[Effect of long-term feeding with tryptophan-free diet on the circadian rhythm in rats].
Effects of long-term feeding with tryptophan (TRP)-free diet on the free running periods of wheel-running rhythm and the central serotonergic neurotransmission were examined in male blinded rats. Long-term feeding with TRP-free diet did not change the periods of wheel-running rhythm calculated from chi 2 periodogram but disordered its pattern, which seemed to be due to masking or entrainment effects. On the other hand, long-term TRP-free diet decreased the concentrations of TRP, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in all brain regions tested; frontal cortex, hippocampus, thalamus, hypothalamus and pons. The density of 5-HT1A receptor (3H-8-OH-DPAT) binding was significantly decreased in only frontal cortex, while no significant change was observed in the density of 5-HT2 receptor (3H-ketanserin) binding in all regions. Although the mechanism of down-regulation of 5-HT1A receptor in frontal cortex is obscure, it was confirmed that TRP-free diet decreased central 5-HT synthesis and 5-HT neurotransmission. This dysfunction of 5-HT neurotransmission by TRP-free diet is suggested to make the circadian rhythm pacemaker susceptible to subtle environmental factors by lowering its intensity.
D000818:Animals; D001766:Blindness; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry / Q000502:physiology; D002940:Circadian Rhythm; D004032:Diet; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D009043:Motor Activity; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D009435:Synaptic Transmission; D014364:Tryptophan / Q000172:deficiency* / Q000378:metabolism
D011985:Receptors, Serotonin; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan