The Preoptic Area and the RFamide-Related Peptide Neuronal System Gate Seasonal Changes in Chemosensory Processing

Area of Science:

• Neuroendocrinology
• Animal Behavior
• Chronobiology

Background:

• Male Syrian hamsters use chemosensory cues for social communication and reproduction.
• Reproductive responses to female cues are suppressed under short-day (SD) photoperiods, even with testosterone (T) replacement.
• The brain regions responsible for seasonally dependent gating of these responses remain unidentified.

Purpose of the Study:

• To identify neural loci where chemosensory processing is gated seasonally.
• To investigate differential neural responses to female chemosignals across photoperiods, independent of T levels.

Main Methods:

• Male Syrian hamsters were housed in long-day (LD) or SD photoperiods, with some SD animals receiving T replacement.
• Animals were exposed to female hamster vaginal secretions (FHVSs) or vehicle.
• Neuronal activation (FOS expression) in chemosensory centers and the neuroendocrine axis was examined.

Main Results:

• Chemosensory pathway activation upstream of the hypothalamus was similar across photoperiods.
• The preoptic area (POA) responded to FHVS only in LD animals.
• RF-amide related peptide (RFRP) neurons, but not kisspeptin neurons, responded to FHVS only in LD animals; T replacement did not restore SD responses.

Conclusions:

• The POA and RFRP neuronal system are key sites for photoperiodic gating of reproductive responses to female cues in male hamsters.
• Seasonal photoperiod, rather than T levels alone, regulates the processing of social chemosignals crucial for reproduction.