[Tectal Evoked Potentials during Retinal Baclofen Application in the Carp].

Changes of primary visual center evoked potentials in response to white light and optic nerve electric stimulation were investigated during retinal GABAb-receptors activation with baclofen in dark-adapted carp. It was found, that baclofen - induced b-wave ERG decreasing, was accompanied by a significant amplitude growing as in the evoked potential to light as in the evoked potential to electric nerve stimulation: It is proposed, that light evoked potential changes reflect the increasing of the third retinal neuron responses to light and/or tectal neuron responsiveness enhancement.

[Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp].

Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.

[Effect of baclofen and muscimol on the evoked potentials of the tectum mesencephali in the carp in response to stimulation of the visual and somatosensory afferent inputs]. / Vliianie baklofena i mustsimola na vyzvannye potentsialy kryshi srednego mozga karpa, voznikaiushchie pri stimuliatsii zritel'nogo i somatosensornogo afferentnykh vkhodov.

The perfusion of (+/-) 10(-5) M baclofen to the optic tectum of the carp greatly reduced evoked potential to the optic nerve stimulation and slightly inhibited evoked potential to the spinal cord stimulation. The perfusion of 10(-4) M muscimol reduced the former evoked potential as well as the latter one. The results permit supposing that tectal visual input is more sensitive to the presynaptic inhibitory influences through GABAB-receptors than the somatosensory afferent input.

[Early positive component of the evoked potential of the midbrain tectum of the dogfish shark during electric stimulation of the optic nerve]. / Rannii pozitivnyi komponent vyzvannogo potentsiala kryshi srednego mozga koliuchei akuly pri élektrostimuliatsii zritel'nogo nerva.

Midbrain tectal evoked responses to electric stimulation of the optic nerve were investigated in shark (Squalus acanthias). An early positive component was found as a part of negative phase of "classic" negative-positive evoked potential. Similar component was recorded from the ipsilateral tectal hemisphere as well. An increase of the positive component along with penetration of the electrode, its resistance to functional blockade by KCl application to the tectum surface and recording of a similar potential from the ventricular floor surface after extirpation of the tectum suggested the localization of the source of this component outside the tectum. Existence of a focus of maximal activity located in the rostral part of undertectal brain structures and disappearance of early positive component after functional blockade and extirpation of this brain area indicate the leading role of thalamic nuclei in generation of this component.