Clonidine-induced sedation is not modified by single or combined neurochemical lesions of the locus coeruleus, the median and dorsal raphe nuclei.
Single or combined neurochemical lesions of the locus coeruleus, the dorsal and the median raphe nuclei were performed on different groups of rats. Starting 10 days after the lesion, the locomotor activity of all rats was measured for 5 min every day in an open-field. For the first 21 days all lesioned rats, independently of the lesion site, were significantly less active than controls, but from the 11th to the 16th day the locomotor activity of lesioned animals increased progressively and, thus on days 15 and 16, the mean activity of all lesioned groups was not significantly different from that of the controls. From the 17th day onwards the sedative effect of small doses of clonidine (5-100 micrograms/kg) was measured. Neither single nor combined lesions modified the response to clonidine and the linear decrease of activity produced by increasing doses of clonidine was the same in all groups, lesioned or not. Biochemical assays showed a marked loss of corresponding amines as a result of the lesions in cortex, hippocampus and the brainstem. These results suggest that the alpha 2-receptors involved in clonidine-induced sedation are located neither on noradrenergic fibers coming from the locus coeruleus, nor on serotoninergic fibers originating in the median and dorsal raphe nuclei.
D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism; D012890:Sleep / Q000187:drug effects* / Q000502:physiology
D012701:Serotonin; D003000:Clonidine; D009638:Norepinephrine