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Biomedical subjects

S Molotchnikoff

Publications and source records attributed to S Molotchnikoff.

87 records · Page 5Linked to original sources
PubMed1977

Corticofugal influence on evoked activity of lateral geniculate neurons in the rabbit.

Corticofugal influence upon lateral geniculate units was evaluated by inactivating the visual cortex with a topical application of 3M KCL in rabbits. The results revealed a decrease of spontaneous firing in slow P cells following cortical depression suggesting a tonic corticofugal influence. The most consistently observed alteration was an enhancement of the ON response with a decrease of the response to the opposite stimulus (OFF); and vice versa: the short latency excitation being augmented. It is suggested that the visual cortex exerts a powerful influence on intra-geniculate inhibitory processes.

Animals↗
PubMed1977

Superior colliculus cell responses to to electrical stimulation of the retina.

Superior colliculus cell discharges in response to electrical stimulation of the retina were investigated in rabbit. In contrast with the responses at the optic tract level both polarities evoked discharges of equal latencies suggesting a convergence of ON- and OFF-centre retinal ganglion cells upon one collicular unit. Three typical patterns of responses could be distinguished. Thus, 40% of cells reacted with a burst, 47% with a prolonged discharge, and 5% responded by a transient inhibition. The responses of the remaining cells could not be classified.

Action Potentials↗
PubMed1977

Response recovery cycles in the visual cortex and superior colliculus following conditioning "ON" and "OFF" stimulation in the rabbit.

The responsiveness of visual cortex (VC) and superior colliculus (SC) was simultaneously compared following conditioning "ON" or "OFF" stimulation, in the rabbit. Average evoked responses were recorded simultaneously from the visual cortex ans superior colliculus. "ON" or "OFF" steps constituted the conditioning stimuli whereas the test stimulus consisted of optic nerve stimulation. All evoked responses exhibited a reversal of their polarity when the electrode was moved in the dorsoventral direction (Negative-Positive in the SC, Positive-Negative in the VC). This assured the somato-dentritic origin of the potentials. The results showed that responsiveness in both structures was significantly higher following an "OFF" simulus than after an "ON" step. Collicular responsiveness was higher than in the VC when the same conditioning stimulus was applied. The spatial distribution of the source of "OFF" responses was circumscribed to the ventral part of the superficial layer of the superior colliculus. These results suggest specific properties associated with the brightening and dimming systems.

Animals↗
PubMed1977

[Corneal response to 'off' in the intact rabbit eye].

The corneal electrical responses of the retina to light OFF are described in this report. The results reveal that high intensities of stimulation evoke an OFF response containing a positive wave. Since this wave was resistant to Sodium aspartate it is concluded that it arises from the receptor level. Negative wave are of double origin a) a negative potential evoked with low light intensities which is resistant to Sodium aspartate b) a second negative wave which is sensitive to the latter drug and thus arises from the internal layers of the retina. It is concluded that, because of the absence of a prominent b wave, the OFF responses permit a more sensitive evaluation of retinal electrophysiology.

Animals↗
PubMed1976

Transient responses of rabbit retinal ganglion cells to photic and electrical stimuli.

The relationships between the center and the surround of the receptive field of the rabbit retinal ganglion cell were investigated. This was done by coupling localized light spots and electrical activation of the retina and by analyzing the time of the excitatory and inhibitory periods. The responsiveness to the electrical transretinal pulse revealed a) that ON stimulation in OFF-center cells and OFF stimulation in ON-center cells, elicited a primary period of inhibition with a short latency; b) the long latency response of surround stimulation was not preceded by an inhibitory period unless the center was simultaneously stimulated in the same direction; c) a transient response to a stationary spot of light is followed by a period of inhibition. These results are discussed in relation to the known cellular retinal networks.

Animals↗
PubMed1975

Simultaneous recordings of visual cortex and superior colliculus field potentials in the rabbit.

The field potentials recorded simultaneously at various depth of the rabbit's visual cortex and superior colliculus were analysed following light ON and light OFF. The collicular ON and OFF potentials exhibited three slow components superimposed by fast rhythmic oscillations. Only the first slow component reversed its polarity with penetration from surface negative to positive in depth. The cortical ON and OFF responses similarly contained three slow waves which all reversed their polarity with electrode penetration: from surface positive to negative in deeper layers. The most striking difference between ON and OFF cortical responses is the absence of fast rhythmic oscillations in the cortical ON response.

Animals↗
PubMedDate not supplied

Latency distribution from orthodromic stimulation at the optic nerve, in the lateral geniculate nucleus and superior colliculus of rabbits.

Latency distribution of responses to optic nerve stimulation has been compared between the Lateral Geniculate Nucleus (L.G.N.) and Superior Colliculus (S.C.), in rabbits. Histograms revealed that in both structures the latency distributions are very similar. Results suggest that all groups of retinofugal fibers project to both sites, although longer latencies are more frequently met at the collicular level. In addition evidence is presented that in rabbit's optic nerve there are at least three populations of axons with different conduction velocities.

Animals↗
PubMedDate not supplied

The conduction velocity and central projections of retinofugal fibers in the rabbit.

IN anesthetized and paralyzed rabbits, action potentials were elicited antidromically following electrical stimulation of optic tract terminals at the geniculate level (LGN). The conduction velocity spectrum extended from 7 m.s-1 to 34 m.s-1. The distribution of conduction velocities indicated four major modes at 10, 18, 22 and 26 m.s-1. Antidromic compound action potentials exhibited good correlation between the conduction latency and the major modes of the distribution histogram. These results suggest that the rabbit optic tract is composed of four classes of fibers varying in their conduction velocities. The central projections of retinofugal axons were studied with electrical stimulations of the Superior Colliculus (CS) and the LGN while recording from the same optic tract fiber. Antidromic spikes could be elicited from all conduction velocity groups and 71% of axons responded to both sites of stimulation. This finding indicates that most retinofugal fibers branch to and innervate both CS and LGN. Further, there is a tendency for fast-conducting axons to have their receptive fields located eccentrically relative to the optic axis of the eye.

Animals↗
PubMedDate not supplied

The influence of transcortical relationships on visual responses in rats.

Visual responses of the 17/18 border of one hemisphere in anesthetized rats were studied while the opposite cortex was depressed. The depression of the opposite cortex was achieved by a cryoblockade of the homotopic area or by bleaching the unstimulated eye. In the first series of experiments field potentials were recorded, whereas in the second experimental series tests were carried out on single units. Bleaching the unstimulated eye produced mostly an enhancement of long latency potentials recorded in deeper layers. Cryoblockade of the contralateral cortex depressed the responses in a more uniform fashion. Most units typically presented a weaker evoked firing after cryoblockade. However, in some neurons the reaction to the treatment depended upon the nature of the stimulus and other units lost their orientation specificity. A single explanation such as a tonic excitatory transcortical influence is insufficient to account for these results.

Animals↗
PubMedDate not supplied

The effect of acute trichloroethylene exposure on electroretinogram components.

The effects of acute exposure to trichloroethylene (TCE) on the electroretinogram (ERG) and oscillatory potentials (OPs) were studied on adult New Zealand rabbits anesthetized with urethane. The ERG and OPs were recorded under photopic conditions with a speculum electrode, with pupils fully dilated and the cornea anesthetized. Emulsified (Intralipid) TCE was given intravenously in three consecutive injections of equal volume for a total dose varying between 24 and 85 mg/kg. Averaged ERG and OPs (50 sweeps) were taken up to 250 minutes after the last TCE injection. Our results indicated that, irrespective of the dose used, there was a significant (p less than 0.001) reduction (average: 50%) in the amplitude of the b-wave of the ERG following TCE injection. In contrast, the OPs showed a differential effect. At low doses, OP4 showed a significant (p less than 0.001) reduction resulting in some cases to its complete extinction, while at higher dose there is a marked increase in amplitude. Our results would suggest that the OPs are a better retinal potential to assess the level of TCE toxicity than is the b-wave of the ERG.

Animals↗
PubMedDate not supplied

Connections between areas 17 and 18 depend on orientation and cell type.

The functional relationships between areas 17 and 18 are still incompletely understood; many experiments indicate that cells sharing like properties are linked together, whereas other studies suggest a deviation from this principle. Here we report the effect of using GABA to block circumscribed area 17 neuronal populations with known orientation preferences. We studied the interaction of this treatment on the responses of simple and complex neurons in area 18. The data suggest that these interactions follow different rules for simple and complex cells: specifically, an iso-orientation linkage appears to hold for simple cells while a cross-orientation linkage appears to hold for complex cells.

Animals↗