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S Molotchnikoff

Publications and source records attributed to S Molotchnikoff.

At least 55 records · Page 3Linked to original sources
PubMed1991

[Pulvina-lateralis posterior nucleus complex of mammals and the visual function].

It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.

Animals↗
PubMed1990

Susceptibility of neurons in area 18a to blockade of area 17 in rats.

The present investigation is aimed at studying the influence of the striate cortex (area 17 or V1) upon responses of area 18a. Electrical activity was recorded from neurons in area 18a through glass micropipettes. At the same time lidocaine hydrochloride was injected in the same retinotopic register of area 17. Forty eight cells were tested to diffuse stroboscopic flashes and to localized stationary or moving slits in the receptive field. In addition, orientation selectivity was analyzed in 15 units. Blockade of area 17 produced the following results: discharges to stroboscopic light were unaltered while responses to stationary, localized targets were diminished in about half of the cells. Fifty percent of movement evoked responses were decreased. The orientation properties were particularly sensitive to blockade of area 17. Out of 15 units, 13 had their orientation tuning curves altered by the treatment. These results seem to suggest that the degree of trigger feature complexity depends upon lateral interactions between areas V1 and V2.

Animals↗
PubMed1990

The effect of iodoacetic acid on the electroretinogram and oscillatory potentials in rabbits.

It has been shown that a single injection of iodoacetic acid selectively (but temporarily) abolishes the b-wave of the electroretinogram. We examined whether such use of this chemical further substantiate our claim that the b-wave of the electroretinogram is a composite potential resulting from the summation (or integration) of faster retinal potentials, usually referred to as the oscillatory potentials. Full-field electroretinograms were recorded from adult New Zealand rabbits before and after a single, bolus injection of 15 mg/kg of buffered iodoacetic acid. Both the 1-1000 Hz electroretinogram and the 100-1000 Hz oscillatory potentials were recorded simultaneously. The oscillatory potentials considered in this study were those normally seen on the rising phase of the b-wave. Following the intravenous injection of iodoacetic acid, there was a progressive decrease in the amplitude and peak time of the b-wave. This observation also was reflected in the oscillatory potential recordings, in which the long-latency oscillatory potentials (3 and 4) progressively disappeared while oscillatory potential 2 remained. We believe that these findings further support our contention that the oscillatory potentials are major components of the b-wave.

Animals↗
PubMed1990

Influence of the superior colliculus on visual responses of cells in the rabbit's lateral posterior nucleus.

The lateral posterior-pulvinar (LP-P) complex of mammals receives a major input from the superior colliculus (SC). We have studied the response properties of LP cells and investigated the effects of reversible inactivation of the colliculus on the visual responses of LP units in anesthetized and paralyzed rabbits. Cells in LP had large receptive fields responsive to either stationary or moving stimuli. One third of the motion-sensitive cells were direction selective. The size of the receptive fields increased with eccentricity and there was a retinotopic organization along the dorso-ventral axis. Comparison of the LP and superior colliculus properties revealed substantial differences in visual response characteristics of these two structures such as the size of the receptive fields and the number of direction-selective cells. Electrical stimulation of the LP evoked antidromic action potentials in tectal cells that were motion sensitive. We found a dorsoventral gradient in the projections of collicular cells. Units located more dorsally in the colliculus sent their axons to LP while cells lying more ventrally sent axons toward the region lying posterior to LP. A micropipette filled with lidocaine hydrochloride was lowered into the superficial layers of the superior colliculus in order to reversibly inactivate a small population of collicular cells. Rendering the superior colliculus inactive produced a sharp attenuation of visual responses in the majority of LP cells. Some neurons ceased all stimulus-driven activity after collicular blockade while a few cells exhibited increased excitability following collicular inactivation. These experiments also indicate that the tecto-LP path is topographically organized. An injection in the colliculus failed to influence the thalamic response when it was not in retinotopic register with the LP cells being recorded. Our results demonstrate that the superior colliculus input to LP is mainly excitatory in nature.

Animals↗
PubMed1990

Presentation of a remote target influences visual responses of rabbit lateral geniculate cells.

The described investigations analyze the influence of presenting a circumscribed target outside the limits of the classical receptive field (CRF) on the responses of lateral geniculate cells in rabbits. Animals were prepared for single cell recordings in acute experiments in the usual fashion. Cells were stimulated with a light-emitting diode (LED) positioned in the CRF and a second stimulus (S2) presented outside the field. The latter stimulus does not modify the spontaneous firing of the neuron when presented in isolation. S2 is either stationary or moving over small distances (total excursion is 3.5 degrees of arc). A moving S2 increases or decreases the responses to the LED by a greater magnitude than a stationary S2. Significantly, in 80 percent of direction-biased cells, centripetal movement of S2, that is, movement toward the receptive field, affected the neuronal discharge if it coincided with the preferred direction of the unit. These results suggest that the introduction of a remote stimulus modifies the responses of geniculate cells in rabbits.

Action Potentials↗
PubMed1989

The effect of diphenylhydantoin on the electroretinogram.

Acute administration of diphenylhydantoin (DPH) in rabbits produces a significant increase in the amplitude of the a-wave. A marked increase in the amplitude of the b-wave is also noted but the time course is slower than that for the a-wave. While in controls the oscillatory potential (OP) recordings essentially consist of three major types, recordings taken after DPH injection consist of one major OP (OP2), which appears to be a result of the fusion of the original OP2 with another OP produced by the DPH injection. A similar blend of OPs was also seen in ERGs recorded from three human subjects on DPH therapy.

Adolescent↗
PubMed1989

Optic nerve blockade influences the retinal responses to flash in rabbits.

The presence of retinopetal fibers in mammals has been debated many times in the past two decades. Do rabbits have a retinopetal system? This question is addressed with the present investigations. In anesthetized and paralysed rabbits the b-wave and the oscillatory potentials (OP) are recorded at the cornea. The optic nerve is isolated retrobulbarly and is gently hooked to a curved injecting capillary. Through the latter lidocaine hydrochloride is pressure injected. This drug interrupts the neuronal flow travelling along the nerve. A steel electrode is positioned in the optic chiasm allowing us to monitor the evoked field potentials from the tested and untested eyes. The optic nerve blockade produces the following observations: (1) the amplitude of the b-wave is not significantly altered; and (2) the amplitudes of the long latency OP are significantly increased. The retinal capacity to respond to a second flash after the application of an initial light pulse was evaluated by varying the interval between the two flashes. After optic nerve blockade the recovery of the retinal responsiveness is considerably slower. Fourier analysis indicated that the highest power increases occurred around 200 Hz. It is difficult to escape the suggestion that rabbits possess retinopetal fibers.

Animals↗
PubMed1988

Influences of cortico-pretectal fibers on responses of rat pretectal neurons.

Responses of pretectal cells were studied following cortical excitation and inactivation in anesthetized rats. The visual cortex was excited electrically and by a topical application of strychnine while it was inactivated by a reversible cryoblockade. In a few experiments the superior colliculus was locally depressed by microinjections of lidocaine hydrochloride. Results showed a large spectrum of response latencies to electrical stimulations of the optic chiasm and visual cortex, and a significant correlation between responses to both sites of stimulation. It appears that pretectal cell responses strongly depend upon corticofugal impulses, as the disruption of the latter results in a profound decline of pretectal discharges. The suppressed-by-light cells were the most affected by a cryoblockade while the ON-tonic units were the least affected. The same types of cells were affected at the retinal level by cortical blockade.

Animals↗
PubMed1988

Maturation of the electroretinogram of the neonatal rabbit.

The development of the electroretinogram in the rabbit has been said to proceed with first the a-wave, then the b-wave and last the oscillatory potentials. The aim of our study was to reexamine this claim with special attention to the oscillatory potentials. Albino rabbits from the same litter were studied at weekly intervals for five weeks from the first week of life. A Grass photostimulator was used in light and dark adaptation and 50 amplified responses were averaged. Both 1-1000 Hz (electroretinogram) and 100-1000 Hz (oscillatory potential) band-widths were recorded simultaneously. The a-wave was the earliest signal to appear, at the second week of life. A rapid growth of the b-wave and oscillatory potentials was then noted between the second and third weeks, followed by a slower change. They evolved at the same rate, each with an increase in amplitude and decrease in peak time. The change in form of the b-wave was consistent with the sequential formation of each potential as the rabbit matured. The finding of simultaneous development of the b-wave and oscillatory potentials in the aging neonatal rabbit is contrary to previous reports.

Animals↗
PubMed1988

[The corticofugal pathways of the visual system].

Cortical neurons belonging to the same topological ensemble send axons to thalamic and mesencephalic structures and also to contra and ipsilateral cortical areas. The projections are called the corticofugal system. This review addresses the organization and the functions of the efferent cortical fibers within the visual network. For example, the cortico-geniculate fibers participate in shaping the structure of the concentric receptive fields of geniculate cells. Namely, the size of the surround area depends on descending impulses from the cortex. By contrast, cortico-mesencephalic fibers have a more global influence on visual responses. Following the interruption of cortical activity all responses to visual stimuli decline; although in rodents and lagomorphs cortical inactivation does not eliminate those visual responses that are sent to the superior colliculus or pretectum directly from the retina. In each hemisphere it has been demonstrated that contra-lateral cortico-cortical fibers participate in the continuity of the two visual hemi-fields, as the interruption of the callosal impulses results in a truncated field in which the contralateral part of the receptive field is missing., overlaps the vertical meridian is missing. Finally, ipsilateral cortico-cortical fibers allow a consolidation of visual properties of cortical cells. It must be added that there are considerable differences among species in the organization of cortico-cortical relationships. However, this survey seems to indicate that all corticofugal axons are excitatory.

Animals↗
PubMed1987

Modulations of collicular visual responses by acoustic stimuli in rabbits.

This study analyzes the influences of an acoustic stimulus upon neuronal light responses of superficial layers of the superior colliculus in anesthetized and paralyzed rabbits. The results have revealed that even if visually-responsive cells fail to be excited by sound, the latter is still capable of modifying light-evoked discharge. The influence may be "short-term" (the discharge rate recovers within 500 ms) or it may be "long-term" (the firing rate remains modified for several seconds). This audio-visual interaction depends upon several factors: the time of occurrence of both stimuli, the physical aspects of the visual target, the relative positions of the speaker and the visual receptive field, and finally, the sensitivity of the unit to movement direction. Data indicates that cells of the most dorsal (hence visual) layers of the superior colliculus are influenced by sound. It is concluded that the colliculus may use the sound as an additional cue to orientate the animal. Also, collicular cells could "memorize" for several seconds various features present in the environment.

Acoustic Stimulation↗
PubMed1986

Components of the electroretinogram: a reappraisal.

During light adaptation a progressive increase in the intensity of a flash stimulus yields ERGs in which the a-wave shows a gradual reduction in peak time, while the b-wave appears to do the opposite. However, close inspection of the different ERG waveforms indicates that the wave identified as the b-wave for a threshold stimulus actually decreases in peak time with progressively stronger stimulus. Furthermore, what is identified as the b-wave for a threshold stimulus delivered in light adaptation will become a part of the a-wave complex if the same stimulus is used in dark adaptation. Data presented here indicate that the identification of the a- and b-waves of the ERG must be constantly revised according to the intensity of the stimulus and/or the level of retinal adaptation. These findings seriously challenge the validity of the a-b-wave nomenclature currently used in electroretinography. An alternative nomenclature, based on the first derivative (dv/dt) of the ERG wave, is proposed.

Adaptation, Ocular↗
PubMed1986

Influence of a local inactivation in the superior colliculus on lateral geniculate responses in rabbits.

The influence of the superficial layers of the superior colliculus (SC) on responses of the lateral geniculate nucleus was studied in anesthetized and paralyzed rabbits. Fifty to one hundred nanoliters of inactivating drugs were injected through a micropipette positioned in the SC in register with the geniculate cells. The latter were tested with discrete moving and stationary targets presented in random sequences. Results revealed that the SC exerted a dual facilitative (n = 19) and inhibitory (n = 25) influence. The latter segment of the response pattern was modified while the initial portion remained unchanged. In some cases differential effects were observed, that is, the responses to one particular stimulus were more affected than responses to other modalities. However, in the majority of cells it was the on-off responses which were most affected. These findings point toward complex influences of the SC upon geniculate responses in rabbits. This complexity is also supported by findings that in cats the colliculo-geniculate synapses are of various types.

Animals↗
PubMed1986

Modifications of light responses in the superior colliculus following cortical cryoblockade.

Responses to light stimuli of cells in the superior colliculus (SC) were studied in anesthetized and paralyzed rabbits after reversible inactivation of corticocollicular impulses by cooling of the visual cortex. The recording of flash-evoked responses and EEG allowed us to monitor the time course of the inactivation and its recovery. The cell's responses were measured prior to, during, and after cortical blockade. In about half of the collicular cells, disruption of cortical functions resulted in a sharp decline of collicular responsivity. All types of response were affected equally. Hence, the cortex has a global tonic excitatory impact.

Action Potentials↗
PubMed1986

Modulations of the lateral geniculate nucleus cell responses by a second discrete conditioning stimulus: implications of the superior colliculus in rabbits.

This study analyzes the interactions between two discrete stimuli located in the visual field of the rabbit at the lateral geniculate level. Single unit recordings were carried out simultaneously from the superior colliculus (SC) and lateral geniculate nucleus (LGN) in anesthetized and paralyzed rabbits. A first conditioning stimulus (most often a moving target) was positioned in the receptive field of the collicular cell to ensure activation of the retino-collicular path. A second test stimulus was introduced into the receptive field of the LGN cell. The presentation of this latter stimulus was timed so as to fire the geniculate cell at various delays after the collicular neuron had responded to its own stimulus. The spontaneous firing of each cell was unaffected by the stimulus appropriate to the complementary unit. The conditioning collicular stimulus produced increases or decreases in geniculate responses. This modulation may eventually reduce the direction specificity of a geniculate unit. The fluctuations of the geniculate responses peaked 200 to 300 ms after collicular cells had responded. In a separate series of experiments the influence of the conditioning stimulus on geniculate responses was abolished when the SC was locally inactivated. These results suggest that the well documented colliculo-geniculate system mediates the interactions of several stimuli in the visual field. The outcome of this processing results in a modulation of geniculate responses.

Action Potentials↗
PubMed1986

Visual cortex controls retinal output in the rat.

The first objective of the present investigation was to shed more light on corticofugal influences on the retina by providing an analysis of the type and proportion of retinal ganglion cells that are affected by cooling the visual cortex in rats. The second question was to determine if the pretectum participates in functional cortico-retinal relationships. In urethane-anesthetized and paralyzed hooded rats, axonal activity of retinal ganglion cells was recorded with glass micropipettes at optic chiasm level. Units were classified as ON, OFF, suppressed-by-light and concentric. The visual cortex was inactivated by cooling its surface with a 4 mm2 steel probe using the Peltier effect. The pretectum was blocked with microinjections of 50 to 100 nanoliters of cobalt ions, lidocaine hydrochloride or KCl. The inactivations and recoveries at both sites were monitored by simultaneously recording evoked field potentials. Interrupting corticofugal impulses caused modifications of the evoked discharge pattern in all types of cells. The concentric type was the group least affected by cortical cooling. A common trend emerged suggesting that cooling of the visual cortex led to an enhancement of the initial evoked excitation. This was often followed by an enhanced post-excitatory inhibition. The Pearson coefficient allowed us to measure the degree of similarity between two histograms. When all data were pooled, a weak correlation between control and test histograms (r = 0.29, N = 56) was found, while the control and recovery patterns averaged a correlation of more than twice that size (r = 0.68). In a second series of experiments, the pretectum and visual cortex (VC) were simultaneously inactivated. It is shown that both sites summed their influence and acted synergistically upon the pattern of ganglion cell responses. The results strongly suggest that the visual cortex exerts a major control over the response pattern of thirty percent of retinal ganglion cells, and that the pretectum participates in the functional relationships between visual cortex and retina in rats.

Animals↗