Effects of intracerebroventricular administration of atrial natriuretic peptide on subcortical EEG activity in conscious rabbits.

Atrial natriuretic peptide (ANP) influences the activity of rat hypothalamic neurons, modifies the membrane excitability of the rat forebrain neurons, and induces changes in membrane potentials in cultured rat glioma cells. In order to explore whether these effects are reflected in the electrical activity of larger subcortical brain areas, we investigated the electroenceophalographic activity (EEG) recorded from 20 male albino (New Zealand White) rabbits. Recordings of EEG were made on restrained, conscious animals 1 week after the implantation of an indwelling intracerebroventricular (i.c.v.) cannula (lateral right ventricle) and two stainless steel electrodes, implanted in the paraventricular (PVN) and supraoptic (SON) nuclei. Animals were classified into two main groups: those with water available ad libitum (group A) and those which were dehydrated for 24 h before EEG recordings (group B). Each group was divided into two subgroups (1 and 2) of five animals each. EEG was recorded at 0 min (control) and 30, 60, and 90 min following the i.c.v. injection of either 25 microliters artificial cerebrospinal fluid (aCSF; subgroup 1) or 1 microgram alpha-human ANP in 25 microliters a CSF (subgroup 2). Each EEG record duration was 6 s. For each EEG record the power spectrum of the digitized waveform was estimated in the frequencies 0.5-48 Hz using the fast Fourier transform, and the energy of each waveform was subsequently calculated. The results were analyzed by repeated-measures ANOVA and by the t-test. The analysis revealed that (1) water deprivation does not affect mean EEG energy and value (2) ANP attenuates (P < 0.05; in comparison with zero time) the mean energy value of EEG recorded from SON at 30 min and 60 min in the frequencies 8-48 Hz, whilst it tends to decrease (P < 0.1) the mean energy of EEG recorded from PVN at 30 min in the frequencies 8-15 Hz. Mean EEG energy changes caused by ANP would reflect its various (mainly inhibitory) effects on the electrical activity recorded from PVN and SON neurons in in vitro and in vivo studies.