Hormones and Behavior 30, 176–185 (1996) Article No. 0022 Courting and Noncourting Male Red-Sided Garter Snakes, Thamnophis sirtalis parietalis: Plasma Melatonin Levels and the Effects of Pinealectomy Mary T. Mendonc¸ a,* ,1 Alan J. Tousignant,* ,2 and David Crews* , ² *Institute of Reproductive Biology, Department of Zoology, and ²Department of Psychology, University of Texas at Austin, Austin, Texas 78712 Previous studies found that pinealectomy of male Cana- (SCN) of the hypothalamus (for review see Turek, 1985; dian red-sided garter snakes (Thamnophis sirtalis pari- Turek and Van Cauter, 1994). However, even the SCN etalis) in the autumn, before prolonged exposure to low is part of a network of multiple coupled circadian oscil- temperatures (hibernation), significantly impaired the ex- lators and, although it may be the master oscillator, pression of courtship behavior upon emergence in the studies indicate some modulation of circadian rhythms spring. Additionally, pinealectomized animals with a dis- by melatonin, the product of the pineal gland (Turek, rupted diel cycle of plasma melatonin did not court while 1985; Rossenwasser and Adler, 1986; Cassone, 1990; those exhibiting a more typical diel pattern did. These Turek and Van Cauter, 1994). Unlike some lower verte- results suggested that the pineal gland functions in the brates, the pineal gland in mammals does not have an transduction of a temperature cue which stimulates autonomous circadian rhythm of melatonin secretion courtship. To test this hypothesis, we pinealectomized (Menaker, 1982). In several species of birds, reptiles, males in the spring after they had undergone a normal hibernation but were still courting. Pinealectomy of and fish, however, the pineal gland does play a major courting males in the spring, in each of the 3 years of role in the organization of the circadian system. Addi- study, had no effect on courtship. This result suggests tionally, its product, melatonin, promotes the coupling that once the cue is transduced, the pineal gland no of multiple subordinate oscillators which may, in turn, longer has a modulatory effect on courtship behavior. be autonomously producing melatonin (e.g., retinae Finally, we took advantage of the fact that, in the labora- and other extra-pineal tissue; for review, see Rossen- tory, there is always a small percentage of males that wasser and Adler, 1986; Cassone and Menaker, 1984; do not court upon emergence. Pinealectomy of these Cassone, 1990). Feedback among the oscillators is nec- noncourters greatly increased the percent of males ex- essary for proper synchronization of circadian rhythms. pressing courtship behavior in each of the study years. Pinealectomy in many species of birds and reptiles can Plasma melatonin levels of unmanipulated courting and cause splitting or abolishment of circadian behavioral noncourting males was measured after emergence in successive years. In both years, courters had a typical rhythms (e.g., locomotory, feeding, drinking, thermo- pattern of melatonin secretion (low in the photophase, regulatory, migratory restlessness), yet in other species high in the scotophase) while persistent noncourters dis- there is no effect, indicating other centers of circadian played the opposite pattern. q 1996 Academic Press, Inc. control (McMillan 1972; Gwinner, 1978; Ralph, Firth, and Turner, 1979; Erskine and Hutchinson, 1981; Un- derwood, 1981; Underwood, 1983; Beldhuis, Dittami and Gwinner, 1988; Janik and Menaker, 1990; Ralph, In mammals, a variety of circadian rhythms (e.g., bio- 1983; Vivien-Roels, 1985; Foa, 1991; Refinetti and Men- chemical, physiological, behavioral) are under the con- aker, 1992). trol of a master pacemaker, the suprachiasmatic nucleus In addition to modifying activity patterns, the pineal gland is also implicated in the regulation of seasonal 1 Present address: Department of Zoology and Wildlife Science, gonadal activity, especially in mammals. Many studies Auburn University, Auburn, AL 36849. have found that it functions as a transducer of photope- 2 Present address: Trevor Zoo, Millbrook School, Millbrook, NY 12545. riodic information and can thus have anti- or pro-go- 176 0018-506X/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.