Benzodiazepine receptors in the medial-posterior hypothalamus mediate the reduction of hippocampal theta frequency by chlordiazepoxide.

Separate sub-populations of benzodiazepine receptors are involved in determining hippocampal theta frequency in freely moving rats. Systemic injection of the benzodiazepine chlordiazepoxide (CDP) reduced the frequency of theta elicited by stimulation of the brainstem reticular formation, and theta recorded during fixed interval (FI) bar pressing. Infusion of the benzodiazepine receptor antagonist flumazenil into the supramammillary nucleus (mSuM) or the posterior hypothalamic nucleus (PH) antagonised CDP in both cases. Flumazenil was similarly effective in mSuM and PH, suggesting that these nuclei are jointly involved in the coding of theta frequency during FI and during high levels of reticular activation. However, benzodiazepine receptors in other brain regions probably participate in determining the frequency of theta at other times.