DEVELOPMENTAL ASPECTS OF HIPPOCAMPAL ELECTRICAL-ACTIVITY AND MOTOR BEHAVIOR IN THE RAT

The developmental aspects of hippocampal electrical activity and motor behavior were studied in freely moving infant rats implanted with microelectrodes in the CA1 and dentate regions. The pup's motor abilities developed concomitantly with hippocampal electroencephalographic (EEG) activity. The uncoordinated and limited locomotion of 6- to 9-day-old pups was associated with very low-amplitude, low-frequency, irregular activity, similar to that accompanying immobility. Starting at 10 days, the EEG-behavior correlation described by Vanderwolf and his colleagues became evident: Voluntary movements were associated with hippocampal theta rhythm whereas immobility was associated with irregular activity. A second, lower-frequency type of theta, not correlated with movement, also appeared at 10 days. It was induced by anticholnesterase drugs and abolished by anticholinergics. Administration of anticholinergics caused minor disruption of movement-related theta, especially in younger animals. Observations of tonic and phasic REM sleep also demonstrated that the two types of theta activity appeared at 10 days of age. Despite the difference in the time course of morphogenesis, the prenatally formed CA1 pyramidal region and the postnatally formed dentate granule region developed in parallel with respect to the appearance of both types of theta activity at about 10 days. Theta frequency and amplitude developed to adult values during the next 2 weeks, but the activity in CA1 remained smaller than in the dentate region. The study thus supported the hypothesis that there are two main generators of theta activity, the CA1 pyramidal region and the dentate region. © 1979.