Effect of temporal synergism of neural oscillations on photorefractoriness in Japanese quail (Coturnix coturnix japonica).J Exp Zool A Comp Exp Biol. 2006 Jan 01; 305(1):3-12.JE
Circadian rhythms in many metabolic functions including neural (transmitters) and hormonal secretion appear to change with physiological condition. It is also reported that seasonal changes in photoperiodism/reproduction and other metabolic conditions may result from a temporal interaction of circadian neural oscillations that change seasonally. To test this hypothesis, the present study was designed to study the effect of temporal synergism of two neural oscillations (serotonin and dopamine) on relative photorefractoriness of Japanese quail. Serotonin and dopamine precursor drugs (5-HTP, 5-hydroxytryptophan and L-DOPA, L-dihydroxyphenylalanine) were administered (intraperitonially 5 mg/100 g body weight) at six different time intervals of 0, 4, 8, 12, 16 and 20 hr in sexually mature quail (>12 weeks old). The birds of control group received two daily injections of normal saline. The treatment was given for 13 days in continuous condition of light and then the quail were shifted to intermediate daylength (LD 13.5:10.5 for experiment 1) and short daylength (LD 8:16 for experiment 2). Six weeks following treatment, birds in intermediate daylength showed regressed cloacal gland and testicular activity except in 12-hr group, which exhibited gonadostimulatory condition. But birds of all the groups in short daylength showed complete regression of cloacal gland after 4 weeks of the treatment. In experiment 3, reproductively quiescent relative photorefractory quail maintained under intermediate daylength (LD 13.5:10.5) received 13 daily injections of 5-HTP and L-DOPA at the interval of 12 hr. At 6 weeks post-treatment, it was observed that unlike cloacal gland of control quail, which remained regressed, that of 12-hr quail showed significant development. These findings indicate that 12-hr temporal interaction of 5-HTP and L-DOPA administration maintained reproductive system in stimulated condition and prevented reproductive regression in photorefractory quail, but did not prevent the onset of scotosensitivity. It is concluded that the 12-hr temporal relationship of circadian serotonergic and dopaminergic oscillations not only eliminates photorefractoriness but may also re-establish photosensitivity in relative photorefractory quail. These findings suggest the regulatory role of neural oscillations and their temporal interaction in the regulation of neuroendocrine-gonadal axis with special reference to photosensitivity/refractoriness.