Quantitative comparison of the hominoid thalamus. I. Specific sensory relay nuclei.

Studies to date have indicated few differences in sensory perception among hominoids. Sensory relay nuclei in the dorsal thalamus--portions of the medial and lateral geniculate bodies (MGBp, LGBd) and the ventrobasal complex (VB)--in two gibbons, one gorilla, one chimpanzee and three humans were examined for anatomical similarity by measuring and estimating the nuclear volumes, neuronal densities, numbers of neurons per nucleus, and volumes of neuronal perikarya. The absolute volumes of these nuclei were larger in the larger brains; however, with the volume of the dorsal thalamus as a standard, these sensory relay nuclei showed negative allometry. The gibbons had about half as many neurons as did the other hominoids. Although the human VB had slightly more neurons, the numbers of neurons in LGBd and MGBp did not significantly differ between the great apes and humans. The volumetric distribution of the neuronal perikarya were similar among these hominoids. Other thalamic nuclei had much more diverse numbers of neurons and relative frequencies of their neuronal perikarya. The sensory relay nuclei appear to be a group of conservative nuclei in the forebrain. These results suggest that as a neurological base for complex behaviors evolved in hominids, not all parts of the brain changed equally.     

A quantitative comparison of the hominoid thalamus: III. A motor substrate—the ventrolateral complex

Nuclear volumes, nerve cell densities, numbers of neurons, and volumes of nerve cell perikarya of the thalamic ventrolateral complex (VL), a neural substrate for movement, were measured in specimens from two gibbons, one gorilla, one chimpanzee, and three humans, and the values were compared. The human VL had about one-and-a-half times as many neurons as did those of the great apes. The relative frequencies of the sizes of nerve cell perikarya differed slightly in the ventrolateral segment of VL; no differences were noted in the rest of VL. Compared with findings from other parts of the thalamus, the differences in the volumes of VL were greater than those found in the thalamic sensory nuclei, similar to those of rest of the thalamus, and less than those found in the whole brain. The increased number of neurons in human VL was similar to that of the somatosensory relay complex, but greater than those of the auditory and visual nuclei and less than those of the limbic and association nuclei. In human evolution, the numbers of neurons in the VL appeared to increase at a faster rate than did neurons of the pyramidal tract, whereas the motor cortex apparently increased at a rate greater than VL.     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropostero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on receptive fields of ON-OFF neurons showed that the excitation of the ACC could change an ON-response on the verge of a receptive field into an ON-OFF response. The above results suggest that the ACC modulation sharpens the response of a VB neuron to a moving stimulus within its receptive field, indicating that the limbic system can modulate tactile ascending sensory information.     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropos-tero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on rec     

A contribution of synaptic plasticity in the basal ganglia to processing of visual information

The mechanism of involvement of the basal ganglia in processing of visual information on the basis of dopamine-dependent modulation of efficacy of synaptic transmission in interconnected parallel associative and limbic loops (cortex--basal ganglia--thalamus--cortex) is proposed. Each loop consists of one of the visual or prefrontal cortical areas connected with the thalamic nucleus and corresponding loci in different nuclei of the basal ganglia. Circulation of activity in such a loop provides reentrance of information into the thalamus and neocortex. Dopamine releasing in response to a visual stimulus oppositely modulates the efficacy of "strong" and "weak" corticostriatal inputs. Subsequent reorganization of activity in the loop leads to a disinhibition (inhibition) of activity of those cortical neurons that were "strongly" ("weakly)" excited by the visual stimulus simultaneously with activation of dopaminergic cells. A selected neuronal pattern in each cortical area represents a property of the visual stimulus processed by this area. Excitation of dopaminergic cells by the visual stimulus via the superior colliculi requires parallel activation of a disinhibitory input to the superior colliculi via the thalamus and a "direct" pathway through the basal ganglia. The prefrontal cortex excited by the visual stimulus via the mediodorsal thalamic nucleus performs a top-down control over the dopaminergic cell activity, supervising simultaneous dopamine release in different striatal loci and thus promotes the interconnected selection of neuronal representations of individual properties of the visual stimulus and their binding in an integrated image.     

Immunocytochemical localization of d-amino acid oxidase in rat brain

d-amino acid oxidase (d-AAO) is a peroxisomal flavoenzyme, the physiological substrate and the precise function of which are still unclear. We have investigated D-AAO distribution in rat brain, by immunocytochemistry, with an affinity-purified polyclonal antibody. Immunoreactivity occurred in both neuronal and glial cells, albeit at different densities. Glial immunostaning was strongest in the caudal brainstem and cerebellar cortex, particularly in astrocytes, Golgi-Bergmann glia, and tanycytes. Hindbrain neurons were generally more immunoreactive than those in the forebrain. Immunopositive forebrain cell populations included mitral cells in the olfactory bulb, cortical and hippocampal neurons, ventral pallidum, and septal, reticular thalamic, and paraventricular hypothalamic nuclei. Within the positive regions, not all the neuronal populations were equally immunoreactive; for example, in the thalamus, only the reticular and anterodorsal nuclei showed intense labelling. In the hindbrain, immunopositivity was virtually ubiquitous, and was especially strong in the reticular formation, pontine, ventral and dorsal cochlear, vestibular, cranial motor nuclei, deep cerebellar nuclei, and the cerebellar cortex, especially in Golgi and Purkinje cells.     

Is the "nonspecific" thalamus still "nonspecific"?

The classical concept of "nonspecific" thalamus, as distinguished from the principal thalamic nuclei (i.e. the primary sensory, motor and limbic relays) is here briefly revisited in the light of anatomical investigations performed in the last decades, and primarily those based on tract tracing techniques. Altogether these data pointed out that the so-called "nonspecific" thalamus is composed by a heterogeneous collection of nuclear masses, which display not only species differences, but also marked internuclear variations in their cytological and neurochemical features, connections, areal and laminar distribution upon the cortex, and functional properties. Thus, the "nonspecific" thalamus exerts a modulatory role on cortical activity, chiefly regulated at the intrathalamic level by the interplay between the thalamic reticular nucleus and the interneurons and projection neurons of the dorsal thalamus. However, each of the components that have been traditionally considered as "nonspecific" also subserves selective roles in the transfer of different kinds of information from the thalamus to the cerebral cortex and basal ganglia.     

Isocortical Hyperemia and Allocortical Inflammation and Atrophy Following Generalized Convulsive Seizures of Thalamic Origin in the Rat

1. Generalized convulsive seizures can be elicited by a single unilateral microinjection of the cholinergic muscarinic agonist, carbachol, into the specific sites of the thalamus including ventral posterolateral and the reticular thalamic nuclei. The implication of the thalamic specific and reticular neurons is reviewed and discussed.2. On the basis of the c-fos regional expression and well-known efferent and afferent pathways linking these regions, a neuronal network relating the limbic, thalamo–striatal–cortical, and central autonomic systems, was constructed.3. The pattern of Fos immunoreactivity associated with long-lasting isocortical vasodilatation elicited by generalized convulsive seizures in anesthetized rat following cholinergic stimulation of the thalamus can be attributed to both the electrocortical activity and the long-lasting increase in cortical blood flow. We propose that the sustained cerebral cortical blood flow response during convulsive epileptic seizures may implicate intracerebral vasodilatory and vasoconstrictory neural mechanisms. Double-labeled NADPH-d and Fos-positive neurons implicated in maintaining the sustained isocortical vasodilatory response were found in the anterior lateral hypothalamic area. Inhibition of these neurons prevented the increase in cortical blood flow despite an increased metabolic demand manifested by the ictal electrocortical activity.4. Medial temporal lobe atrophy, including hippocampus, amygdala, and parahippocampal gyrus (piriform and entorhinal cortices) are the most common pathology in man. However the origin of medial lobe atrophy remain uncertain. Our results provide evidence that the allocortical microvascular inflammation may be in origin of the neurovascular degenerative processes leading to atrophy.     

Calcium-Binding Proteins in the Turtle Thalamus. Analysis in the Light of Hypothesis of the “Core-Matrix” Thalamic Organization in Relation to the Problem of Homology of Thalamic Nuclei among Amniotes

Distribution of immunoreactivity (IR) to Ca-binding proteins (CaBPr) (calbindin, Calb, parvalbumin, Parv., and calretinin, Calr) was studied in the thalamus of the Central Asian terrestrial turtles (Testudo horsfieldi) and fresh water turtles (Emys orbicularis). There has been established a wide spread of these proteins, which combines overlapping and a relative alternation of distribution of different CaBPr in individual nuclei. A comparison of IR was made in two relay nuclei of the visual system, GLd and Rot. Both nuclei had IR to all CaBPr, but with different degree of intensity. In the terrestrial turtles, the amounts of Calb-, Parv-, and Calr-IR neurons in the cellular plate of the GLd were close. In this plate and in the neuropil part of this nucleus there was observed CaBPr-innervation of various density. Calr-IR neurons in the GLd of the fresh water turtles dominated over Parv- and Calb-IR neurons, whose detection varied significantly. In Rot, a clear predominance of Calb-IR neurons was shown over Parv- and Calr-IR cells by constancy of their detection, the number (1.5–2-fold higher), and intensity of the immune label, as well as the highest density of Calb and Parv innervation. The character of IR in the Rot was similar in the both turtle species. In the auditory and somatic relay thalamic nuclei and in the non-sensory anterior thalamic nuclei (Dma, Dla) there were present neurons and terminals with IR to all CaBPr without any predominance of Parv-IR in the relay nuclei and Calb-IR in the anterior thalamic nuclei. The constant and characteristic feature of Enta in the turtles of both species is a dense population of Parv-IR neurons, whose topography and cellular composition coincide with those of population of GABA-IR neurons in this nucleus. The data obtained have shown that the alternative presence of different CaBPr in the relay sensory and non-sensory thalamic nuclei, which has been established as a characteristic feature of the mammalian thalamus, is not characteristic at all of turtles. It seems that in the course of evolution there occurred a reorganization of distribution of different CaBPr in thalamic nuclei of amniotes due to changes of their functional loading. The reptilian thalamic sensory relay nuclei are likely to be represented mainly by less specific parts comparable with Calb-IR matrix of specific nuclei in the higher amniotes (mammals), while their more specialized (core) Parv-IR regions are formed later in evolution. Therefore, the distribution of Parv- and Calb-IR neurons in the turtle thalamic nuclei cannot be a criterion at evaluation of homology of thalamic nuclei in amniotes, but permits judging about the degree of their specialization.     

Reactions of neurons of the parietal associative cortex field 7 to electric stimulation of the latero-dorsal and postero-lateral thalamic nuclei]

Neuronal responses of the parietal associative cortex (PAC) field 7 to the electrical stimulation of laterodorsal (LD) and posterolateral (PL) thalamic nuclei were studied in calypsol-narcotized cats. A correlation between depth, duration of the background activity inhibition and latent periods was determined for distribution of neurons responding to stimulation of associative nuclei by impulses. It is shown that there are functional relations between LD and field 7 of PAC. Common and specific peculiarities of neuronal responses of the associative cortex were found when a volley of impulses came from LD- and PA-nuclei of the thalamus.     

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.     

Neuronal Types in the Human Anterior Ventral Thalamic Nucleus: A Golgi Study

Neurons in the anterior ventral (AV) thalamic nucleus of human adults were impregnated by Golgi-Kopsch impregnation method. Results showed that at least three morphological types of neurons could be recognized in the human AV thalamic nucleus. Type I neurons were medium to large with rich dendritic arborization. Both tufted and radiating dendritic branching patterns were seen in almost every neuron of this type. Only the initial axonal segments of these cells were impregnated suggesting that these axons were heavily myelinated. Type II neurons were medium in size with poor to moderate dendritic arborization. Many of these cells possess a few dendritic grape-like appendages. Long segments (up to 300 μm) of their axons were impregnated suggesting that these axons were either unmyelinated or thinly myelinated. These axons change their direction and form loops very often. No local branches were seen for these axons suggesting that they could be projection axons. Type III neurons were small with only one or two dendrites with poor arborization. No axons for these cells were seen in this study. The three neuronal types in the human AV thalamic nucleus were compared with neuronal types already described in other thalamic nuclei of human and non-human species. The results of this study might provide a morphological basis for further electrophysiological and / or pathological studies.     

Properties of thalamocortical cells identified by antidromic stimulation in the ventrolateral and ventrobasal thalamic nuclei in rats

The physiological and pharmacological properties of thalamocortical neurons, identified by electrical antidromic stimulation of the frontoparietal cortex, were studied in the ventrobasal and ventrolateral thalamic nuclei in urethane anaesthetized rats. The spontaneous activity and conduction velocity of these neurons were similar in both nuclei. At both sites, thalamocortical neurons could be excited through iontophoretic application of acetylcholine and muscarinic or nicotinic agonists. Despite the known differences in thalamic organization of the two species, these properties are quite similar to those described in cat by other authors.     

Responses of neurons of the anterodorsal nucleus of the thalamus and comparative analysis of 3 limbic nuclei

Comparison of the three limbic thalamic nucleic shows that in spite of some common features of organization and connections, these nuclei presumably play different functional roles. N. AV may be regarded as an important "on-line" functional link of the limbic circuit. N. AD, possibly serves as input from the specific auditory structures to the limbic system. N. AM may participate in regulation of the general level of activity together with unspecific thalamic nuclei.     

Chondroitin sulfate proteoglycans in the rat thalamus: expression during postnatal development and correlation with calcium-binding proteins in adults

Postnatal expression of chondroitin sulfate proteoglycans was studied in the rat thalamus by immunocytochemistry and Western immunoblotting techniques with monoclonal antibodies that recognize carbohydrate epitopes (clones CS-56, 1-B-5, 2-B-6). The complex of the results shows that these antibodies recognize mostly nonoverlapping molecules whose expression is regulated during postnatal development. Chondroitin sulfate proteoglycans, recognized by antibody CS-56, and hyaluronan, identified by antibody 1-B-5 after hyaluronidase digestion, are abundant in the neuropil of most thalamic nuclei at the perinatal stage and progressively decrease during the second week of life, attaining levels barely detectable by immunocytochemistry at the end of the third week. In adult thalamus, chondroitin sulfate proteoglycans of high molecular mass, bearing glycosaminoglycans unsulfated in the linking region, and recognized by antibody 1-B-5 are confined to perineuronal nets around neurons chiefly localized in thalamic reticular nucleus. The immunoreactvity for antibody 2-B-6, specific for chondroitin-4-sulfate, is low at the perinatal stage and is not detectable in adult thalamus. Double-immunolabeling has shown that, along the rostrocaudal extension of reticular nucleus, the most developed perineuronal nets are associated with a subset of neurons expressing calretinin, and not with parvalbumin-positive neurons, which represent the largest neuronal population of the nucleus. The distribution of perineuronal nets supports the presence, in thalamic reticular nucleus, of neuronal subpopulations with different morphological and physiological features.     

The early topography of thalamocortical projections is shifted in Ebf1 and Dlx1/2 mutant mice

The prevailing model to explain the formation of topographic projections in the nervous system stipulates that this process is governed by information located within the projecting and targeted structures. In mammals, different thalamic nuclei establish highly ordered projections with specific neocortical domains and the mechanisms controlling the initial topography of these projections remain to be characterized. To address this issue, we examined Ebf1(-/-) embryos in which a subset of thalamic axons does not reach the neocortex. We show that the projections that do form between thalamic nuclei and neocortical domains have a shifted topography, in the absence of regionalization defects in the thalamus or neocortex. This shift is first detected inside the basal ganglia, a structure on the path of thalamic axons, and which develops abnormally in Ebf1(-/-) embryos. A similar shift in the topography of thalamocortical axons inside the basal ganglia and neocortex was observed in Dlx1/2(-/-) embryos, which also have an abnormal basal ganglia development. Furthermore, Dlx1 and Dlx2 are not expressed in the dorsal thalamus or in cortical projections neurons. Thus, our study shows that: (1) different thalamic nuclei do not establish projections independently of each other; (2) a shift in thalamocortical topography can occur in the absence of major regionalization defects in the dorsal thalamus and neocortex; and (3) the basal ganglia may contain decision points for thalamic axons' pathfinding and topographic organization. These observations suggest that the topography of thalamocortical projections is not strictly determined by cues located within the neocortex and may be regulated by the relative positioning of thalamic axons inside the basal ganglia.     

Significance of local synchronization and oscillatory processes of thalamic neurons in goal-directed human behavior

The time-frequency characteristics and interaction in the cell ensembles of the nonspecific (CM-Pf) and motor (Voi) thalamus were analyzed. Neuronal activity was registered by microelectrode technique during 18 stereotactic neurosurgery operations in spasmodic torticollis patients. The presentation of functionally significant verbal stimuli was accompanied by the emergence of short-term (0.5–1.5 s) local synchronization and stabilization of the oscillatory (3–6 Hz) activity in neighboring neurons of the nonspecific (CM-Pf) thalamus. These focuses of synchronized oscillatory neuronal activity were correlated with the moment of the greatest concentration of selective attention. A similar phenomenon of shortterm synchronization was observed in the motor (Voi) and nonspecific (CM-Pf) thalamus of the human brain during voluntary movements. Synchronization of neuronal activity occurred at the height of the implementation of the motor act, correlating with the maximum muscle tension, as well as in the aftereffect of the voluntary movement. In general, the findings suggest an important role of the local oscillations (3–6 Hz) and synchronization of thalamic neurons in the mechanisms of the relevant information transmission during goal-directed human behavior.