Tauba Pasik

The Internal Organization of the Neostriatum in Mammals

Publisher Summary This chapter describes the internal organization of the neostriatum in mammals. Biochemical and pharmacological investigations into the nature of extrapyramidal disorders have brought forward the role of the neostriatum as the nodal structure of the basal ganglia system; hence, the paramount importance of unraveling the intricate organization of this nuclear mass. Three types of neurons are present in the cat caudate nucleus, on the basis of size. The medium size cells measuring 9–18 μm comprise over 98% of all neurons. They have a large round and pale nucleus and a narrow rim of pale cytoplasm. A larger version of this type contains Nissl bodies, and the nucleus is indented. The large cells are over 20 μm and represent less than 1% of the population. Their nucleus is indented and large amounts of Nissl bodies are present. The small cells, less than 8 μm in diameter and of similar frequency as the large cells, have rather dark cytoplasm and no Nissl bodies.

The visual world of monkeys deprived of striate cortex: Effective stimulus parameters and the importance of the accessory optic system

Abstract Behavioral and anatomic studies were conducted to define the effective stimulus parameters and the necessary structures for visually guided behavior after complete exclusion of the striate cortex. It was found that operated monkeys mastered several combinations of total luminous flux-equated targets differing in luminance with markedly less errors in successive tests, thus showing a certain degree of brightness constancy. Some of these animals could also learn a triangle vs. circle discrimination, and exhibited signs of color vision. Enlarging the lesions to include most of areas 18 and 19 resulted in monkeys which could not master a brightness and size discrimination in the absence of luminous flux cues. Section of the optic chiasma did not affect the residual luminous flux discrimination whereas destruction of the accessory optic system abolished this capacity. Following eye-enucleations, electron microscopic examination revealed “dark” degeneration without a hyperfilamentous stage in the contralateral and ipsilateral accessory optic nuclei. Findings suggest that monkeys without striate area may still exhibit some of the approximate constancies which allow the perception of a structured visual space, provided that the peristriate and parastriate cortices are relatively preserved. The accessory optic system appears to be necessary for the basic discrimination of total luminous flux. Its nucleus receives crossed and uncrossed optic fibers, and many other non-optic afferents.

Extrageniculostriate vision in the monkey: discrimination of luminous flux-equated figures.

Six monkeys (Macaca mulatta) were tested before and after histologically confirmed total removal of the striate area and complete degeneration of the lateral geniculate nuclei. Using Kluvers pulling-in technique with nonmovable transillu-minated targets, two discrimination problems were given at both a high and a low photometric level. In the first test, the targets were of equal area and differed in luminance and total luminous flux (B-F problem). In the second test, figures differed in luminance and area in an inverse proportion (BA problem) which resulted in their being closely matched for total luminous flux. Postoperatively, the animals showed significant deficits on all tests. Every monkey, however, achieved criterion level of performance not only on the B-F but on the BA problem as well. Performance on the latter test did not change after dilatation of the pupils, or when minimal flux differences were eliminated as cues by making the rewarded target to have the lesser flux in half of the trials and the greater flux in the other half. These findings indicate that monkeys can be trained to discriminate between stimuli equated for total luminous flux after exclusion of the geniculostriate system. Although it is possible that other stimulus parameters are discriminated by such animals, our results do not necessarily negate Kluvers original concept. Indeed, destriated monkeys may still utilize a luminous flux cue to discriminate flux-equated figures through the detection of differences in the rate of change of this parameter during eyes, head and/or body movements.

Extrageniculostriate vision in the monkey. IV. Critical structures for lightvs. no-light discrimination

Abstract The purpose of the study was to determine which brain structures were critical for the capacity to perform a gross luminous flux discrimination in the absence of striate cortex. Fourteen monkeys were trained to a criterion of successful performance, set at 90% correct responses in 30 consecutive trials, on a light vs. no-light discrimination test, using specially designed automatic equipment which allowed predetermination of Gellerman schedules. All monkeys were able to relearn the test after complete bilateral excision of striate cortex and partial ablation of areas 18 and 19 (histologically verified). Additional bilateral lesions of the temporal neocortex, or posterior parahippocampal and retrosplenial allocortex, or pulvinars, or superior colliculi did not interfere significantly with the relearned habit. Instead, when the additional damage involved the superior colliculi and medial pretectum, there was a major discrimination deficit, but eventually these monkeys could reach the criterion level. Only when the lateral pretectal region was included in the latter lesion was there a failure to master the test in 6000 trials of postoperative testing. The effective damage caused bilateral severe degeneration of the nucleus of the accessory optic tract. Findings indicate that the mesodiencephalic junction contains critical structures for extrageniculostriate vision in the monkey and suggest that the accessory optic system could be one main source of visual input for the capacity to perform luminous flux discrimination tests in the absence of striate cortex.

Visual Functions in Monkeys after Total Removal of Visual Cerebral Cortex1

Publisher Summary This chapter presents a detailed account of a study conducted on 82 rhesus monkeys with total bilateral ablation of the striate cortex. This study revealed a wide repertoire of visual functions retained or recovered after surgery. The lateral geniculate nuclei of the destriated monkeys contained viable neurons that were identified as local circuit interneurons with ubiquitous membrane properties for developing presynaptic sites at any region of the cell surface. The results of additional lesions demonstrated the critical role assumed by various structures in the absence of striate cortex. The primate striate cortex has a preeminent role in all types of visual functions, with the exception of pupillary and blink reactions. Some sort of reorganization must occur in other structures after striate resections. These studies have influenced significantly the search for residual capacities in humans with lesions of the geniculostriate system, which have revealed a retention or recovery similar to that shown by experimentally damaged monkeys.

Vertical optokinetic nystagmus in the split-brain monkey

Abstract Electrooculograms during optokinetic stimulation in the vertical plane were recorded from seven monkeys ( Macaca mulatta ) before and after section of pregeniculate visual pathways or midsagittal division of brain commissures, or both. Section of one optic tract or of the chiasma did not alter the response. Additional cutting of the corpus callosum resulted in a nystagmus of lower frequency and perverted direction with an oblique component toward the side of the visually “deprived” hemisphere. The deficits in the monkeys with section of the optic chiasma appeared only on monocular stimulation. Additional division of massa intermedia, anterior, posterior, habenular, and intercollicular commissures, completely abolished the nystagmus upward. This defect was also present on binocular stimulation of animals with section of the optic chiasma. These findings support the concept that both sides of the brain must receive adequate visual input, either through the classic optic pathway or through the commissures, to result in normal optokinetic nystagmus in the vertical plane. Subcortical commissures, particularly the posterior commissure, may be more related to the oculomotor output since their section affects the response even on binocular stimulation of monkeys with division of both the optic chiama and the corpus callosum. Since optokinetic nystagmus is a most sensitive indicator of the integrity of the oculomotor system, the possibility of defective eye movements should be considered in the interpretation of the results of visual tests in split-brain monkeys.

Total luminous flux: a possible response determinant for the normal monkey.

Thirteen normal monkeys (Macaca mulatta) trained to discriminate between transilluminated figures of equal area and different luminance, and consequently different luminous flux, made similar numbers of errors during training on a new problem with the same luminance values but with targets equated for luminous flux. These findings together with results of critical trials suggest that the significant cue in the original problem was luminous flux. This behavior is strikingly similar to what has been reported for the monkey following exclusion of the geniculostriate system.

Early postnatal development of monkey subthalamic nucleus: a light and electron microscopic study

The subthalamic nuclei of 9 rhesus monkeys, ranging in age from newborn to 17 weeks, were examined at the light and/or electron microscopic levels, using computer assisted quantitative methods. The volume of the structure does not change significantly over the period of study. The mean cross-sectional area of neuronal somata, however, decreases by 33%, and most markedly during the first month. This is paralleled by a similar change in the mean area of cell nuclei but the perikaryon/nucleus ratio increases steadily after the first week. There is an overall decline in total cell numbers from newborn to 17 weeks. Ultrastructural features include dendritic growth cones in the neonatal monkey, and signs of axonal degeneration during the entire period. In addition to conventional axosomatic and axodendritic synapses, there are also synaptic junctions between vesicle-containing profiles which are seen only after the first month. The distributions of plaque diameters were reconstructed by the Coupland stereologic method from linear measurements of synaptic profiles and used to calculate synaptic densities and estimate the total number of synapses. This number is stable during the first postnatal month, declines markedly in the second month, and to a lesser degree thereafter, reaching a value of 55% of that at birth by 16 weeks. Findings indicate the occurrence of substantial changes within the subthalamic nucleus during the first 4 postnatal months, the most prominent of which is a marked synapse elimination.

A newly recognized element in the monkey dorsal lateral geniculate nucleus exhibiting both presynaptic and postsynaptic sites.

SummaryThe dorsal lateral geniculate nucleus (LGNd) of four normal monkeys (Macaca mulatta) and of two other such animals with total unilateral ablation of the visual cortices (4–6 days survival) were examined in serial thin sections with the electron microscope. In these materials we have observed a new neuropil component which has the cytologic characteristics of principal cell (P-cell) dendrites, i.e. large and dark mitochondria, smooth endoplasmic cisterns and filamentous, non-synaptic contacts with retinal terminals. In addition, these elements contain large round synaptic vesicles and can be seen forming asymmetric synapses exclusively with presynaptic dendrites belonging to interneurons (I-cells). Occasionally, a reciprocal synapse is formed between the two profiles. The novel elements are postsynaptic to various vesicle-containing profiles, i.e. axonal boutons of presumably retinal and cortical origin, and I-cell presynaptic dendrites. They are found more frequently in the specimens with cortical ablations, although their number is still much lower than that of the other classic components of the neuropil. Measurements made on × 80 000 electron micrographs of spheroid vesicles within presumptive retinal terminals, cortical endings and the new profile described in this report, result in mean diameters of 38.6nm, 33.3nm and 44.3 nm, respectively. The differences between the means are statistically significant.Although the profile with large dark mitochondria and large round vesicles may represent a dendrite of a different I-cell type, or a recurrent axon collateral of a P-cell, it appears more probable that it is a presynaptic dendrite of a P-cell. The infrequent but consistent occurrence of these elements suggests that at least some P-cells can develop presynaptic sites on their dendrites, a property which contributes to the synaptic complexity of the LGNd.

SYNAPTIC ORGANIZATION OF THE STRIATUM AND PALLIDUM IN THE MONKEY

Publisher Summary nThis chapter discusses new information on the components and synaptology of the globus pallidus. It presents a diagram of the second type of spiny neuron in the striatum, the Spiny II. It differs from the Spiny I in that the spine density is considerably lower, and spines in Spiny II are present not only on the distal branches but on the proximal dendrites and the soma. A common feature is the long axon that shows extensive collateralization of the proximal portion. These neurons vary greatly in size, some elongated ones reaching 60 m in the long axis. The axon hillock and the initial segment of the Aspiny I neuron also receives synaptic input, although less commonly than in the case of spiny cells. Axosomatic synapses are rare; however, proximal and distal dendrites are contacted by numerous profiles that contain small round vesicles and make both symmetric and asymmetric synapses.