Central administration of serotonin decreases tyrosine hydroxylase catalytic activity and messenger ribonucleic Acid signal levels in the hypothalamus of female rats

Pharmacological strategies for sexual recovery in men undergoing antipsychotic treatment

INTRODUCTION

: First- and second-generation antipsychotics are highly accountable for causing a plethora of medical side effects, ranging from metabolic imbalances to sexual dysfunction (SD), that frequently undermine patient-doctor relationships. Nevertheless, to date antipsychotics are one of the best treatment options for dealing with numerous either acute or chronic conditions like agitation, suicidality, depression, dementia, and of course psychosis. For these reasons, clinicians need to handle them wisely to preserve patients' sexual health, avoid poor therapeutic adherence and prevent high rates of therapy drop-out.

AREAS COVERED

: This article reviews the literature on pharmacologic approaches for management strategies in men who are administered with antipsychotics and developed SD. The etiology of antipsychotic-induced SD is also discussed.

EXPERT OPINION

: Clinicians must consider sexual life as a major health domain. To do so, a first step would be to measure and monitor sexual function by means of psychometric tools. Secondly, primary prevention should be conducted when choosing antipsychotics, i.e., picking sex-sparing compounds like aripiprazole or brexpiprazole. Thirdly, if sexolytic compounds cannot be dismissed, such as first-generation antipsychotics, risperidone, paliperidone, or amisulpride, then aripiprazole 5-20 mg/day adjunctive therapy has proven to be most effective in normalizing prolactin levels and consequently treating antipsychotic-induced SD.

Neuroendocrine regulation of lactation and milk production

Prolactin (PRL) released from lactotrophs of the anterior pituitary gland in response to the suckling by the offspring is the major hormonal signal responsible for stimulation of milk synthesis in the mammary glands. PRL secretion is under chronic inhibition exerted by dopamine (DA), which is released from neurons of the arcuate nucleus of the hypothalamus into the hypophyseal portal vasculature. Suckling by the young activates ascending systems that decrease the release of DA from this system, resulting in enhanced responsiveness to one or more PRL-releasing hormones, such as thyrotropin-releasing hormone. The neuropeptide oxytocin (OT), synthesized in magnocellular neurons of the hypothalamic supraoptic, paraventricular, and several accessory nuclei, is responsible for contracting the myoepithelial cells of the mammary gland to produce milk ejection. Electrophysiological recordings demonstrate that shortly before each milk ejection, the entire neurosecretory OT population fires a synchronized burst of action potentials (the milk ejection burst), resulting in release of OT from nerve terminals in the neurohypophysis. Both of these neuroendocrine systems undergo alterations in late gestation that prepare them for the secretory demands of lactation, and that reduce their responsiveness to stimuli other than suckling, especially physical stressors. The demands of milk synthesis and release produce a condition of negative energy balance in the suckled mother, and, in laboratory rodents, are accompanied by a dramatic hyperphagia. The reduction in secretion of the adipocyte hormone, leptin, a hallmark of negative energy balance, may be an important endocrine signal to hypothalamic systems that integrate lactation-associated food intake with neuroendocrine systems.

TIDAL WAVES: Network mechanisms in the neuroendocrine control of prolactin release

Neuroendocrine tuberoinfundibular dopamine (TIDA) neurons tonically inhibit pituitary release of the hormone, prolactin. Through the powerful actions of prolactin in promoting lactation and maternal behaviour while suppressing sexual drive and fertility, TIDA neurons play a key role in reproduction. We summarize insights from recent in vitro studies into the membrane properties and network behaviour of TIDA neurons including the observations that TIDA neurons exhibit a robust oscillation that is synchronized between cells and depends on intact gap junction communication. Comparisons are made with phasic firing patterns in other neuronal populations. Modulators involved in the control of lactation - including serotonin, thyrotropin-releasing hormone and prolactin itself - have been shown to change the electrical behaviour of TIDA cells. We propose that TIDA discharge mode may play a central role in tuning the amount of dopamine delivered to the pituitary and hence circulating prolactin concentrations in different reproductive states and pathological conditions.

Inhibitory effect of neural transections of dorsal raphe nucleus on induction of nocturnal prolactin surge by vaginal stimulation in ovariectomized rats

The effect of complete (CC), anterior (AC) or posterior (PC) cut of the dorsal raphe nucleus (DRn) on induction of the nocturnal prolactin (PRL) surge by electrical vaginal stimulation (VS) was investigated in ovariectomized rats. Plasma level of PRL was measured by radioimmunoassay before and after VS. The data revealed that PRL levels increased in early morning on the day following VS in the rats without brain surgery or with sham-operation. In contrast, the nocturnal PRL surge did not occur in the CC, AC, or PC rats. These results suggest that both the anterior and the posterior fibers of the DRn plays an important role in induction of nocturnal PRL surge by VS in ovariectomized rats.

Effect of deprivation of serotonin by p-chlorophenylalanine on induction and maintenance of pseudopregnancy in female rats

The effect of serotonin synthesis inhibitor, p-chlorophenylalanine (PCPA), on induction and maintenance of pseudopregnancy as indicated by deciduoma formation was examined in female rats. Animals were injected with 1 mg/kg b.wt. of reserpine on the day of metestrus, and silk thread was passed through and placed in the left uterine horn 3 days after reserpine to induce deciduoma. PCPA (100 mg/kg b.wt.) was injected daily for 4 days before or after reserpine in 15 and 13 rats, respectively. A single injection of PCPA was administered before reserpine in nine females. In another group of rats (N = 16), instead of PCPA, saline was injected four times before reserpine. Nineteen female rats were treated with reserpine only as a control group. Results showed 89% of the control and 81.3% of the saline-treated females had massive deciduoma in traumatized uterine horn. In contrast, only 33.3% or 46.2% females with daily treatments of PCPA for 4 days before or after reserpine showed positive decidual reaction. In addition, 88.9% of females with single injection of PCPA possessed uterine horns with deciduoma. These results suggest that 4 days of treatment with PCPA eliminate induction and/or maintenance of pseudopregnancy. Thus, some levels of serotonin are required to induce and maintain pseudopregnancy.

Effect of morphine on hypothalamic tyrosine hydroxylase mRNA levels in dopaminergic neurons and on preoptic DOPAC levels measured by microdialysis

Morphine not only suppresses norepinephrine-induced increases in LHRH mRNA levels but, in these same animals, it simultaneously amplifies norepinephrine (NE)-induced LH release. These observations suggest that NE may activate parallel mechanisms which independently increase LHRH mRNA levels and LHRH release and suggest that some of these effects could be mediated indirectly via morphine's action on different components of the hypothalamic dopamine (DA) system. Accordingly, in the present studies we examined the effects of morphine on various components of this dopamine system using as our index of altered DA neuronal activity, the changes which occur in tyrosine hydroxylase (TH) mRNA levels following morphine. As an ancillary index of changes which occur in dopamine neuronal activity, we measured, by microdialysis, the changes which occur in preoptic dihydroxyphenylacetic acid (DOPAC) levels after either subcutaneous injections or following microinfusions of morphine into the zona incerta (ZI). In a final study, we evaluated whether DA when given alone (icv infusion) or prior to icv NE would altered LH release. Single cell levels of TH mRNA in preoptic A15 and periventricular anterior hypothalamic A14 DA neurons were not affected by morphine 1, 5 and 24 h later. In contrast, within 1 h after morphine, TH mRNA levels in ZI A13 neurons were significantly elevated and they remained high at 5 nd 24 h compared to controls. Morphine also resulted in a significant rise in TH mRNA levels in tuberoinfundibular DA neurons (TIDA) (A12) within 1 h and these levels remained high to 5 h. Thereafter, by 24 h, message levels had returned to control values. Morphine also resulted in a rapid rise in plasma prolactin (Prl) with peak values occurring at 20 min and then returning to baseline by 90 min. When morphine was given sc it resulted, within 15 min, in a rapid rise in preoptic DOPAC levels and these levels continued to rise such that they were 217% higher than pretreatment values by 105 min. Preoptic 5-hydroxyindoleacetic acid (5-HIAA) levels also increased by 25-75% after sc morphine. The microinfusion of morphine into ZI also resulted in elevated preoptic DOPAC but not 5-HIAA levels within 15 min. The icv infusion of DA alone had no effect on plasma LH whereas, NE (icv) produced a modest but significant increase in plasma LH. When DA was given 15 min prior to the infusion of NE, neither amplification nor inhibition of NE-induced LH release occurred. From these and other studies we conclude that the morphine-induced suppression of TIDA neuronal activity may allow NE to release greater amounts of LHRH from axon terminals in the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)