Altered response characteristics of cat visual neurons after systemic administration of the dihydropyridine calcium antagonist nimodipine

Abstract

Nimodipine, a cerebrovasotropic dihydropyridine calcium antagonist, has gained increasing interest in geriatric research during last years and is discussed with regard to its possible involvement in restoration and preservation of brain plasticity. Single unit responses were recorded by microelectrodes in the visual cortex of anaesthetized adult cats. Receptive fields were stimulated with light bars moved forward and backward or flashed On/Off. Neuronal activity was recorded before and 5 and 30 min after i.v. administration of 0.1 mg/kg nimodipine. On the basis of penstimulus-time-histograms (PSTH) the response was analysed. There was a marked variability of the response after stimulation with both stationary and moving bars. Median firing rate was reduced 5 min after injection following On-stimulation but generally rose 30 min both after stimulation with light bars flashed On or Off Following stimulation with moving light bars about 60% of neurons showed decreased firing rates and 40% of neurons increased firing rates after injection of the calcium antagonist. The latency following On/Off-stimulation was rather constant, whereas the median latency following stimulation with moving light bars increased by about 15O ms after administration of nimodipine. In conclusion, nimodipine alters neuronal response characteristics in the visual cortex of the cat.