The development of carbachol-induced EEG 'theta' examined in hippocampal formation slices.

The development of carbachol-induced EEG theta (theta) activity was studied in the CA1 and dentate regions of hippocampal formation slices obtained from neonatal rats (4, 6, 8, 10, 12 and 14 days of age). When perfused with carbachol (50 microM), 4- and 6-day-old hippocampal slices exhibited only short-lasting irregular activity. The initial appearance of carbachol-induced rhythmic waves were observed in slices obtained from 8-day-old rats. From the time that theta appeared at 8 days of age, a steady increase in amplitude and frequency was noted. This observed in vitro developmental pattern of hippocampal theta-rhythm closely resembles the development of theta activity in in vivo preparations.