clozapine-n-oxide and Depressive-Disorder--Major

Numerous human clinical studies have suggested that decreased locomotor activity is a common symptom of major depressive disorder (MDD), as well as other psychiatric diseases. In MDD, the midbrain ventral tegmental area (VTA) dopamine (DA) neurons are closely related to regulate the information processing of reward, motivation, cognition, and aversion. However, the neural circuit mechanism that underlie the relationship between VTA-DA neurons and MDD-related motor impairments, especially hypolocomotion, is still largely unknown. Herein, we investigate how the VTA-DA neurons contribute to the hypolocomotion performance in chronic social defeat stress (CSDS), a mouse model of depression-relevant neurobehavioral states. The results show that CSDS could affect the spontaneous locomotor activity of mice, but not the grip strength and forced locomotor ability. Chemogenetic activation of VTA-DA neurons alleviated CSDS-induced hypolocomotion. Subsequently, quantitative whole-brain mapping revealed decreased projections from VTA-DA neurons to substantia nigra pars reticulata (SNr) after CSDS treatment. Optogenetic activation of dopaminergic projection from VTA to SNr with the stimulation of phasic firing, but not tonic firing, could significantly increase the locomotor activity of mice. Moreover, chemogenetic activation of VTA-SNr dopaminergic circuit in CSDS mice could also rescued the decline of locomotor activity. Taken together, our data suggest that the VTA-SNr dopaminergic projection mediates CSDS-induced hypolocomotion, which provides a theoretical basis and potential therapeutic target for MDD.

Topics: Animals; Channelrhodopsins; Chronic Disease; Clozapine; Depressive Disorder, Major; Disease Models, Animal; Dopamine; Dopaminergic Neurons; Genes, Reporter; Genetic Vectors; Hand Strength; Locomotion; Male; Mice; Mice, Inbred C57BL; Neural Pathways; Optogenetics; Pars Reticulata; Receptor, Muscarinic M3; Recombinant Proteins; Rotarod Performance Test; Social Defeat; Stress, Psychological; Tyrosine 3-Monooxygenase; Ventral Tegmental Area

Negative affect is critical for conferring vulnerability to opiate addiction as reflected by the high comorbidity of opiate abuse with major depressive disorder (MDD). Rodent models implicate amygdala prodynorphin (Pdyn) as a mediator of negative affect; however, evidence of PDYN involvement in human negative affect is limited. Here, we found reduced PDYN mRNA expression in the postmortem human amygdala nucleus of the periamygdaloid cortex (PAC) in both heroin abusers and MDD subjects. Similar to humans, rats that chronically self-administered heroin had reduced Pdyn mRNA expression in the PAC at a time point associated with a negative affective state. Using the in vivo functional imaging technology DREAMM (DREADD-assisted metabolic mapping, where DREADD indicates designer receptors exclusively activated by designer drugs), we found that selective inhibition of Pdyn-expressing neurons in the rat PAC increased metabolic activity in the extended amygdala, which is a key substrate of the extrahypothalamic brain stress system. In parallel, PAC-specific Pdyn inhibition provoked negative affect-related physiological and behavioral changes. Altogether, our translational study supports a functional role for impaired Pdyn in the PAC in opiate abuse through activation of the stress and negative affect neurocircuitry implicated in addiction vulnerability.

Topics: Adult; Amygdala; Animals; Clozapine; Corticosterone; Depressive Disorder, Major; Designer Drugs; Enkephalins; Female; Fluorine Radioisotopes; Fluorodeoxyglucose F18; GTP-Binding Protein alpha Subunits, Gi-Go; Heroin Dependence; Humans; Hungary; Limbic System; Male; Middle Aged; Neuroimaging; Neurons; Positron-Emission Tomography; Protein Precursors; Radiopharmaceuticals; Rats; Rats, Long-Evans; Recombinant Fusion Proteins; RNA, Messenger; United States