Biochemical differences in the reactions of visual cortex neurons to deprivation]

Early visual deprivation was interferometrically shown to entail changes in the concentration and contents of the protein substance with simultaneous changes of the neurons size. The changes are statistically significant in the lamina V and not in the laminasIII and IV. The changes in each lamina are associated with definite group of the neurons the development of which is, probably, determined by visual stimuli.     

reflection of stimulus orientation in reactions of visual cortex neurons

A mathematical model of neuronal target structure with spatial anisotropy of lateral inhibition is discussed. The positions of the neuronal target to oriented sensory stimuli are investigated by computer simulation. It is suggested that visual stimuli orientation is coded in the late phase of dynamic responses of cortical neurons. This idea is in agreement with the data obtained in experiments on guinea pig visual cortex neurons.     

Synaptic reactions of sensomotor cortex neurons to stimulation of emotionally significant brain structures

The study deals with synaptic and spike responses of neurones in the rat sensorimotor cortex to stimulation of the lateral and medial hypothalamus, locus coeruleus and raphe nuclei. The activity of 57 neurones was recorded, 41 of them intracellularly and quasi-intracellularly, in response to the stimulation of sites in these structures, which were previously identified as "emotionally/ significant. No considerable differences in the effects of the stimulation of different "emotiogenic" zones were found. The stimulation parameters, differing from the "behavioural" ones by a greater strength, elicited in the majority of neurones clear post-synaptic responses, often in the form of EPSP-IPSP. Latencies of the responses varied from 3 to 80 msec. The most stable and pronounced responses were obtained to the stimulation of the lateral hypothalamus. No significant correlations of the latencies of the responses to the stimulation of different "emotiogenic" structures were found.     

Response of rabbit visual cortex neurons to direct stimulation by current of different intensities

Response was investigated in 47 rabbit visual cortex neurons to direct intracortical electrical stimulation consisting of single biphasic pulses of increasing intensities within the 150–2,700 µA range. Minimum level for generating all components of response to electrical stimulation remained similar from one neuron to the next, ranging between 150 and 600 µA. Three different patterns of dependence between numbers of spikes at different stages of response and current amplitude were identified: stable, gradual and selective patterns. Percentages of stable dependences were lower for after-discharges in comparison with initial firing (at 11 and 26% respectively) and the proportion of selective dependences were somewhat higher (at 32 and 21%). The selective dependence observed could imply the existence of optimum current levels at which peak neuronal response occurs. At the same time, duration of inhibitory pauses lengthened uniformly in the response of all test neurons during increasing intensity of the electrical stimuli. Findings obtained during this study may have a practical application in matters connected with visual prosthetics in the blind.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 239–247, March–April, 1989.     

Nuclear and cytoplasmic RNA in visual cortex neurons of adult rats following visual deprivation and photic stimulation

It has been shown by two-wavelength cytospectrophotometry of gallocyanin-chrome alum-stained sections that visual deprivation in adult rats kept in a complete darkness for 30 days resulted in an accumulation of cytoplasmic RNA by layer V neurons of the visual cerebral cortex and by the cells of the perineuronal neuroglia of this layer. The nuclear RNA content remained unchanged. Stimulation of intact rats with a flickering or constant light induced an increase in the cytoplasmic RNA in these neurons rather than in the nuclear RNA as well as in RNA in their glial satellite cells. Similar light stimulation of the deprived animals gave rise to a complete return of the neuronal RNA to normal with only a slight decrease in the deprivation-induced RNA accumulation by the neuroglial cells. Neither visual deprivation nor light stimulation affected the RNA content in the neurons and neuroglia of layer V of the motor cerebral cortex. Compartmentation of RNA metabolism within the neuronal-neuroglial unit is discussed.     

Discharge pattern of reticular neurons subjected to direct mechanical stimulation

Changes in neuronal discharge pattern due to direct mechanical stimulation through the recording extracellular micropipette were studied in 30 neurons of the rat's mesencephalic reticular formation. Results parallel closely the polarization experiments, i.e. changing the firing rate one group of neurons shows stable pattern whereas the other change their pattern significantly. It is concluded that the first group presumably reflects the decrease in membrane potential only, whereas in the second group overall synaptic inflow is influenced.     

Role of the frontal cortex in organizing emotional-behavioral reactions induced by hypothalamic stimulation and natural stimuli

Study of the effects of a functional switching off the sensorimotor neocortex area in cats by means of cooling reveals its inhibitory influence on emotional-behavioral reactions to hypothalamic stimulation. Multiple (up to 12) switchings off of the frontal neocortex are attended with a gradual compensation of its inhibitory function by the activity of other brain structures. On the other hand inactivation of the sensorimotor cortex reduces the ability of natural provoking stimuli to lower the thresholds of goal-directed rage which develops when these stimuli are combined with an electrical stimulation of the hypothalamus. A conclusion has been made on the participation of the frontal neocortex in the systemic organization of estimation of biologically significant stimuli.