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T Pasik

Publications and source records attributed to T Pasik.

17 recordsLinked to original sources
PubMed1991

The magnocellular and parvocellular divisions of the monkey subthalamic nucleus as revealed by cluster analysis of neuronal sizes.

Cluster analysis of neuronal somal sizes in the subthalamic nucleus of rhesus monkeys from newborn to adult age allows the segregation of two territories with predominance of small and large cells, respectively. The topographic distribution of the 'parvocellular' and 'magnocellular' segments is similar when samples are obtained from coronal, horizontal and sagittal series of sections. The parvocellular component occupies the rostral pole, the entire rostrocaudal extent of the medial tip and dorsomedial border, and probably also the caudal cap. The magnocellular segment is in the central core extending to the ventrolateral border except for the medial tip. These findings and their correlation with the results of other morphologic and physiologic studies allow the following conclusions. (1) The monkey subthalamic nucleus contains at least two differentially distributed cell subpopulations. (2) The magnocellular division is more related to the pallido-subthalamic-pallidal loop involving the lateral pallidal segment. (3) The parvocellular division appears strategically located to control the pallidal output to diencephalic and mesencephalic targets. (4) Cluster analysis can reveal the existence of more than one neuronal population in a particular brain structure where an overall unimodal distribution of cell sizes may suggest the presence of a single type.

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PubMed1991

Different types of synaptic triads in the monkey dorsal lateral geniculate nucleus.

Characteristic synaptic complexes, the triadic synapses, were investigated in long series of sections of parvicellular and magnocellular laminae of the monkey lateral geniculate nucleus. Electron microscopic observations revealed the presence of different triadic types, the intercalated element being in all cases a presynaptic dendrite or soma of an interneuron (I-cell), and the output component being constantly a dendrite or soma of a geniculocortical projection or principal neuron (P-cell). The axonal input to the triads, however, was found to be of three different types: (1) the majority were retinal axon terminals; (2) a smaller fraction were the axonal endings of corticogeniculate fibers, always connected to thin, distal P-cell dendrites; (3) others were terminals with pleomorphic or flattened, small synaptic vesicles, probably belonging to axons of I-cells and/or of thalamic reticular nucleus origin. It was observed also that the retinal terminals established multiple synaptic contacts with both P-cell and I-cell dendrites. Essentially, two types of triadic arrangements with retinal input were recognized: the "simple" unit, frequent in parvicellular laminae, in which the retinal axon was accompanied by only 1-2 presynaptic dendrites; and the "complex" unit, found mostly in the magnocellular laminae, characterized by the presence of up to eight presynaptic dendrites. In the glomerular "complex" units, "closely packed" classical triads, with the three synaptic junctions localized close to each other, coexisted with triads "at a distance" where the synapses were distributed relatively far from each other. The coupling by presynaptic dendrites of "closely-packed" and "at a distance" triads resulted in the formation of multiple triadic arrangements. Since cortical and inhibitory triads were never seen to be involved in multiple triadic complexes, the latter appeared exclusively retinal in nature. The possible functional significance of multiple triads in "ON-gating" operation is briefly discussed.

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PubMed1979

Downward gaze in monkeys: stimulation and lesion studies.

Ten monkeys were stimulated unilaterally and bilaterally through bipolar electrodes placed stereotactically on each side of the midline under light barbiturate anaesthesia. Bilateral simultaneous stimulation elicited straight downward binocular movements from a core of tissue about 40 mm3 on each side which included the fields of Forel, zona incerta, subthalamic nucleus, oral pole of the red nucleus, fasciculus retroflexus and 'area tegmentalis'. Unilateral stimulation of the same points yielded downward eye movements in only 25 per cent of the instances. Upward deviation of the globes could be elicited by bilateral stimulation of tissue located more caudal, ventral and medial than that from which downward movements were obtained. Bilateral electrolytic lesions within the region outlined above caused significant defects in downward gaze both in saccadic and slow pursuit binocular movements. Passive bending of the head backwards, however, resulted in downward deviation of the globes (oculocephalic reflex). Optokinetic nystagmus and after-nystagmus downward were abolished. Oblique (45 degrees) optokinetic stimulation elicited a perverted response in the horizontal plane. Vestibulo-ocular reflexes elicited by bilateral warm irrigation of both ear canals with the monkey in the erect position, or by turning the animal while lying on one side, caused a strong tonic deviation upward with absence of nystagmus downward. Some of these monkeys showed additional alterations in upward gaze but they were less severe in intensity and duration than those of downward gaze. All eye deviations in the horizontal plane were consistently normal. Recovery occurred in all types of vertical binocular movements except in the rapid motions (saccades and quick phases of nystagmus) below the horizontal meridian. A unilateral lesion had no effect. The minimal damage producing downward gaze defects was about 1.7 mm in diameter, cetred in the prerubral fields, rostral and medial to the red nuclei with minimal involvement of the oral pole of these structures. The nuclei of Cajal, Darkschewitsch and interstitialis of the posterior commissure, as well as the fasciculus retroflexus and the posterior commissure, were spared by this lesion. The so-called rostral interstitial nucleus of the medial longitudinal fasciculus and the nucleus campi Foreli appear to be destroyed. These structures are known to receive an input from the paramedian pontine reticular formation and project on to the oculomotor nerve nucleus. These results demonstrate that the prerubral fields contain structures which are critical for rapid eye movements downward, and therefore an isolated downward gaze palsy is a strong indicator of a bilateral lesion of this zone. The findings in the few reported cases with this sign and available pathological analysis suggest that our conclusions from the experimental monkey apply to man as well. The concept of bilateral innervation for vertical eye movements is amply confirmed for the downward vectors...

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PubMed1976

A Golgi study of neuronal types in the neostriatum of monkeys.

Examination of the nestriatum of monkeys prepared by the Golgi-Kopsch perfusion method revealed the presence of at least 6 neuronal types. The spiny type I is medium size with a high density of dendritic spines. The axon extends well beyond the dendritic field and gives off many collaterals. The spiny type II is either medium or large size, has long thick dendrites with a relatively low density of spines, and an axon similar to that of the previous type but with fever collaterals. The aspiny type I is medium size with varicose dendrites and a thin axon arborizing in the immediate vicinity of the soma. The aspiny type II is large, with many thick and thin varicose dendrites. The aspiny type III is medium size with smooth dendrites and an axon ramifying profusely within the dendritic field. The neurogliform cell is small with many branching processes. Findings indicate that the neostriatum has 2 distinct types of spiny neurons with long axons (spiny I and II), some of which may contribute to the efferent system. There are also 2 (aspiny I and III) or perhaps as many as 4 categories (aspiny I, II, III and neurogliform) of typical Golgi type II cells. Large neurons belong to 2 separate populations, one with dendritic spines and a long axon (large version of spiny II), and one with varicosities and presumably a short axon (aspiny II). A realistic interpretation of neurophysiologic data on the neostriatum must take into account all cell types instead of the current view of considering it as a pool of interneurons with few output cells.

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PubMed1976

Synapses between interneurons in the lateral geniculate nucleus of monkeys.

Electron microscopic examination of the monkey lateral geniculate nucleus, pars dorsalis (LGNd) reveals the occurrence of synaptic contacts between profiles belonging to interneurons (I-cells). Almost all combinations are observed, namely, axodendritic, dendrodendritic, dendrosomatic and somatodendritic, the most frequent being the dendrodentritic synapses between the presynaptic dendrites characteristic of I-cells. Quantitative analysis of 5 samples, each consisting of 200 mum2 of net LGNd neuropil, shows that presynaptic membrane specializations present in I-cell axonal and dendritic elements amount to a mean of 3.73 mum or 8.16% of the surface of such profiles. Only 61% of this extent is in contact with principal cells (P-cells), and an unexpectedly high 39% engages other I-cell profiles. A tentative segregation of axonal and dendritic endings revealed the following significant mean differences: dendritic terminals are more numerous and larger; axonal profiles have more of their surface occupied by synaptic sites and each contact is longer. Findings suggest the existence of a network of interconnected interneurons which are presumably inhibitory in nature. Such an arrangement can provice a certain measure of anisotropic disinhibition which may be responsible for specific transformations occurring in the LGNd depending upon the size and velocity of the stimulus as well as of the degree of synchronicity of temporal patterns.

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PubMed1975

A comparison between two types of visually-evoked nystagmus in the monkey.

Similarities between optokinetic nystagmus (O.K.N.) and flicker-induced nystagmus (F.I.N.) include: response buildup and occurrence during the entire period of stimulation; absence of habituation; after-nystagmus in the same direction, occasional after-after-nystagmus to the opposite side; frequency spectrum, peak frequency and existence of lower and upper frequency thresholds. Phenomena are different in that for O.K.N. the stimulus is in motion; binocular and monocular stimulation are effective; direction is determined by direction of motion; unidirectionality is absent; there is minimal influence of background illumination, posture, labyrinthine receptors, and section of crossed optic fibers. For F.I.N. the stimulus is stationary; the response is elicited only by monocular stimulation; the direction is determined by the stimulated eye; there is exclusive unidirectionality; it is abolished by background illumination, optic chiasm section and bilateral labyrinthectomy; it is strongly influenced by posture. This comparison suggests that O.K.N. and F.I.N. are separate responses and that the effective stimulus for F.I.N. may activate selectively the crossed optic fibers.

Animals↗
PubMed1975

Postnatal differentiation of "presynaptic dendrites" in the lateral geniculate nucleus of the rhesus monkey.

The most characteristic synaptic arrangement in the LGN is the triadic unit, in which a retinal terminal is presynaptic to a principal cell (P cell) and to a Golgi interneuron (I cell) dendrite, which contains synaptic vesicles and is in turn presynaptic to the same P-cell element. The ontogenetic differentiation of these "presynaptic dendrites" was studied in monkey LGN by standard and quantitative electron microscopy. The dendrites and axonal arborization of I cells are well developed in the newborn monkey. Scattered synaptic vesicles are present in the dendrites, but these profiles exhibit only postsynaptic sites. The dendrodendritic synapse of the triadic arrangement is missing, although contacts between P-cell and I-cell dendrites can be observed. Conversely, the I-cell axons in the newborn establish numerous synapses with dendrites and perikarya of P cells. At about 2 weeks of age, presynaptic sites appear in the I-cell dendrites, resulting in the formation of synaptic triads. Parallel to the development of "axonal" properties in the dendrites, the number of true I-cell axonal profiles decreases sharply. These transformations become progressively more frequent with age, and beyond 8 weeks the LGN ultraarchitectonics approaches that of the mature animal. The percentage of the surface of interneuron processes occupied by presynaptic sites is similar at all developmental stages at about the 2.6% level. The relative contribution of presynaptic dendrites and of axons changes, however, so that the actual length of contacts in the mature monkey is only one-half that of the newborn for the axonal sites, and over 50 times longer for the dendritic sites. The correlation of these findings with electrophysiologic and behavioral references suggests that some but not all axonal functions may be taken over by the dendrites, that the possible inhibitory phasing of P-cell discharge would appear only after the second postnatal week, and that the triadic arrangement may not be indispensable for brightness or total luminous flux discrimination but could be required for more complex forms of visually guided behavior.

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