N. Goel et al., REMOVAL OF THE OLFACTORY BULBS DELAYS PHOTIC REENTRAINMENT OF CIRCADIAN ACTIVITY RHYTHMS AND MODIFIES THE REPRODUCTIVE AXIS IN MALE OCTODON-DEGUS, Brain research, 792(2), 1998, pp. 229-236
The diurnal rodent, Octodon degus, exhibits robust sex differences in
several circadian measures, including circadian period (tau) and reent
rainment rates to photic and nonphotic (social) zeitgebers. The neural
substrates underlying such physiological differences remain unknown.
In female degus, olfactory bulbectomies (BX) inhibit socially-facilita
ted reentrainment, but do not alter photic reentrainment, entrained me
asures, or tau in constant darkness (DD). This experiment investigated
the effects of EX in male degus on (i) photic reentrainment rates of
circadian rhythms following a 6-h phase advance of the Light-dark (LD)
cycle; (ii) photic entrainment; (iii) tau of free-running activity rh
ythms in DD; and (iv) body weight, paired testis weight, and the repro
ductive hormones, testosterone, androstenedione and follicle stimulati
ng hormone (FSH). EX significantly delayed photic reentrainment rates.
They did not, however, modify tau, the phase of activity onset or off
set, amplitude or duration (alpha) of the activity rhythm, mean daily
locomotor activity levels, or body weight. FSH, testosterone and andro
stenedione were unaffected by EX, whereas paired testis weights were s
ignificantly greater in EX degus compared with shams. Thus, the olfact
ory bulbs influence photic reentrainment of circadian rhythms and mode
stly affect the reproductive axis in male degus. Our results suggest t
hat the olfactory bulbs may be a neural source of observed sex differe
nces in photic reentrainment in degus, and highlight interspecies vari
ation in the olfactory bulbs' effects on entrained and free-running ci
rcadian rhythms and on reproduction. (C) 1998 Elsevier Science B.V.