Pathways for GnRH control of elasmobranch reproductive physiology and behavior

✍ Scribed by Demski, Leo S.

• Book ID: 102892990
• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 958 KB
• Volume: 252
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402520403

✦ Synopsis

In elasmobranchs, seasonal and developmental changes in reproduction and sexual behavior appear to be regulated by gonadotropin-releasing hormone (GnRH). Circumstantial evidence indicates that GnRH control is primarily via the systemic circulation to pituitary gonadotrophs in the ventral lobe. Additional GnRH effects on other pituitary gonadotrophs and the gonads may also be important. Several forms of GnRH have been reported in sharks and rays; however, the functional significance of the different types is unknown. While immunoreactive-GnRH is present in the preoptic area and hypothalamus, there appears to be little GnRH-staining in the median eminence region. The observations are consistent with a major nonportal distribution of GnRH. Recent studies suggest that the terminal nerve (TN) may be a major source of GnRH. The TN extends from the olfactory sac to the basal telencephalon. It contains abundant immunoreactive-GnRH and has endings in cerebral blood vessels where processes packed with dense-cored vesicles sit adjacent to endothelial cells with active vesicle formation indicative of transcytosis. The TN also projects centrally into the septopreoptic area. The structure may distribute GnRH, both directly to brain nuclei and the olfactory epithelium via synaptic connections and indirectly to brain areas and peripheral reproductive tissues via systemic blood. TN activity may be modulated either through afferent chemical stimulation or via synaptic output from the brain. The results are summarized in a model of suggested neural and endocrine pathways involved in elasmobranch reproduction.