Conditional GSK3β deletion in parvalbumin-expressing interneurons potentiates excitatory synaptic function and learning in adult mice

Conditioning and pseudoconditioning differently change intrinsic excitability of inhibitory interneurons in the neocortex

Many studies indicate a broad role of various classes of GABAergic interneurons in the processes related to learning. However, little is known about how the learning process affects intrinsic excitability of specific classes of interneurons in the neocortex. To determine this, we employed a simple model of conditional learning in mice where vibrissae stimulation was used as a conditioned stimulus and a tail shock as an unconditioned one. In vitro whole-cell patch-clamp recordings showed an increase in intrinsic excitability of low-threshold spiking somatostatin-expressing interneurons (SST-INs) in layer 4 (L4) of the somatosensory (barrel) cortex after the conditioning paradigm. In contrast, pseudoconditioning reduced intrinsic excitability of SST-LTS, parvalbumin-expressing interneurons (PV-INs), and vasoactive intestinal polypeptide-expressing interneurons (VIP-INs) with accommodating pattern in L4 of the barrel cortex. In general, increased intrinsic excitability was accompanied by narrowing of action potentials (APs), whereas decreased intrinsic excitability coincided with AP broadening. Altogether, these results show that both conditioning and pseudoconditioning lead to plastic changes in intrinsic excitability of GABAergic interneurons in a cell-specific manner. In this way, changes in intrinsic excitability can be perceived as a common mechanism of learning-induced plasticity in the GABAergic system.

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30-45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Effects of chronic lithium treatment on neuronal excitability and GABAergic transmission in an Ank3 mutant mouse model

Bipolar disorder (BD) is a common psychiatric disease that can lead to psychosocial disability, decreased quality of life, and high risk for suicide. Genome-wide association studies have shown that the ANK3 gene is a significant risk factor for BD, but the mechanisms involved in BD pathophysiology are not yet fully understood. Previous work has shown that ankyrin-G, the protein encoded by ANK3, stabilizes inhibitory synapses in vivo through its interaction with the GABAA receptor-associated protein (GABARAP). We generated a mouse model with a missense p.W1989R mutation in Ank3, that abolishes the interaction between ankyrin-G and GABARAP, which leads to reduced inhibitory signaling in the somatosensory cortex and increased pyramidal cell excitability. Humans with the same mutation exhibit BD symptoms, which can be attenuated with lithium therapy. In this study, we describe that chronic treatment of Ank3 p.W1989R mice with lithium normalizes neuronal excitability in cortical pyramidal neurons and increases inhibitory GABAergic postsynaptic currents. The same outcome in inhibitory transmission was observed when mice were treated with the GSK-3β inhibitor Tideglusib. These results suggest that lithium treatment modulates the excitability of pyramidal neurons in the cerebral cortex by increasing GABAergic neurotransmission, likely via GSK-3 inhibition. In addition to the importance of these findings regarding ANK3 variants as a risk factor for BD development, this study may have significant implications for treating other psychiatric disorders associated with alterations in inhibitory signaling, such as schizophrenia, autism spectrum disorder, and major depressive disorder.

Effects of combined exposure to ethanol and delta-9-tetrahydrocannabinol during adolescence on synaptic plasticity in the prefrontal cortex of Long Evans rats

Significant exposure to alcohol or cannabis during adolescence can induce lasting disruptions of neuronal signaling in brain regions that are later to mature, such as the medial prefrontal cortex (mPFC). Considerably less is known about the effects of alcohol and cannabis co-use, despite its common occurrence. Here, we used male and female Long-Evans rats to investigate the effects of early-life exposure to ethanol, delta-9-tetrahydrocannabinol (THC), or their combination on high frequency stimulation (HFS)-induced plasticity in the prelimbic region of the mPFC. Animals were injected daily from postnatal days 30 to 45 with vehicle or THC (escalating doses, 3-20 mg/kg) and allowed to drink vehicle (0.1% saccharin) or 10% ethanol immediately after each injection. In vitro brain slice electrophysiology was then used to record population responses of layer V neurons following HFS in layer II/III after 3-4 weeks of abstinence. We found that THC exposure reduced body weight gains observed in ad libitum fed rats, and reduced intake of saccharin and ethanol. Compared to controls, there was a significant reduction in HFS-induced long-term depression (LTD) in rats exposed to either drug alone, and an absence of LTD in rats exposed to the drug combination. Bath application of indiplon or AR-A014418, which enhance GABAA receptor function or inhibit glycogen synthase kinase 3β (GSK3β), respectively, suggested the effects of ethanol, THC or their combination were due in part to lasting adaptations in GABA and GSK3β signaling. These results suggest the potential for long-lasting adaptations in mPFC output following co-exposure to alcohol and THC.

Pharmacogenetic activation of parvalbumin interneurons in the prefrontal cortex rescues cognitive deficits induced by adolescent MK801 administration

The cognitive symptoms of schizophrenia (SZ) present a significant clinical burden. They are treatment resistant and are the primary predictor of functional outcomes. Although the neural mechanisms underlying these deficits remain unclear, pathological GABAergic signaling likely plays an essential role. Perturbations with parvalbumin (PV)-expressing fast-spiking (FS) interneurons in the prefrontal cortex (PFC) are consistently found in post-mortem studies of patients with SZ, as well as in animal models. Our studies have shown decreased prefrontal synaptic inhibition and PV immunostaining, along with working memory and cognitive flexibility deficits in the MK801 model. To test the hypothesized association between PV cell perturbations and impaired cognition in SZ, we activated prefrontal PV cells by using an excitatory DREADD viral vector with a PV promoter to rescue the cognitive deficits induced by adolescent MK801 administration in female rats. We found that targeted pharmacogenetic upregulation of prefrontal PV interneuron activity can restore E/I balance and improve cognition in the MK801 model. Our findings support the hypothesis that the reduced PV cell activity levels disrupt GABA transmission, resulting in the disinhibition of excitatory pyramidal cells. This disinhibition leads to an elevated prefrontal excitation/inhibition (E/I) balance that could be causal for cognitive impairments. Our study provides novel insights into the causal role of PV cells in cognitive function and has clinical implications for understanding the pathophysiology and management of SZ.

Resveratrol Protects SH-SY5Y Cells Against Oleic Acid-Induced Glucolipid Metabolic Dysfunction and Cell Injuries Via the Wnt/β-Catenin Signalling Pathway

Resveratrol (RES) is a polyphenol with diverse beneficial biological and pharmacological activities, and our previous results have demonstrated its neuroprotective effects in several metabolic diseases, including non-alcoholic fatty liver disease. The aim of the present study is to investigate the potential effect of RES against oleic acid (OA)-induced cell injuries in SH-SY5Y cells and explore the possible mechanism. Based on the dose- and time-dependent effects of OA on cell proliferation and LDH release, SH-SY5Y cells were challenged with OA and incubated with or without RES (10^-5-10^-9 mM) or sitagliptin (STG, 10^-7 mM). Lipid accumulation, SREBP1 and PPARα protein expression, glucose consumption and IRS1, AKT, ERK phosphorylation under insulin stimulation, and ROS production were detected. The protein expression of brain-derived neurotrophic factor (BDNF), Copine 6, and key molecules in the Wnt/β-catenin signalling pathway were measured via western blot. The expression of Wnt 1 was also measured via immunofluorescence staining. The results showed that RES treatment could alleviate the neurotoxicity induced by OA, as indicated by the increased cell proliferation and the decreased concentration of LDH in the supernatant. The increased lipid deposition and protein expression of SREBP1 and PPARα induced by OA was also reversed by treatment with RES. Moreover, RES could upregulate glucose consumption and the protein expression of phosphorylated IRS1, AKT, ERK and reduced ROS production in OA-induced SH-SY5Y cells. Furthermore, RES treatment reversed the imbalanced protein expression of BDNF, Copine 6, p-β-catenin, and Wnt 1 in SH-SY5Y cells induced by OA and decreased the hyperexpression of p-GSK3β. However, these effects were suppressed by DKK1, which is a specific antagonist of the Wnt signalling pathway. These results suggested that RES has a neuroprotective effect against OA-induced cell injury and dysfunctional glucolipid metabolism, and the mechanism might involve its ability to regulate oxidative stress and insulin resistance via the Wnt/β-catenin signalling pathway.

The Effects of GABAergic System under Cerebral Ischemia: Spotlight on Cognitive Function

In this review, we present evidence about the changes of the GABAergic system on the hippocampus under the ischemic environment, which may be an underlying mechanism to the ischemia-induced cognitive deficit. GABAergic system, in contrast to the glutamatergic system, is considered to play an inhibitory effect on the central nervous system over the past several decades. It has received widespread attention in the area of schizophrenia and epilepsy. The GABAergic system has a significant effect in promoting neural development and formation of local neural circuits of the brain, which is the structural basis of cognitive function. There have been a number of reviews describing changes in the GABAergic system in cerebral ischemia in recent years. However, no study has investigated the changes in the system in the hippocampus during cerebral ischemic injury, which results in cognitive impairment, particularly at the chronic ischemic stage and the late phase of ischemia. We present a review of the changes of the GABAergic system in the hippocampus under ischemia, including GABA interneurons, extracellular GABA neurotransmitter, and GABA receptors. Several studies are also listed correlating amelioration of cognitive impairment by regulating the GABAergic system in the hippocampus damaged under ischemia. Furthermore, exogenous cell transplantation, which improves cognition by modulating the GABAergic system, will also be described in this review to bring new insight and strategy on solving cognitive deficits caused by cerebral ischemia.