Konrad Górski

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

The push-pull perfusions of the infundibular nucleus-median eminence (IN/ME) were made in lactating ewes (n=7) 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.

The Possible Involvement of Salsolinol and Hypothalamic Prolactin in the Central Regulatory Processes in Ewes During Lactation

Salsolinol, a dopamine-related compound and prolactin-producing cells were found in the ovine hypothalamus. This study was designed to test the hypothesis that salsolinol, acting from the CNS level, is able to stimulate pituitary prolactin release as well as prolactin mRNA expression in the anterior pituitary cells (AP) and in the mediobasal hypothalamus (MBH) in lactating ewes. The intracerebroventricular infusions of salsolinol in two doses, total of 50 ng or 5 μg, were performed in a series of five 10-min infusions at 20-min intervals. All infusions were made from 12:30 to 15:00 and the pre-infusion period was from 10:00 to 12.30 h. The prolactin concentration in plasma samples, collected every 10 min, was determined by radioimmunoassay; prolactin mRNA expression in AP and MBH tissues was determined by real-time PCR. The obtained results showed that salsolinol infused at the higher dose significantly (p < 0.001) increased plasma prolactin concentration in lactating ewes, when compared with the concentration noted before the infusion and with that in lactating controls. In lactating ewes, the relative levels of prolactin mRNA expression in the AP and MBH were up to twofold and fivefold higher respectively than in non-lactating ewes (p < 0.05). In our experimental design, salsolinol did not significantly affect the ongoing process of prolactin gene expression in these tissues. We conclude that in ewes, salsolinol may be involved, at least, in the process of stimulation of prolactin release during lactation and that hypothalamic prolactin plays an important role in the central mechanisms of adaptation to lactation.

Effects of a structural analogue of salsolinol, 1-MeDIQ, on pituitary prolactin release and dopaminergic activity in the mediobasal hypothalamus in nursing sheep.

The prolactin release caused by salsolinol (a derivative of dopamine, DA) in rats could be prevented by its structural analogue 1-methyl-3,4-dihydroisoqinoline (1-MeDIQ). To study the participation of salsolinol in the neural stimulatory mechanism of prolactin release in lactating sheep, we tested whether 1-MeDIQ, acting at the central nervous system (CNS) level, would diminish basal prolactin release and reduce prolactin surge induced by suckling. A series of intracerebroventricular (icv) infusions of 1-MeDIQ (5 x 60 microg/60 microl/30 min, at 30-min intervals) were performed in nursing ewes (n=8) during the fifth week of lactation. Additionally, by combining these infusions with push-pull perfusion, we studied the concentration of dopaminergic components, i.e., salsolinol, DA and 3,4-dihydroxyphenylacetic acid (DOPAC) within the infundibular nucleus/median eminence (IN/ME) in four of the ewes. Treatment with 1-MeDIQ significantly (P<0.001) reduced either the basal prolactin release during the non-suckling period or the suckling-induced prolactin surge. Specifically, the suppressive effect occurred gradually, affecting both the duration and amplitude of the prolactin surge. In the control ewes, the perfusate salsolinol concentration increased significantly (P<0.001) during suckling, while in the ewes treated with 1-MeDIQ only vestigial amounts of this compound were found during the non-suckling period. No DA was detected in the perfusates collected from the IN/ME of control and 1-MeDIQ-treated groups and no significant differences were found in the DOPAC concentrations between these groups. In conclusion, 1-MeDIQ is able to inhibit prolactin secretion in lactating sheep, acting at the CNS level. In addition, one of the way of 1-MeDIQ action may be directed to the local salsolinol release within the mediobasal hypothalamus.

Salsolinol Up-Regulates Oxytocin Expression and Release During Lactation in Sheep.

Salsolinol (1‐methyl‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline) is a dopamine‐derived compound present in the central nervous system and pituitary gland. Several previous studies on lactating sheep and rats have reported that salsolinol plays a crucial role in the regulation of prolactin secretion. The present study investigated the effects of salsolinol, which was infused into the third ventricle of the brain, on oxytocin expression and release in lactating sheep, 48 h after weaning of 8‐week‐old lambs. Serial 30‐min infusions of salsolinol and vehicle were performed at 30‐min intervals from 10.00 to 15.00 h. Blood samples were collected every 10 min. The supraoptic nucleus (SON), paraventricular nucleus (PVN) and posterior pituitary were collected immediately after the experiment. Expression levels of mRNAs for oxytocin and peptidylglycine α‐amidating monooxygenase (PAM), the terminal enzyme in the oxytocin synthesis pathway, were measured using a real‐time polymerase chain reaction. Oxytocin peptide content in the posterior pituitary was measured by an enzyme‐linked immunosorbent assay, and plasma oxytocin concentration was measured by radioimmunoassay. Salsolinol treatment significantly up‐regulated oxytocin and PAM gene expression in the SON (P < 0.01 and P < 0.05, respectively), PVN (P < 0.01 and P < 0.05, respectively) and posterior pituitary (P < 0.05 and P < 0.05, respectively). Oxytocin peptide content in the posterior pituitary and the area under the response curve of plasma oxytocin were significantly (P < 0.05 and P < 0.01, respectively) higher in salsolinol‐treated sheep than in control animals. The present study shows for the first time that salsolinol stimulates oxytocin secretion during lactation in sheep.

Opioid-salsolinol relationship in the control of prolactin release during lactation

Endogenous opioid peptides (EOP) and dopamine (DA)-derived salsolinol are implicated in the suckling-induced prolactin surge. The aim of this study was to investigate the relationship between the opioidergic and salsolinergic activity in the mediobasal hypothalamus of nursing sheep. The sheep were infused intracerebroventricularly with opioid receptors antagonists: naloxone (all types of receptors, n=6); naloxonazine (μ receptor, n=6) or the vehicle (control, n=6) in a series of five 30-min infusions (60 μg/60 μl) from 10:00 to 15:00, at 30-min intervals. The period of the experiment included the non-suckling (10:00-12:30) and suckling (12:30-15:00) periods. Simultaneously, a push-pull perfusion of the infundibular nucleus/median eminence was performed in every sheep to study the dopaminergic system activity. Blood samples were also collected at 10-minute intervals to determine plasma prolactin concentration. Both the mean perfusate salsolinol and plasma prolactin concentrations were higher during the suckling vs. non-suckling (P<0.001) period in the control. The perfusate DA concentration was below the detection limit in this group. Treatment with either naloxone or naloxonazine significantly (P<0.01) diminished plasma prolactin concentration, as compared with the controls and blocked the prolactin surge during suckling. In drug-infused sheep, the perfusate salsolinol concentration was below the detection limit but the increased DA and its metabolite 3,4-dihydroxyphenylacetic acid concentrations were observed. In conclusion, the stimulatory action of EOP on prolactin secretion in nursing females is mediated, at least in part, by salsolinol, and the ligands for μ opioid receptor may be the primary factors of this relationship, especially with respect to the suckling-induced prolactin surge.

Different types of opioid receptors involved in the suppression of LH secretion in lactating sheep

To learn the involvement of endogenous opioid peptides (EOP) in the regulation of reproductive activity in ruminants, the effects of different opioid antagonists on luteinizing hormone (LH) secretion were determined in sheep during the early stage of lactation. The opioid receptor antagonists: naloxone (all types of receptors, n=5), naloxonazine (μ receptor, n=5), GNTI- (κ receptor, n=5), naltrindole (δ receptor, n=5) or the vehicle (control, n=5) were infused intracerebroventricularly in a series of five 30-min infusions (60μg/60μl) at 30-min intervals. The period of the experiment included the non-suckling (10:00-12.30) and suckling (12.30-15.00) periods. Blood samples were collected from 10.00 to 15.00 at 10-min intervals, and plasma LH concentration was assayed by the radioimmunoassay method. The obtained results showed that blocking of the EOP action within the central nervous system in lactating sheep caused a significant (p<0.001) increase in LH concentration in all treated groups, in comparison to the control. In the naloxone-treated group, a significant (p<0.05) increase in LH secretion also occurred during suckling. The amplitude of LH pulses increased significantly in the naloxonazine- (p<0.01) and naltrindole- (p<0.05) treated ewes compared to the control; there were no significant differences in the frequency of LH pulses among the groups. In conclusion, our study indicates that EOP play a crucial role in the mechanism inhibiting GnRH/LH axis activity in lactating sheep and that the ligands for μ opioid receptor may have the highest inhibitory effect.

Does nanobiotechnology create new tools to combat microorganisms

Abstract Antimicrobial resistance is still a crucial global problem related to the overuse of antibiotics and natural microorganism capability for rapid horizontal evolution. Even new generations of drugs are not able to overcome bacterial defence mechanisms. A novel solution for this immense medical challenge can be nanomaterials. Researchers indicate that modern nanoforms can effectively support and perhaps in the long-term replace traditional bactericidal agents. Because of their unique physicochemical properties, nanotechnology products can exert multiple actions against bacteria, which might be efficient against even multidrug-resistant pathogens. In this review, we discuss the documented achievements and concerns associated with broad potential applications of nanoforms in the fight against microorganisms.