Biology subjects

Medrihan, L.

Publications and source records attributed to Medrihan, L..

7 recordsLinked to original sources

bioRxiv2024

Astrocyte-derived extracellular matrix proteins regulate synapse remodeling in stress-induced depression

Major depressive disorder (MDD) is a common mood condition affecting multiple brain regions and cell types. Changes in astrocyte function contribute to depressive-like behaviors. However, while neuronal mechanisms driving MDD have been studied in some detail, molecular mechanisms by which astrocytes promote depression have not been extensively explored. To uncover astrocyte contributions to MDD, we subjected male mice to chronic social defeat stress precipitated by encounters with a dominant male. Animals exposed to this treatment exhibit symptoms indicative of MDD, including reduced social interactions, anxiety, despair, and anhedonia. We then measured astrocyte translating mRNA expression changes in mice that underwent chronic social defeat and control animals using ribosome affinity purification. Bioinformatic analyses reveal significant alterations in the prefrontal cortex (PFC), consistent with previous studies implicating this brain region in MDD. Expression of genes encoding extracellular matrix (ECM) proteins, cell-cell interaction proteins, and proteins controlling glutamatergic synaptic function are significantly altered. These changes correlate with perturbation of glutamatergic transmission, measured by electrophysiology, and increased synaptic cleft size. Among ECM genes, increased expression of mRNA encoding the synaptic remodeling protein secreted protein acidic and rich in cysteine (Sparc) correlates the most with the depressive phenotype. Furthermore, presence of SPARC and other ECM proteins in synaptosomes is also increased and overexpressing Sparc in PFC partially alleviates stress symptoms. Our results raise the possibility that increased expression of Sparc may be a natural protective mechanism against stress-induced synaptic dysfunction in depression.

neuroscience↗

bioRxiv2022

Glutamatergic projections from ventral hippocampus to nucleus accumbens cholinergic neurons are altered in a mouse model of depression

The cholinergic interneurons (ChATs) of the nucleus accumbens (NAc) have a critical role in the activity of this region, specifically in the context of major depressive disorder. To understand the circuitry regulating this behavior we sought to determine the areas that directly project to these cells/interneurons by utilizing the monosynaptic cell-specific tracing technique. Mapping showed monosynaptic projections that are exclusive to NAc ChATs. To determine if some of these projections are altered in a depression mouse model, we used mice that do not express the calcium binding protein p11 specifically in ChATs (ChAT-p11 cKO) and display a depressive-like phenotype. Our data demonstrated that while the overall projection areas remain similar between wild type and in ChAT-p11 cKO mice, the number of projections coming from the ventral hippocampus (vHIP) is significantly reduced in the ChAT-p11 cKO mice. Furthermore, using optogenetics and electrophysiology we showed that glutamatergic projections from vHIP to NAc ChATs are severely altered in mutant mice. These results show that specific alterations in the circuitry of the accumbal ChAT interneurons could play an important role in the regulation of depressive-like behavior, reward seeking behavior in addictions, or psychiatric symptoms in neurodegenerative diseases.

neuroscience↗

bioRxiv2021

HCN2 in cholinergic interneurons of the nucleus accumbens mediates reward response

Cholinergic interneurons (ChIs) of the nucleus accumbens (NAc) are important for mediating the behavioral response to rewarding stimuli. A major role for these cells is to regulate dopamine (DA) transmission by activating cholinergic receptors at local DAergic nerve terminals. However, the mechanisms that enable cholinergic neurons to enhance DA release in response to reward remain unknown. Here we report that the hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) in NAc ChIs mediates an enhancement in DA signaling in response to rewarding stimuli. The HCN current in NAc ChIs and its modulation by DA, as well as the increase in cholinergic efflux by local cocaine infusion were impaired in mice with deletion of HCN2 in cholinergic cells. Enhancement in the DA efflux and signaling in the NAc in response to rewarding stimuli, as well as cocaine conditioning were also dependent on HCN2 in ChIs. These results provide a mechanistic link between the activity of NAc ChIs and reward encoding.

neuroscience↗

bioRxiv2021

Molecular and cellular adaptations in hippocampal parvalbumin neurons mediate behavioral responses to chronic social stress

Parvalbumin-expressing interneurons (PV neurons) maintain inhibitory control of local circuits implicated in behavioral responses to environmental stressors. However, the roles of molecular and cellular adaptations in PV neurons in stress susceptibility or resilience have not been clearly established. Here, we show behavioral outcomes of chronic social defeat stress (CSDS) are mediated by differential neuronal activity and gene expression in hippocampal PV neurons in mice. Using in vivo electrophysiology and chemogenetics, we find increased PV neuronal activity in the ventral dentate gyrus is required and sufficient for behavioral susceptibility to CSDS. PV neuron-selective translational profiling indicates mitochondrial oxidative phosphorylation is the most significantly altered pathway in stress-susceptible versus resilient mice. Among differentially expressed genes associated with stress-susceptibility and resilience, we find Ahnak, an endogenous regulator of L-type calcium channels which are implicated in the regulation of mitochondrial function and gene expression. Notably, Ahnak deletion in PV neurons impedes behavioral susceptibility to CSDS. Altogether, these findings indicate behavioral effects of chronic stress can be controlled by selective modulation of PV neuronal activity or a regulator of L-type calcium signaling in PV neurons.

neuroscience↗

bioRxiv2021

A Developmental Role for Microglial Presenilin 1 in Memory

Microglia, the macrophages of the brain, are increasingly recognized to play a key role in synaptic plasticity and function; however, the underlying mechanisms remain elusive. Presenilin 1 (PS1) is an essential protein involved in learning and memory, through neuronal mechanisms. Loss of Presenilin function in neurons impairs synapse plasticity and causes cognitive deficits in mice. Surprisingly, here we show memory enhancement in mice by deleting PS1 selectively in microglia. We further demonstrate increased synapse transmission and in vivo neuronal activity in mice by depleting PS1 during microglial development, but not after microglial maturation. Remarkably, conditional deletion of PS1 in microglia during development increased memory retention in adulthood and was dependent on the NMDA receptor subunit GluN2B. In vivo calcium imaging of freely behaving mice revealed increased amplitude of neuronal Ca2+ transients in the CA1 hippocampus of PS1 cKO mice compared to control mice, suggesting a greater CA1 engagement during novel object exploration. Finally, loss of PS1 in microglia mitigated synaptic and cognitive deficits in a mouse model of Alzheimers disease. Together our results reveal a novel mechanism and function of PS1 in microglia in which modulation can enhance neuronal activity, learning and memory in mice.

neuroscience↗

bioRxiv2019

Reduced Kv3.1 Activity in Dentate Gyrus Parvalbumin Cells Induces Vulnerability to Depression.

Parvalbumin (PV)-expressing interneurons are important for cognitive and emotional behaviors. These neurons express high level of p11, a protein associated with depression and action of antidepressants. Here we show that either specific deletion of p11 (p11 cKO) or chemogenetic inhibition in dentate gyrus (DG) PV neurons leads to anxiety-like behavior and susceptibility to depression in mice. DG PV neurons from p11 cKO mice showed reduced level and function of Kv3.1, and consequentially reduced capacity of high-frequency firing and altered short-term plasticity at synapses on granule cells. Activation of Kv3.1 or overexpression of the channel attenuated the vulnerability to depressive behavior.

neuroscience↗

bioRxiv2019

Serotonin receptor 4 in mature excitatory hippocampal neurons modulates mood and anxiety

Serotonin receptor 4 (5-HT4R) plays an important role in regulating mood, anxiety, and cognition, and drugs that activate this receptor have fast-acting antidepressant (AD)-like effects in preclinical models. However, 5-HT4R is widely expressed throughout the central nervous system (CNS) and periphery, making it a poor therapeutic target and difficult to pinpoint the cell types and circuits underlying its effects. Therefore, we generated a Cre-dependent 5-HT4R knockout mouse line to dissect the function of 5-HT4R in specific brain regions and cell types. We show that the loss of functional 5-HT4R specifically in the mature excitatory neurons of hippocampus led to robust AD-like behavioral responses and an elevation in baseline anxiety. 5-HT4R was necessary to maintain the proper excitability of mature dentate gyrus (DG) granule cells and cell type specific molecular profiling revealed a dysregulation of genes necessary for normal neural function and plasticity in cells lacking 5-HT4R. These adaptations were accompanied by an increase in the number of immature neurons in ventral, but not dorsal, dentate gyrus, indicating a broad impact of 5-HT4R loss on the local cellular environment. This study is the first to use conditional genetic targeting to demonstrate a direct role for hippocampal 5-HT4R signaling in modulating mood and anxiety. Our findings also underscore the need for cell type-based approaches to elucidate the complex action of neuromodulatory systems on distinct neural circuits.

neuroscience↗