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.     

Connections of neurons of the cat somatosensory cortex with the thalamic relay nuclei

Of 103 neurons in the rostral part of the posterior sigmoid gyrus of the cat cortex 30 responded to stimulation of the ventro-posterolateral and ventrolateral nuclei of the thalamus (VPL and VL), 42 responded to stimulation of VL only, and 31 to stimulation of VPL only. It was shown by intracellular recording that stimulation of VPL induces a spike response with or without subsequent IPSPs in some neurons and an initial IPSP in others. The spike frequency of single neurons reached 60/sec, but the IPSP frequency never exceeded 10–20/sec. Stimulation of VL was accompanied by: a) antidromic spike responses; b) short-latency monosynaptic EPSPs and spikes capable of following a stimulation frequency of 100/sec; c) long-latency polysynaptic EPSPs and spikes appearing in response to stimulation at 4–8/sec; d) short-latency IPSPs; e) long-latency IPSPs increasing in intensity on repetition of infrequent stimuli. It is concluded that the afferent inputs from the relay nuclei to neurons of the somatosensory cortex are heterogeneous. An important role is postulated for recurrent inhibition in the genesis of the long-latency IPSPs arising in response to stimulation of VL, and for direct afferent inhibition during IPSPs evoked by stimulation of VPL. It is shown that the rostral part of the posterior sigmoid gyrus performs the role of somatic projection and motor cortex simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 245–255, May–June, 1972.     

Interaction of heterosensory afferent impulses on neurons of thalamic associative nuclei

The character and particular features of interaction between visual, auditory, and electrodermal afferent impulses on neurons of the pulvinar, posterolateral, and mediodorsal thalamic nuclei were studied in acute experiments on cats anesthetized with a mixture of pentobarbital and chloralose. Interaction discovered on cells of both groups of structures was of two types. In the first (the one most frequently found) only inhibition was observed or inhibition followed by facilitation of the response to testing stimulation; in the second type only facilitation or facilitation followed by inhibition of unit activity was found. Overall ability for interaction to take place on neurons of the mediodorsal nucleus was weaker than on cells of the pulvinar-posterolateral complex (P<0.05). Interaction was strongest on trisensory cells; it was also observed on monosensory cells or on cells which did not respond to isolated stimulation.Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 478–485, September–October, 1978.     

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 350–358, July–August, 1971.     

Role of the human thalamic parafascicular (CM-Pf) complex in neuronal mechanisms of selective attention

Responses of 93 single units of the human thalamic CM-Pf complex to relevant and irrelevant verbal (or sensory) stimuli were studied using microelectrode technique in alert diskinetic patients suffering from the tonic forms of spasmodic torticollis during 11 stereotaxic operations. The response patterns of two types units with irregular unitary (A-type) and low-threshold bursting Ca(2+)-dependent (B-type) spike activity were studied. Three main conclusions emerge from the studies: 1) high reactivity of both A- and B-units to presentation of relevant verbal stimuli with differences of their response patterns as determined by the type of constituent elements; 2) close functional connectivity of these neuronal changes with the level of selective attention; 3) at the moment of attention activation, the appearance of transient interneuronal interactions between adjacent A and B cells characterized by the local synchronization and stabilization of rhythmic oscillations. These data point to considerable contribution of the thalamic CM-Pf complex and its neuronal mechanisms into organization of the human selective attention and triggering verbal-related processing during performance of purposive speech-provoked voluntary acts.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Branching-pattern analysis of the dendritic arborization in the thalamic nuclei of the rat brain

We investigated the dendritic patterns of rapid Golgi-impregnated, highly similar multipolar neurons from two functionally different thalamic regions of the rat brain: two dorsal nuclei (the nucleus laterodorsalis thalami, pars dorsomedialis and the nucleus laterodorsalis thalami, pars ventrolateralis), and two ventral nuclei (the nucleus ventrolateralis thalami and the nucleus ventromedialis thalami). The analysis involved conventional morphometric parameters (height and size) and a new parameter derived from graph theory, the relative imbalance (RI), derived from the branching patterns of the dendrites, which permits quantitative characterization of the dendritic arborization of a neuron. On this basis, neurons can be grouped into three fundamentally different types: type A, or highly-polarized (imbalanced) neurons (RI values close to 1); type B, or medium-polarized neurons (RI values around 0.5); and type C, or balanced neurons with low polarization (RI values close to 0). The orientations of the dendritic arbor, and thus the receptive fields, of the dorsal and ventral thalamic neurons, were mutually perpendicular. The H and S values indicated that the neurons in the dorsal and ventral thalamic nuclei differed significantly. However, their RI values demonstrated that they were similar neurons of type B. Our data reveal that 1 ) the dendritic arbor cannot be reliably characterized purely on the basis of height and size, and 2) RI is a valuable morphometric parameter that identifies the true nature of the dendritic arborization.     

Distribution of sugar-binding sites within interphase nuclei and mitotic chromosomes of a human cell line

Using gold labelled neoglycoproteins containing either alpha-D-glucose, N-acetyl-beta-D-glucosamine, alpha-D-mannose, 6-phospho-alpha-D-mannose, and alpha-L-fucose (BSA), we investigated their intranuclear binding sites in the TG human cell line. Although gold-labelled BSA did not give any noticeable labelling, the presence of 1% free BSA in the medium containing the gold labelled neoglycoproteins was revealed to be a key factor of the labelling. During interphase in the presence of free BSA most of the labelling was detected in the nucleoplasm. The border of the condensed chromatin, known to be the site of hnRNA synthesis as well as the interchromatin areas enriched in RNPs were labelled. Condensed chromatin also contained binding-sites. The nucleolus was seen to present low labelling in comparison with the labelling observed over the nucleoplasm. These nucleolar binding sites were located both in the dense fibrillar and granular components. No labelling could be detected over the fibrillar centers which are very conspicuous in this cell line. During mitosis sugar-binding sites were observed over the chromosomes. Data reported here show for the first time that lectin-like proteins and chromatin components are colocalized both during interphase and mitosis. In addition, within the nucleolus the presence of sugar-binding proteins was seen to be restricted to the dense fibrillar and granular components.     

Transient structures of the human fetal brain: subplate, thalamic reticular complex, ganglionic eminence

Morphological features of the subplate, the thalamic reticular complex and the ganglionic eminence, which represent three major transient structures of the human fetal forebrain, are summarized with special reference to their functional roles. The subplate harboring various neuronal types is an outstandingly wide zone subjacent to the cortical plate in the human fetal brain. Within the subplate various cortical afferents establish synaptic contacts for a prolonged period before entering the cortical plate. Therefore, the subplate is regarded as a "waiting compartment" which is required for the formation of mature cortical connections. Next to the thalamic reticular nucleus, within the fibers of internal capsule, the perireticular nucleus is located which has been established as a distinct entity during development. Its various neuronal types express a number of different neuroactive substances. Perinatally, the perireticular nucleus is drastically reduced in size. It is involved in the guidance of corticofugal and thalamocortical fibers. The ganglionic eminence is a conspicuous proliferative area that persists throughout nearly the entire fetal period. In the human fetal brain it extends medially upon the dorsal thalamic nuclei which receive precursor cells from the ganglionic eminence. Postmitotic cells in the marginal zone of the ganglionic eminence serve as an intermediate target for growing axons. On the whole, all three structures establish transient neural circuitries that may be essential for the formation of adult projections. The characteristics of the three transient structures are particularly relevant for developmental neuropathology as these structures may be damaged in disorders that preferentially occur in preterm infants.     

Reactions of cat motor cortex neurons to stimulation of the pyramidal tract and ventroposterolateral thalamic nuclei

Responses of neurons of motor cortex evoked by stimulations of pyramidal tract (PT) and ventroposterolateral (VPL) nucleus of thalamus were studied in cats immobilized by Myorelaxin. Antidromic spikes were found in 22.6% and in 9.9% of cortical cells when PT and VPL were stimulated, respectively. Fast- and slow-conducting PT-neurones could be differentiated according to antidromic excitation latencies. PT stimulation evoked EPSPs in 46.3% of studied neurones and VPL stimulation--in 48.2% ones. Monosynaptic EPSPs were identified in responses of fast- and slow-conducting PT-units and of neurones projecting in VPL; mechanisms and functional role of such reactions are discussed. Di- and polysynaptic IPSPs were evoked in 74.5% of units by PT stimulation and in 94.4%--by VPL stimulation. Three groups of IPSPs were classified with durations to 120, 130-280 and more than 300 ms. Duration of PT-evoked IPSPs was higher in cortical neurones from surface layers and VPL-evoked ones--in units localized in deep layers.     

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.     

Identification of growth-hormone- and prolactin-containing neurons within the avian brain

Prolactin (PRL)- and growth-hormone (GH)-containing perikarya and fibers independent of the anterior pituitary gland have been reported to exist in the central nervous system of several mammalian species. The specific distributions of PRL- or GH-like neurons in the avian forebrain and midbrain, however, have not been reported. The objective of the study was to identify GH- and PRL-containing neurons in the hypothalamus and a few extrahypothalamic areas of two avian species. Brain and peripheral blood samples were collected from laying and broody turkey hens and ring doves. Broody turkey hens and doves had significantly higher plasma PRL concentrations compared with laying hens. Coronal brain sections were prepared and immunostained using anti-turkey GH and anti-chicken synthetic PRL antibodies. In turkey hens, the most dense GH-immunoreactive (ir) perikarya and fibers were found in hippocampus (Hp), periventricular hypothalamic nucleus, paraventricular nucleus, inferior hypothalamic nucleus, infundibular hypothalamic nucleus, medial and lateral septal area, and external zone of the median eminence (ME). In the ring dove, a similar pattern of distribution of GH-ir neurons was noticed at the brain sites listed above except that GH-ir fibers and granules were found only in the internal zone of ME and not in the external zone. In both turkeys and doves, the most immunoreactive PRL-ir perikarya and fibers were found in the medial and lateral septal area, Hp (turkey only), and bed nucleus of the stria terminalis pars magnocellularis. There were no apparent differences in the staining pattern of GH- or PRL-ir neurons between the laying and broody states in either species. However, the presence of GH-ir- and PRL-ir perikarya and fibers in several hypothalamic nuclei indicates that GH and PRL may influence parental behavior, food intake, autonomic nervous system function, and/or reproduction.     

Modulating effect of electric acupuncture stimulation on the bioelectrical activity of neurons of specific and nonspecific thalamic nuclei

Bioelectric reactions of individual neurons in specific and nonspecific thalamus nuclei were studied in acute experiments on cats. Auricular or body point electroacupuncture (EAP) was shown to affect the functions of spontaneously active neurons in the nuclei under study. Two types of spontaneously active neurons were identified: some were activated and some inhibited in response to EAP stimulation. The number of neurons activated in response to EAP was 50% greater in specific thalamus nuclei than in nonspecific ones, while inhibition was mostly observed in nonspecific thalamus cells.     

Aspects of excitation and inhibition produced in parietal association cortex neurons by stimulating thalamic association nuclei

Neuronal response to single stimuli applied to the thalamic dorsolateral and posterolateral nuclei (DLN and PLN resepctively) was investigated in the parietal association cortex. Primary IPSP following DLN and PLN stimulation was noted in 62.5% and 79.6% of instances respectively. Latencies of EPSP and IPSP when stimulating the two nuclei were longer for the DLN. The amplitude of EPSP evoked by stimulating association nuclei rose and declined smoothly, while that of IPSP showed a fast rise and a more steady decline. The EPSP appearing during the evolution of IPSP were of higher amplitude than control level of resting potential. Both amplitude and duration of IPSP induced in a single unit by stimulating different association nuclei were extremely similar, thus confirming the involvement in this operation of the same inhibitory cortical interneurons. Duration of IPSP was shorter than that of inhibitory background spike activity. It is postulated that the discrepancy in duration can largely be ascribed to properties of the neurons themselves.State University, Odessa. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 529–536, September–October, 1991.     

Nitroxidergic neurons in nuclei of rat and human medulla oblongata

Four types of neurons distinguished by NADPH-diaphorase reaction have been identified in seven nuclei of human and rat medulla oblongata. It was found that nitrogen oxide (NO)-positive neurons had similar distributions; neurons with high NO-synthase activity predominated in vasomotor nuclei and, in sensitive nuclei, most neurons had low NO-syntase activity.