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P Pasik

Publications and source records attributed to P Pasik.

At least 37 records · Page 2Linked to original sources
PubMed1983

Differential frequency of P-cells and I-cells in magnocellular and parvocellular laminae of monkey lateral geniculate nucleus. An ultrastructural study.

Acute retrograde ultrastructural changes resulting from complete removal of areas 17, 18 and 19 were used to develop criteria for identification of principal or projective neurons (P-cells) and local interneurons (I-cells) in the dorsal lateral geniculate nucleus (LGNd) of monkeys. Four and six days after axotomy, marked chromatolytic alterations and diminution of rough endoplasmic reticulum were noted in 89 examined neurons of medium or large size, with rich cytoplasmic matrix, large mitochondria, and exhibiting only postsynaptic sites on the perikarya and dendrites. Seventeen other neurons showing no signs of degeneration had a pale matrix, small dense mitochondria and both postsynaptic and presynaptic sites on their perikarya and dendrites. It was concluded that the former group represented P-cells and the latter was characteristic of I-cells. The morphologic criteria derived from this study were applied to the quantitative analysis of neuronal populations in separate magnocellular and parvocellular laminae. The findings indicate that the latter contain 4.4% of I-cells whereas the former have 15.6% of this neuronal category. The dissimilarity suggests the more preeminent role of I-cells in the magnocellular laminae where they could maintain the transient responses of Y-cells which are known to be the predominant population among the P-cells of these laminae.

Animals↗
PubMed1983

The internal organization of the pallidum in mammals.

A survey of morphologic data on the pallidum indicate that this structure contains at least two types of efferent neurons probably related to its GABA mediated inhibitory and Substance P mediated excitatory action on target cells. In addition, there are short-axoned neurons with presynaptic dendrites forming triadic synapses of unknown significance. Characterization of afferent axon terminals suggest that the majority originate in the striatum, are gabaergic and inhibitory. Enkephalins may coexist in these afferents. Other striatal fibers are excitatory and may contain Substance P. Possible afferents from the subthalamic nucleus form inhibitory synapses and their action may be mediated by glycine. Brain stem afferents from the substantia nigra, pars compacta (dopaminergic), raphe nuclei (serotoninergic) and n. tegmentalis pedunculopontinus (transmitter unknown) are excitatory on pallidal cells on morphologic and/or physiologic grounds.

Afferent Pathways↗
PubMed1982

A Golgi and ultrastructural study of the monkey globus pallidus.

Golgi preparations reveal that the most frequent type of pallidal neuron (principal cell), which has been recognized in all previous reports, is large (20-50 microns), fusiform, with dendrites up to 700 microns long. Large neurons of globular shape are less frequently impregnated. The morphology of dendrites varies considerably within the same neuron. Some exhibit numerous spines and protrusions and are seen to terminate in elaborate arborizations. A small interneuron (12 microns), with relatively short dendrites, up to 150 microns, and a short sparsely branching axon is observed less frequently. At least two types of afferent axons are present. A small-diameter fiber from the neostriatum enters the pallidum in bundles and gives rise to numerous thin branching processes with varicosities about 1 micron in size. The axon collaterals are oriented orthogonal to the main axon and parallel to the dendrites of principal cells. A large-caliber fiber with clusters of 2-3 microns swellings can also be seen in close proximity to large pallidal dendrites. Ultrastructurally, principal cell dendrites (trunks, spines, and protrusions) are totally covered by synapsing axon terminals. In contrast, some small dentrites, presumed to belong to interneurons, form very few synapses. At least six categories of profiles containing vesicles are observed. One group has cytologic features of dendrites and participates in serial and triadic synapses with other profiles in the pallidal neuropil. Results suggest that the synaptic organization of the globus pallidus may be viewed as a repetitive, geometric arrangement of striatal and other afferent axons ensheathing and synapsing with the dendrites of principal cells. This pattern is interrupted by the presence of presynaptic dendrites, probably belonging to interneurons, which participate in complex synaptic arrangements.

Afferent Pathways↗
PubMed1982

Serotoninergic afferents in the monkey neostriatum.

Golgi and electron microscopic observations of the neostriatum of macaque monkeys reveal the presence of thin axons of extrinsic origin which produce a profuse arborization of very fine beaded branches. The varicosities contain pleomorphic synaptic vesicles, and may form strongly asymmetric axospinous synapses. Immunocytochemical methods utilizing an unlabeled antibody against serotonin followed by peroxidase-antiperoxidase complex and further histochemical visualization demonstrate that some elements conforming to the above description exhibit specific immunoreactivity. Relatively few of the labeled profiles form synapses and did so with small dendritic spines. In these cases the membrane specializations are strongly asymmetric. The neuropil also contains many unstained elements of similar morphology. The findings provide the morphologic features of serotoninergic axons in the neostriatum. Their properties may be shared by other monoaminergic afferents. It is suggested that serotonin is released as a neurotransmitter from synapsing boutons, and as a neuromodulator from non-synapsing varicosities. This distinction may correlate with the serotonin receptors 1 and 2 which apparently are responsible for excitatory and inhibitory actions respectively.

Afferent Pathways↗
PubMed1981

Extrageniculostriate vision in the monkey. VIII. Critical structures for spatial localization.

Eight monkeys (Macaca mulatta) were trained on a spatial localization task before and after either total ablation of the striate cortices with partial damage to circumstriate cortices, complete colliculus removals, or combined ablations. The lesions were histologically verified. The task, given under normal room illumination, required the animals to reach for a target randomly placed in one of eight equal segments of a while disk located at arm's length. An apple cube, affixed to the center of the target, served as the reward for accurate reaching. A correct response consisted of an initial contact with either the target or the apple cube directly. The animal was trained sequentially to a criterion level of performance set at 90% correct responses over four 56-trial consecutive sessions using black disks of decreasing diameter (i.e., 90 mm, 55 mm, 35 mm, and 15 mm). Finally, only the apple cube, about 10 mm on a side, was presented. Four animals with complete or almost complete bilateral superior colliculus removals were unimpaired in their performances. The other four subjects with total striate cortex removals could be trained to reach accurately for all targets, but with marked deficits on the first and last tests, i.e., the 90 mm disk and the apple cube. When the striate cortex was ablated in the colliculectomized animals, they failed to attain a criterion level of performance in almost 6,000 trials. These results indicate that the superior colliculus is at least one structure that is critical for spatial localization in the absence of striate cortex, but it is not crucial for this capacity in the otherwise intact animal. In addition, the findings confirmed previous studies which showed that monkeys with total bilateral striatectomies could require the ability to execute accurate visually guided reaches. The present and earlier studies emphasize the primary importance of the geniculostriate system for the function explored and do not support a sharp dichotomy between two independent visual systems in the monkey.

Animals↗
PubMed1980

Early postnatal development of the monkey neostriatum: a Golgi and ultrastructural study.

Paired specimens of the neostriatum were taken from monkeys at zero (newborn), one, two, four, eight, and 16 weeks of age, and prepared for Golgi impregnations and electron microscopy. Light microscopy shows that in the first postnatal week, the structure contains the five neuronal types and four categories of afferent axons described in the adult, as well as some cells too undifferentiated to classify. Most neurons exhibit immature dendritic features, including local enlargements, terminal growth cones with filopodia, and filiform processes. In spiny type I cells, various levels of maturity may coexist in regions of a single dendrite, in different dendrites of the same neuron, and among individual cells. Spine density increases progressively with age, but the relative distribution of spine types remains about the same. Spiny type II neurons show some decline in spine density, and generally mature sooner than spiny type I cells. The long axons of spiny neurons have varicosities which disappear at about eight weeks. In younger animals (newborn and one week), the dendrites of aspiny neurons (types I, II, and III) may have a "spiny" appearance, exhibiting many spine-like and filiform processes. Concurrently, the short axons vary in degree of arborization from very immature to well developed. Electron microscopy corroborates the developmental features recognized in the Golgi material: dendritic and axonal growth cones, filopodia and varicosities, as well as various stages of maturation in somata and dendrites. Degenerating elements, mostly of an axonal nature, are seen up to eight weeks. The synapses which reach maturity at birth are of the asymmetric axospinous type, in which the axonal profile contains small round vesicles, and of the symmetric axodendritic class, with the presynaptic elements having pleomorphic vesicles. Some synapses are slower to mature and appear at one to eight postnatal weeks. These include those made by profiles with pleomorphic vesicles, forming either symmetric contacts with somata and axon initial segments, or asymmetric contacts with spines. The same applies to the asymmetric axodendritic synapses made by elements containing small round vesicles. Finally, profiles containing large round or flat vesicles are the latest to participate in mature synapses formation. Findings indicate that a considerable degree of qualitative and quantitative change takes place in the monkey neostriatal neuropil during early postnatal development, especially in the first eight-week period.

Animals↗
PubMed1980

Ultrastructure of Golgi-impregnated and gold-toned spiny and aspiny neurons in the monkey neostriatum.

Golgi-impregnated, gold-toned spiny and aspiny neurons in the monkey neostriatum were deimpregnated and examined at the electron microscope level. Spiny type I neurons have relatively large nuclei with few indentations and aggregates of chromatin under the nuclear membrane which in some regions give the appearance of a dark rim. The small quantity of surrounding cytoplasm is poor in organelles. Aspiny type I neurons have eccentric, highly indented nuclei. The relatively large proportion of cytoplasm is rich in organelles especially Golgi apparatus and rough endoplasmic reticulum which often appears in stacks. Synapses with symmetric membrane densities are common on the somata of spiny type I neurons. Those on the proximal and distal dendritic shafts are few in number and asymmetric, and those on spines more frequent and primarily asymmetric. Aspiny type I neurons have few synapses on their cell bodies. Proximal and distal dendrites, however, are contacted by numerous profiles which contain small round vesicles and make both symmetric and asymmetric synapses. The same axon terminals also synapse with dendritic spines of spiny neurons, indicating that an input, most likely of afferent origin, is shared by both cell types. Other less frequently occurring profiles forming symmetric membrane densities also contact the dendrites of aspiny and spiny neurons. The axon hillocks and initial segments of both neuronal types receive a synaptic input, which is more common on spiny cells. Results offer unequivocal evidence for the differences in the ultrastructure of these two most common categories of medium-size neostriatal neurons, which may help in their proper identification in standard material, as well as information on the types and distributions of synaptic inputs onto these neurons. Moreover, the findings clarify some controversies in the literature probably originating from observations on a mixed population of cells of medium size.

Animals↗
PubMed1980

Extrageniculostriate vision in the monkey. VII. Contrast sensitivity functions.

1. Psychophysical and electrophysiological experiments have indicated the importance of spatial frequency components and their respective contrasts and orientations for the recognition of patterns. It is in the striate cortex where these types of information first converge, a fact that lends support to the accepted crucial role of this structure in pattern discrimination. 2. Monkeys with total bilateral ablation of the striate cortex, however, retain a residual capacity for pattern discrimination and also can differentiate between a vertical and an oblique luminous bar. The present study explores their capacity for spatial frequency detection both as a function of contrast and, by extrapolation, at maximum contrast (visual acuity measure). 3. Monkeys were presented with a forced choice between a homogeneous target and a vertically oriented sinusoidal grating in a pulling-in apparatus. Stimuli were produced by the transillumination of transparencies at spatial frequencies of 0.5, 1.0, 2.0, 4.0, 8.0, 16, and 32 cycles/deg, in 0.1-log unit steps of contrast from 0.79 to 0.006. The stimuli subtended 8 degrees of visual angle and were matched for mean luminance at 20 cd/m2. After mastering the discrimination of one spatial frequency at the highest contrast, contrast thresholds were first estimated by a staircase technique, and then determined by the method of constant stimuli. The procedure was repeated for each spatial frequency before and after histologically verified total bilateral removal of striate cortex and partial damage to circumstriate cortices. 4. Discrimination at all spatial frequencies was mastered by all normal monkeys. Postoperatively, they could solve only problems with frequencies between 0.5 and 4.0 cycles/deg. 5. Contrast sensitivity (threshold-1) functions for normal and destriated monkeys have the characteristic inverted J shape. The high- and low-frequency limbs are related exponentially to spatial frequency, and the peak of the curve is about 2.0 cycles/deg. The dimensions of the functions, however, change significantly following the ablation. Sensitivity is depressed at all spatial frequencies. The mean "visuogram" indicates a 26-dB flat loss. 6. The mean high-frequency cutoff point is 43 cycle/deg preoperatively and 12 cycles/deg postoperatively, equivalent to 0.7' and 2.5' of arc, respectively. The latter value is not worse than 20/80 on the Snellen chart. 7. The variability of the response at each spatial frequency in the staircase method and the slope of the psychometric function derived from the method of constant stimuli provide a measure of "instability" and "precision," respectively, which are inversely related. Preoperatively, precision is significantly greater at high than at low spatial frequencies. Postoperatively, it is similar at all frequencies, and the values are lower than those determined preoperatively. 8. The results demonstrate that destriated monkeys can detect gratings, although to a lesser degree than normal animals...

Animals↗
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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