A GABAergic increase of principal neural activity promotes stress resilience and reversal of the detrimental effects of chronic stress exposure in brain region- and sex-specific manner
Restricted (Penn State Only)
- Author:
- Jiang, Tong
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 14, 2025
- Committee Members:
- Timothy J Jegla, Professor in Charge/Director of Graduate Studies
Donna Korzick, Outside Unit & Field Member
Yingwei Mao, Chair of Committee
Nikki Crowley, Major Field Member
Bernhard Luscher, Major Field Member & Dissertation Advisor - Keywords:
- Chronic stress
Stress resilience
Neurobiology
Neuroscience
GABAergic interneuron
Chemogenetics
Rodent behavior - Abstract:
- Chronic stress is a major contributory factor to nearly all neuropsychiatric disorders, including but not limited to anxiety disorders, major depressive disorder, and post-traumatic stress disorder. These disorders are typically characterized by changes in negatively and positively regulated motivated behavior that manifest as heightened anxiety and anhedonia, respectively. Comparable changes in motivated behavior are observed in mice exposed to chronic stress. Individuals show differences in their vulnerability to stress, which in turn points to variable degrees of naturally occurring stress resilience. In addition, marked sex differences in the prevalence of these disorders point to possible differences in the brain regions that mediate vulnerability and resilience to stress-based neuropsychiatric disorders. Preclinical studies in mice have shown that stress resilience is an active process that typically involves greater stress-induced gene expression changes than observed in stress-vulnerable animals. Previous studies have mainly focused on the reward circuitry as a substrate of stress resilience. However, the increased stress vulnerability of the hippocampus and medial prefrontal cortex, and their established role in the etiology of major depressive disorder and in the regulation of emotion and cognition in rodents suggest that these cortical brain regions may be equally important as substrates of stress resilience. Both conventional antidepressants that modulate monoaminergic pathways and more recently developed antidepressants that act rapidly by changing the function of amino acid neurotransmitters are known to mitigate the detrimental effects of chronic stress, and hence to promote stress resilience. However, the mechanisms and neural substrates through which they act remain incompletely understood. Of special interest are the somatostatin (SST)-positive, GABAergic interneurons (SSTNs) because they have been identified as critical elements that regulate the vulnerability to stress-related psychiatric disorders. Conversely, our lab has shown that global disinhibition of SSTNs in mice results in resilience to the behavioral effects of chronic stress exposure. This raised the question of whether more direct activation of these neurons in specific brain regions and selectively in adulthood would lead to similar stress resilience, whether such manipulation is sufficient to reverse the detrimental effects of chronic stress, and whether male and female mice differ in any of these parameters. Here, we developed a low-dose, chronic chemogenetic protocol to map stress-induced changes in positively and negatively motivated behaviors to specific brain regions. Cre-recombinase-dependent, hM3Dq-carrying adeno-associated virus (AAV) vectors and empty vector controls were stereotaxically and bilaterally injected into the prelimbic cortex (PLC) or the ventral hippocampus (vHPC) of Cre-transgenic mice segregated by sex to enable the expression of hM3Dq selectively in SSTNs. Clozapine-N-oxide (CNO), the agonist for the hM3Dq construct, was then delivered to the brains of all mice using implantation of semi osmotic minipumps. CNO mediated and AAV-hM3Dq-dependent chronic activation of SSTNs in the PLC had antidepressant drug-like effects on anxiety- and anhedonia-like motivated behaviors in male but not female mice. Analogous manipulation of the vHPC had such effects in female but not male mice. Moreover, the activation of SSTNs in the PLC of male mice and in the vHPC of female mice resulted in stress resilience. By contrast, analogous activation of parvalbumin-positive interneurons (PVNs) in PLC of male mice increased the stress susceptibility of the mice. Moreover, chronic activation of SSTNs in the PLC reversed prior chronic stress-induced deficits in motivated behavior in males but was ineffective in females. Conversely, activation of SSTNs in the vHPC reversed chronic stress-induced behavioral alterations in females but not males. These findings show that the resilience to chronic stress and the reversal of detrimental effects of chronic stress mediated by SSTN activation are strictly brain region- and sex-specific. To further evaluate the effect of SSTN activation on the activity of their putative pyramidal cell targets in the PLC of male mice, we employed immunohistochemical staining for c-Fos and FosB as proxies for neural activity, along with cell-type specific markers that enabled the mapping of these neural activity markers to different neuron types. Quantitation of c-Fos+ and FosB+ neurons in chronic stress-exposed brains revealed that chronic activation of PLC SST neurons leads to a paradoxical increase in pyramidal neuron (PN) activity by a mechanism independent of altered PVN activity. Similar analyses with the PLC of non-stressed mice revealed an SSTN-mediated increase in FosB but not c-Fos expression in pyramidal neurons, suggesting the presence of two distinct populations of PNs that respond differently to SSTN activation. Finally, to assess the accuracy of our stereotaxic manipulations and evaluate possible differences in experimental outcomes between unilaterally and bilaterally manipulated mice, we performed immunohistochemical analyses of AAV vector expression of all the mice that were part of the above studies. Overall, very few mice showed ectopic or unilateral expression. Post hoc reevaluation of the key behavioral experiments showed that the omission of the mice with ectopic or unilateral virus expressions did not affect the behavioral test results. Behavioral measures from PLC-injected mice with unilateral AAV expression did not differ from those showing bilateral expression, suggesting that unilateral manipulation of the PLC is sufficient to drive SSTN-induced behavior changes. Collectively, these data demonstrate that GABAergic microcircuits driven by dendrite targeting SSTNs enable sex- and brain-region-specific neural plasticity that promotes stress resilience and reverses stress-induced anxiety- and anhedonia-like motivated behavior. Chronic activation of SSTNs leads to paradoxically increased activity of cortical output neurons and replicates the anxiolytic and antidepressant-like behavioral effects seen by others following direct, optogenetic stimulation of pyramidal neurons. The data provide a rationale for the lack of antidepressant efficacy of benzodiazepines and superior efficacy of dendrite-targeting, low-potency GABAA receptor agonists, independent of sex and despite striking sex differences in the relevant brain substrate.