Food and temperature change photoperiodic responses in two vole species:
different roles for hypothalamic genes
Abstract
Seasonal timing of reproduction in voles is driven by photoperiod. Here
we hypothesize that a negative energy balance can modify
spring-programmed photoperiodic responses in the hypothalamus,
controlling reproductive organ development. We manipulated energy
balance by the ‘work-for-food’ protocol, in which voles were exposed to
increasing levels of food scarcity at different ambient temperatures
under long photoperiod. We reveal that common (Microtus arvalis)
and tundra voles (Microtus oeconomus), reduce photoperiodic
induced pars tuberalis thyroid-stimulating hormone β-subunit (Tshβ)
expression to inhibit gonadal development when food is scarce. Reduction
in gonadal size is more pronounced in tundra voles, in which the
hypothalamic Kisspeptin (Kiss1) system seems involved in downregulating
gonadal development, especially in males. Low temperature additionally
leads to decreased hypothalamic RF-amide related peptide (Rfrp3) levels,
which may facilitate further suppression of gonadal growth. Shutting off
the photoperiodic-axis when food is scarce in spring may be an adaptive
response to save energy, leading to delayed reproductive organ
development until food resources are sufficient for reproduction,
lactation and offspring survival. Defining the mechanisms through which
metabolic cues modify photoperiodic responses will be important for a
better understanding of how environmental cues impact reproduction.