Effects of 6-hydroxydopa and 5,6-dihydroxytryptophan treatment on spontaneous motor activity and brain monoamines in mice

Skin conductance activity after intraventricular administration of 6-hydroxydopa in rats

Absence of skin conductance response (SCR) and failure of its habituation are psychophysiological signs observed in most schizophrenics. In the present experiments, skin conductance activity was studied in rats before and after intraventricular administration of 6-hydroxydopa (6-OHdopa), a neurotoxin that selectively destroys noradrenaline nerve terminals and induces denervation supersensitivity at the synapse. All intact rats studied (n = 32) showed SCR and its habituation to repeated auditory stimuli (500 Hz, 90 dB, 1 sec, 20 times). They also showed some spontaneous fluctuation (SF) of the skin conductance. In the early stage following the 6-OHdopa (100 micrograms) administration (n = 16), it was noted that the SCR disappeared and the SF were markedly reduced in frequency (p less than 0.001). From the third day to the fourth week after this treatment, there was some recovery of the SF rate, and the SCR tended to reappear with a marked slowing down of its habituation. Eight weeks after the treatment, the majority (11/16) of the 6-OHdopa rats showed habituation failure of the SCR (p less than 0.005); vehicle-treated rats (n = 16) did not show these alterations. Estimation of catecholamine concentration after the experiment confirmed the selective depletion of brain noradrenaline. These results suggest that destruction of the noradrenergic fibers after the 6-OHdopa treatment and denervation supersensitivity which developed later are the cause of the nonresponding and nonhabituating changes of SCR, respectively.