In three experiments a total of 23 sham-operated and 63 brainlesioned killifish were maintained for 12%-16% weeks under constant environmental conditions, with regular feeding. Regression of the testes and pituitary gonadotropes, seen in 13 fish, was correlated with lesions in the parvocellular region and/or tract of the nucleus lateral tuberis pars anterior (NLTa). Marked hypertrophy of the thyroid and pituitary thyrotropes, seen in nine fish, was associated with severe lesions of the nucleus anterior tuberis (NAT). A highly significant increase in growth rate, seen in four fish, was correlated with lesions in the nucleus preopticus (NPO), but there was no change in the pituitary somatotropes. Increased appetite, resulting from the presumed destruction of a satiety center, is a possible explanation.Hypothalamic regulation of the pituitary in teleost fishes has been reviewed repeatedly (Ball, '81; Peter, '73, '78; Jackson, '78; Stetson and Grau, '801, but there are many unresolved and conflicting problems. Some of these derive from little understood species differences, and the present investigation was undertaken to resolve several aspects of the problem in the euryhaline killifish, Fundulus heteroclitus, for which a minimum of information is available. Three aspects are considered in the present contribution: the regulation of the gonads, the thyroid, and growth. A review of recent literature in these areas, restricted to teleostean species, provides a necessary background for the interpretation of the results.
Regulation of gonad maturationEarlier investigations (Peter, '701, supplemented by more recent studies (Rai, '73; Pavlovie and PantiC, '73; Viswanathan and Sundararaj, '74; Pantic and Lovren, '75), have established a correlation between the secretory activity of the nucleus lateral tuberis (NLT) and the nucleus preopticus (NPO) with the annual reproductive cycle in various teleosts. Hypothalamic lesions in these areas, during gonadal recrudescence in the goldfish, result in gonad regression (Peter, '70; Peter and Crim, '78), but in the male parr ofSalmo salar only lesions in the NLT were effective (Dodd et al., '78). Injections of mammalian luteinizing releasing hormone (LRH) can stimulate the pituitary gonadotrophs with the release of gonadotropin and subsequent spawning (Peter and Crim, '79; Harvey and Hoar, '79; Peter, '80; Crim et al., '81). Furthermore, a series of investigations summarized by Crim et al. ('78) have established the presence of an LRH-like factor in the hypothalamus of some teleosts, although its chemical nature is unresolved and its identity with mammalian LRH is questioned (Breton et al., '75; Goos and van Oordt, '78; King and Millar, '79a, '80). Under these circumstances the term gonadotropin-releasing hormone (GRH), rather than LRH, should be employed. Attempts to identify the hypothalamic areas concerned with the synthesis and transport of GRH, using the immunoreactive response to synthetic LRH, tend to support involvement of the NPO and NLT (Schreibman et al., '79; Pan et al., ...
