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Journal of Experimental Biology, Vol 200, Issue 23 3079-3090, Copyright © 1997 by Company of Biologists
JOURNAL ARTICLES |
F Saenz, U Garcia and U Arechiga
Departamento de Fisiologia, Biofisica y Neurociencias, Centro de Investigacion y de Estudios Avanzados, IPN, Mexico.
The effect of 5-hydroxytryptamine (5-HT) was tested in a population of X organ neurosecretory cells in the eyestalk of the crayfish Procambarus clarkii. Tests were conducted both in situ and on isolated neurones kept in culture. The application of 5-HT induced action potentials in silent cells. In spontaneously active neurones, 5-HT increased the firing rate and either induced firing or enhanced bursting activity. The effect of 5-HT was dose-dependent within the range 1-100 micromol l-1 in cells of the intact organ. The effect persisted for 20-30 min after 5-HT had been removed from the bathing solution. Successive applications of 5-HT onto the same neurone reduced responsiveness, suggesting that desensitization had occurred. The effects of 5-HT were blocked by prior incubation with the 5-HT antagonist methysergide. In X organ cells whose axons and branches in the neuropile had been severed, 5-HT induced a depolarisation associated with a slow inward current. In X organ neurones isolated from the eyestalk and kept in culture, 5-HT was capable of evoking bursts of action potentials and elicited a slow inward current. This effect was also blocked by methysergide (10(-4 )mol l-1). These results suggest a direct modulatory effect of 5-HT on the pattern of electrical activity in the X organ cells.
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