Histaminergic regulation of seasonal metabolic rhythms in Siberian hamsters.
Bottom Line: A ribosomal toxin (saporin) conjugated to orexin-B was infused into the ventral tuberomammillary region of the hypothalamus, since most histaminergic neurons express orexin receptors.This caused not only 75-80% loss of histaminergic neurons in the posterior hypothalamus, but also some loss of other orexin-receptor expressing cells e.g. MCH neurons.In summary, ablation of orexin-responsive cells in the posterior hypothalamus blocks the short-day induced decline in body weight by preventing seasonal hypophagia, evidence consistent with the hypothesis that central histaminergic mechanisms contribute to long-term regulation of body weight.
Affiliation: Biology Department, Washington and Lee University, Lexington, VA, USA.Show MeSH
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Mentions: In general, daily variation in both ingestive (Fig. 9) and metabolic parameters (Fig. 10) was attenuated in amplitude in both groups of hamsters under the short day photoperiod, consistent with other observations we have made with the CLAMS . The small increase in food intake in the OXSAP-treated hamsters measured in home cages was not observed when the hamsters were studied in the metabolic cages (Fig. 9). Two factor ANOVA revealed a significant interaction between group and time on both occasions (SD week 10–11, F = 10.9; week 17–18 F = 11.3, P < 0.001), suggesting that the OXSAP-treated hamsters had a decreased food intake in the light phase reflecting a decrease in the frequency of feeding bouts (Fig. 9, bottom). At both weeks 10–11 (F = 6.67, P < 0.0001) and weeks 17–18 (F = 5.86, P < 0.0001) in short days there was a significant effect of time on VO2 (Fig. 10 top), but no effect of group, though the large amplitude dark phase rise in metabolic rate that was observed in hamsters during long day photoperiods in the first study was not as apparent in hamsters in short days on either occasion (Fig. 10 top vs Fig. 5 top). Analysis of RER values revealed that on both occasions in short days there were significant group × time interactions (week 10–11: F = 6.23, P < 0.001, weeks 17–18 F = 4.71, P < 0.01), thus RER values were lower for parts of the daily cycle in the OXSAP-treated hamsters (Fig. 10). Finally, locomotor activity did not differ over a 24-hour period between lesioned and sham hamsters at 9 or 17 weeks in short days (Fig. 10, bottom). In addition, the marked elevation in night-time activity that was observed in hamsters during long day photoperiods (Fig. 5, bottom: note the 2-fold difference in scale vs Fig. 10 bottom) was reduced to a small elevation in activity at the onset of the dark phase in short day exposed hamsters (Fig. 10).
Affiliation: Biology Department, Washington and Lee University, Lexington, VA, USA.