Biomedical subjects
Publications and source records attributed to S Molotchnikoff.
This paper describes a cryoprobe constructed of glass capillary tubes commonly employed for cellular recordings. It is inexpensive, it is easily and rapidly constructed and most importantly it can easily be adjusted to cool larger areas and tightly fit brain curvatures and gyri.
These investigations are aimed at studying the influence of the electrical stimulation of the VIth nucleus (abducens nucleus) on responses of lateral geniculate cells in rabbits. The animals were prepared in the usual fashion for single cell recordings at the lateral geniculate nucleus (LGN). Results show that: Electrical stimulation of the VIth nucleus always produced excitatory discharges whose latency varied from 30 to 400 ms. Interestingly, an electrical pulse applied to the abducens nucleus was capable of enhancing the light-evoked responses without altering the spontaneous rate of firing. It thus seems that the ascending influence of the VIth nucleus manifests itself when it coincides with light responses. Most cells which were sensitive to electrical activation of the abducens nucleus had their receptive field located peripherally (greater than 50 degrees). Histological reconstructions of recording electrode tracts suggest that cells which responded to electrical stimulation were located in a narrow band lying dorsally relative to the LGN. This area can be paralleled with the perigeniculate area observed in other mammals, although not identified in rabbits. It is suggested that these extraretinal impulses which reach the LGN and emerge from an area surrounding the VIth nucleus are associated with corollary discharges.
The impact of the 60 Hz notch (rejection) filter was examined in typical photopic electroretinograms recorded with two different bandwidths: 1-1000 Hz and 100-1000 Hz. The peak times of the major ERG components (a- and b-waves) are not modified by the line filter. The amplitude of the b-wave decreases by 30%, and the morphology of the ERG wave changes slightly. Segmental analysis of the ascending limb of the b-wave reveals that the sole reduction in the amplitude of its first step (from the a-wave trough to the peak of the first oscillatory potential) accounts for more than 70% of the overall reduction measured for the b-wave. Similar results are also found in ERGs recorded with the 100-1000 Hz bandwidth. The data suggests that the b-wave of the ERG should be considered as a composite of potentials rather than as a single potential.
The aim of these investigations was to advance our knowledge of the influence of extrinsic ocular muscle (EOM) stretching on cell excitability of the retinocortical pathway. The initial goal was the lateral geniculate; however, histologic analysis indicated that most cells that responded to stretching were located near its superior edge, in an area analogous to the perigeniculate. Rabbits were anaesthetized and prepared for single-cell recordings. The extraocular muscles were detached from the eye and attached to a rigid tungsten hook. The hook was soldered to the pivot of a galvanometer that was controlled by a waveform generator. Precise and repeated length changes were obtained with extension and relaxation ramps of constant velocity. Thirty percent of the units (N = 250) responded to EOM stretching. These stimuli evoked either an excitation or a decrease of the units' spontaneous activity. Several experimental controls provided evidence that the signals that evoked the geniculate responses originated from proprioceptors belonging to the EOM. Most responding cells had their receptive fields located eccentrically (greater than or equal to 50 degrees). Also, cells that reacted to EOM stretching responded to optic nerve stimulation with a significantly shorter latency than cells that were unresponsive. Pairing the EOM stretching with light stimuli produced the following results. In about half of the units the light-evoked responses augmented, but in 28% of the cells the light-evoked discharges decreased. These effects were obtained even though EOM stretching delivered singly failed to elicit a reaction from the cell. Histologic reconstructions indicated that cells were distributed in a discrete region lying rostral and dorsomedial to the lateral geniculate nucleus. This area has been associated with the perigeniculate nucleus in cats and rats.
Unitary discharges of the lateral geniculate nucleus (LGN) were analyzed in anesthetized and paralyzed rats after inactivation of visual cortical areas (VC) by cryoblockade or by depositing a cotton wick soaked in KCl (3 M). The receptive fields were mapped prior to and following the interruption of the cortico-geniculate feedback. The responsiveness of the VC was controlled by monitoring evoked potentials and the EEG. In most off-center and about half on-center cells the surround excitatory responses were markedly reduced and even totally abolished. In contrast, the center excitation remained unchanged or increased suggesting a parallel decline of the inhibitory surround. This differential influence of cortical blockade on on- or off-responses failed to appear in on-off cells whose receptive field was nonconcentrically organized. It is proposed that the VC exerts a complex influence upon geniculate physiology while the spatial center-surround relationships are under the control of the VC. The results of this investigation are comparable to those obtained in rabbits and cats.
The objective of the present investigation was to answer the following question: Does the visual cortex affect the neuronal firing of retinal ganglion cells in the rat? To test this hypothesis, the visual cortex was inactivated by a reversible cryoblockade. Action potentials of a ganglion cell were recorded from its axon at the optic tract level prior to, during, and following cortical blockade. The results indicated that indeed the visual cortex influenced the retinal output since its inactivation led to a modification of the firing pattern evoked in response to a flash of light. In most cases the modification was an increase of the bursting pattern of the evoked discharges. By contrast cooling nonvisual areas failed to modify ganglion cells' discharge. A comparison between cortico-geniculate and cortico-retinal feedback loops seems to suggest that the first path is involved mostly with the spatial organization of center-surround receptive fields, whereas the second path is associated with temporal aspects of the retinal responses in the rat.
Cells in area 17 of the cortex are generally activated either directly through a retino-thalamic pathway or indirectly via a contralateral hemisphere-callosal pathway. The aim of the present experiment was to evaluate the effects of eliminating this second pathway on the binocular activation of cells in the primary visual cortex. The optic tract was sectioned on one side in 18 cats and unit activity was recorded in the contralateral hemisphere. This hemisphere should receive normal thalamo-cortical inputs but no visual callosal input. These animals were compared to 21 normal cats. Extracellular electrophysiological recordings were carried out in the conventional way using tungsten microelectrodes and N2O anaesthesia. Results indicated that the proportion of binocular cells found in the cortex of tract sectioned animals was lower than that found in normal animals. However, this decrease in binocularity could be essentially attributed to cells having receptive fields situated to within 4 degrees of the vertical meridian of the visual field. These results are interpreted as being congruent with the demonstrated anatomo-physiological projections of the callosal system.
Descending and ascending influences of the superior colliculus (CS) were studied in the following way. In anesthetized and paralyzed rabbits two tungsten micro-electrodes were lowered in the (CS) and the Lateral Geniculate Nucleus (LGN) for single unit recordings. A third semi-micro-electrode (dia. 100 microns) was positioned in the vicinity of the oculomotor nuclei. The final position of this electrode was determined at a location which yielded an eye movement with the lowest intensity of the electrical pulse. The typical experimental procedures required that a spontaneous collicular spike triggered the flash presentation and data acquisition. Results indicated that collicular endogeneous activity may be capable of modifying simultaneously the evoked neuronal responses of the LGN and in the vicinity of the oculomotor nuclei.
In anesthetized, immobilized rabbits recordings were made simultaneously from cells in the Lateral Geniculate Nucleus (CGL) and Superior Colliculus (CS), in order to study how the CS influences the CGL. The experimental protocol consisted of three steps. In the initial step (first control) the light stimulus was triggered electronically. In the second step (Test), the same stimulus was triggered by a spontaneous spike arising from a collicular cell. Thus the stimulus presentation was time-locked to collicular endogenous activity. The third step was the same as the first and constituted a second control. The frequencies of stimulus application were gated to be approximately the same. The results indicated that the CS exerts two separate effects on CGL units. In 37 pairs (26%), conditioning the stimulus presentation to collicular firing produced a significant enhancement of geniculate responses. In 24 pairs (17%), the geniculate responses declined. In 82 pairs (57%), no significant influence was noted. The colliculo-geniculate influence is transient. The effects peaked between 100 to 200 msec after the collicular spike and returned to their control levels within 300 msec. Collicular cells producing a decline were encountered mostly in the ventral part of the stratum griseum superficiale, and the stratum opticum, whereas collicular cells that were related to an increased geniculate response were more frequently found dorsally. Increments were more pronounced if the distance (D) between receptive fields was short (0 degrees less than D less than 40 degrees) or if the collicular and geniculate fields were far apart (120 degrees less than D less than 180 degrees). The decrement effect was attenuated as the distance separating the two receptive fields. This study suggests that the superior colliculus is capable of generating an internal signal powerful enough to modulate at the geniculate nucleus the visual message conveyed toward the visual cortex. A possible role of the CS in the initiation of the corollary discharge is briefly discussed.
Explore the source record for details and available documents.
In anesthetized rats the retina is electrically stimulated. The evoked responses are recorded in the lateral geniculate cells with glass micro-pipettes filled with NaCl. Two patterns of discharges are elicited: non-alternating responses (NA) and alternating responses (A). The evoked responses are abolished when cobalt or aspartate is injected into the eye suggesting that the discharges are generated at the outer plexiform layer of the retina. Furthermore these data indicate that the electrical current does not activate directly the retinal ganglion cells. Glycine and G A B A had differential effects on the evoked responses. The results are compared with those obtained on rabbits.
Explore the source record for details and available documents.
Interactions between retino-collicular and retino-cortical pathways at the level of the lateral geniculate nucleus were studied in anesthetized and paralyzed rabbits. In a first series of experiments the cortico-geniculate influence was analyzed by cortical depression. The disruption of cortical functions led to a specific abolition of the geniculate responses to right-left movement of the stimulating spot. The response to the opposite direction was unaffected. In a second series of experiments the stimulus presentation was triggered by a spontaneous collicular spike. This resulted in a significant modification of the geniculate responses recorded simultaneously suggesting that the superior colliculus is capable of modifying the transmission that occurs through the geniculate. Data are discussed in view of the visuo-motor integration.
In anesthetized rabbits, the receptive fields of lateral geniculate cells were mapped prior to and following the interruption of the corticogeniculate feed-back. Visual cortex (V.C.) was depressed by a focal application of 3 M KCl. The responsiveness of the V.C. was verified by monitoring the visually evoked potentials. In off- and on-center cells, the surround excitatory responses were remarkably reduced and even fully abolished in most units. In contrast, the center excitation remained unmodified. These effects were reversible. In some on-center units the center response had also decreased, and was replaced by an evoked inhibitory response. Relay cells and interneurons which yielded on and off responses over the entire area of the receptive field exhibited a loss of only one of the evoked discharges. It is concluded that the V.C. exerts mostly a specific desinhibitory action upon the geniculate network. This action affects either the center or the surround responses differentially. The results are compared with those obtained from cats.
In anesthetized and paralyzed rabbits unitary discharges of lateral geniculate nucleus (LGN) were studied after cortical excitation by strychnine and following electrical stimulation of the visual cortex (VC). Results showed that local application of strychnine produced a general increase of the spontaneous and evoked activity of geniculate cells. By contrast, cortical depression with KCl led to a differential decrement of one of the evoked responses (on or off). Electrical cortical stimulation paired with on or off stimuli led to a differential increment of on or off responses. The results support the notion that, in rabbits, the corticogeniculate system is center-surround organized. A diagrammatic model is proposed to account for the relationship between the VC and the LGN in rabbits.
In anesthetized and paralyzed rabbits, unit responses of lateral geniculate nucleus (LGN) cells to focal electrical stimulation of the superior colliculus were studied. Geniculate responses to collicular stimulation (SCS) were compared with responses to optic nerve shock (ONS). A weak correlation coefficient suggested that collicular stimulation did not fire geniculate cells through collateral activation. Further differentiation between collicular and retinofugal inputs to LGN was made possible by repetitive stimulation. Geniculate cells which responded to collicular stimulation were relay cells as they were antidromically invaded from the visual cortex. This ruled out recordings from the ventral geniculate, since this area does not project to the visual cortex. A direct colliculo-geniculate pathway was revealed by antidromic activation of collicular cells by stimulation of the dorsal LGN. Finally, triggering flashes by collicular firing resulted in a marked modification of the geniculate test response. The results suggest that the superior colliculus sends fibers to the LGN and is capable of modulating the retino-cortical neuronal message at the level of the LGN.
Electrical stimulation of the retina evokes at the optic tract level rhythmic bursts of activity whose temporal structure is predictable from the polarity of the stimulation and the receptive field type. The reaction of lateral geniculate units to this input was studied in fast and slow relay cells as well as in interneurons. The results revealed that fast relaty cells presented a response whose temporal structure remained essentially unmodified in comparison to that observed at the optic tract level: that both anodal and cathodal polarities produced rythmic pattern of excitation the latency of which depended upon receptive field type and polarity applied. In slow relay cells and interneurons responses with equal latencies could be evoked for both polarities. Following cortical depression with 3 M KCl the latency of first bursts was unaffected in relay cells, while about one third of interneurons showed a temporal pattern which was similar to that recorded at the optic tract level after the treatment. This suggests that both ON and OFF retinal networks converge upon one geniculate slow P cell and interneuron, whereas fast relay cells are mostly driven by one of the two systems. Furthermore this convergence may be achieved through visual cortex in some units.
The aim of this study was to compare the b- and d-waves of the ERG, evoked respectively by ON and OFF stimuli. The experiments were carried out on frogs. The d-wave is facilitated by light adaptation and relatively high stimulus intensity. The depth profiles of b- and d-waves are different. Aspartic acid abolished only the b-wave whereas nembutal affected the d-wave. These results suggested that b- and d-waves were produced by separate neuronal mechanisms, even though both appeared as positive deflection in the corneal ERG and were sensitive to K+ ion.