title: Photostimulated fos-like immunoreactivity in tuberal hypothalamus of photosensitive vs. photorefractory turkey hens.
abstract: Photorefractoriness in commercial turkey hens can be viewed as a failure of previously sexually stimulatory photoperiods to maintain egg production via activation of cGnRH I neurons, but the neural locus of photorefractoriness, i.e., where in the brain failure occurs, is not known. We used a c-fos antiserum that detects c-Fos and Fos-related antigens to characterize Fos-like immunoreactivity (FLI) as a measure of neuronal activation. FLI was measured in somatically mature, photosensitive hens (held on short photoperiods [8L:16D] for at least 10 weeks) before (non-photostimulated-photosensitive group) and after 48 h of exposure to long photoperiods (16L:8D; photostimulated-photosensitive group). We also measured FLI in hens that had become photorefractory, transferred to short photoperiods for 1 week--an insufficient time period to reverse photorefractoriness--and then exposed to long photoperiods for 48 h (photostimulated-photorefractory group). FLI was nearly absent in the tuberal hypothalamus of non-photostimulated-photosensitive hens but FLI was abundant in photostimulated-photosensitive hens. FLI was greatly reduced (P<0.01) in the rostral tuberal hypothalamus of photostimulated-photorefractory hens. All hens showed variable extra-tuberal FLI in locations associated with stress, e.g., paraventricular nucleus, lateral septal area, and nucleus taenia. Double-label fluorescence immunohistochemistry with c-fos antiserum and anti-Neu-N, a neuron-specific protein, showed that a substantial fraction of tuberal FLI-positive cells in photostimulated-photosensitive hens were neuronal. These results implicate neurons in the rostral tuberal hypothalamus as a potential neural locus of photorefractoriness, as FLI in this region appears coupled with cGnRH I activation in photostimulated-photosensitive but not photostimulated-photorefractory turkey hens.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology* / Q000528:radiation effects; D005260:Female; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D009474:Neurons / Q000378:metabolism / Q000528:radiation effects; D017440:Photoperiod; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism / Q000528:radiation effects*; D012098:Reproduction / Q000502:physiology / Q000528:radiation effects; D014422:Turkeys / Q000502:physiology*
chemical_list: D016760:Proto-Oncogene Proteins c-fos