limbic cortex of the rat

Using retrograde axonal transport of horseradish peroxidase, studies have been made on the thalamic projections in the anterior and posterior parts of the limbic cortex with special reference to exterosensory system projections (visual, auditory and somatic). Projections of the retinorecipient nuclei of the anterior hypothalamus and classic thalamic visual relays (n. geniculatus lateralis dorsalis, n. lateralis posterior, pretectum) were found in the anterior and posterior limbic cortex. There are also inputs from the thalamic relays of the auditory (n. geniculatus medialis) and somatic (n. ventralis posterior) systems in the posterior limbic cortex The data obtained indicate: 1) that sensory supply of the limbic cortex in rats may be realized via direct pathways from sensory thalamic relays; 2) that thalamic sensory supply of the anterior limbic cortex differs from that of the posterior one. In the former, projections of the thalamic relays of the visual, auditory and somatic systems were found, whereas in the posterior cortex only visual system is presented. Topographic organization of the thalamic nuclear areas sending afferents to the anterior limbic cortex differs from that of the posterior limbic cortex.