Selective accumulation of hydroxytryptamines by frog tectal neurones.
By means of histofluorescence microscopy, 5,7-dihydroxytryptamine was shown to be taken up by selective populations of brain neurones of the frog, Rana pipiens, following both intracranial administration and in vitro incubation with isolated brain preparations. Presumptive non-aminergic cell bodies of the superficial aspect of tectal lamina 6 exhibited more avid uptake than did putative serotonin perikarya of the raphe complex. Within the tectum, 5,7-dihydroxytryptamine uptake appeared to be restricted to large piriform neurons; in the torus semicircularis, it occurred in a morphologically dissimilar group of scattered cells. The same tectal cell system accumulated 5-hydroxytryptamine and 6-hydroxytryptamine, but not N-acetylserotonin, melatonin, or noradrenaline. 5,7-Dihydroxytryptamine uptake was insensitive to cold or imipramine; however, it was blocked by ouabain at high but not low temperature. At concentrations greater than or equal to 100 microM, 5,7-dihydroxytryptamine-induced fluorescence was sufficiently intense to permit tracing of intratectal dendrites and tectofugal axonal processes projecting to a lateral diencephalic neuropil and an ipsilateral isthmic neuropil. While previous monoamine histofluorescence and immunohistologic studies have not revealed serotonin-containing perikarya in the ranid tectum, our findings demonstrate that lamina 6 piriform projection neurones, presumably lacking indolamine-synthesizing enzymes, possess a striking capability for accumulating hydroxylated tryptamines.
D015116:5,7-Dihydroxytryptamine / Q000378:metabolism; D000818:Animals; D001931:Brain Mapping; D005260:Female; D008297:Male; D008856:Microscopy, Fluorescence; D011894:Rana pipiens; D012701:Serotonin / Q000378:metabolism*; D013477:Superior Colliculi / Q000033:anatomy & histology / Q000378:metabolism* / Q000502:physiology; D014795:Visual Pathways / Q000033:anatomy & histology; D014796:Visual Perception / Q000502:physiology
D015116:5,7-Dihydroxytryptamine; D012701:Serotonin