Molecular and Cellular Endocrinology 156 (1999) 45 – 53 Evidence for regulation of basic fibroblast growth factor gene expression by photoperiod and melatonin in the ovine pars tuberalis E. Scott Graham a,b, *, David G. Hazlerigg b , Peter J. Morgan a a Molecular Neuroendocrinology Unit, Rowett Research Institute, Greenburn Rd, Bucksburn, Aberdeen, AB21 9SB, UK b Department of Agriculture, Uniersity of Aberdeen, MacRobert Building, 581 King Street, Aberdeen, AB24 5UA, UK Received 3 March 1999; accepted 2 July 1999 Abstract In the ovine pituitary the in vivo expression of the bFGF gene was studied using in situ hybridisation and Northern analysis. Expression of bFGF mRNA was highest in the pars tuberalis (PT) and zona tuberalis (ZT) and this expression was higher in the pituitaries of animals acclimited to long days than in those from short day housed animals. Expression in the pars intermedia (PI) was also detectable but the pars distalis (PD) showed negligible expression compared with the PT. Regulation of bFGF gene was investigated in primary cultured PT cells. Both forskolin and PMA increased bFGF mRNA expression significantly and melatonin was able to inhibit these effects partially, however there was no independent effect of melatonin on bFGF mRNA levels. Despite the inducibility of the bFGF gene, bFGF protein levels in PT culture media were insensitive to the same stimuli and detectable bFGF protein declined with time. Exogenous bFGF had no effect on c -fos mRNA levels and did not increase prolactin secretion from ovine lactotrophs. In contrast c -fos mRNA was induced in GH3 cells by bFGF. These data suggest that although basic fibroblast growth factor (bFGF) mRNA expression in the ovine PT is photoperiodically-sensitive, it is not directly involved in the seasonal regulation of lactotrophic activity. © 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Pars tuberalis; Melatonin; Pituitary; c -fos ; Pars distalis; Photoperiod www.elsevier.com/locate/mce 1. Introduction Seasonal changes in mammalian physiology and be- haviour result from changes in endocrine hormone levels driven by photoperiod (Wittkowski et al., 1988; Curlewis, 1992; Lincoln, 1994; Badura, 1996). The am- bient photoperiod is transduced through the pineal hormone melatonin, but the molecular basis of mela- tonin action is incompletely understood (Morgan et al., 1994; Morgan and Williams, 1996). All seasonally sen- sitive animals studied to date, express melatonin recep- tors in the pars tuberalis (PT) of the anterior pituitary. This finding has led to speculation that the PT may be involved in the processing of photoperiodic information via melatonin (reviewed by Morgan et al., 1994). The PT is ideally located to communicate with the pars distalis (PD) (Fitzgerald, 1979) and potentially affect endocrine hormone production. Indirect evidence that the PT indeed plays such a role may be derived from the observation that photoperiodic cycles of prolactin persist in hypothalamo-pituitary disconnected (HPD) rams (Lincoln and Clarke, 1994). This surgical manipu- lation excludes the involvement of hypothalamic fac- tors, such as thyrotropin-releasing hormone (TRH) (Sheward et al., 1985), prolactin-releasing peptide (PrRP) (Hinuma et al., 1998) or dopamine (DA) (Ben- Jonathan, 1985). A role for the PT in seasonal control of prolactin secretion is also suggested by in vitro observations which have shown that the ovine PT (oPT) produces an unidentified prolactin releasing fac- tor that has been called tuberalin (Hazlerigg et al., 1996; Morgan et al., 1996). Many bioactive molecules have been implicated in the regulation of prolactin secretion. Of these, basic fibroblast growth factor (bFGF) is notable for the high * Corresponding author. E-mail address: pjm@rri.sari.ac.uk (E. Scott Graham) 0303-7207/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved. PII:S0303-7207(99)00146-X