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L A Benevento

Publications and source records attributed to L A Benevento.

At least 19 recordsLinked to original sources
PubMed1995

gamma-Aminobutyric acid and somatostatin immunoreactivity in the visual cortex of normal and dark-reared rats.

Our previous single unit and ultrastructural studies of visual cortex of dark-reared rats revealed an impairment of intracortical inhibitory mechanisms [2,3,5]. Neurochemical changes in inhibitory neurotransmitter and/or neuropeptides, such as gamma-aminobutyric acid (GABA) and somatostatin (SS), respectively, may contribute to the observed alterations. The present study was designed to measure GABA and SS alterations in the visual cortex of the same dark-reared preparation, as possible neurochemical correlates of the changes seen both physiologically and anatomically in previous companion studies. In the present investigation the mean densities of GABA- and SS-immunoreactive neurons in area 17 of dark-reared rats were determined and compared to the density of those of rats reared in normal lighting conditions. Dark-rearing resulted in a significant decrease in the density of GABA-immunoreactive neurons in all cell layers of area 17 of the rat visual cortex; not limited to the thalamorecipient layer(s). There was also a higher mean density of total cortical cells in dark-reared animals. No differences, however, were seen in the density of SS-immunoreactive neurons. The alterations of GABA-immunoreactive neurons in all cortical layers agree with the altered synaptic ultrastructure and physiological responses seen in all cortical layers as reported in our previous companion studies. Taken together, these studies further support the notion of a deficit in intracortical inhibitory mechanisms in the visual cortex of dark-reared adult rats.

Animals↗
PubMed1992

The effects of dark-rearing on the electrophysiology of the rat visual cortex.

Our previous two studies have shown that dark-rearing affects the morphology and chemistry of adult rat primary visual cortex (area 17). In this study we demonstrate correlated physiological alterations with single unit recordings in the same preparation. Rats were raised from birth in either 14 h light/10 h dark (Lt/Dk) or in total darkness (Dk). At the age of 3 months, single units were recorded in area 17 of both groups. The cortical cells of Dk animals showed significantly more spontaneous activity during ambient lighting. The mean rate of randomly appearing spontaneous activity was greatly increased in Dk animals. Moreover, many cells in Dk animals also exhibited a particular type of spontaneous activity which occurred as 'bursts' of spikes, i.e. quantified groupings of fast firing spikes, separated by randomly appearing spontaneous activity. The mean number of bursts per min seen in Dk animals was also significantly more than any such activity seen in Lt/Dk animals. Visual stimuli consisted of white or dark bars moving with different orientations and directions at slow and fast speeds, and full field flashes. In response to moving stimuli, notably fewer cells were orientation- or direction tuned in dark-reared animals, and when they did respond to moving bar stimuli, the responses were of relatively longer duration. The pathologically high spontaneous activity rate, as well as lack of tuning and relatively prolonged duration of responses to moving stimuli indicate that intracortical inhibitory mechanisms are seriously compromised in both the unstimulated and stimulated states and is in agreement with our previous findings (Bakkum, B.W., Port, J.D., Cohen, R.S. and Benevento, L.A., Soc. Neursci. Abst., 15 (1989) 797) of a decreased number of synapses and GABA-containing cells in the visual cortex of the same preparation. Other evidence suggests that there may be a decrease in stimulus-bound excitatory drive. Significantly fewer cells in Dk animals were excited by all visual stimuli, and responses elicited by flashes had relatively longer 'on' latencies, relatively shorter durations, and were generally weaker. This may correlate with our finding of a significantly smaller number of perforated postsynaptic densities in the cortex of the same preparation (Bakkum, B.W., Benevento, L.A. and Cohen, R.S., J. Neurosci. Res., 23 (1991) 65-80).

Action Potentials↗
PubMed1992

An immunocytochemical method for marking microelectrode tracks following single-unit recordings in long surviving, awake monkeys.

We describe an immunocytochemical method for marking microelectrode tracks made during single-unit recordings in long surviving, awake monkeys. This procedure detects the increase in glial fibrillary acidic protein in the glial cells along a microelectrode track using commercially available antibodies. We have successfully marked electrode tracks in tissue from preparations having postrecording survival times ranging into months even though the gliosis can no longer be detected with conventional stains for cell bodies. When this method is combined with data from electrophysiological recordings in chronic preparations it will be possible to reconstruct functional architecture using chronic preparations, as has been done previously with acute preparations.

Animals↗
PubMed1991

Effects of light/dark- and dark-rearing on synaptic morphology in the superior colliculus and visual cortex of the postnatal and adult rat.

Several synaptic parameters, previously shown to undergo alterations with changes in the internal and external environment, were examined in the visual system of light/dark- and dark-reared postnatal and adult rats. Animals were raised in either 14 hr light/10 hr dark (Lt/Dk) or in total darkness (Dk). The specific synaptic parameters in the superficial layers of the superior colliculus (SC), visual cortex (laminae II/III and IV) (VC), and, as control, the auditory cortex (laminae II/III and IV) (AC), examined during the postnatal period (i.e., postnatal days 7, 14, 21, and 28) and in the adult (i.e., day 56) included: 1) mean number of synapses, 2) mean synaptic length, 3) percentages of perforated postsynaptic densities, 4) percentages of asymmetric and symmetric synapses, 5) percentages of dendritic, spinous, and somatic synapses, and 6) percentages of synapses with positive, negative, or no curvature. Developmental patterns in rats reared in normal lighting conditions were noted. Specifically, in the SC and VC of Lt/Dk animals, the number of synapses increased up to postnatal day (PND) 21 and then decreased; no significant changes in the mean number of synapses between PND = 28 and 56 were detected in any of the areas examined. Changes in synaptic length in the SC and VC were not observed during postnatal development of in the adult in any of the aforementioned brain areas. Low percentages of postsynaptic densities (PSDs) were found at all time points and in all brain areas during the postnatal period. Increases in perforated PSDs were seen at PND=56 compared to PND=28 in the VC. In the VC and AC, there was a decrease in symmetric synapses with age. Asymmetric synapses were prevalent in all brain areas at PND=28 and 56. Dendritic synapses predominated in the SC, while spinous synapses were the preponderant type in the VC and AC during postnatal development and in the adult. A decrease in the percentage of spinous synapses in the SC was observed at PND = 56 vs. PND=28. A decrease in the percentage of negatively curved synapses with age and a trend toward a concomitant increase in the percentage of positively curved synapses were seen in all brain areas during development and in the adult. Quantitative analyses of the SC and VC tissues examined from all postnatal animals demonstrated no significant differences between Lt/Dk and Dk animals in all the synaptic parameters measured.(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1988

An investigation of collateral projections of the dorsal lateral geniculate nucleus and other subcortical structures to cortical areas V1 and V4 in the macaque monkey: a double label retrograde tracer study.

Previous anterograde studies in the macaque monkey have shown that, in addition to the projection to striate cortex (V1), the dorsal lateral geniculate nucleus (DLG) has a sparse, horizontally segregated projection to layers IV and V of prestriate cortex (V4). However, the distribution and degree of axon collateralization of DLG cells which give rise to these projections are unknown. This study was designed to answer these questions. The DLG (along with the pulvinar and other subcortical regions) was examined for the presence of single- or double-labeled cells after injections of two different (fluorescent or HRP) retrograde tracers into corresponding retinotopic points in visual cortical areas V1 and V4. In the DLG, it was found that cells projecting to V4, which reside in or near the tectorecipient interlaminar zones of the DLG, do not project to V1 and thus represent a separate population of cells. The organization of the macaque geniculo-prestriate projection thus seems quite different from that of carnivores. Both single- and double-labeled cells were found in other subcortical areas, e.g., single-labeled cells were found in the claustrum, hypothalamus and lateral pulvinar, and a double-labeled cell population was found in the inferior pulvinar.

Animals↗
PubMed1988

Transient global amnesia and thalamic infarction.

We describe the clinical and neuroradiologic features of a patient with two episodes of transient amnesia who later developed persistent amnesia and an acute infarction in the left thalamus. The neurobehavioral manifestations were strikingly similar in all three episodes. Cranial computed tomography was normal following the first two episodes. Thalamic ischemia could explain some cases of transient global amnesia.

Aged↗
PubMed1986

Histochemical and architectonic differentiation of zones of pretectal and collicular inputs to the pulvinar and dorsal lateral geniculate nuclei in the macaque.

The pattern of acetylcholinesterase (AChE) reactivity was studied in the pulvinar and dorsal lateral geniculate nucleus (DLG) of the adult macaque monkey. Discrete islands of AChE reactivity were found that correlated precisely in location with the pattern of projections from the superior colliculus and pretectum. Specifically, AChE overlies terminal fields of superior colliculus projections in the DLG, in four foci in the medial and lateral pulvinar, and in several foci in the inferior pulvinar. All of these tectal projection areas have very high AChE reactivity such that they are easily distinguished. In addition, the pretectum projects to a specific focus in the lateral pulvinar that also has a very dense AChE histochemical reaction. A number of these AChE foci could be further distinguished from other areas in the pulvinar by myeloarchitectonic characteristics. Some of the foci in the lateral and inferior pulvinars could also be distinguished by unique cytoarchitectonic features (as seen with both Nissl and Golgi stains). In an attempt to determine the possible origin of a cholinergic input to the pulvinar, horseradish peroxidase (HRP) injections and choline acetyltransferase immunohistochemistry were also done. The results of this experiment indicate that the AChE reactivity seen in the midbrain projection zones to the thalamus may be due to the precise overlap of terminal projections from the brainstem cholinergic cell groups, Ch5, Ch6, and Ch8. These results, taken together, imply that there are several anatomically and histochemically distinct zones related to extrageniculate pathways located within classically defined thalamic boundaries.

Acetylcholinesterase↗
PubMed1986

Direct retinal pathways to the limbic thalamus of the monkey.

Tritiated proline, horseradish peroxidase (HRP), and wheat germ agglutinin conjugated to HRP (WGA-HRP) were used as anterograde tracers in the monkey to reveal visual pathways. After intravitreal injections, three separate, direct routes of labeled retinal axons were followed to the thalamus. These routes eventually converged to innervate the lateral dorsal and anterodorsal thalamic nuclei. Thus, retinal input may reach the posterior cingulate cortex after a single synapse in lateral and anterior thalamic nuclei.

Animals↗
PubMed1983

The organization of connections between the pulvinar and visual area MT in the macaque monkey.

Injections of horseradish peroxidase were placed in visual area MT which is located in the superior temporal sulcus of the macaque monkey occipital cortex. Overlapping retrogradely filled cells and anterogradely transported terminal grains were found to be located only within a crescent shaped region which traverses the brachium of the superior colliculus to include the inferior pulvinar and dorsal overlying lateral pulvinar. The connections between MT and the pulvinar crescent are reciprocal and topographically organized, with the lower visual field represented dorsally and the upper visual field represented ventrally. There is an expanded representation of central vision located caudally within the crescent while peripheral vision is represented rostrally. These findings indicate that any functional properties derived from the visual thalamus must arise from this crescent shaped region of the pulvinar.

Animals↗
PubMed1981

The afferent and efferent organization of the lateral geniculo-prestriate pathways in the macaque monkey.

Both anterograde (autoradiographic) and retrograde (horseradish peroxidase) tracing techniques were used to identify and characterize projections from the dorsal lateral geniculate nucleus (DLG) of the thalamus to the subdivisions of occipital prestriate cortex (generally defined by areas 18 and 19) in macaque monkeys. It was found that the DLG projects to area 19 and the anterior portion of area 18 located on the lateral, ventral, and ventromedial surfaces of the hemisphere. There is a general topographical organization such that the medial portion of the DLG projects to dorsal prestriate located between the lunate and superior temporal sulci, while the lateral portion of the DLG projects to ventral prestriate extending from the inferior occipital to the occipitotemporal sulci. The DLG projects to most of the occipitotemporal sulcus. In contrast DLG inputs to the lunate, superior temporal, and inferior occipital sulci are limited in extent, and involve only a portion of the bank or shoulder of each sulcus which is continuous with the cortex located on the surfaces of the surrounding preoccipital gyri. The projection to the inferior occipital sulcus is more extensive than the ones to the lunate and superior temporal sulci and involves the floor as well as the ventral bank. This means that there are certain functional subdivisions, such as those located within the lunate (eg, visual area 2) and superior temporal sulci which do not receive DLG input. Regardless of the location of these projections the terminal pattern was the same and occurred in horizontally segregated "patches" which were restricted to layer V and the lower, adjacent portion of layer IV. In contrast, the projections from the nearby pulvinar to cortical layers IV, III, and I of the same prestriate areas do not overlap with those from the DLG. An attempt was made to identify possible afferent inputs to these DLG-prestriate paths. The HRP experiments reveal that the DLG-prestriate cells are concentrated in the DLG interlaminar zones and that their distribution overlaps the distribution of terminals from the superior colliculus and, as shown previously, prestriate cortex. Intraocular injections of radioactive precursors demonstrated transsynaptic transport to a number of structures except prestriate cortex. While the latter result does not prove that the DLG-prestriate cells do not receive retinal input, one conclusion is that the DLG-prestriate projection could be organized like pulvino-prestriate systems which receive their inputs from the midbrain and cortex.

Afferent Pathways↗
PubMed1981

The projection from the dorsal lateral geniculate nucleus of the thalamus to extrastriate visual association cortex in the macaque monkey.

Both autoradiographic and horseradish peroxidase tracing techniques were used to characterize a projection from the dorsal lateral geniculate (DLG) nucleus of the thalamus to visual association cortex (extrastriate cortex) in the macaque monkey. The results show that medium to large caliber DLG axons end to discontinuous terminal "patches" in layers V and lower IV of extrastriate cortex. There is a topographical organization to these projections which are mainly to area 19 and anterior 18 located on the lateral and medial surfaces of the hemisphere. Apparently there are no DLG projections to any of the cortical subdivision located within the lunate and superior temporal sulci.

Afferent Pathways↗
PubMed1981

Visual responses of single neurons in the caudal lateral pulvinar of the macaque monkey.

Single unit recordings were made in the portion of the lateral pulvinar which forms the lateral aspect of the caudal pole of the thalamus, i.e., PL gamma (Rezak, M., and L. A. Benevento (1977) Soc. Neurosci. Abstr. 3:573; Rezak, M. (1978) Soc. Neurosci. Abstr. 4: 642), of macaque monkeys. PL gamma receives convergent inputs from the occipital cortex and has strong reciprocal interconnections with the visual association cortex, including the inferotemporal cortex (areas 20 and 21). It was found the that PL gamma has a poor or nonexistent retinotopic organization. Many of the neurons had large, unflanked, overlapping receptive fields which often included the fovea. A few neurons could be influenced by a visual stimulus placed anywhere in the visual field described by a tangent screen. The receptive fields could be bilateral or located entirely within the contralateral or ipsilateral hemifields. The majority of units were binocular and exhibited various types of binocular interaction which could be quite complex. The binocular response was not predictable from the algebraic sum of the monocular responses and could be of the opposite sign (e.g., excitatory when the monocular response was inhibitory). Neurons which were also sensitive to the direction of movement of stimuli projected upon the tangent screen formed a major group. Of the units sensitive to tangentially moving stimuli, two special subgroups were found. One group of neurons gave sustained responses to static levels of luminance, while the other group was sensitive to simuli which moved toward or away from the eyes. The nonlinear rate of change of the apparent size of approaching or receding stimuli was described by a mathematical function which also describes the response of the neurons to the same stimuli. For many of these units which were sensitive to tangentially moving stimuli and one other class of stimuli, such as luminance levels of movement in depth, the responses to one class were seemingly unrelated to the responses to the other class. The same statement may be made for monocular and binocular responses. It may be, then, that different wiring diagrams describe these different types of inputs. These physiological results are discussed in terms of the inputs to PL gamma as well as its cortical targets.

Animals↗
PubMed1980

A horseradish peroxidase study of the innervation of the internal structures of the eye. Evidence for a direct pathway.

The sources of innervation of the internal structures of the eye in monkey and rabbit were investigated by injecting horseradish peroxidase (HRP) intraocularly and monitoring its retrograde transport. HRP-labeled cells were found in the ciliary ganglia and in the midbrain throughout the dorsoventral extent of the midline of the oculomotor complex. The results suggest that a direct pathway exists from the midbrain, and it is argued that this pathway is for the control of accomodation. Either this pathway is direct, with no synapse interposed, or the postsynaptic neurons are near or in the intrinsic musculature. A third but not so likely possibility is that retrograde transsynaptic transport of HRP occurred across electrotonic synapses in the ciliary ganglion. These findings may challenge the commoly held view that the entire pathway for the control of the intrinsic musculature synapses in the ciliary ganglion. On the other hand, it may be that this direct path is a sensory system much like the mesencephalic nucleus of the trigeminal nerve.

Accommodation, Ocular↗
PubMed1979

A comparison of the organization of the projections of the dorsal lateral geniculate nucleus, the inferior pulvinar and adjacent lateral pulvinar to primary visual cortex (area 17) in the macaque monkey.

Both anterograde and retrograde transport tracing methods were used to study the organization of the projections of the dorsal lateral geniculate (DLG), the inferior pulvinar and subdivisions of the lateral pulvinar to primary visual cortex (striate cortex or area 17). The DLG projects only to striate cortex. These projections are retinotopically organized, and do not extend to any cortical layers above layer IVA. In contrast the inferior pulvinar (PI) and the immediately adjacent portion of the lateral pulvinar (PL alpha 48) project to both striate and prestriate cortex. The projections from these two thalamic areas to the striate cortex are also retinotopically organized and exist in parallel with those from the DLG. In contrast to the DLG, the projections from PI and PL alpha terminate above layer IVA in striate cortex, i.e. layers I, II and III. In prestriate cortex the layers of termination include layers IV, III and I. The pulvinar terminations in layers II and III of area 17 occur in segregated patches as do the geniculate terminations in layers IVC and IVA. On the other hand the pulvinar terminations in layer I which overlie those in layers II and III of area 17 appeared to be continuous. Control studies show that the remainder of the lateral pulvinar overlying PL alpha does not project to striate cortex. It is concluded that there are 3 visuotopically organized inputs from the lateral thalamus to primary visual cortex and that each of these inputs have different layers of termination. The inputs from PI and DLG can convey direct retinal inputs while those from PI and PL alpha can also be involved in intrinsic cortico-thalamocortical connection with prestriate cortex. It remains, then that it cannot be tacitly assumed that the ascending inputs which influence the response properties of the primary cortical neurons arise solely from the dorsal lateral geniculate nucleus. It is also argued that these inputs to the supragranular layers may be excitatory as those from the DLG to the IVth layer.

Animals↗