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Serotonin elicits long-lasting enhancement of rhythmic respiratory activity in turtle brain stems in vitro
S M Johnson1, J E Wilkerson, D R Henderson
1Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Dr. West, Madison, WI 53706, USA. johnsons@svm.vetmed.wisc.edu
Abstract:
Brain stem preparations from adult turtles were used to determine how bath-applied serotonin (5-HT) alters respiration-related hypoglossal activity in a mature vertebrate. 5-HT (5-20 microM) reversibly decreased integrated burst amplitude by approximately 45% (P < 0.05); burst frequency decreased in a dose-dependent manner with 20 microM abolishing bursts in 9 of 13 preparations (P < 0.05). These 5-HT-dependent effects were mimicked by application of a 5-HT(1A) agonist, but not a 5-HT(1B) agonist, and were abolished by the broad-spectrum 5-HT antagonist, methiothepin. During 5-HT (20 microM) washout, frequency rebounded to levels above the original baseline for 40 min (P < 0.05) and remained above baseline for 2 h. A 5-HT(3) antagonist (tropesitron) blocked the post-5-HT rebound and persistent frequency increase. A 5-HT(3) agonist (phenylbiguanide) increased frequency during and after bath application (P < 0.05). When phenylbiguanide was applied to the brain stem of brain stem/spinal cord preparations, there was a persistent frequency increase (P < 0.05), but neither spinal-expiratory nor -inspiratory burst amplitude were altered. The 5-HT(3) receptor-dependent persistent frequency increase represents a unique model of plasticity in vertebrate rhythm generation.