Serotonin Discharge Regulation by Additional Neurotransmitters of Rat Hippocampus Associated With the Continence Central Circuit

Purpose: The lower urinary tract is believed to be centrally regulated with the involvement of a range of neurotransmitters. The parasympathetic excitatory input to the urinary bladder is suppressed when the serotonergic system is activated, and thereby voiding is blocked. In healthy people, continence is usually underpinned by hippocampal formation (circuit 3). In order to advance knowledge of how serotoninergic neurons and additional nerve fibers were correlated, the purpose of the present work was to research how the discharge of serotonin from hippocampal slices was affected by different neurotransmitters in rat models.Methods: The adopted procedure involved administration of the central neurotransmitters acetylcholine, norepinephrine, dopamine, N-methyl-D-aspartate (NMDA), gamma-aminobutyric acid (GABA), glycine, and neuropeptide Y as well as monitoring of the alterations in the discharge of [3H]5-hydroxytryptamine (5-HT). Furthermore, to determine whether the effect of the neurotransmitters was influenced by interneuron, tetrodotoxin was also employed.Results: Acetylcholine (10-5M) did not alter [3H]5-HT discharge, whereas more 5-HT was discharged from the hippocampal slices of rats under stimulation by norepinephrine (10-5M) as well as dopamine (10-5M) and tetrodotoxin (10-6M) did not inhibit the discharge. By contrast, tetrodotoxin inhibited the discharge of [3H]5-HT that was exacerbated by NMDA (10-4M). Meanwhile, compared to control, GABA (10-5M), glycine (10-5M), or neuropeptide Y (10-6M) did not alter the [³H]5-HT discharge.Conclusions: From the research findings, it can be concluded that 5-HT discharge from rat hippocampus is enhanced by norepinephrine and dopamine through direct effect on the 5-HT neuronal terminal. By contrast, 5-HT discharge is intensified by NMDA by activating interneurons.

The mitotic checkpoint protein MAD2 delivers monoamine transporters to endocytosis.

Monoamine transporters retrieve serotonin (SERT), dopamine (DAT) and norepinephrine (NET) from the synaptic cleft. Surface levels of transporters are also regulated by internalization. Clathrin-mediated endocytosis of cargo proteins requires adaptor protein 2 (AP2), which recruits cargo to the nascent clathrin-cage. The transporter C-terminus is required for internalization but lacks an AP2-binding site. In the present work, we show that internalization of SERT and DAT relies on MAD2, a protein of the mitotic spindle assembly checkpoint (SAC). A MAD2-interaction motif in the transporter C-terminus interacts with MAD2. This binding is contingent on the closed conformation of MAD2 and allowed for the recruitment of two additional SAC proteins, BubR1 and p31COMET as well as AP2. MAD2, BubR1 and p31COMET are present in serotoninergic neurons of the dorsal raphe, corroborating a biological role of the identified interactions. Depletion of MAD2 in HEK-293 cells stably expressing SERT and DAT decreases constitutive and triggered endocytosis, respectively. Altogether, our study describes a candidate mechanism, which connects monoamine transporters to the endocytic machinery and thus supports their internalization.

Not Just a Bystander: The Emerging Role of Astrocytes and Research Tools in Studying Cognitive Dysfunctions in Schizophrenia

Cognitive dysfunction is one of the core symptoms in schizophrenia, and it is predictive of functional outcomes and therefore useful for treatment targets. Rather than improving cognitive deficits, currently available antipsychotics mainly focus on positive symptoms, targeting dopaminergic/serotoninergic neurons and receptors in the brain. Apart from investigating the neural mechanisms underlying schizophrenia, emerging evidence indicates the importance of glial cells in brain structure development and their involvement in cognitive functions. Although the etiopathology of astrocytes in schizophrenia remains unclear, accumulated evidence reveals that alterations in gene expression and astrocyte products have been reported in schizophrenic patients. To further investigate the role of astrocytes in schizophrenia, we highlighted recent progress in the investigation of the effect of astrocytes on abnormalities in glutamate transmission and impairments in the blood–brain barrier. Recent advances in animal models and behavioral methods were introduced to examine schizophrenia-related cognitive deficits and negative symptoms. We also highlighted several experimental tools that further elucidate the role of astrocytes. Instead of focusing on schizophrenia as a neuron-specific disorder, an additional astrocytic perspective provides novel and promising insight into its causal mechanisms and treatment. The involvement of astrocytes in the pathogenesis of schizophrenia and other brain disorders is worth further investigation.

Ketamine selectively enhances AMPA neurotransmission onto a subgroup of identified serotoninergic neurons of the rat dorsal raphe

ABSTRACTAlthough the fast antidepressant effect of ketamine is now well established clinically, neither its mechanism(s) nor its main site(s) of action is clearly defined. Because enhanced serotoninergic (5-HT) transmission is an important part of the antidepressant effect of various drug classes, we asked whether ketamine and one of its metabolites (hydroxynorketamine [HNK]), both used in their racemic form, may modulate the excitatory drive onto these neurons.Using whole-cell recordings from pharmacologically identified 5-HT and non-5-HT neurons in juvenile rat dorsal raphe slices, we found that both ketamine and HNK (10 µM) increase excitatory AMPA neurotransmission onto a subset (50%) of 5-HT neurons, whereas other 5-HT cells were unaffected. Both compounds increased the amplitude as well as the frequency of spontaneous excitatory post-synaptic currents (sEPSCs) mediated by AMPA receptors. The effect of ketamine was more robust than the one of HNK, since it significantly enhanced the charge transfer through AMPA channels, whereas HNK did not. The increase in the excitatory drive induced by ketamine was dependent on NMDA receptor blockade. In the presence of tetrodotoxin, the effect of ketamine was markedly reduced. Non-5-HT neurons, on the other hand, were unaffected by the drugs.We conclude that ketamine and HNK increase the excitatory drive onto a subset of 5-HT neurons by promoting glutamate release and possibly also through a postsynaptic action. The effect of ketamine is dependent on NMDA receptor modulation and appears to involve a network effect. These findings improve our understanding of the fast-acting antidepressant effect of ketamine.SIGNIFICANCE STATEMENTThe mechanisms of ketamine’s antidepressant effect are currently controversial. We asked whether the drug would produce changes is the strength of synaptic inputs onto serotoninergic neurons of the dorsal raphe. We found that this is indeed the case in about half of these neurons. The action of ketamine was mimicked to some extent by its well-known metabolite hydroxynorketamine, was dependent on NMDA receptor activation and probably involved a local network effect. It remains to be determined if the differential susceptibility of serotoninergic neurons to the drug correlates with any differential inputs and/or outputs.

Establishment of a Large Collection of Cells from Major Depressive Disorder Patients to Model Disease and Therapy Response in Vitro

Major Depressive Disorder (MDD) is a multifactorial psychiatric condition that affects 4.4% of the world population, causing substantial personal suffering, disability and social costs. Current pharmacological treatments for MDD do not effect remission in 30% of patients. The development of in vitro models for MDD will aid the understanding of this disorder, its pharmacogenomics, and the development of new therapies. Although hiPSCs from 6 MDD patients have been established, given the complexity and heterogeneity of the disease much larger sample sizes may be needed to fully model the disorder in vitro. To this end, we established a collection of 66 primary cells and 10 induced pluripotent stem cells (hiPSCs) from a sample of clinically well-characterized MMD patients, who were participants of a clinical study that compared the effect of transcranial direct current stimulation (tCDS) versus escitalopram on the treatment of MDD. Cells were differentiated in vitro into serotoninergic neurons, a clinically relevant cell type for MMD. This collection of cells increases significantly the number of available samples from MDD patients, and thus will contribute to research into the molecular basis of depression.