Increased VIP and Decreased GnRH Expression in Photorefractory Dark-Eyed Juncos (Junco hyemalis)

Colin J. Saldanha, Pierre Deviche, Rae Silver

Research output: Contribution to journalArticle

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Abstract

Most temperate zone birds show dramatic seasonal cycles in responsiveness to light. In the spring the hypothalamo-pituitary-gonadal axis of photosensitive birds is stimulated by long days. In the late summer birds no longer respond to long days, their gonads regress, and they are said to be photorefractory. After several weeks of refractoriness birds regain photosensitivity. During refractoriness circulating concentrations of luteinizing hormone are low and prolactin levels are high. These fluctuations in peripheral hormones result from changes in the brain rather than in the pituitary and/or the gonads. In the present study we examined seasonal changes in expression of vasoactive-intestinal polypeptide (VIP) and gonadotropin-releasing hormone (GnRH) in the brain of dark-eyed juncos (Junco hyemalis). Birds were photosensitive and exposed to long photoperiod (20:4 LD) for 1 day, 45-60 days, or not at all, or they were photorefractory (housed in 20:4 LD). The results indicate that VIP expression was similar in all photosensitive birds. However, photorefractory birds had significantly higher numbers of VIP-positive neurons in the infundibulum compared to photosensitive birds. The number of GnRH-positive neurons in the preoptic area was significantly lower in photorefractory birds and significantly higher in long-term photostimulated birds. These results indicate that the inverse relationship between circulating prolactin (released by VIP) and luteinizing hormone (released by GnRH) during refractoriness may result from neural changes in VIP and GnRH expression, respectively.

Original languageEnglish (US)
Pages (from-to)128-136
Number of pages9
JournalGeneral and Comparative Endocrinology
Volume93
Issue number1
DOIs
StatePublished - Jan 1994
Externally publishedYes

Fingerprint

Junco hyemalis
vasoactive intestinal peptide
Vasoactive Intestinal Peptide
gonadotropin-releasing hormone
Gonadotropin-Releasing Hormone
Birds
birds
Gonads
luteinizing hormone
Luteinizing Hormone
prolactin
Prolactin
gonads
neurons
preoptic area
Gastrointestinal Hormones
brain
Neurons
Preoptic Area
Peptide Hormones

ASJC Scopus subject areas

  • Endocrinology

Cite this

Increased VIP and Decreased GnRH Expression in Photorefractory Dark-Eyed Juncos (Junco hyemalis). / Saldanha, Colin J.; Deviche, Pierre; Silver, Rae.

In: General and Comparative Endocrinology, Vol. 93, No. 1, 01.1994, p. 128-136.

Research output: Contribution to journalArticle

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