Hippocampal electrical activity in the diabetes insipidus (Brattleboro) rat.

Theta rhythm was recorded from the hippocampus in normal male and female rats, and from female rats with homozygous alleles (HODI) and heterozygous alleles of diabetes insipidus (HEDI). Second-by-second spectral analysis of the complete period of rapid eye-movement sleep indicated that HODI and HEDI rats had the same theta frequency range as normals, but the mean theta frequency (6.4 cycles c/s) was lower than normal (6.8 c/s), mainly in having a smaller proportion of frequencies greater than or equal to 7.8 c/s. Pharmacological studies in the waking rat demonstrated a theta rhythm in the HODI and normal rats after atropine or after urethane and eserine, indicating the presence of both atropine-sensitive and atropine-resistant pathways. However, after eserine, a huge increase in hippocampal fast waves (30 to 55 c/s) accompanying struggling (as compared with immobility) was found in the HODI rat, which was double that in the normal rat. An enhanced cholinergic input or response at the septal or hippocampal level may account for the large fast wave as well as the lower mean theta frequency in the HODI rat.