Seasonal biology Flashcards
Hoffmann and Reiter 1985
Px in Syrian hamsters = testes stayed large
Goldman 1984
9/12h melatonin infusion
Nett 1982
Sheep in long PP and mel injection
Bittman 1983
4 year sheep experiment
Van Oort 2005
Svalbard reindeer: weak circadian clock, strong circannual clock
Stokkan 1994
Reindeer: skeleton mel profile
Reierch 1999
Ptarmigan: skeleton mel profile
Visser 2010
PP main cue but others too e.g. temp - climate change?
Lu 2010
Rodents in constant dark = maintain circa 24h activity/rest cycle, rhythmic clock gene expression and rhythmic oscillations of melatonin.
Reindeer = gene expression and mel rhythm becomes arrythmic
Hanon 2008
Staining of M1 melatonin GCPRs in pars tuberalis: present in both long and short PPs
Moetner 1991
Thyroidectomy
Translation of melatonin signal in pars tuberalis
PT is interface between hypothalamis and main pituitary. Contains thyrotrophs which produce TSH. But no TRH receptors!
TSH made of two subunits, one of which - BTSH - is strongly activated by long PP (i.e. short melatonin signal). Long PP = more BTSH subunit so PT produces more TSH.
TSH is then used by tanycytes in 3rd ventricle of hypothalamus (form bridge between ht and main pituitary).
Tanycytes have high expression of deiodinase enzymes e.g. DIO2 - used to convert inactive thyroid hormone (T4) to T3 (active). So more thyroid hormone released from pituitary (generates neuroendocrine output) which can be received by thyroid hormone receptors and drive seasonal reproductive changes.
BTSH is photoperiodic due to eya3 (transcriptional coactivator) which is under circadian control - peaks 12h after melatonin onset i.e. suppressed by melatonin. In long PP there is less melatonin = stronger eya3 peak, more TSH made, more DIO2 conversion of T4 to T3 etc.
Messager 2000
Siberian hamster. Light directly correlated with per clock gene expression
