NEURONAL FIRING PATTERNS OF ORGANOTYPIC RAT SPINAL-CORD CULTURES IN NORMAL AND IN ACTH/ALPHA-MSH(4-10) ANALOG (BIM-22015)-SUPPLEMENTED MEDIUM

The spontaneous and evoked electrical patterns of spinal cord explants from 13- to 14-day old rat fetuses grown from 2 to 8 weeks in vitro were compared when fed either with a standard or with an adrenocorticotropic hormone/alpha-melanocyte stimulating hormone (4-10) analog (BIM 22015)-supplemented medium. Standard and BIM 22015-treated cultures developed similar patterns of extracellularly recorded activity which consisted of mostly phasic but also tonic discharges. The standard cultures when treated by BIM 22015 in acute experiments (100-mu-g/ml) showed a decrease in their frequency of discharges which fired in a regular tonic pattern. These effects were neither age- nor dose-dependent but were increased in Ca2+ free medium. The ventral cord neurons chronically fed with BIM 22015 showed a strongly bursting pattern resembling strychnine-induced synchronized bursts. Both these effects, inhibitory (acute) and excitatory (chronic), of the BIM upon spinal cord cultured ventral horn neurons are discussed as possible calcium-dependent phenomena.