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Biomedical subjects

P Pasik

Publications and source records attributed to P Pasik.

At least 55 records · Page 3Linked to original sources
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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