1. The effects of corticotropin-releasing hormone (CRH) on synaptically evoked population and intracellular responses in the isolated rat CA1 region of hippocampal slices were studied to evaluate possible differences between adult and juvenile rats. 2. The amplitude of orthodromically evoked (stratum radiatum stimulation) population spikes was reversibly enhanced by 0.2-0.6 microM CRH to a greater extent in slices from juvenile rats than from adult rats. In no case, however, did CRH cause seizure-like activity to develop under normal recording conditions. 3. In the presence of 10-30 microM bicuculline, interictal-like bursts of population spikes and corresponding intracellularly recorded action potentials could be evoked starting at postnatal day 8. The number of spikes and the duration of the evoked bursts in the CA1 region were reversibly increased by CRH (0.2-0.6 microM) to a greater extent in slices from juvenile than from adult rats. 4. The amplitude of the afterhyperpolarization following intracellularly evoked bursts of action potentials in CA1 pyramidal cells was reduced by 0.2 microM CRH to a similar degree in both young and adult rats. No consistent changes in input resistance or membrane potential were observed. 5. No correlation was found between the magnitude of the CRH-induced increase in responsiveness and the initial excitability in controls, suggesting that the CRH-induced changes were independent of any age-dependent differences in general slice excitability. 6. Our results indicate that, in the CA1 region, CRH augments bicuculline-induced bursts to a greater extent in slices from young versus adult rats.(ABSTRACT TRUNCATED AT 250 WORDS)