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: Patterns of food intake were also analyzed in the CLAMS system at 17 weeks post surgery (Fig. 4). Two factor ANOVA revealed a clear effect of time (F = 23.7, P < 0.0001), thus food intake was higher in both groups during the dark phase than during the light phase (Fig. 4, top) reflecting a significantly increased frequency of feeding (F = 70.5, P < 0.0001; Fig. 4, bottom). There was also a significant time × group interaction (F = 5.62, P = 0.0001), thus food intake in the OXSAP group was higher in the dark phase but lower in the first 8 h of the light phase (Fig. 4, top). This reflected significant differences in meal size (Fig. 4, bottom), as there were no significant differences in frequency of feeding between the groups (Fig. 4, middle). Metabolic rate as inferred from the VO2 measurements was significantly higher during the first part of the dark phase in the OXSAP-treated hamsters compared with SAP-treated controls (Fig. 5, top). The daily profile of fuel metabolism, as measured by respiratory exchange ratio (RER), also differed between the groups (Fig. 5, middle). Two factor ANOVA revealed not only a clear effect of time (F = 9.15, P < 0.0001) but also a significant group × time interaction (F = 2.93, P < 0.0001), thus RER values were similar during the dark phase, but lower during the light phase in the OXSAP-treated hamsters (Fig. 5, middle). Locomotor activity was much more variable between individuals; there was a trend (p = 0.09) towards higher activity during the dark phase in OXSAP-treated hamsters compared with the SAP-treated controls (Fig. 5 bottom), but no differences in activity levels were detected in the light phase (Fig. 5, bottom).
Affiliation: Biology Department, Washington and Lee University, Lexington, VA, USA.