Hypertrophy of gonadotropin releasing hormone‐containing neurons after castration in the teleost, Haplochromis burtoni

Abstract

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.

Social regulation of the brain-pituitary-gonadal axis.

“…The results show that gonadal steroids constrain the size of these neurons. This accords with the results of a previous experiment in which we found a significant negative regression of soma size on residual GSI in T males with various amounts of gonad removed (16). These results indicate that the association between large testes and large POA irGnRH neurons in the T males does not result from the stimulatory effects of gonadal androgens on the POA neurons.…”

“…These 3-mm pellets contained the selected hormone and vehicle (cholesterol, microcrystalline cellulose, lactose, di-and tricalcium phosphate, calcium and magnesium stearate, and stearic acid; Innovative Research of America). The amount of hormone to be released was based on measurements of circulating hormone levels in T males (16). Replacement pellets contained either 5 mg of testosterone or 1 mg of l1-ketotestosterone.…”

Photoperiod-Independent Hypothalamic Regulation of Luteinizing Hormone Secretion in a Free-Living Sonoran Desert Bird, the Rufous-Winged Sparrow <i>(Aimophila carpalis)</i>

“…However, it could also indicate increased storage of GnRH. Enlarged GnRH cells are commonly observed during breeding or when GnRH production is believed to be high in birds [Foster et al, 1987;Goldsmith et al, 1989;Hahn and Ball, 1995;Parry et al, 1997;Cho et al, 1998;Deviche et al, 2000;MacDougall-Shackleton et al, 2001;Moore et al, 2006], mammals [Kawamoto et al, 2000], and fish [Davis and Fernald, 1990;Francis et al, 1992;White and Fernald, 1993]. Ultrastructural studies of neurons in mammals show increased endoplasmic reticulum and number of granulated vesicles associated with increased cell body size [King et al, 1974;Tsuruo et al, 1984;Rance et al, 1990] which is consistent with increased peptide production.…”

Neuropeptide Y in the forebrain of the adult male cichlid fish Oreochromis mossambicus: Distribution, effects of castration and testosterone replacement

“…Castration increased the GnRH mRNA levels and augmented the number and size of GnRH cells in the preoptic area (Francis et al, 1992;Soma et al, 1996;Parhar et al, 1998;Soga et al, 1998;Amano et al, 1999). However, testosterone and estradiol caused massive augmentation of the salmon GnRH in ventral telencephalon and preoptic area of the rainbow trout (Breton and Sambroni, 1996).…”