Molecular and functional changes in glucokinase expression in the brainstem dorsal vagal complex in a murine model of type 1 diabetes

In situ microwave fixation provides an instantaneous snapshot of the brain metabolome

Brain glucose metabolism is highly heterogeneous among brain regions and continues postmortem. In particular, we demonstrate exhaustion of glycogen and glucose and an increase in lactate production during conventional rapid brain resection and preservation by liquid nitrogen. In contrast, we show that these postmortem changes are not observed with simultaneous animal sacrifice and in situ fixation with focused, high-power microwave. We further employ microwave fixation to define brain glucose metabolism in the mouse model of streptozotocin-induced type 1 diabetes. Using both total pool and isotope tracing analyses, we identified global glucose hypometabolism in multiple brain regions, evidenced by reduced 13C enrichment into glycogen, glycolysis, and the tricarboxylic acid (TCA) cycle. Reduced glucose metabolism correlated with a marked decrease in GLUT2 expression and several metabolic enzymes in unique brain regions. In conclusion, our study supports the incorporation of microwave fixation for more accurate studies of brain metabolism in rodent models.

Protein Kinase C-Dependent Effects of Neurosteroids on Synaptic GABAA Receptor Inhibition Require the δ-Subunit

The dorsal motor nucleus of the vagus (DMV) contains preganglionic motor neurons important for interpreting sensory input from the periphery, integrating that information, and coding the appropriate parasympathetic (vagal) output to target organs. Despite the critical role of hormonal regulation of vagal motor output, few studies examine the role of neurosteroids in the regulation of the DMV. Of the few examinations, no studies have investigated the potential impact of allopregnanolone (Allo), a neuroactive progesterone-derivative, in the regulation of neurotransmission on the DMV. Since DMV neuronal function is tightly regulated by GABAA receptor activity and Allo is an endogenous GABAA receptor ligand, the present study used in vitro whole cell patch clamp to investigate whether Allo alters GABAergic neurotransmission to DMV neurons. Although Allo did not influence GABAergic neurotransmission during initial application (5-20 min), a TTX-insensitive prolongment of decay time and increase in frequency of GABAergic currents was established after Allo was removed from the bath for at least 30 min (LtAllo). Inhibition of protein kinase C (PKC) abolished these effects, suggesting that PKC is largely required to mediate Allo-induced inhibition of the DMV. Using mice that lack the δ-subunit of the GABAA receptor, we further confirmed that PKC-dependent activity of LtAllo required this subunit. Allo also potentiated GABAA receptor activity after a repeated application of δ-subunit agonist, suggesting that the presence of Allo encodes stronger δ-subunit-mediated inhibition over time. Using current clamp recording, we demonstrated that LtAllo-induced inhibition is sufficient to decrease action potential firing and excitability within DMV neurons. We conclude that the effects of LtAllo on GABAergic inhibition are dependent on δ-subunit and PKC activation. Taken together, DMV neurons can undergo long lasting Allo-dependent GABAA receptor plasticity.

FGF19 in the Hindbrain Lowers Blood Glucose and Alters Excitability of Vagal Motor Neurons in Hyperglycemic Mice

Fibroblast growth factor 19 (FGF19) is a protein hormone that produces antidiabetic effects when administered intracerebroventricularly in the forebrain. However, no studies have examined how FGF19 affects hindbrain neurons that participate directly in autonomic control of systemic glucose regulation. Within the dorsal hindbrain, parasympathetic motor neurons of the dorsal motor nucleus of the vagus (DMV) express fibroblast growth factor receptors and their activity regulates visceral homeostatic processes, including energy balance. This study tested the hypothesis that FGF19 acts in the hindbrain to alter DMV neuron excitability and lower blood glucose concentration. Fourth ventricle administration of FGF19 produced no effect on blood glucose concentration in control mice, but induced a significant, peripheral muscarinic receptor-dependent decrease in systemic hyperglycemia for up to 12 h in streptozotocin-treated mice, a model of type 1 diabetes. Patch-clamp recordings from DMV neurons in vitro revealed that FGF19 application altered synaptic and intrinsic membrane properties of DMV neurons, with the balance of FGF19 effects being significantly modified by a recent history of systemic hyperglycemia. These findings identify central parasympathetic circuitry as a novel target for FGF19 and suggest that FGF19 acting in the dorsal hindbrain can alter vagal output to produce its beneficial metabolic effects.

Musings on the wanderer: What's new in our understanding of vago-vagal reflexes? VI. Central vagal circuits that control glucose metabolism

Neurons in the brain stem dorsal vagal complex (DVC) take part in a continuous bidirectional crosstalk, in which they receive and respond to a vast array of signaling molecules, including glucose. Importantly, chronic dysregulation of blood glucose concentration, a hallmark of high prevalence pathologies, such as diabetes and metabolic syndrome, can induce neuroplasticity in DVC neural networks, which is hypothesized to either contribute to or compensate for the glycemic or insulinemic dysregulation observed in these conditions. Here, we revisit the topic of vagal reflexes to review recent research on the importance of DVC function in regulating systemic glucose homeostasis and the neuroplastic changes in this brain region that are associated with systemic glucose alterations. We also discuss the critical connection between these nuclei and the gut and the role of central vagal circuits in the favorable outcomes associated with bariatric surgical procedures for metabolic disorders.

Fibroblast Growth Factor 19 Increases the Excitability of Pre-Motor Glutamatergic Dorsal Vagal Complex Neurons From Hyperglycemic Mice

Intracerebroventricular administration of the protein hormone fibroblast growth factor 19 (FGF19) to the hindbrain produces potent antidiabetic effects in hyperglycemic mice that are likely mediated through a vagal parasympathetic mechanism. FGF19 increases the synaptic excitability of parasympathetic motor neurons in the dorsal motor nucleus of the vagus (DMV) from hyperglycemic, but not normoglycemic, mice but the source of this synaptic input is unknown. Neurons in the area postrema (AP) and nucleus tractus solitarius (NTS) express high levels of FGF receptors and exert glutamatergic control over the DMV. This study tested the hypothesis that FGF19 increases glutamate release in the DMV by increasing the activity of glutamatergic AP and NTS neurons in hyperglycemic mice. Glutamate photoactivation experiments confirmed that FGF19 increases synaptic glutamate release from AP and NTS neurons that connect to the DMV in hyperglycemic, but not normoglycemic mice. Contrary to expectations, FGF19 produced a mixed effect on intrinsic membrane properties in the NTS with a trend towards inhibition, suggesting that another mechanism was responsible for the observed effects on glutamate release in the DMV. Consistent with the hypothesis, FGF19 increased action potential-dependent glutamate release in the NTS in hyperglycemic mice only. Finally, glutamate photoactivation experiments confirmed that FGF19 increases the activity of glutamatergic AP neurons that project to the NTS in hyperglycemic mice. Together, these results support the hypothesis that FGF19 increases glutamate release from AP and NTS neurons that project to the DMV in hyperglycemic mice. FGF19 therefore modifies the local vago-vagal reflex circuitry at several points. Additionally, since the AP and NTS communicate with several other metabolic regulatory nuclei in the brain, FGF19 in the hindbrain may alter neuroendocrine and behavioral aspects of metabolism, in addition to changes in parasympathetic output.

Glucokinase in stellate ganglia cooperates with P2X3 receptor to develop cardiac sympathetic neuropathy in type 2 diabetes rats

Glucokinase (GCK) may be involved in inflammatory pathological changes, while the P2X3 receptor in the stellate ganglia (SG) is related to diabetic cardiac autonomic neuropathy. In this study, we explored the relationship between the upregulated GCK in SG and diabetic cardiac sympathy. The expression and location of GCK and P2X3 in SG of type 2 diabetes mellitus (T2DM) rats were assessed. Changes in cardiac function were determined by measuring blood pressure, sympathetic nerve activity, heart rate, and heart rate variability. P2X3 agonist-activated currents in isolated stellate ganglion neurons and cultured human embryonic kidney 293 (HEK293) cells were recorded using whole-cell patch clamp techniques. The upregulated expression of GCK in SG of T2DM rats was decreased after treatment with GCK short hairpin RNA (shRNA). GCK shRNA treatment also improved the blood pressure, sympathetic nerve activity, heart rate, and heart rate variability in T2DM rats. By contrast, the expression of P2X3 and tumor necrosis factor α (TNF-α) was lessened by GCK shRNA treatment. In addition, adenosine triphosphate (ATP)-activated currents in stellate ganglion neurons and HEK293 cells co-transfected with GCK and P2X3 receptor plasmids were reduced after GCK shRNA treatment. In T2DM rats, knockdown of GCK relieved the diabetic cardiac sympathy mediated by P2X3 receptor-involved upregulation of GCK in SG.

Diabetes, and its treatment, as an effector of autonomic nervous system circuits and its functions

Diabetes increases the risk of cardiovascular complications, including heart failure, hypertension, and stroke. There is a strong involvement of autonomic dysfunction in individuals with diabetes that exhibit clinical manifestations of cardiovascular diseases (CVD). Still, the mechanisms by which diabetes and its treatments alter autonomic function and subsequently affect cardiovascular complications remain elusive. For this reason, understanding the brainstem circuits involved in sensing metabolic state(s) and enacting autonomic control of the cardiovascular system are important to develop more comprehensive therapies for individuals with diabetes at increased risk for CVD. We review how autonomic nervous system circuits change during these disease states and discuss their potential role in current pharmacotherapies that target diabetic states. Overall, this review proposes that the brainstem circuits provide an integrative sensorimotor network capable of responding to metabolic cues to regulate cardiovascular function and this network is modified by, and in turn affects, diabetes-induced CVD and its treatment.

Hypoglycemia causes dysregulation of Neuregulin 1, ErbB receptors, Ki67 in cerebellum and brainstem during diabetes: Implications in motor function

Hypoglycemia induced brain injury poses a major setback to optimal blood glucose regulation during diabetes. It causes irreversible injury in several brain regions culminating in improper function. Neuregulin 1 and ErbB receptors are involved in regeneration during adulthood as well as in glucose homeostasis. We intended to understand the influence of extreme discrepancies in glycemic levels on Neuregulin 1, ErbB receptor subtypes and Ki67 expression in relation to motor deficits as a consequence of cellular dysfunction/degeneration in the cerebellum and brainstem during diabetes. Elevated oxidative stress and compromised antioxidant system havocs cerebellum and brainstem related function. Cellular alteration of Purkinje neurons in the cerebellum and presence of axonal spheroids in the brainstem are suggestive of impairment to neural circuits involved in motor function. Down regulation of Neuregulin 1, ErbB 2, ErbB 3, ErbB 4 and Ki67 expression observed during diabetes and hypoglycemia may critically cause regenerative deficiency in cerebellum. The coincident up regulation of Neuregulin 1, ErbB 2, ErbB 3 and ErbB 4 in brainstem during diabetes is an attempt to maintain regenerative homeostasis to ensure its function. However, hypoglycemic insults results in down regulation of Neuregulin 1, ErbB 4 expression that severely compromises their role in brainstem. Grid walking test confirmed motor impairment during diabetes that showed further deterioration due to hypoglycemic stress. Thus altered expression of Neuregulin 1, ErbB receptor subtypes and Ki67 during diabetes and hypoglycemia contributes to reduced cellular proliferation and deficits in motor function.

A voltage-dependent depolarization induced by low external glucose in neurons of the nucleus of the tractus solitarius: interaction with KATP channels

KEY POINTS

Neurons from the brainstem nucleus of the tractus solitarius (NTS) participate in the counter-regulatory mechanisms in response to hypoglycaemia. ATP-sensitive potassium (K_ATP ) channels are expressed in NTS neurons, and are partially open at rest in normoglycaemic 5 mM glucose. In normoglycaemic conditions, most NTS neurons depolarize in response to low external glucose (0.5 mM), via a voltage-dependent mechanism. Conversely, most NTS neurons incubated in hyperglycaemic 10 mM glucose do not respond to low glucose due to a more positive resting membrane potential caused by the closure of K_ATP channels following increased intracellular metabolic ATP. Our findings show that in hyperglycaemic conditions, NTS neurons failed to sense rapid changes in external glucose, which could be related to hypoglycaemia-associated autonomic failure.

ABSTRACT

The nucleus of the tractus solitarius (NTS) is an integrative centre for autonomic counter-regulatory responses to hypoglycaemia. K_ATP channels link the metabolic status of the neuron to its excitability. Here we investigated the influence of K_ATP channels on the membrane potential of NTS neurons in normo- and hyperglycaemic external glucose concentrations, and after switching to a hypoglycaemic concentration, using in vitro electrophysiological recordings in brainstem slices. We found that in normoglycaemic (5 mM) glucose, tolbutamide, a K_ATP channel antagonist, depolarized the membrane of most neurons, and this effect was observed in more hyperpolarized neurons. All neurons hyperpolarized after pharmacological activation of K_ATP channels. Most NTS neurons depolarized in the presence of low glucose (0.5 mM), and this effect was only seen in hyperpolarized neurons. The effect of glucose was caused by a cationic current with a reversal potential around -50 mV. In the presence of hyperglycaemic glucose (10 mM), neurons were more depolarized, and fewer neurons responded to K_ATP blockage. Application of 0.5 mM glucose solution to these neurons depolarized the membrane only in more hyperpolarized neurons. We conclude that NTS neurons present with K_ATP channels open at rest in normoglycaemic conditions, and their membrane potential is affected by extracellular glucose. Moreover, NTS neurons depolarize the membrane in response to the application of a low glucose solution, but this effect is occluded by membrane depolarization triggered by K_ATP blockage. Our data suggest a homeostatic regulation of the membrane potential by external glucose, and a possible mechanism related to the hypoglycaemia-associated autonomic failure.

A hindbrain inhibitory microcircuit mediates vagally-coordinated glucose regulation

Neurons in the brainstem dorsal vagal complex integrate neural and humoral signals to coordinate autonomic output to viscera that regulate a variety of physiological functions, but how this circuitry regulates metabolism is murky. We tested the hypothesis that premotor, GABAergic neurons in the nucleus tractus solitarius (NTS) form a hindbrain micro-circuit with preganglionic parasympathetic motorneurons of the dorsal motor nucleus of the vagus (DMV) that is capable of modulating systemic blood glucose concentration. In vitro, neuronal activation or inhibition using either excitatory or inhibitory designer receptor exclusively activated by designer drugs (DREADDs) constructs expressed in GABAergic NTS neurons increased or decreased, respectively, action potential firing of GABAergic NTS neurons and downstream synaptic inhibition of the DMV. In vivo, DREADD-mediated activation of GABAergic NTS neurons increased systemic blood glucose concentration, whereas DREADD-mediated silencing of these neurons was without effect. The DREADD-induced hyperglycemia was abolished by blocking peripheral muscarinic receptors, consistent with the hypothesis that altered parasympathetic drive mediated the response. This effect was paralleled by elevated serum glucagon and hepatic phosphoenolpyruvate carboxykinase 1 (PEPCK1) expression, without affecting insulin levels or muscle metabolism. Activity in a hindbrain inhibitory microcircuit is sufficient to modulate systemic glucose concentration, independent of insulin secretion or utilization.

Altered A-type potassium channel function in the nucleus tractus solitarii in acquired temporal lobe epilepsy

Sudden unexpected death in epilepsy (SUDEP) is among the leading causes of death in people with epilepsy. Individuals with temporal lobe epilepsy (TLE) have a high risk for SUDEP because the seizures are often medically intractable. Neurons in the nucleus tractus solitarii (NTS) have been implicated in mouse models of SUDEP and play a critical role in modulating cardiorespiratory and autonomic output. Increased neuronal excitability of inhibitory, GABAergic neurons in the NTS develops during epileptogenesis, and NTS dysfunction has been implicated in mouse models of SUDEP. In this study we used the pilocarpine-induced status epilepticus model of TLE (i.e., pilo-SE mice) to investigate the A-type voltage-gated K⁺ channel as a potential contributor to increased excitability in GABAergic NTS neurons during epileptogenesis. Compared with age-matched control mice, pilo-SE mice displayed an increase in spontaneous action potential frequency and half-width 9-12 wk after treatment. Activity of GABAergic NTS neurons from pilo-SE mice showed less sensitivity to 4-aminopyridine. Correspondingly, reduced A-type K⁺ current amplitude was detected in these neurons, with no change in activation or inactivation kinetics. No changes were observed in K_v4.1, K_v4.2, K_v4.3, KChIP1, KChIP3, or KChIP4 mRNA expression. These changes contribute to the increased excitability in GABAergic NTS neurons that develops in TLE and may provide insight into potential mechanisms contributing to the increased risk for cardiorespiratory collapse and SUDEP in this model. NEW & NOTEWORTHY Sudden unexpected death in epilepsy (SUDEP) is a leading cause of death in epilepsy, and dysfunction in central autonomic neurons may play a role. In a mouse model of acquired epilepsy, GABAergic neurons in the nucleus tractus solitarii developed a reduced amplitude of the A-type current, which contributes to the increased excitability seen in these neurons during epileptogenesis. Neuronal excitability changes in inhibitory central vagal circuitry may increase the risk for cardiorespiratory collapse and SUDEP.

Improved glucose homeostasis in male obese Zucker rats coincides with enhanced baroreflexes and activation of the nucleus tractus solitarius

Young adult male obese Zucker rats (OZR) develop insulin resistance and hypertension with impaired baroreflex-mediated bradycardia and activation of nucleus tractus solitarius (NTS). Because type 1 diabetic rats also develop impaired baroreflex-mediated NTS activation, we hypothesized that improving glycemic control in OZR would enhance compromised baroreflexes and NTS activation. Fasting blood glucose measured by telemetry was comparable in OZR and lean Zucker rats (LZR) at 12-17 wk. However, with access to food, OZR were chronically hyperglycemic throughout this age range. By 15-17 wk of age, tail samples yielded higher glucose values than those measured by telemetry in OZR but not LZR, consistent with reports of exaggerated stress responses in OZR. Injection of glucose (1g/kg ip) produced larger rises in glucose and areas under the curve in OZR than LZR. Treatment with metformin (300 mg·kg^-1·day^-1) or pioglitazone (5 mg·kg^-1·day^-1) in drinking water for 2-3 wk normalized fed glucose levels in OZR with no effect in LZR. After metformin treatment, area under the curve for blood glucose after glucose injection was reduced in OZR and comparable to LZR. Hyperinsulinemia was slightly reduced by each treatment in OZR, but insulin was still greatly elevated compared with LZR. Neither treatment reduced hypertension in OZR, but both treatments significantly improved the blunted phenylephrine-induced bradycardia and NTS c-Fos expression in OZR with no effect in LZR. These data suggest that restoring glycemic control in OZR enhances baroreflex control of heart rate by improving the response of the NTS to raising arterial pressure, even in the presence of hyperinsulinemia and hypertension.

Adenovirus-mediated suppression of hypothalamic glucokinase affects feeding behavior

Glucokinase (GK), the hexokinase involved in glucosensing in pancreatic β-cells, is also expressed in arcuate nucleus (AN) neurons and hypothalamic tanycytes, the cells that surround the basal third ventricle (3V). Several lines of evidence suggest that tanycytes may be involved in the regulation of energy homeostasis. Tanycytes have extended cell processes that contact the feeding-regulating neurons in the AN, particularly, agouti-related protein (AgRP), neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART) and proopiomelanocortin (POMC) neurons. In this study, we developed an adenovirus expressing GK shRNA to inhibit GK expression in vivo. When injected into the 3V of rats, this adenovirus preferentially transduced tanycytes. qRT-PCR and Western blot assays confirmed GK mRNA and protein levels were lower in GK knockdown animals compared to the controls. In response to an intracerebroventricular glucose injection, the mRNA levels of anorexigenic POMC and CART and orexigenic AgRP and NPY neuropeptides were altered in GK knockdown animals. Similarly, food intake, meal duration, frequency of eating events and the cumulative eating time were increased, whereas the intervals between meals were decreased in GK knockdown rats, suggesting a decrease in satiety. Thus, GK expression in the ventricular cells appears to play an important role in feeding behavior.

High glucose increases action potential firing of catecholamine neurons in the nucleus of the solitary tract by increasing spontaneous glutamate inputs

Glucose is a crucial substrate essential for cell survival and function. Changes in glucose levels impact neuronal activity and glucose deprivation increases feeding. Several brain regions have been shown to respond to glucoprivation, including the nucleus of the solitary tract (NTS) in the brain stem. The NTS is the primary site in the brain that receives visceral afferent information from the gastrointestinal tract. The catecholaminergic (CA) subpopulation within the NTS modulates many homeostatic functions including cardiovascular reflexes, respiration, food intake, arousal, and stress. However, it is not known if they respond to changes in glucose. Here we determined whether NTS-CA neurons respond to changes in glucose concentration and the mechanism involved. We found that decreasing glucose concentrations from 5 mM to 2 mM to 1 mM, significantly decreased action potential firing in a cell-attached preparation, whereas increasing it back to 5 mM increased the firing rate. This effect was dependent on glutamate release from afferent terminals and required presynaptic 5-HT₃Rs. Decreasing the glucose concentration also decreased both basal and 5-HT₃R agonist-induced increase in the frequency of spontaneous glutamate inputs onto NTS-CA neurons. Low glucose also blunted 5-HT-induced inward currents in nodose ganglia neurons, which are the cell bodies of vagal afferents. The effect of low glucose in both nodose ganglia cells and in NTS slices was mimicked by the glucokinase inhibitor glucosamine. This study suggests that NTS-CA neurons are glucosensing through a presynaptic mechanism that is dependent on vagal glutamate release, 5-HT₃R activity, and glucokinase.

Glutamatergic drive facilitates synaptic inhibition of dorsal vagal motor neurons after experimentally induced diabetes in mice

The role of central regulatory circuits in modulating diabetes-associated glucose dysregulation has only recently been under rigorous investigation. One brain region of interest is the dorsal motor nucleus of the vagus (DMV), which contains preganglionic parasympathetic motor neurons that regulate subdiaphragmatic visceral function. Previous research has demonstrated that glutamatergic and GABAergic neurotransmission are independently remodeled after chronic hyperglycemia/hypoinsulinemia. However, glutamatergic circuitry within the dorsal brain stem impinges on GABAergic regulation of the DMV. The present study investigated the role of glutamatergic neurotransmission in synaptic GABAergic control of DMV neurons after streptozotocin (STZ)-induced hyperglycemia/hypoinsulinemia by using electrophysiological recordings in vitro. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was elevated in DMV neurons from STZ-treated mice. The effect was abolished in the presence of the ionotropic glutamate receptor blocker kynurenic acid or the sodium channel blocker tetrodotoxin, suggesting that after STZ-induced hyperglycemia/hypoinsulinemia, increased glutamatergic receptor activity occurs at a soma-dendritic location on local GABA neurons projecting to the DMV. Although sIPSCs in DMV neurons normally demonstrated considerable amplitude variability, this variability was significantly increased after STZ-induced hyperglycemia/hypoinsulinemia. The elevated amplitude variability was not related to changes in quantal release, but rather correlated with significantly elevated frequency of sIPSCs in these mice. Taken together, these findings suggest that GABAergic regulation of central vagal circuitry responsible for the regulation of energy homeostasis undergoes complex functional reorganization after several days of hyperglycemia/hypoinsulinemia, including both glutamate-dependent and -independent forms of plasticity.

Insights into the role of neuronal glucokinase

Glucokinase is a key component of the neuronal glucose-sensing mechanism and is expressed in brain regions that control a range of homeostatic processes. In this review, we detail recently identified roles for neuronal glucokinase in glucose homeostasis and counterregulatory responses to hypoglycemia and in regulating appetite. We describe clinical implications from these advances in our knowledge, especially for developing novel treatments for diabetes and obesity. Further research required to extend our knowledge and help our efforts to tackle the diabetes and obesity epidemics is suggested.

Differential effects of rapamycin treatment on tonic and phasic GABAergic inhibition in dentate granule cells after focal brain injury in mice

The cascade of events leading to post-traumatic epilepsy (PTE) after traumatic brain injury (TBI) remains unclear. Altered inhibition in the hippocampal formation and dentate gyrus is a hallmark of several neurological disorders, including TBI and PTE. Inhibitory synaptic signaling in the hippocampus is predominately driven by γ-aminobutyric acid (GABA) neurotransmission, and is prominently mediated by postsynaptic type A GABA receptors (GABAAR's). Subsets of these receptors involved in tonic inhibition of neuronal membranes serve a fundamental role in maintenance of inhibitory state, and GABAAR-mediated tonic inhibition is altered functionally in animal models of both TBI and epilepsy. In this study, we assessed the effect of mTOR inhibition on hippocampal hilar inhibitory interneuron loss and synaptic and tonic GABAergic inhibition of dentate gyrus granule cells (DGCs) after controlled cortical impact (CCI) to determine if mTOR activation after TBI modulates GABAAR function. Hilar inhibitory interneuron density was significantly reduced 72h after CCI injury in the dorsal two-thirds of the hemisphere ipsilateral to injury compared with the contralateral hemisphere and sham controls. Rapamycin treatment did not alter this reduction in cell density. Synaptic and tonic current measurements made in DGCs at both 1-2 and 8-13weeks post-injury indicated reduced synaptic inhibition and THIP-induced tonic current density in DGCs ipsilateral to CCI injury at both time points post-injury, with no change in resting tonic GABAAR-mediated currents. Rapamycin treatment did not alter the reduced synaptic inhibition observed in ipsilateral DGCs 1-2weeks post-CCI injury, but further reduced synaptic inhibition of ipsilateral DGCs at 8-13weeks post-injury. The reduction in THIP-induced tonic current after injury, however, was prevented by rapamycin treatment at both time points. Rapamycin treatment thus differentially modifies CCI-induced changes in synaptic and tonic GABAAR-mediated currents in DGCs.