Seasonal Rhythm of Serotonin Content in the Crayfish Eyestalk

5-Hydroxytryptamine (5-HT) is a common neurotransmitter and modulator in crustaceans. It has been shown to participate in a wide variety of functions, such as a) the facilitation of neuromuscular transmission (Glusman and Kravitz 1982, Dixon and Atwood 1985), b) the enhancement of visual input (Arechiga et al. 1990) and of mechanoreception (El Manira et al. 1991, Rossi-Durand 1993, Pasztor and Golas 1993), c) the induction of the complete behavioral pattern of aggressiveness and social dominance (Kravitz 2000) and the modulation of the escape behavior (Glanzman and Krasne 1986, Yeh et al. 1996), d) the regulation of heart activity (Battelle and Kravitz 1978, Listerman et al. 2000), e) neurohormone release, facilitating that of the crustacean hyperglycemic hormone (Keller and Beyer 1968, Lee et al. 2000), and the molt-inhibit-ing hormone (Mattson and Spaziani 1985) and f) modulating the electrical activity of neurosecretory cells (Saenzetal. 1997, Glowiketal. 1997, Alvarado-Alvarez et al. 2000), and of neurons at various levels of the crustacean central nervous system (Zhang and Harris-Warrick 1994).