The Histochemical Journal 33: 685–694, 2001. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. Corticotropin-releasing hormone-like immunoreactivity in the brain of the snake Bothrops jararaca P.F. Silveira 1,2 , M.C. Breno 2 , G. Puorto 3 , M.P. Mart´ ın del R´ ıo 1 & J.M. Mancera 1,∗ 1 Department of Animal Biology, Faculty of Marine Science, University of C´ adiz, 11510 Puerto Real, C ´ adiz, Spain 2 Laboratory of Pharmacology and 3 Biological Museum, Instituto Butantan, 05503-900 S˜ ao Paulo, Brazil ∗ Author for correspondence Received 23 November 2001 and in revised form 20 March 2002 Summary The distribution of corticotropin-releasing hormone in the brain of the snake Bothrops jararaca was studied immunohistochem- ically. Immunoreactive neurons were detected in telencephalic, diencephalic and mesencephalic areas such as dorsal cortex, subfornical organ, paraventricular nucleus, recessus infundibular nucleus, nucleus of the oculomotor nerve and nucleus of the trigeminal nerve. Immunoreactive fibres ran along the hypothalamo-hypophysial tract to end in the outer layer of the median eminence and the neural lobe of the hypophysis. In general, immunoreactive fibres occurred in the same places of immunoreac- tive neurons. In addition, immunoreactive fibres were observed in the septum, amygdala, lamina terminalis, supraoptic nucleus, nucleus of the paraventricular organ, ventromedial hypothalamic nucleus and interpeduncular nucleus. These results indicate that, as for other vertebrates, corticotropin-releasing hormone in B. jararaca brain, besides being a releasing hormone, may also act as a central neurotransmitter and/or neuromodulator. Introduction The superfamily of corticotropin-releasing hormones (CRH) comprises several peptides conserved in phylogeny (Lederis et al. 1990, Lovejoy & Balment 1999). In vivo and in vitro studies have shown that CRH stimulates the secretion of adrenocorticotropin (ACTH), β -endorphin and melanotropin (MSH) in the adenohypophysis (Vale et al. 1981, Sakly et al. 1982) and inhibits the release of gonadotropin-releasing hormone, growth hormone-releasing hormone, somatostatin, arginine vasopressin and oxytocin (Rivier & Plotsky 1986, Zadina & Kastin 1986). The distribution of perikarya and fibres containing immunoreactive CRH has been described in the brain of sev- eral mammalian species, such as rat (Bloom et al. 1982, Merchenthaler et al. 1982, Olschowka et al. 1982, Kawata et al. 1983, Swanson et al. 1983, Champagne et al. 1998), sheep (Paull et al. 1982, Kolodziejczyk et al. 1983), dog (Bugnon et al. 1984, Stolp et al. 1987), cat (Bugnon et al. 1984), goat (Kikusui et al. 1997) and man (Bugnon et al. 1982). In addition to the hypothalamus, the expression of the CRH gene has been detected in the cerebral cortex and in extracerebral sites (Usui et al. 1988). The distribution of CRH-immunoreactive elements has also been studied in the brain of non-mammalian vertebrates such as birds (P´ eczely & Antoni 1984, Yamada & Mikami 1985, Bons et al. 1988, Ball et al. 1989), amphibians (Tonon et al. 1985, Olivereau et al. 1987, Miranda & Dezi 1997), and teleost and elas- mobranch fishes (Olivereau et al. 1984, Yulis et al. 1986, Olivereau & Olivereau 1988, Vallarino et al. 1989, Mancera & Fern´ andez-Ll´ ebrez 1995, Polenov et al. 1997, Zupane et al. 1999). In mammalian and non-mammalian species, CRH- immunoreactive hypothalamic neurons exert their hypophys- iotropic action by projecting axons to the outer layer of the median eminence or the neural lobe. In all vertebrates, CRH- immunoreactive fibres and CRH receptors have been detected in addition to the hypothalamus, in several other areas of the central nervous system (CNS). This suggests that CRH might also act as a neuromodulator or neurotransmitter (Bugnon et al. 1984, Zadina & Kastin 1986, Perrin & Vale 1999, Van Pett et al. 2000). In reptiles, the CRH system has been described in the turtles Pseudemys scripta elegans (Bugnon et al. 1984) and Mauremys caspica (L´ opez Avalos et al. 1993) and in the snake Natrix maura (Mancera et al. 1991b). Whereas CRH-like immunoreactive neurons have been observed in the nucleus of the paraventricular organ in P. scripta elegans (Bugnon et al. 1984) and in the paraventricular nucleus of N. maura (Mancera et al. 1991b) and M. caspica (L´ opez Avalos et al. 1993), CRH-like immunoreactive fibres have also been described occupying hypothalamic as well as extrahypothalamic areas. By their phylogenetic position, studies on the peptider- gic system in snakes are of great interest. Since no detailed anatomical study on the distribution of CRH-like immunore- active perikarya and nerve fibres exist for the viperid snake, we investigated this distribution in the brain of the ter- restrial brazilian pit viper Bothrops jararaca. The results are compared with those described in other reptiles and vertebrates.