Light-induced Fos expression is attenuated in the suprachiasmatic nucleus of serotonin 1B receptor knockout mice.
The hypothalamic suprachiasmatic nucleus (SCN) is a circadian oscillator that receives a dense serotonergic innervation from the median raphe nucleus. Serotonin (5-HT) modulates the effects of light on circadian behavior by acting on 5-HT1B receptors on retinohypothalamic (RHT) terminals in the SCN. Activation of 5-HT1B presynaptic receptors on RHT terminals inhibits glutamate release. However, 5-HT1B receptor knockout (5-HT1B KO) mice have attenuated behavioral responses to light [P.J. Sollars, M.D. Ogilvie, A.M. Simpson, G.E. Pickard, Photic entrainment is altered in the 5-HT1B receptor knockout mouse, J. Biol. Rhythms 21 (2006) 21-32]. To assess the cellular response of the 5-HT1B KO SCN to light, light-induced Fos expression was analyzed in 5-HT1B KO and wild-type (WT) mice. In addition, the distribution of melanopsin containing retinal ganglion cells that contribute the majority of axons to the RHT was examined in 5-HT1B KO mice and compared to that of WT mice. Light-induced Fos expression in the SCN was reduced in 5-HT1B KO mice compared to WT mice at circadian time (CT) 16 and CT 23 in a manner similar to the reduction previously described in light-induced behavioral phase shifts. The number of melanopsin retinal ganglion cells was similar in WT and 5-HT1B KO mice. These data taken together with previous data suggest that functional removal of the 5-HT1B receptor results in reduced functional light input to the SCN.
Division of Neuroscience, Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA. psollars@lamar.colostate.edu
Patricia J
PJ
Sollars
Anne M
AM
Simpson
Malcolm D
MD
Ogilvie
Gary E
GE
Pickard
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology* / Q000528:radiation effects; D007150:Immunohistochemistry / Q000379:methods; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016761:Oncogene Proteins v-fos / Q000378:metabolism*; D044302:Receptor, Serotonin, 5-HT1B / Q000172:deficiency*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000528:radiation effects
D016761:Oncogene Proteins v-fos; D044302:Receptor, Serotonin, 5-HT1B