The beneficial metabolic actions of prolactin

Traumatic brain injury and prolactin

Traumatic brain injury (TBI) is a well-known etiologic factor for pituitary dysfunctions, with a prevalence of 15% during long-term follow-up. The most common hormonal disruption is growth hormone deficiency, followed by central adrenal insufficiency, central hypogonadism, and central hypothyroidism in varying order across studies. The prevalence of serum prolactin disturbances ranged widely from 0 to 85%. Prolactin release is mainly regulated by hypothalamic dopamine inhibition, and mediators such as TRH, serotonin, cytokines, and neurotransmitters have modulatory effects. Many factors, such as hypothalamic and/or pituitary gland injuries, as well as fluctuations in dopaminergic activity and other mediators and stress response, may cause derangements in serum prolactin levels after TBI. Although it is challenging to investigate the direct effects of TBI on serum prolactin levels due to many confounders, basal prolactin measurements and stimulation tests provide insight into the functionality of the hypothalamus and pituitary gland after TBI. Moreover, during the acute phase of TBI, prolactin levels appear to correlate with TBI severity. In contrast, in the chronic phase, hypoprolactinemia may function as an indirect indicator of pituitary dysfunction and reduced pituitary volume. Further investigations are needed to elucidate the pathophysiologic mechanisms underlying the prolactin trend following TBI, its significance, and its associations with other pituitary hormone dysfunctions. In this article, we re-evaluated our patients' TBI data regarding prolactin levels during prospective long-term follow-up, and reviewed the literature regarding the prevalence, pathophysiology, and clinical implications of serum prolactin disturbances during acute and chronic phases following TBI.

A Century of Prolactin: Emerging Perspectives as a Metabolic Regulator

Prolactin, a hormone that has been studied for almost a century, has evolved from a reproductive regulator to a key player in metabolic health. Initially identified for its lactogenic role, the impact of prolactin on glucose and lipid metabolism became evident in the 1970s, leading to a paradigm shift in our understanding. Deviations in prolactin levels, including hyperprolactinaemia and hypoprolactinaemia, have been associated with adverse effects on glucose and lipid metabolism. Mechanistically, prolactin regulates metabolic homoeostasis by maintaining islet abundance, regulating the hypothalamic energy regulatory centre, balancing adipose tissue expansion, and regulating hepatic metabolism. Given the widespread use of pharmaceutical agents that affect prolactin levels, it is important to examine prolactin-related metabolic effects. Recently, a profound exploration of the intricate metabolic role of prolactin has been conducted, encompassing its rhythm-dependent regulatory influence on metabolism and its correlation with cognitive impairment associated with metabolic diseases. In this review, we highlight the role of prolactin as a metabolic regulator, summarise its metabolic effects, and discuss topics related to the association between prolactin and metabolic comorbidities.

Could low prolactin levels after radiotherapy predict the onset of hypopituitarism?

Both local and external cranial radiotherapy (RT) can induce neurotoxicity and vascular damage of the hypothalamic-pituitary area, which can promote neuroendocrine alterations. While anterior pituitary insufficiency after RT has been extensively characterized, data on the effect of RT on prolactin (PRL) secretion are limited and heterogeneous, with different patterns of PRL behavior described in the literature. A progressive decline in PRL levels, reflecting a time-dependent, slowly evolving radiation-induced damage to the pituitary lactotroph cells has been reported. To date, the association between hypopituitarism and hypoprolactinemia in patients undergoing RT has not yet been fully investigated. The few available data suggest that lower PRL levels can predict an extent damage of the pituitary tissue and a higher degree of hypothalamic dysfunction. However, most studies on the effect of RT on pituitary function do not properly assess PRL secretion, as PRL deficiency is usually detected as part of hypopituitarism and not systematically investigated as an isolated disorder, which may lead to an underestimation of hypoprolactinemia after RT. In addition, the often-inadequate follow-up over a long period of time may contribute to the non-recognition of PRL deficiency after RT. Considering that hypoprolactinemia is associated with various metabolic complications, there is a need to define appropriate diagnostic and management criteria. Therefore, hypoprolactinemia should enter in the clinical investigation of patients at risk for hypopituitarism, mainly in those patients who underwent RT.

Neuregulin 1 mitigated prolactin deficiency through enhancing TRPM8 signaling under the influence of melatonin in senescent pituitary lactotrophs

The age-related alterations in pituitary function, including changes in prolactin (PRL) production contributes to the systemic susceptibility to age-related diseases. Our previous research has shown the involvement of Nrg1 in regulating the expression and secretion of PRL. However, the precise role of Nrg1 in mitigating the senescence of pituitary lactotrophs and the underlying mechanisms are yet to be comprehended. Here, data from the GEPIA database was used to evaluate the association between transient receptor potential cation channel subfamily M member 8 (TRPM8) and PRL in normal human pituitary tissues, followed by immunofluorescence verification using a human pituitary tissue microarray. TRPM8 levels showed a significant positive association with PRL expression in normal human pituitary tissues, and both TRPM8 and PRL levels declined during aging, suggesting that TRPM8 may regulate pituitary aging by affecting PRL production. It was also found that treatment with exogenous neuregulin 1 (Nrg1) markedly delayed the senescence of GH3 cells (rat lactotroph cell line) generated by D-galactose (D-gal). In addition, melatonin reduced the levels of senescence-related markers in senescent pituitary cells by promoting Nrg1 / ErbB4 signaling, stimulating PRL expression and secretion. Further investigation showed that Nrg1 attenuated senescence in pituitary cells by increasing TRPM8 expression. Downregulation of TRPM8 activation eliminated Nrg1-mediated amelioration of pituitary cell senescence. These findings demonstrate the critical function of Nrg1 / ErbB signaling in delaying pituitary lactotroph cell senescence and enhancing PRL production via promoting TRPM8 expression under the modulation of melatonin.

Cardiometabolic effects of hypoprolactinemia

The fall of PRL levels below the lower limit of the normal range configures the condition of hypoprolactinemia. Unlike PRL excess, whose clinical features and treatments are well established, hypoprolactinemia has been only recently described as a morbid entity requiring prompt identification and proper therapeutic approach. Particularly, hypoprolactinemia has been reported to be associated with the development of metabolic syndrome and impaired cardiometabolic health, as visceral obesity, insulin-resistance, diabetes mellitus, dyslipidaemia, chronic inflammation, and sexual dysfunction have been found more prevalent in patients with hypoprolactinemia as compared to those with normoprolactinemia. This evidence has been collected mainly in patients on chronic treatment with dopamine agonists for PRL excess due to a PRL-secreting pituitary tumour, and less frequently in those receiving the atypical antipsychotic aripiprazole. Nowadays, hypoprolactinemia appears to represent a novel and unexpected risk factor for cardiovascular diseases, as is the case for hyperprolactinemia. Nevertheless, current knowledge still lacks an accurate biochemical definition of hypoprolactinemia, since no clear PRL threshold has been established to rule in the diagnosis of PRL deficiency enabling early identification of those individual subjects with increased cardiovascular risk directly ascribable to the hormonal imbalance. The current review article focuses on the effects of hypoprolactinemia on the modulation of body weight, gluco-insulinemic and lipid profile, and provides latest knowledge about potential cardiovascular outcomes of hypoprolactinemia.

Diagnosis of hypoprolactinemia

Prolactin is a polypeptide hormone composed of 199 amino acids, synthesized by lactotroph cells. Its primary effects are on the mammary gland and gonadal axes, but it also influences different organs and systems, particularly metabolic functions. Current literature has mainly focused on the diagnosis, monitoring, and treatment of hyperprolactinemia. Due to the lack of a well-established effective treatment for hypoprolactinemia, it is not clinically emphasized. Therefore, data on its diagnosis is limited. Hypoprolactinemia has been associated with metabolic dysfunctions such as type 2 diabetes mellitus, fatty liver, dyslipidemia, fertility problems, sexual dysfunction, and increased cardiovascular disease. While often seen as a part of combined hormone deficiencies due to pituitary damage, isolated prolactin deficiency is rare. Hypoprolactinemia can serve as a marker for extensive pituitary gland damage and dysfunction.Low or undetectable serum prolactin levels and the absence of a sufficient prolactin peak in the thyrotropin-releasing hormone (TRH) stimulation test are considered diagnostic for hypoprolactinemia. Gender appears to influence both basal prolactin levels and TRH stimulation test responses. Basal prolactin levels of, at least, 5 ng/mL for males and 7 ng/mL for females can be used as cut-off levels for normal prolactin reserve. Minimum peak prolactin responses of 18 ng/mL for males and 41 ng/mL for females to TRH stimulation can exclude hypoprolactinemia. However, larger population studies across different age groups and sexes are needed to better define normal basal prolactin levels and prolactin responses to the TRH stimulation test.

Diagnosing and treating the elderly individual with hypopituitarism

Hypopituitarism in the elderly is an underestimated condition mainly due to the non-specific presentation that can be attributed to the effects of aging and the presence of comorbidities. Diagnosis and treatment of hypopituitarism often represent a challenging task and this is even more significant in the elderly. Diagnosis can be insidious due to the physiological changes occurring with aging that complicate the interpretation of hormonal investigations, and the need to avoid some provocative tests that carry higher risks of side effects in this population. Treatment of hypopituitarism has generally the goal to replace the hormonal deficiencies to restore a physiological balance as close as possible to that of healthy individuals but in the elderly this must be balanced with the risks of over-replacement and worsening of comorbidities. Moreover, the benefit of some hormonal replacement therapies in the elderly, including sex hormones and growth hormone, remains controversial.

The diagnosis and prevalence of hypoprolactinemia in patients with panhypopituitarism and the effects on depression and sexual functions

PURPOSE

We aimed to investigate the prevalence and the diagnostic criteria of hypoprolactinemia in patients with panhypopituitarism and the effects of hypoprolactinemia on depression and sexual functions.

MATERIALS AND METHODS

Forty-eight patients with panhypopituitarism and 20 healthy volunteers were included. Basal hormone levels were measured and a TRH stimulation test was performed. For the evaluation of sexual functions, questionnaries of Female Sexual Functional Index (FSFI) for females and International Erectile Functional Index for males were performed to the subjects. Depressive symptoms were evaluated by Beck Depression Envontory score (BDI-II).

RESULTS

The peak PRL response to TRH stimulation test at 5th percentile in the control group was 18.6 ng/ml in males and 41.6 ng/ml in females and accepted as the cut-offs for sufficient response of PRL. Prolactin was insufficient in 42(87.5%) patients. A basal PRL level of ≤ 5.7 ng/ml in males and 7.11 ng/ml in females was 100% specific in predicting an inadequate response to TRH stimulation test with 80% and 70% sensitivity respectively. A basal PRL level of ≥ 8.5 ng/dl in males was 100% specific and 76% sensitive, and in females a level of ≥ 15.2 ng/dl was 96% specific and 66% sensitive in predicting an adequate response to TRH. PRL deficient patients with panhypopituitarism had higher depression scores compared to the controls, lower sexual function scores in males.

CONCLUSION

PRL deficiency is prevalent among individuals with panhypopituitarism, with the potential to result in elevated depression scores in both sexes and impaired sexual functions in males. A basal PRL level seems to be sufficient for the diagnosis of hypoprolactinemia in routine clinical practice.

Correlation of Serum Prolactin Levels With Metabolic and Cardiovascular Risk in Greek Women With Polycystic Ovarian Syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a common endocrine disorder among females. PCOS is associated with various metabolic and cardiovascular complications, including insulin resistance, dyslipidemia, and an increased risk of type 2 diabetes mellitus and cardiovascular disease. The role of serum prolactin (PRL) in the development of these complications in PCOS is not well understood.

AIM

This study aims to investigate the correlation between serum PRL levels and metabolic and cardiovascular risk factors in Greek women with PCOS.

METHODS

The study utilized secondary outcomes from a prospectively collected patient database at the Third Department of Obstetrics and Gynecology, Medical School of the University of Athens. Data were collected from patients who visited the Gynecological Endocrinology - Pediatric and Adolescence Endocrinology Outpatient Clinic between January 2007 and December 2015. Measurements of various parameters, including PRL levels, BMI, waist circumference, hormone levels, lipid profiles, and insulin sensitivity, were obtained. Statistical analyses, including Mann-Whitney tests, chi-square tests, Spearman correlations, and multiple linear regression analyses, were conducted using SPSS software (IBM Corp., Armonk, NY, USA).

RESULTS

The study included 247 women with PCOS, with a mean age of 24.7 years. Participants were divided into two groups based on the median PRL level. Women with higher PRL levels (>14.9) had lower BMI and waist circumference, higher levels of certain hormones and insulin sensitivity, and lower levels of fasting insulin, total cholesterol, and total lipids. Factors associated with lower PRL levels included being overweight/obese and smoking more than 10 cigarettes per day. Higher age, BMI, waist circumference, and certain hormone levels were associated with lower PRL levels.

CONCLUSION

The findings suggest a correlation between serum PRL levels and metabolic and cardiovascular risk factors in Greek women with PCOS. Further research is needed to elucidate the role of PRL in the pathophysiology of PCOS and to explore its potential as a diagnostic and therapeutic target.

Dopamine D2 receptor antagonist counteracts hyperglycemia and insulin resistance in diet-induced obese male mice

Obesity leads to insulin resistance (IR) and type 2 diabetes. In humans, low levels of the hormone prolactin (PRL) correlate with IR, adipose tissue (AT) dysfunction, and increased prevalence of T2D. In obese rats, PRL treatment promotes insulin sensitivity and reduces visceral AT adipocyte hypertrophy. Here, we tested whether elevating PRL levels with the prokinetic and antipsychotic drug sulpiride, an antagonist of dopamine D2 receptors, improves metabolism in high fat diet (HFD)-induced obese male mice. Sulpiride treatment (30 days) reduced hyperglycemia, IR, and the serum and pancreatic levels of triglycerides in obese mice, reduced visceral and subcutaneous AT adipocyte hypertrophy, normalized markers of visceral AT function (PRL receptor, Glut4, insulin receptor and Hif-1α), and increased glycogen stores in skeletal muscle. However, the effects of sulpiride reducing hyperglycemia were also observed in obese prolactin receptor null mice. We conclude that sulpiride reduces obesity-induced hyperglycemia by mechanisms that are independent of prolactin/prolactin receptor activity. These findings support the therapeutic potential of sulpiride against metabolic dysfunction in obesity.

Prolactin levels in functional hypothalamic amenorrhea: a retrospective case-control study

PURPOSE

Functional hypothalamic amenorrhea (FHA) is due to hypothalamic dysregulation. Literature lacks data about prolactin in FHA women, although both prolactin levels and FHA are associated with stress. Moreover, polycystic ovarian morphology is common in FHA and there is an association between FHA and polycystic ovary syndrome. Thus, the aim of this study was to assess prolactin levels in FHA patients and controls with a special focus on factors influencing prolactin levels, that could be considered as "sensors" of the hypothalamic-pituitary dysregulation.

METHODS

In a retrospective cohort study, 140 women with clearly defined FHA were compared to 70 healthy, normally ovulating women matched for age. The main outcome parameter was prolactin. Factors associated with prolactin levels > 12 µg/L were tested using a multivariable binary logistic regression model.

RESULTS

The median prolactin level was 11.5 µg/L (interquartile range, IQR 7.5-14.4), which was similar to the control group (median 10.7, IQR 8.3-14.5; p = 0.065). Only two women had hyperprolactinemia (prolactin > 25 µg/L; 1.4%). In a multivariable binary logistic regression model eating disorder (odds ratio, OR 0.206; p = 0.040), excessive exercise (OR 0.280; p = 0.031) and TSH (OR 1.923; p = 0.020) were significantly associated with prolactin levels > 12 µg/L.

CONCLUSION

Women with FHA have similar prolactin levels to healthy age-matched individuals. Eating disorders and excessive exercise where associated with prolactin levels < 12 µg/L, in contrast to TSH.

Effect size and inferential statistical techniques coupled with machine learning for assessing the association between prolactin concentration and metabolic homeostasis

BACKGROUND AND OBJECTIVE

Recent guidelines classify low prolactin levels as low as <7 ng/mL and high levels as >25 ng/mL, while the "Homeostatically Functionally Increased Transient Prolactinemia" (HomeoFIT-PRL) range (25-100 ng/mL) suggests that a temporary increase in prolactin could be metabolically beneficial if no related health issues are present. The aim of this study was to investigate the association between mean prolactin concentrations and disturbances in glycidic and lipidic metabolism and to identify the gray zone associated with prolactin inflection points that correlate with these metabolic changes.

METHODS

This cross-sectional study involved 65,795 adults who underwent HOMA-IR, glucose, insulin, total cholesterol, HDL-c, LDL-c, and triglyceride tests. Data was categorized into 106 partitions based on prolactin results. Employing an approach referred to in this study as "Hierarchical Multicriteria Analysis of Differences Between Groups - Statistical and Effect Size Approach" (HiMADiG-SESA) comparing the mean concentrations of metabolic tests across prolactin ranges. A machine learning model was utilized to determine inflection points and their corresponding confidence intervals (CIs). These CIs helped establish gray zones in mean prolactin results related to metabolic changes.

RESULTS

Statistically and clinically, metabolic test means differed for prolactin <7 ng/mL, except insulin. In the HomeoFIT-PRL range, means were lower except for HDL-c. The gray zones of the mean prolactin results associated with changes in glycidic and lipidic metabolism were 9.58-12.87 ng/mL and 13.81-18.73 ng/mL, respectively.

CONCLUSION

A strong correlation was identified between mean prolactin concentrations and the results of metabolism tests below the gray zones associated with inflection points, indicating the potential role of prolactin in the appearance of metabolic disorders. Mean prolactin results can provide deeper insight into metabolic balance.

Prolactin in Polycystic Ovary Syndrome: Metabolic Effects and Therapeutic Prospects

Polycystic ovary syndrome (PCOS) is the most prevalent endocrine and metabolic disorder in premenopausal women, characterized by hyperandrogenism, ovulatory dysfunction, and polycystic ovaries. Patients frequently present comorbidities, including obesity, insulin resistance, and impaired glucose and lipid metabolism. The diverse clinical presentation may mimic various endocrine disorders, making the diagnosis challenging in some clinical circumstances. Prolactin (PRL) is a recommended biomarker in the initial diagnostic workup to rule out hyperprolactinemia (HPRL). The traditional role of PRL is linked to lactation and the reproductive system. Recent research highlights PRL's emerging role in metabolic homeostasis. PRL influences metabolism directly by interacting with the pancreas, liver, hypothalamus, and adipose tissue. Its influence on an individual's metabolism is intricately tied to its serum concentration. While deficient and very high levels of PRL can negatively affect metabolism, intermediate-normal to moderately high levels may promote metabolic health. In women with PCOS, PRL levels may be altered. Research results on different aspects of the relationship between PCOS and the impact of various levels of PRL on metabolic homeostasis are limited and inconsistent. In this narrative literature review, we comprehensively examined data on serum PRL levels in PCOS patients. We investigated the correlation between a favorable metabolic profile and serum PRL levels in this population. Furthermore, we explored the concept of beneficial PRL effects on metabolism and discussed the potential therapeutic application of dopamine agonists in PCOS treatment. Lastly, we emphasized several promising avenues for future research in this field.

Hypoprolactinemia. Does it matter? Redefining the hypopituitarism and return from a mumpsimus : "Absence of proof is not the proof of absence"

Prolactin (PRL) is secreted by the lactotroph cells in the anterior pituitary gland which is under inhibitory control of dopamine. The mature human PRL has more than 300 physiological actions including lactation, reproduction, homeostasis, neuroprotection, behavior, water and electrolyte balance, immunoregulation and embryonic and fetal development. PRL is involved in the growth and development of mammary gland, preparation of the breast for lactation in the postpartum period, synthesis of milk, and maintenance of milk secretion. Abnormalities in the synthesis and secretion of PRL may result in hyperprolactinemia or hypoprolactinemia. Although hyperprolactinemia has been extensively investigated in the literature, because of the subtle or unclearly defined symptoms, hypoprolactinemia is a less-known and neglected disorder. Failure of lactation is a well-known clinical manifestation of hypoprolactinemia. Recent studies reveal that hypoprolactinemia may have some effects beyond lactation such as increased risk for metabolic abnormalities including insulin resistance, abnormal lipid profile, obesity and sexual dysfunction. Very low level of PRL is suggested to be avoided in patients receiving dopamin agonist treatment to prevent unwanted effects of hypoprolactinemia. Another important point is that hypoprolactinemia is not included in the classification of hypopituitarism. Anterior pituitary failure is traditionally classified as isolated, partial and complete (panhypopituitarism) hypopituitarism regardless of prolactin level. Therefore, there are two kinds of panhypopituitarism: panhypopituitarism with normal or high PRL level and panhypopituitarism with low PRL level. In this review, we present two personal cases, discuss the diagnosis of hypoprolactinemia, hypoprolactinemia associated clinical picture and suggest to redefine the classification of hypopituitarism.

The Diversity of Gut Microbiota at Weaning Is Altered in Prolactin Receptor-Null Mice

Maternal milk supports offspring development by providing microbiota, macronutrients, micronutrients, immune factors, and hormones. The hormone prolactin (PRL) is an important milk component with protective effects against metabolic diseases. Because maternal milk regulates microbiota composition and adequate microbiota protect against the development of metabolic diseases, we aimed to investigate whether PRL/PRL receptor signaling regulates gut microbiota composition in newborn mice at weaning. 16SrRNA sequencing of feces and bioinformatics analysis was performed to evaluate gut microbiota in PRL receptor-null mice (Prlr-KO) at weaning (postnatal day 21). The normalized colon and cecal weights were higher and lower, respectively, in the Prlr-KO mice relative to the wild-type mice (Prlr-WT). Relative abundances (Simpson Evenness Index), phylogenetic diversity, and bacterial concentrations were lower in the Prlr-KO mice. Eleven bacteria species out of 470 differed between the Prlr-KO and Prlr-WT mice, with two genera (Anaerotruncus and Lachnospiraceae) related to metabolic disease development being the most common in the Prlr-KO mice. A higher metabolism of terpenoids and polyketides was predicted in the Prlr-KO mice compared to the Prlr-WT mice, and these metabolites had antimicrobial properties and were present in microbe-associated pathogenicity. We concluded that the absence of the PRL receptor altered gut microbiota, resulting in lower abundance and richness, which could contribute to metabolic disease development.

Improved Insulin Secretion Response and Beta-cell Function Correlated with Increased Prolactin Levels After Laparoscopic Sleeve Gastrectomy in Morbidly Obese Patients with Acanthosis Nigricans

OBJECTIVE

To explore insulin secretion patterns, β-cell function, and serum prolactin (PRL) concentrations in Chinese morbidly obese patients with Acanthosis nigricans (AN) and their alterations after laparoscopic sleeve gastrectomy (LSG).

METHODS

A total of 138 morbidly obese subjects undergoing LSG were categorized as simple obesity without AN (OB group, n = 55) and obesity with AN (AN group, n = 83). Oral glucose tolerance test (OGTT), PRL, and related metabolic indices were performed pre- and 12 months post-LSG. Insulin secretion patterns were derived from insulin secretion peak time during OGTT: type I (peak at 30 or 60 min) and type II (peak at 120 or 180 min).

RESULTS

Preoperatively, AN group showed significantly higher proportions of type II insulin secretion pattern, fasting insulin (FINS), and homeostatic model assessment of insulin resistance (HOMA-IR) whereas lower oral glucose insulin sensitivity (OGIS), insulinogenic index (IGI), and disposition index (DI) than OB group, which were improved significantly at 12 months postoperatively in both groups, more pronounced in AN group. Intriguingly, serum PRL declined substantially in AN group than OB group at baseline whereas elevated only in the AN group post-LSG. After adjusting for confounding factors, elevated PRL correlated significantly with increased IGI and DI, and decreased HOMA-IR in both genders, as well as increased OGIS in females, which was detected only in the AN group CONCLUSION: Morbidly obese patients with AN presented delayed insulin secretion response, impaired insulin secretion, and β-cell dysfunction, which were significantly improved by LSG and might benefit from elevated PRL.

Obesity-derived alterations in the lactating mammary gland: Focus on prolactin

Obesity is a modern pandemic with negative consequences in women's reproductive health. Women with overweight and obesity can develop mammary gland alterations that unable exclusive breastfeeding. Obesity associates with a disturbed lactating mammary gland endocrine environment including a decreased action of the hormone prolactin (PRL), the master regulator of lactation. The PRL receptor and the action of PRL are reduced in the mammary gland of lactating rodents fed an obesogenic diet and are contributing factors to impaired lactation in obesity. Also, treatment with PRL improves milk yield in women with lactation insufficiency. This review focuses on the impact of diet-induced obesity in the lactating mammary gland and how obesity impairs the lactogenic action of PRL. Although obesity alters lactation performance in humans and rodents, the responsible mechanisms have been mainly addressed in rodents.