title: Deep-brain photoreceptors (DBPs) involved in the photoperiodic gonadal response in an avian species, Gallus gallus.
abstract: Three primitive photoreceptors [melanopsin (Opn4), neuropsin/opsin5 (Opn5) and vertebrate ancient opsin (VAOpn)] were reported as possible avian deep-brain photoreceptors (DBPs) involved in the perception of photoperiodic information affecting the onset and development of reproduction. The objective of this study was to determine the effect of long-day photostimulation and/or sulfamethazine treatment (SMZ, a compound known to advance light-induced testes development) on gene expression of DBPs and key hypothalamic and pituitary genes involved in avian reproductive function. Two-week old chicks were randomly selected into four experimental groups: short-day control (SC, LD8:16), short-day+SMZ (SS, LD8:16, 0.2% diet SMZ), long-day control (LC, LD16:8), and long-day+SMZ (LS, LD16:8, 0.2% diet SMZ). Birds were sampled on days 3, 7, and 28 after initiation of a long-day photoperiod and/or SMZ dietary treatments. Three brain regions [septal-preoptic, anterior hypothalamic (SepPre/Ant-Hypo) region, mid-hypothalamic (Mid-Hypo) region, posterior-hypothalamic (Post-Hypo) region], and anterior pituitary gland were dissected. Using quantitative real-time RT-PCR, we determined changes of expression levels of genes in distinct brain regions; Opn4 and Opn5 in SepPre/Ant-Hypo and Post-Hypo regions and, VAOpn in the Mid-Hypo region. Long-day treatment resulted in a significantly elevated testes weight on days 7 and 28 compared to controls, and SMZ augmented testes weight in both short- and long-day treatment after day 7 (P<0.05). Long-day photoperiodic treatment on the third day unexpectedly induced a large 8.4-fold increase of VAOpn expression in the Mid-Hypo region, a 15.4-fold increase of Opn4 and a 97.8-fold increase of Opn5 gene expression in the Post-Hypo region compared to SC birds (P<0.01). In contrast, on days 7 and 28, gene expression of the three DBPs was barely detectable. LC group showed a significant increase in GnRH-1 and TRH mRNA in the Mid-Hypo compared to SC on day 3. Pituitary LHβ and FSHβ mRNA were significantly elevated in LC and LS groups compared to SC on days 3 and 7 (P<0.05). On days 3 and 7, TSHβ mRNA level was significantly elevated by long-day treatment compared to the SC groups (P<0.05). Results suggest that long-day photoperiodic activation of DBPs is robust, transient, and temporally related with neuroendocrine genes involved in reproductive function. Additionally, results indicate that two subsets of GnRH-1 neurons exist based upon significantly different gene expression from long-day photostimulation and long-day plus SMZ administration. Taken together, the data indicate that within 3 days of a long-day photoperiod, an eminent activation of all three types of DBPs might be involved in priming the neuroendocrine system to activate reproductive function in birds.
authors.affiliation: Department of Poultry Science, Center of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR, United States. Electronic address: swkang@uark.edu.
authors.forename: Seong W
authors.initials: SW
authors.lastname: Kang
authors.affiliation: Department of Poultry Science, Center of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR, United States. Electronic address: wkuenzel@uark.edu.
authors.forename: Wayne J
authors.initials: WJ
authors.lastname: Kuenzel
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002645:Chickens / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D037201:Follicle Stimulating Hormone, beta Subunit / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D008027:Light; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics / Q000378:metabolism; D008297:Male; D017440:Photoperiod; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013418:Sulfamethazine / Q000494:pharmacology; D013737:Testis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D037322:Thyrotropin, beta Subunit / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D037201:Follicle Stimulating Hormone, beta Subunit; D037101:Luteinizing Hormone, beta Subunit; D012333:RNA, Messenger; D037322:Thyrotropin, beta Subunit; D007987:Gonadotropin-Releasing Hormone; D013418:Sulfamethazine
keywords: HPG axis; Opn4; Opn5; Sulfamethazine; VAOpn