Potentiation of light-induced phase shifts by 5-hydroxy-L-tryptophan in Pygmy field mice: a preliminary report

Abstract

Serotonergic agents usually attenuate light-induced phase shifts in nocturnal species. L-5-Hydroytrytptophan (5-HTP) is a non-specific serotonergic agonist and the natural precursor of serotonin. We investigated the ability of 5-HTP to potentiate or attenuate light-induced phase shifts using a comparatively lower intensity of light (∼70 lux). Mice free-running in DD were given either light exposure at circadian times (CTs) 15 and 21 with saline (light-exposed control) or 50 mg/kg of 5-HTP (Himedia) at 0.5 circadian h prior to light exposure. L-5-Hydroytrytptophan potentiated the phase advance of the rhythm caused by light at CT 21; however, 5-HTP fails to significantly attenuate/potentiate phase delays. Total activity increased during phase advance potentiation, compared to control, indicating that this phenomenon may possibly be at least partially behavioral arousal-dependent. These preliminary findings are interesting and unexpected; further experimentation is necessary, and the results indicate possible scope for use of 5-HTP in chronotherapy.

Keywords:

• Pygmy field mice
• 5-Hydroxytryptophan
• potentiation
• phase shifts

Acknowledgments

Financial aid to MS by Banaras Hindu University vide grant No.F(A)1-14(G)/3449, Research grant through UGC Major Research Project (No. P01/644) to MS, CSIR-UGC (University Grants Commission, New Delhi, India) Senior Research Fellowship to PB and help with animal handling by Mr. Punit Kumar are thankfully acknowledged.