Contribution of the stress-induced degeneration of the locus coeruleus noradrenergic neurons to the pathophysiology of depression: a study on an animal model

Genetic Polymorphism of rs13306146 Affects α2AAR Expression and Associated With Postpartum Depressive Symptoms in Chinese Women Who Received Cesarean Section

Postpartum depressive symptom (PDS) is a common psychological and mental disorder after giving birth. Our previous studies showing the application of dexmedetomidine, an α₂-AR agonist, can significantly improve maternal sleep, as well as relieve and reduce the incidence of PDS. This study investigated the association between α_{2 A} AR gene polymorphisms and PDS. A total of 568 cesarean section patients were enrolled; the incidence of PDS is 18.13% (103 with PDS, 465 with non-PDS). The Edinburgh Postpartum Depression Scale score ≥10 was used to diagnose PDS at 42 days after delivery. The single-nucleotide polymorphisms of α_2AR were sequenced by pyrosequencing. The effect of rs13306146 A > G polymorphism on α_2AR transcription and the regulation of miR-646 on α_2AR expression were assessed by dual luciferase reporter assays or gene transfection. Increased stress during pregnancy, poor relationship between mother-in-law and daughter-in-law, spousal relationship, domestic violence, antenatal depression, self-harm ideation, and stressful life events were all associated with increased PDS incidence (p < 0.05). The logistic regression analysis found that the α_2AAR rs13306146 polymorphism was associated with PDS after adjusting confounding variables. The transcriptional function of the α_2AAR rs13306146 A allele was decreased compared with the G allele, and the α_2AAR expression level was correspondingly decreased (p < 0.05), as the strongest binding ability of miR-646 to the α_2AAR rs13306146 AA genotype. The effect of α_2AAR rs13306146 A > G polymorphism may change the binding ability of miR-646 at the 3'UTR of the α_2AAR gene, affecting the expression of α_2AAR. This study supports the involvement of the norepinephrine system in the pathogenesis of PDS. Genotypes of α_2AAR may be novel and useful biomarkers for PDS.

G-protein-coupled receptor type A heteromers as an emerging therapeutic target

INTRODUCTION

The discovery of receptor-receptor interactions (RRIs) in the early 1980s provided evidence that G-protein-coupled receptors (GPCRs) operate not only as monomers but also as heteromers, in which integration of the incoming signals takes place already at the plasma membrane level through allosteric RRIs. These integrative mechanisms give sophisticated dynamics to the structure and function of these receptor assemblies in terms of modulation of recognition, G-protein signaling and selectivity and switching to β-arrestin signaling.

AREAS COVERED

The present review briefly describes the concept of direct RRI and the available data on the mechanisms of oligomer formation. Further, pharmacological data concerning the best characterized heteromers involving type A GPCRs will be analyzed to evaluate their profile as possible targets for the treatment of various diseases, in particular of impacting diseases of the CNS.

EXPERT OPINION

GPCR heteromers have the potential to open a completely new field for pharmacology with likely a major impact in molecular medicine. Novel pharmacological strategies for the treatment of several pathologies have already been proposed. However, several challenges still exist to accurately characterize the role of the identified heteroreceptor complexes in pathology and to develop heteromer-specific ligands capable of efficiently exploiting their pharmacological features.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

Morphological alterations of the synapses in the locus coeruleus in Parkinson's disease

Parkinson's disease is the most common movement disorder in the broad spectrum of neurodegenerative diseases, associated frequently with gradual decline of the higher mental faculties. From the morphological point of view it is characterized by the degeneration of a substantial number of dopaminergic neurons of the substantia nigra and a considerable degeneration of neuronal networks in locus coeruleus, putamen, globus pallidus, thalamus and some areas of the cortex of the brain hemispheres. Filamentous inclusions, in the form of Lewy bodies and Lewy neuritis, composed mainly of alpha synuclein, been the hallmark of diffuse Lewy body dementia, have been described in the neurons of the substantia nigra in many cases of Parkinson's disease associated with dementia. In previous studies we have described the morphological alterations in the synapses in the caudate nucleus and the globus pallidus in cases of Parkinson's disease. In the present study we attempted to describe the morphological and morphometric alterations of the locus coeruleus in patients who suffered from Parkinson's disease with normal cognitive function and in patients who suffered from Parkinson's disease associated with dementia, comparing them with normal controls. The morphological alterations of the neurons, the dendrites, the retrograde axonic collaterals and the synapses were more impressive in cases of Parkinson's disease associated with dementia than in Parkinson's disease with normal cognitive function. The majority of the synapses demonstrated changes in size and shape of the pre- and postsynaptic components, polymorphism of the synaptic vesicles and marked morphological alterations of the mitochondria. The morphological alterations of the synapses in cases of Parkinson's disease associated with dementia, plead in favor of the importance of the neuronal circuits of locus coeruleus in cognitive functions.