Participation of the cholinergic system in the excessive grooming behavior induced by neuropeptide (N) glutamic acid (E) isoleucine (I) amide (NEI)

Integrated 16S rRNA sequencing and metabolomics analysis to investigate the antidepressant role of Yang-Xin-Jie-Yu decoction on microbe-gut-metabolite in chronic unpredictable mild stress-induced depression rat model

Objectives: Our goals were to evaluate the antidepressant efficacy of Yang-Xin-Jie-Yu Decoction (YXJYD) in Chronic Unpredictable Mild Stress (CUMS)-induced depression rat model and to investigate the underlying mechanisms.

Design: We used CUMS-induced depression rat model to evaluate whether oral administration of YXJYD with different doses (2.1 g/kg, 1.05 g/kg and 0.525 g/kg, respectively) improve the depressive-like symptoms, and then performed UHPLC-Q-TOF-MS to explore the active ingredients of YXJYD. Subsequently, rat’s cecal contents, serum, and urine were collected from the control group, CUMS model group, and YXJYD high-dose (2.1 g/kg) treatment group. The 16S rRNA sequencing was performed on the cecal contents, based on Illumina MiSeq platform, and ANOVA analysis were used to analyze the composition variety and screen differential expression of gut bacteria in the three groups. 1H Nuclear Magnetic Resonance (NMR) analysis was used for analyzing the metabolites obtained from cecal contents, serum, and urine, and KEGG enrichment analysis was used to identify pathways of differential metabolites. An integrated 16S rRNA sequencing and metabolomic data were conducted to characterize the underlying mechanisms of YXJYD

Results: The gut microbial communities, and serum, cecal content, urine metabolic compositions were significantly significantly altered in CUMS-induced depressive rats, while YXJYD effectively ameliorated the CUMS-associated gut microbiota dysbiosis, especially of Monoglobus, and alleviated the disturbance of serum, cecal content, urine metabolome and reversed the changes of key depressive and gut microbiota-related metabolites, such as succinic acid, taurine, hippuric acid, melatonin. With an integrated study of the gut microbiota and metabolomes, we identified the pathway of tricarboxylic acid cycle (TCA cycle) and propanoate metabolism as the regulated target of YXJYD on host-microbiome interaction.

Conclusion: Our findings further confirmed the imbalance of metabolism and intestinal microbial is closely related to CUMS-induced depression. YXJYD regulates gut microbiome to affect body metabolomes and then produce antidepressant-like effect in CUMS-induced depressive rats while its molecular mechanism possibly be increased Monoglobus abundance in gut microbiota and regulated the TCA cycle pathway and propanoate metabolism in host.

Substantial acetylcholine reduction in multiple brain regions of Mecp2-deficient female rats and associated behavioral abnormalities

Rett syndrome (RTT) is a neurodevelopmental disorder with X-linked dominant inheritance caused mainly by mutations in the methyl-CpG-binding protein 2 (MECP2) gene. The effects of various Mecp2 mutations have been extensively assessed in mouse models, but none adequately mimic the symptoms and pathological changes of RTT. In this study, we assessed the effects of Mecp2 gene deletion on female rats (Mecp2^+/−) and found severe impairments in social behavior [at 8 weeks (w), 12 w, and 23 w of age], motor function [at 16 w and 26 w], and spatial cognition [at 29 w] as well as lower plasma insulin-like growth factor (but not brain-derived neurotrophic factor) and markedly reduced acetylcholine (30%–50%) in multiple brain regions compared to female Mecp2^+/+ rats [at 29 w]. Alternatively, changes in brain monoamine levels were relatively small, in contrast to reports on mouse Mecp2 mutants. Female Mecp2-deficient rats express phenotypes resembling RTT and so may provide a robust model for future research on RTT pathobiology and treatment.

Differential effects of hypo- and hyperthyroidism on remodeling of contacts between neurons expressing the neuropeptide EI and tyrosine hydroxylase in hypothalamic areas of the male rat

The Neuropeptide EI (NEI, glutamic acid- isoleucine amide) participates in neuroendocrine function. Previously we demonstrated that NEI concentration is regulated by thyroid hormones in discrete hypothalamic areas in rats. We observed that the thyroid status affects the dopaminergic regulation of the pituitary hormones. In this study we explored possible interactions between NEI and tyrosine hydroxylase (TH) containing elements in selected hypothalamic areas of male rats. Neuronal somas, terminals and boutons were assessed by confocal microscopy, in hypo- and hyperthyroid animals. We observed a remodeling of the contacts between the TH and NEI immunoreactive elements in the incerto-hypothalamic area (IHy, also known as rostromedial zona incerta) according to thyroid function. However, in the dorsolateral zone of the peduncular part of the lateral hypothalamus (DL-PLH) the thyroid hormones affect the dendritic trees of the neurons without perturbing the overall NEI/TH contacts. Also, we demonstrated that TRH Receptor 1 (TRH-R1) is colocalized in NEI immunoreactive neurons in the peduncular part of the lateral hypothalamus (PLH) and NEI precursor mRNA expression increased by hypothyroidism indicating that NEI neurons are responsive to the feedback mechanisms of the Hypothalamic Pituitary-Thyroid Axis (HPT). In conclusion, the hypothyroid status seems to increase the interactions between the NEI neurons and the dopaminergic pathways while hyperthyroidism either decreases or displays no effects. Altogether these observations support the participation of the IHy and PLH NEI as a modulating component of the HPT suggesting that altered neuroendocrine, behavioral and cognitive dysfunctions induced by dysthyroidism could be in part mediated by NEI.

Amino acid metabolic dysfunction revealed in the prefrontal cortex of a rat model of depression

Major depressive disorder (MDD) is a debilitating mood disorder. However, the molecular mechanism(s) underlying depression remain largely unknown. Here, we applied a GC-MS-based metabonomic approach in the chronic unpredictable mild stress (CUMS) model, a well-established rodent model of depression, to investigate significant metabolic changes in the rat prefrontal cortex (PFC). Multivariate statistical analysis - including principal component analysis, partial least squares-discriminate analysis, and pair-wise orthogonal projections to latent structures discriminant - was applied to identify differential PFC metabolites between CUMS rats and healthy controls. As compared to healthy control rats, CUMS rats were characterized by lower levels of isoleucine and glycerol in combination with higher levels of N-acetylaspartate and β-alanine. These findings should provide insight into the pathophysiological mechanism(s) underlying MDD and preliminary leads relevant to diagnostic biomarker discovery for depression.

Effects of thyroid status on NEI concentration in specific brain areas related to reproduction during the estrous cycle

We previously showed that short-term hypo- and hyperthyroidism induce changes in neuropeptide glutamic-acid-isoleucine-amide (NEI) concentrations in discrete brain areas in male rats. To investigate the possible effects of hypo- and hyperthyroidism on NEI concentrations mainly in hypothalamic areas related to reproduction and behavior, female rats were sacrificed at different days of the estrous cycle. Circulating luteinizing hormone (LH), estradiol and progesterone concentrations were measured in control, hypothyroid (hypoT, treated with PTU during 7-9 days) and hyperthyroid (hyperT, l-T4 during 4-7 days) animals. Both treatments blunted the LH surge. Hypo- and hyperthyroidism increased estradiol concentrations during proestrus afternoon (P-PM), although hypoT rats showed lower values compared to control during proestrus morning (P-AM). Progesterone levels were higher in all groups at P-PM and in the hyperT during diestrus morning (D2). NEI concentrations were lower in hypoT rats during the estrous cycle except in estrus (E) in the peduncular part of the lateral hypothalamus (PLH). They were also reduced by both treatments in the perifornical part of the lateral hypothalamus (PeFLH) during P-PM. Hypothyroidism led to higher NEI concentrations during P-PM in the organum vasculosum of the lamina terminalis and anteroventral periventricular nucleus (OVLT+AVPV). The present results indicate that NEI concentration is regulated in a complex manner by hypo- and hyperthyroidism in the different areas studied, suggesting a correlation between NEI values and the variations of gonadal steroid levels during estrous cycle. These changes could be, in part, responsible for the alterations observed in the hypothalamic-pituitary-gonadal axis in these pathologies.

Hypo- and hyperthyroidism affect NEI concentration in discrete brain areas of adult male rats

To date, there has been only one in vitro study of the relationship between neuropeptide EI (NEI) and the hypothalamic-pituitary-thyroid (HPT) axis. To investigate the possible relationship between NEI and the HPT axis, we developed a rat model of hypothyroidism and hyperthyroidism that allows us to determine whether NEI content is altered in selected brain areas after treatment, as well as whether such alterations are related to the time of day. Hypothyroidism and hyperthyroidism, induced in male rats, with 6-propyl-1-thiouracil and l-thyroxine, respectively, were confirmed by determination of triiodothyronine, total thyroxine, and thyrotropin levels. All groups were studied at the morning and the afternoon. In rats with hypothyroidism, NEI concentration, evaluated on postinduction days 7 and 24, was unchanged or slightly elevated on day 7 but was decreased on day 24. In rats with hyperthyroidism, NEI content, which was evaluated after 4 days of l-thyroxine administration, was slightly elevated, principally in the preoptic area in the morning and in the median eminence-arcuate nucleus and pineal gland in the afternoon, the morning and afternoon NEI contents being similar in the controls. These results provide the bases to pursue the study of the interaction between NEI and the HPT axis.

Anatomy, function and regulation of neuropeptide EI (NEI)

This review is focused on the anatomy, role and behavior of neuropeptide-glutamic acid-isoleucine (NEI), providing a general report on the neuropeptide. In addition to hormone release, this peptide also takes part in the regulation of grooming behavior and locomotor activity. NEI is produced by cleavage of prepro-MCH that probably takes place at the Lys(129)-Arg(130) and Arg(145)-Arg(146) sites (the glycine residue on the C-terminus of NEI strongly suggests that this peptide is amidated). This same prohormone is also the precursor of MCH, widely studied in relation to food and water intake, and NGE, of which little is known. NEI and MCH are extensively colocalized throughout the central nervous system (CNS), and NEI is also present in peripheral tissues. The latter is also effective in stimulating luteinizing hormone (LH) release and, to a lesser extent, FSH from primary pituitary cell cultures. In addition to releasing LH from the medial eminence, NEI also acts directly on gonadotropes. Lastly, this neuropeptide also acts at the CNS level on gonadotropin-releasing hormone (GnRH) neurons.

Effect of β-adrenoceptors on the behaviour induced by the neuropeptide glutamic acid isoleucine amide

Excessive grooming behaviour is induced by intracerebroventricular injections of the neuropeptide glutamic acid isoleucine amide (neuropeptide-EI), via the activation of A-10 dopaminergic neurons and the noradrenergic system. Our object was to study the latter system involved in these behaviours, using male Wistar rats weighing 250-300 g with i.c.v. implants. The results show that all the adrenoceptor antagonists "per se" do not affect excessive grooming behaviour or motor activity. Intracerebroventricular administration of propranolol, a general beta-adrenoceptor antagonist, before neuropeptide-EI, inhibited the induced excessive grooming behaviour in a dose dependent manner. Metoprolol, a beta(1)-adrenoceptor antagonist, also blocked this behaviour. However, intracerebroventricular injections of phentolamine, an alpha-adrenoceptor antagonist, and ((+/-)-1-[2,3-(Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol), a beta(2)-adrenoceptor antagonist, had no effect on the behaviour induced by neuropeptide-EI induced behaviour for any of the doses tested. On the other hand, isoproterenol, a general beta-adrenoceptor agonist and dobutamine, a beta(1)-adrenoceptor agonist, both elicited similar behaviours as those induced by neuropeptide-EI. These results support the hypothesis that a relationship exists between neuropeptide-EI and beta-adrenoceptors, more specifically the beta(1)-adrenoceptor, as found with other similar endogenous peptides such as neurotensin, cholecystin, substance P and alpha-melanocyte stimulating hormone. Hence, neuropeptide-EI could probably be exerting a neuromodulating effect on the central nervous system.

Melanin-concentrating hormone is expressed in the laterodorsal tegmental nucleus only in female rats

Melanin-concentrating hormone (MCH) is a neuropeptide originating from prepro-MCH. In male rats, neurons expressing MCH are found in the lateral hypothalamic area and medial zona incerta, as well as, sparsely, in the olfactory tubercle and pontine reticular formation. The wide distribution of MCH fibers suggests the involvement of this neuropeptide in a variety of functions, including arousal, neuroendocrine control and energy homeostasis. In lactating females, MCH is expressed in the preoptic area, indicating sexual dimorphism in MCH gene activation according to the female reproductive state. We hypothesized that MCH is also expressed differentially in the brainstem of female rats. Adult male rats and female rats (in the afternoon of diestrus and proestrus days; ovariectomized; or on lactation days 5, 12 and 19) were perfused between 2 and 4 p.m., and the brainstems were processed for in situ hybridization using a 35S-labeled prepro-MCH riboprobe. As described in males, prepro-MCH was expressed in the pontine reticular formation of females. We also observed consistent prepro-MCH expression in the caudal laterodorsal tegmental nucleus (LDT) of females but no differential expression comparing the various female reproductive states. Using dual-label immunohistochemistry or dual-label in situ hybridization, we found that brainstem MCH neurons coexpress glutamic acid decarboxylase mRNA, the gamma aminobutyric acid (GABA) processing enzyme, but do not colocalize choline acetyl transferase (acetylcholine processing enzyme). Since changes in LDT GABAergic cell activity are associated with rapid eye movement (REM) sleep, our findings suggest that MCH interacts with LDT GABAergic neurons and plays a role in REM sleep regulation.

Repeated intracerebroventricular infusion of nicotine prevents kainate-induced neurotoxicity by activating the α7 nicotinic acetylcholine receptor

We examined whether (-)-nicotine infusion can affect kainic acid (KA)-induced neurotoxicity in rats. Although treatment with a single nicotine infusion (0.5 or 1.0 microg/side, i.c.v.) failed to attenuate KA-induced neurotoxicity, repeated nicotine infusions (1.0 microg/side/day for 10 days) attenuated the seizures, the severe loss of cells in hippocampal regions CA1 and CA3, the increase in activator protein (AP)-1 DNA binding activity, and mortality after KA administration. alpha-Bungarotoxin and mecamylamine blocked the neuroprotective effects of nicotine. These results suggest that repeated nicotine treatment provides alpha7 nicotinic acetylcholine receptor-mediated neuroprotection against KA toxicity.

Neuropeptide glutamic acid-isoleucine may induce luteinizing hormone secretion via multiple pathways

Neuropeptide glutamic acid-isoleucine (NEI) is a 14-amino acid peptide processed from prepro-melanin-concentrating hormone (ppMCH). In males, the localization of NEI is almost identical to that of MCH, the cell bodies of both being located primarily in the lateral hypothalamic area and zona incerta, projecting fibers throughout the brain. Although MCH has been widely studied, the role that NEI plays in brain circuitry has been poorly investigated. Recently, we showed that intracerebroventricular injection of NEI increases serum luteinizing hormone (LH) levels. In order to identify the anatomical substrate underlying this effect, we used combined immunohistochemistry methods to analyze the forebrains of females on the diestrus and proestrus days, as well as those of ovariectomized females treated with estradiol benzoate, with estradiol benzoate plus progesterone or with sesame oil (control animals). We found that ovariectomized females with no steroid treatment showed an increased number of NEI-immunoreactive neurons in the medial zona incerta. In addition, we observed dense to moderate NEI innervation of areas related to reproduction, including the organum vasculosum of the lamina terminalis, the anteroventral periventricular nucleus (AVPV) and the median eminence. The NEI fibers were in close apposition with the AVPV and gonadotropin-releasing hormone (GnRH) neurons expressing Fos in the afternoon of the proestrus day or following administration of estradiol benzoate plus progesterone. In the median eminence, NEI varicosities and terminal-like structures were in close proximity to blood vessels and GnRH fibers. Our results suggest that NEI might induce LH secretion in one of the following ways: by direct release into the median eminence, by modulation of GnRH neurons located in the preoptic area, by modulation of the GnRH terminals located in the median eminence or by an additive effect involving other neurotransmitters or neurohormones. Release of NEI might also induce LH secretion indirectly by modulating AVPV neurons.

Intracerebroventricular injection of neuropeptide EI increases serum LH in male and female rats

Melanin concentrating hormone (MCH) precursor-derived neuropeptide EI (NEI) has not yet been extensively studied. The aim of this study was to determine the effect of neuropeptide EI on serum levels of LH in normal male rats and chronically ovariectomized (CHR-OVX) female rats treated with estrogen benzoate (EB) and with a low dose of progesterone. The peptide, administered intracerebroventricularly in male and chronically ovariectomized female rats, increased LH serum levels compared to the controls injected with artificial cerebrospinal fluid. It is important to note that there is some relation between neuropeptide EI-melanin concentrating hormone and alpha-melanocyte stimulating hormone (alpha-MSH) indicating that all three peptides are associated in a complex inter-relationship. Therefore, the question that arises is if neuropeptide EI could also be related with the receptors for melanin concentrating hormone or alpha-melanocyte stimulating hormone.

Melanin-concentrating hormone signaling systems in fish

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide synthesized as a preprohormone in the hypothalamus of all vertebrates. This neuropeptide binds to G-protein-coupled seven transmembrane receptor(s) to mediate its function. MCH was named after its function in teleosts, in which it causes aggregation or concentration of melanin granules in melanophores, thus regulating body color. The function of central MCH that has attracted most attention is its involvement in regulating food intake and energy homeostasis in mammals, a role confirmed through a series of experiments, including central administration of MCH or MCH receptor blockers, and genetic manipulation of MCH and its receptors. The aim of this article is to review the recent data on MCH and MCH receptor signaling systems in fish.