Neuroendocrine regulation of reproduction in male domestic animal species: Role of excitatory amino acids

Abstract

The ability to control and enhance reproduction in male domestic animal species requires a sound understanding of the mechanisms functioning within the hypothalamic-pituitary-testicular axis. Recent evidence suggests that the excitatory amino acids (ExAA) are important neurotransmitters that participate in the neuroendocrine control of anterior pituitary hormone secretion. In general, treatment with agonists of different ExAA receptor types, such as n-methyl-D,L-aspartate (NMA), stimulate release of most anterior pituitary hormones in boars, bulls, and rams, and these effects are manifested mainly at the level of the central nervous system. In some experimental models, inhibitory effects of ExAA on LH secretion have also been reported. Whether ExAA act directly on neurons that secrete hypothalamic-releasing hormones or indirectly by action on other neuronal systems is not clear. Data from boars, however, suggest that the catecholamines do not modulate the effects of NMA on LH or GH secretion. Although some data indicate that the ExAA are involved in the processes that culminate in sexual maturation, more research is needed before definitive conclusions can be drawn.

Growth Associated Hormones Response and Fat Metabolism Change in Finishing Pigs Fed with n-Methyl-d, L-Aspartate

“…Effects of NMA with i.v. injection on animal endocrine system, particularly in reproductive hormones, have been well documented (Estienne et al, 1997(Estienne et al, , 1999. Only few papers reported the effects of NMA on animals with oral administration.…”

“…Excitatory amino acids (EAA), such as glutamate and asparate, are major neurotransmitter in the mammalian central neurons system, which generally stimulate (primary via N-methyl-d-aspartate, NMDA receptor) the release of neuropeptides from the central nervous system, thereby influencing pituitary functions. Abundant studies have indicated that n-methyl-d,l-aspartate (NMA), an agonist of glutamate, increases pituitary secretion of LH and GH under appropriate conditions in a variety of domestic animal species (Estienne et al, 1996a(Estienne et al, , 1997. For example, NMA at an i.v.…”