Major Depressive Disorder is associated with reduced concentrations of γ-aminobutyric acid (GABA) that are normalized by antidepressant therapies. Moreover, depressive-like phenotypes of GABAA receptor mutant mice can be reversed by treatment with conventional antidepressants drugs, as well as by subanesthetic doses of ketamine. Thus, GABAergic deficits may causally contribute to depressive disorders, while antidepressant therapies may enhance GABAergic synaptic transmission. Here we tested the hypothesis that sustained enhancement of GABAergic transmission alone is sufficient to elicit antidepressant-like behavior, using disinhibition of GABAergic interneurons. We focused on somatostatin-positive (SST+)-GABAergic interneurons because of evidence that their function is compromised in MDD. To disinhibit SST+ interneurons we inactivated the γ2 subunit gene of GABAA receptors selectively in these neurons (SSTCre:γ2f/f mice). Loss of inhibitory synaptic input resulted in increased excitability of SST+ interneurons. In turn, pyramidal cell targets of SST+ neurons showed an increased frequency of spontaneous inhibitory postsynaptic currents. The behavior of SSTCre:γ2f/f mice mimicked the effects of anxiolytic and antidepressant drugs in a number of behavioral tests, without affecting performance in a spatial learning- and memory-dependent task. Lastly, brain extracts of SSTCre:γ2f/f mice showed decreased phosphorylation of the eukaryotic elongation factor eEF2, reminiscent of effects of ketamine. Importantly, these effects occurred without altered activity of the mTOR pathway, nor did they involve altered expression of SST. However, they were associated with reduced Ca2+/calmodulin-dependent auto-phosphorylation of eEF2 kinase, which controls the activity of eEF2 as its single target. Thus, enhancing GABAergic inhibitory synaptic inputs from SST+ interneurons to pyramidal cells and corresponding chronic reductions in the synaptic excitation:inhibition ratio represents a novel strategy for antidepressant therapies that reproduces behavioral and biochemical endpoints of rapidly acting antidepressants.

Background Major depressive disorder (MDD) is increasingly recognized to involve functional deficits in both GABAergic and glutamatergic synaptic transmission. To elucidate the relationship between these phenotypes we made use of GABAA receptor γ2 subunit heterozygous (γ2+/−) mice, which we previously characterized as a model animal with construct, face and predictive validity for MDD. Methods To assess possible consequences of GABAergic deficits on glutamatergic transmission we quantitated the cell surface expression of NMDA- and AMPA-type glutamate receptors and the function of synapses in the hippocampus and medial prefrontal cortex of γ2+/− mice. In addition, we analyzed the effects of an acute dose of the experimental antidepressant ketamine on all these parameters in γ2+/− vs. wild-type mice. Results Modest defects in GABAergic synaptic transmission of γ2+/− mice resulted in a strikingly prominent homeostatic-like reduction in the cell surface expression of NMDA- and AMPA-type glutamate receptors, along with prominent functional impairment of glutamatergic synapses in the hippocampus and medial prefrontal cortex (mPFC). A single subanesthetic dose of ketamine lastingly normalized the glutamate receptor expression and synaptic function of γ2+/− mice to wild-type levels, along with antidepressant-like behavioral consequences selectively in γ2+/− mice. GABAergic synapses of γ2+/− mice were potentiated by ketamine in parallel but only in mPFC. Conclusions Depressive-like brain states that are caused by GABAergic deficits involve a homeostatic-like reduction of glutamatergic transmission that is reversible by an acute, subanesthetic dose of ketamine, along with regionally selective potentiation of GABAergic synapses. The data merge the GABAergic and glutamatergic deficit hypothesis of MDD.

The incidence of myocardial infarction rises sharply at menopause, implicating a potential role for estrogen (E(2)) loss in age-related increases in ischemic injury. We aimed to identify quantitative changes to the cardiac mitochondrial proteome of aging females, based on the hypothesis that E(2) deficiency exacerbates age-dependent disruptions in mitochondrial proteins. Mitochondria isolated from left ventricles of adult (6 mo) and aged (24 mo) F344 ovary-intact or ovariectomized (OVX) rats were labeled with 8plex isobaric tags for relative and absolute quantification (iTRAQ; n = 5-6/group). Groups studied were adult, adult OVX, aged, and aged OVX. In vivo coronary artery ligation and in vitro mitochondrial respiration studies were also performed in a subset of rats. We identified 965 proteins across groups and significant directional changes in 67 proteins of aged and/or aged OVX; 32 proteins were unique to aged OVX. Notably, only six proteins were similarly altered in adult OVX (voltage-dependent ion channel 1, adenine nucleotide translocator 1, cytochrome c oxidase subunits VIIc and VIc, catalase, and myosin binding protein C). Proteins affected by aging were primarily related to cellular metabolism, oxidative stress, and cell death. The largest change occurred in monoamine oxidase-A (MAO-A), a source of oxidative stress. While acute MAO-A inhibition induced mild uncoupling in aged mitochondria, reductions in infarct size were not observed. Age-dependent alterations in mitochondrial signaling indicate a highly selective myocardial response to E(2) deficiency. The combined proteomic and functional approaches described here offer possibility of new protein targets for experimentation and therapeutic intervention in the aged female population.

Reduced efficacy of cardioprotective interventions in the aged female heart, including estrogen replacement, highlights the need for alternative therapeutics to reduce myocardial ischemia-reperfusion (I/R) injury in postmenopausal women. Here, we sought to determine the efficacy of protein kinase-Cε (PKCε)-mediated cardioprotection in the aged, estradiol-deficient rat heart. Infarct size and functional recovery were assessed in Langendorff-perfused hearts from adult (5 mo) or aged (23 mo) female Fisher 344 ovary-intact or ovariectomized (OVX) rats administered a PKCε-activator, receptor for activated C kinase (ψεRACK) prior to 47-min ischemia and 60-min reperfusion. Proteomic analysis was conducted on left ventricular mitochondrial fractions treated with ψεRACK prior to I/R, utilizing isobaric tags for relative and absolute quantitation (iTRAQ) 8plex labeling and tandem mass spectrometry. Real-time PCR was utilized to assess connexin 43 (Cx43) and RACK2 mRNA post-I/R. Greater infarct size in aged OVX (78%) vs. adult (37%) was reduced by ψεRACK (35%, P < 0.0001) and associated with greater mitochondrial PKCε localization (P < 0.0003). Proteomic analysis revealed three novel mitochondrial targets of PKCε-mediated cardioprotection with aging (P < 0.05): the antioxidant enzymes glutathione peroxidase (GPX) and MnSOD2, and heat shock protein 10. Finally, decreased levels of Cx43 and RACK2 mRNA seen with age were partially abrogated by administration of ψεRACK (P < 0.05). The mechanisms described here may represent important therapeutic candidates for the treatment of acute myocardial infarction in postmenopausal women and age-associated estradiol deficiency.

Ketamine is a fast acting experimental antidepressant with significant therapeutic potential for emotional disorders such as major depressive disorder and alcohol use disorders. Of particular interest is binge alcohol use, which during intermittent withdrawal from drinking involves depressive-like symptoms reminiscent of major depressive disorder. Binge drinking has been successfully modeled in mice with the Drinking in the Dark (DID) paradigm, which involves daily access to 20% ethanol, for a limited duration and selectively during the dark phase of the circadian light cycle. Here we demonstrate that DID exposure reduces the cell surface expression of NMDAand AMPA-type glutamate receptors in the prelimbic cortex (PLC) of female but not male mice, along with reduced activity of the mammalian target of rapamycin (mTOR) signaling pathway. Pretreatment with an acute subanesthetic dose of ketamine suppresses binge-like ethanol consumption in female but not male mice. Lastly, DID-exposure reduces spontaneous glutamatergic synaptic transmission in the PLC of both sexes, but synaptic transmission is rescued by ketamine selectively in female mice. Thus, ketamine may have therapeutic potential as an ethanol binge suppressing agent selectively in female subjects.