ANTAGONISM OF RESERPINE-INDUCED SUPPRESSION OF SPONTANEOUS MOTOR-ACTIVITY BY STIMULATION OF 5-HT1A RECEPTORS IN RATS

The 5-HT1A and the DA D-2 receptor agonists 8-OH-DPAT (0.05-3.2 mg kg( -1) subcutaneously, -20 min.) and quinpirole (0.08-1.25 mg kg(-1) subc utaneously, -20 min.),respectively, both partially antagonized reserpi ne-induced (5 mg kg(-1) subcutaneously, -16 hr) suppression of spontan eous motor activity in the rat. Four different aspects of the spontane ous motor activity were recorded in a photocell-equipped open-field (8 x8 photocells, 90 mm apart, defining two horizontal planes): locomotor , activity (all photocell counts at the lower level); rearing (all pho tocell counts at the upper level); forward locomotion (the proportion movements across the arena); peripheral activity (the proportion locom otor activity as picked up by the photocell beam closest to the wall, i.e. 25 mm). As defined by these variables, the pattern of activity pr oduced by 8-OH-DPAT or quinpirole were indistinguishable. The effects produced by 8-OH-DPAT were fully antagonized by the 5-HT, antagonist ( -) pindolol (4 mg kg(-1) subcutaneously, -30 min.), but not by the DA D-2 receptor antagonist raclopride (2 mg kg(-1) subcutaneously, -30 mi n.) nor by the 5-HT2 receptor antagonist ritanserin (2 mg kg(-1) subcu taneously, -30 min.), whereas effects produced by quinpirole were full y antagonized by raclopride (2 mg kg(-1) subcutaneously, -30 min.). Ef fects produced by quinpirole, but not 8-OH-DPAT, were potentiated by a dministration of the DA D-1 agonist SKF-38,393 (3 mg kg(-1) subcutaneo usly, -20 min.). It is concluded that effects by 8-OH-DPAT on spontane ous motor activity in the reserpine treated rat primarily are due to s timulation of postsynaptic S-HT1A receptors.