Serotonin (5-HT) levels in the hemolymph of crustaceans has been implied to alter aggressiveness which influences social interactions. The activation of IP3 as a second messenger cascade within crayfish motor neurons in response to application of 5-HT, suggests that the 5-HT receptor subtypes on the motor neurons are analogous to the vertebrate 5-HT2A receptors. Based on evidence in other systems, it would be expected that chronically sustained 5-HT levels in aggressive individuals would result in a compensatory negative feed-back regulation and/or that target tissues would diminish their sensitivity to high levels of circulating, free 5-HT. We addressed the issue of up- and down-regulation in the sensitivity of the responsiveness to exogenously applied 5-HT at the NMJs of crayfish in which the animals have altered endogenous 5-HT levels. Injections of the 5-HT1 and 5-HT2 vertebrate receptor agonist, 1-(3-Chlorophenyl) piperazine dihydrochloride (m-CPP), for 1 week resulted in a decreased responsiveness to application of 5-HT. The compound p-chlorophenylalanine (p-CPA) blocks the enzymatic synthesis of 5-HT and following 7 days of p-CPA injections, a super-sensitivity to exogenous application of 5-HT for both tonic and phasic neuromuscular junctions (NMJs) was observed. However, acute applications of p-CPA and m-CPP, followed by extensive saline washing, did not reveal any altered receptivity to 5-HT application.
|Number of pages||9|
|State||Published - Oct 19 2001|
Bibliographical noteFunding Information:
Appreciation is expressed to Mr Austin Cooper and Dr Wendi Neckameyer (St. Louis University School of Medicine) for editorial comments and to Dr Julie G. Hensler (University of Texas Health Science Center at San Antonio, TX) for helpful experimental suggestions. Funding was provided by NSF grants IBN-9808631 (RLC), NSF-ILI-DUE 9850907 (RLC) and an undergraduate training fellowship from Howard Hughes Medical Institute (RJC) as well as a G. Ribble Fellowship for undergraduate studies in the School of Biological Sciences at the University of Kentucky (RJC and JT).
ASJC Scopus subject areas
- Neuroscience (all)
- Molecular Biology
- Clinical Neurology
- Developmental Biology