Chemical requirements of vasopressins for barrel rotation convulsions and reversal by oxytocin.

When vasopressin is administered into the lateral ventricles of rats it produces severe convulsive activity characterized by a rapid barrel rotation. Electrical recordings from the dorsal hippocampus indicate marked elevations in the amplitude and frequency at doses of 5 microliter of 2 x 10(-5) M vasopressin. No significant behavioral effects were noted with oxytocin, somatostatin, beta-melanophore-stimulating hormone, adrenocorticotropin, or leu-enkephalin. Pretreatment of the rats with intraventricularly administered oxytocin, beta-MSH, or systemically administered Dilantin prevented the vasopressin-induced seizures. With the use of chemical and enzymic modification procedures, the essential fragment and amino acids of vasopressin needed for the activity were determined. It was concluded that although the peptide could be acting by vasoconstricting blood arterioles and capillaries in the brain, it may also be exerting a direct excitatory action on neurons.