AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 2 199-R206, Copyright © 1986 by American Physiological Society
Photic cues induce multiple neuroendocrine adjustments in testicular function
J. L. Blank and C. Desjardins
Neuroendocrine responses were evaluated in an outbred population of deer
mice (Peromyscus maniculatus nebrascensis) after exposure to an inhibitory
photoperiod (8:16 light-dark) for 10 wk. Deer mice were chosen as an animal
model for this study because they are typical of naturally selected species
that rely on environmental factors to signal the onset or cessation of
annual reproductive effort. Short photoperiods induced multiple
neuroendocrine adjustments as judged by three types of spermatogenic
responses: normal, intermediate, and azoospermic individuals. Plasma
concentrations of luteinizing hormone and testosterone coincided with
gradations in spermatogenic activity. In contrast, plasma concentrations of
follicle-stimulating hormone were unaffected. Prolactin secretion was
lowered in all mice exposed to short day lengths, regardless of sperm
count. These results demonstrate that short photoperiods engage at least
three types of neuroendocrine adjustments: 1) a suppression in luteinizing
hormone and testosterone secretion accompanying spermatogenic arrest, 2) a
reduction in prolactin secretion independent of changes in testicular
function, and 3) a null response in gonadotrophic hormone secretion in
which spermatogenesis is unimpaired by short day lengths. The
neuroendocrine subsets identified in this model provide new evidence that
photic cues induce three types of adjustments in pituitary-testicular
function. These subsets are readily identified, and they can be easily
exploited to dissect and manipulate the suite of neural, endocrine, and
metabolic adaptations triggered by environmental lighting among mammals
with annual reproductive strategies.
