Electroencephalographic spreading depression and concomitant behavioral changes induced by intrahippocampal injections of ACTH1-24 and D-Ala2-Met-enkephalinamide in the rat.
ACTH1-24 (0.5 or 10 micrograms = 0.17 or 3.45 nmol) and D-Ala2-Met-enkephalinamide (DAME; 10 micrograms = 17.05 nmol) were injected unilaterally into the hippocampus of freely moving rats to examine their effects on EEG activity, DC potentials and behavior. In 85% of the rats DAME elicited spreading depression (SD) with epileptiform discharges preceding and following the wave of SD. The following behavioral changes were recorded. DAME- and KCl-induced SD were accompanied by an increase in locomotor activity and wet-dog shaking behavior, which occurred only during the period of SD. After a wave of SD induced by DAME a biphasic pattern of activity, consisting of an initial depression in locomotion followed by hyperactivity, appeared in 59% of the rats. ACTH1-24 elicited SD in 13% of the rats tested. Neither the dosage of ACTH1-24 nor the strain of rats influenced the occurrence of SD and the incidence of ACTH-induced grooming behavior. SD induced by KCl also resulted in excessive grooming comparable to that induced by ACTH1-24. In the case of KCl-induced SD, grooming began directly after the injection of KCl and was frequently interrupted by short periods of locomotion. ACTH-induced grooming had a later onset and episodes of stretching and yawning were observed. It can be concluded that the behavioral effects of the injection of DAME are unspecific responses to SD and seizure activity. However, ACTH-induced grooming is not solely a byproduct of SD, since it occurred also in the absence of SD.