Identification of salsolinol in the mediobasal hypothalamus of lactating ewes and its relation to suckling-induced prolactin and GH release

Abstract

The push-pull perfusions of the infundibular nucleus-median eminence (IN/ME) were made in lactating ewes (nZ7) twice, to identify dopamine (DA)-derived salsolinol and the changes in its extracellular concentration in response to suckling. The perfusate collecting period in every ewe consisted of control non-suckling period, 1000-1230 h (five perfusates), and suckling period, 1230-1500 h (next five perfusates). Simultaneously, blood samples were collected from 1000 to 1500 h at 10-min intervals. The perfusate concentrations of salsolinol and DA were measured by HPLC, and plasma prolactin and GH concentrations were assayed by the RIA. Mean concentrations of salsolinol in perfusates collected from the anterior and posterior parts of the IN/ME (according to post-mortem localization of a perfusion site) increased significantly (P!0 . 05 and P!0 . 001 respectively) during the suckling period, when compared with those noted during the non-suckling period. While no DA was found in the anterior part, only vestigial amounts of DA were found in a few perfusates collected from the posterior part. Salsolinol was not detected in the IN/ME of ewes 10 weeks after weaning (seasonal anoestrus). Mean plasma prolactin and GH concentrations during suckling were significantly (P!0 . 001) higher than those noted during the non-suckling period. In conclusion, our current study reveals that salsolinol is present in the IN/ME of lactating ewes and that its extracellular concentration increases during suckling. Moreover, it supports the role of salsolinol as a neurotransmitter involved in the regulatory process of prolactin secretion at least during lactation.

Prolactin and the physiological regulation of its secretion. A review

“…Suckling is a one among many other powerful stimulators for PRL secretion in mammals (Grattan, 2002;Misztal et al, 2008Misztal et al, , 2010a. The stimulatory action of suckling on PRL release might result from many processes, which most important are two: a decrease of inhibitory effect of DA and other inhibitors of PRL release, and an increase of stimulatory secretagogue on lactotrophs and/or both of these events (Ben-Jonathan and Hnasko, 2001;Stojilkovic et al, 2010;Tachibana et al, 2011).…”

“…Indeed, the opioid peptides reduce hypothalamic dopaminergic system activity in rats by marked suppression of tyrosine hydroxylase gene expression during lactation (Arbogast and Voogt, 1998). More recently, attention has been paid for a DA-derived product, salsolinol, (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, Figure 1), which stimulatory properties for prolactin secretion were described either in rodents or ruminants (Toth et al, 2001(Toth et al, , 2002Hashizume et al, 2008 a,b;Misztal et al, 2008, 2010aHasiec et al, 2012).…”

“…1-MeDIQ was proved to be very potent inhibitor of salsolinolinduced PRL release and blocked PRL release in suckling and stressed lactating rats (Bodnar et al, 2004). Since the stimulatory action of salsolinol on PRL release might occur at the hypothalamic as well as at the pituitary level (Toth et al, 2001(Toth et al, , 2002Hashizume et al, 2008a;Misztal et al, 2008Misztal et al, , 2010bGórski et al, 2010;Hasiec et al, 2012) it is assumed that salsolinol can act indirectly through modulation of the dopaminergic system in the hypothalamus as well as directly through stimulation of specific receptors in pituitary gland. Although exact salsolinol receptors have not been found on prolactin cells the stimulatory effect of salsolinol on PRL release from lactotrophs has been observed in the studies using cell culture systems in rats (Toth et al, 2001) and young 7-8-month old heifers (Hashizume et al, 2008a) but not on 1 month old animals (Hashizume et al, 2009).…”

The Effect of Physiological and Environmental Factors on the Prolactin Profile in Seasonally Breeding Animals

“…Another important compound stimulating the release of prolactin induced by sucking is represented by salsolinol produced by the dopaminergic system in the lactation period. Infusion of exogenous salsolinol into the CNS in the group of lactating sheep gave rise to the release of prolactin into blood [31].…”

Up-regulation of oxytocin receptor gene and protein in the sheep anterior pituitary by a dopamine derivative (salsolinol)

“…As a dopamine derivate, salsolinol has been generally associated with dysfunction of dopaminergic neurons, though presently it is also considered to be a physiological stimulator of PRL release in rodents (Toth et al 2001) and ruminants (Hashizume et al 2008;Misztal et al 2008). In lactating sheep, the suckling stimulus increases the extracellular content of salsolinol in the infundibular nucleus-median eminence, simultaneously with PRL release into the peripheral circulation (Misztal et al 2008). Intracerebroventricular (i.c.v.)…”