Effects of Pinealectomy on Hypothalamic Metabolic and Clock Gene Rhythms
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A neuroendocrine loop model has been proposed for explaining the generation of avian circadian rhythms. The basis of this model is that the circadian system is composed of interconnected circadian pacemakers residing within the suprachiasmatic nucleus (SCN) complex, retina and pineal gland, which control the phase of rhythmicity of peripheral oscillators in the absence of photic or neuroendocrine input from the rest of the system (Cassone and Menaker, 1984). However, recent data question the validity of the neuroendocrine loop model by suggesting that although melatonin administration affects overt clock function, (Lu and Cassone, 1993) it has no effect on the transcription of clock genes (Yasuo et al., 2002). Thus, expression of these genes could be independent of pineal function. My research attempts to elucidate whether metabolic rhythms in the vSCN and clock gene expression in the vSCN and mSCN are coupled and to reveal the effects of pineal melatonin on these rhythms. This is done by comparing the affects of pinealectomy on 2DG uptake and canonical "clock" gene expression in the hypothalamus of house sparrows, Passer domesticus. Since other brain structures exhibit metabolic and clock gene rhythms, investigation of clock gene expression and 2DG uptake will also be undertaken in peripheral structures, e.g. the habenula and optic tectum. Currently, analysis of 2DG uptake at Day 0 has been completed and the process of analysis for Day 10 has begun. Using in situ hybridization techniques, I will quantify clock gene expression in both the vSCN and mSCN to determine if clock gene rhythms persist despite the absence of the pineal gland, the source of rhythmic melatonin for passerine birds. Because in situ analysis must be done from all timepoints and conditions simultaneously, and given the breadth of this experiment, these analyses are still being undertaken.
Clauson, Amanda (2006). Effects of Pinealectomy on Hypothalamic Metabolic and Clock Gene Rhythms. Available electronically from