Basal forebrain (BF) plays an important role in the regulation of cortical activation. Somatostatin (SOM) is present both in local neurons as well as in fibers in the BF. In previous studies, SOM axons were found to innervate corticopetal cholinergic cells and SOM was found to presynaptically modulate GABA and glutamate release onto cholinergic neurons in the BF. However, no systematic analysis is available about the EEG effects of SOM or its analog, octreotide (OCTR) injected directly into the BF. In the present experiments, EEG changes were examined following an OCTR injection (0.5 microliter, 500 nmol) into the BF areas containing several choline acetyl transferase-immunoreactive neurons of urethane-anaesthetized rats. Fronto-occipital EEG was recorded on both sides and relative EEG power was calculated in the delta (0-3 Hz), theta (3-9 Hz), alpha (9-16 Hz) and beta (16-48 Hz) frequency bands. OCTR injected to the BF failed to induce significant EEG changes and did not affect tail pinch-evoked cortical activation. Lack of effect may be attributed to the urethane anaesthesia as well as to the possible complex interactions between SOM and BF cholinergic and GABAergic neurons.