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Tanycytes in the ependymal layer of the third ventricle act both as a barrier and a communication gateway between the cerebrospinal fluid, brain and portal blood supply to the pituitary gland. However, the range, importance and mechanisms involved in the function of tanycytes remain to be explored. In this study, we have utilized a photoperiodic animal to examine the expression of three unrelated gene sequences in relation to photoperiod-induced changes in seasonal physiology and behaviour. We demonstrate that cellular retinol binding protein [corrected] (CRBP1), a retinoic acid transport protein, GPR50, an orphan G-protein-coupled receptor and nestin, an intermediate filament protein, are down-regulated in short-day photoperiods. The distribution of the three sequences is very similar, with expression located in cells with tanycyte morphology in the region of the ependymal layer where tanycytes are located. Furthermore, CRBP1 expression in the ependymal layer is shown to be independent of a circadian clock and altered testosterone levels associated with testicular regression in short photo-period. Pinealectomy of Siberian hamsters demonstrates CRBP1 expression is likely to be dependent on melatonin output from the pineal gland. This provides evidence that tanycytes are seasonally responsive cells and are likely to be an important part of the mechanism to facilitate seasonal physiology and behaviour in the Siberian hamster.

Castrate male sheep (wethers, average liveweight 38 +/- 0.6 kg) were given one of the following diets for 10 weeks followed by euthanasia (n = 8/group): high-energy high-protein providing 1-5 times the energy required to maintain liveweight (maintenance) (group 1.5 M), low-energy low-protein at 0.5 maintenance (0.5 M), or low-energy high-protein at 0.5 maintenance (0.5 M + P). 1.5 M wethers gained 22% liveweight whereas 0.5 M and 0.5 M + P wethers lost 18 and 13% liveweight respectively. Relative to the 1.5 M group, the 0.5 M and 0.5 M + P groups had similar plasma concentrations of glucose and cortisol throughout, but elevated non-esterified fatty acids (P < 0.001) and reduced IGF-I and insulin (P < 0.05, 0.01 or 0.001) from 1 week onwards. Each week blood samples were taken every 12 min for 4 h and plasma assayed for LH. Mean concentration over 4 h, LH pulse frequency and LH pulse amplitude showed no progressive change in 1.5 M sheep. However, in both 0.5 M and 0.5 M + P groups mean LH increased (P < 0.001 and P < 0.01 respectively), pulse frequency decreased (P < 0.01 and P < 0.01) and pulse amplitude increased (P < 0.001 and P < 0.01) over the 10-week period. Anterior pituitary. LH content was greater in 0.5 M (P < 0.01) and 0.5 M + P (P < 0.05) than in 1.5 M sheep. Coronal sections (20 microns) of hypothalamic brain tissue were subjected to in situ hybridisation to determine gene expression for neuropeptide Y (NPY). NPY mRNA was concentrated in the arcuate nucleus and median eminence, with total amounts greater in both 0.5 M (310%, P < 0.001) and 0.5 M + P (333%, P < 0.01) groups than in 1.5 M sheep (100%). These data reveal that chronic low dietary energy intake by long-term castrates, with high or low protein intake, reduces LH pulse frequency but increases the circulating levels of LH by virtue of an increase in pulse amplitude, and concomitantly increases hypothalamic NPY gene expression.