Removal of the olfactory bulbs delays photic reentrainment of circadian activity rhythms and modifies the reproductive axis in male Octodon degus

• Published in: Brain research 1998-05, Vol.792 (2), p.229-236
• Main Authors: Goel, Namni, Lee, Theresa M, Pieper, David R
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Body weight; Chronobiology; Circadian Rhythm - physiology; Denervation; Diurnal; Follicle Stimulating Hormone - blood; Free-running; FSH; Fundamental and applied biological sciences. Psychology; Male; Olfactory Bulb - physiology; Olfactory Bulb - surgery; Organ Size; Photic Stimulation; Reproduction - physiology; Rodent; Rodentia; Sex difference; Sex Factors; Testis; Testis - physiology; Testosterone; Testosterone - blood; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/S0006-8993(98)00134-6

The diurnal rodent, Octodon degus, exhibits robust sex differences in several circadian measures, including circadian period ( τ) and reentrainment rates to photic and nonphotic (social) zeitgebers. The neural substrates underlying such physiological differences remain unknown. In female degus, olfactory bulbectomies (BX) inhibit socially-facilitated reentrainment, but do not alter photic reentrainment, entrained measures, or τ in constant darkness (DD). This experiment investigated the effects of BX 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) τ of free-running activity rhythms in DD; and (iv) body weight, paired testis weight, and the reproductive hormones, testosterone, androstenedione and follicle stimulating hormone (FSH). BX significantly delayed photic reentrainment rates. They did not, however, modify τ, the phase of activity onset or offset, amplitude or duration ( α) of the activity rhythm, mean daily locomotor activity levels, or body weight. FSH, testosterone and androstenedione were unaffected by BX, whereas paired testis weights were significantly greater in BX degus compared with shams. Thus, the olfactory bulbs influence photic reentrainment of circadian rhythms and modestly affect the reproductive axis in male degus. Our results suggest that the olfactory bulbs may be a neural source of observed sex differences in photic reentrainment in degus, and highlight interspecies variation in the olfactory bulbs' effects on entrained and free-running circadian rhythms and on reproduction.