Probes for INS

We previously confirmed that postprandial alterations in the circulation and metabolism after a single oral dose of flavan 3-ols (mixture of catechin and catechin oligomers) were involved in an increase in sympathetic nervous activity. However, it is well known that, in response to various stresses, activation of the hypothalamic-pituitary-adrenal (HPA) axis occurs together with sympathetic nerve activity, which is associated with activation of the sympathetic-adrenal-medullary (SAM) axis. In this study, we examined whether the HPA axis was activated after a single dose of flavan 3-ols. We administered an oral dose of 10 or 50 mg/kg flavan 3-ols to male ICR mice, removed the brains, and fixed them in paraformaldehyde-phosphate buffer. Other animals that were treated similarly were decapitated, and blood was collected. In the paraventricular nucleus (PVN), c-fos mRNA expression increased significantly at 15 min after administration of either 10 or 50 mg/kg flavan 3-ols. Corticotropin-releasing hormone (CRH) mRNA expression levels significantly increased at 240 min after administration of 10 mg/kg flavan 3-ols, and at 60 min after administration of 50 mg/kg flavan 3-ols. Plasma corticosterone levels were also significantly increased at 240 min after ingestion of 50 mg/kg flavan 3-ols. In this experiment, we confirmed that the ingestion of flavan 3-ols acted as a stressor in mammals with activation both the SAM and HPA axes.

Parvalbumin (PV) expressing GABAergic interneurons provide large source of GABA to spiny projection neurons (SPNs) in the striatum. However, the roles of PV+ interneurons in the regulation of SPNs in the ventral striatum and emotional states are largely unknown. Here, we investigated whether stimulation of ventral striatal (accumbal) PV+ interneurons would drive emotional valence in mice. We found that during conditioned place preference (CPP) training, activation of accumbal PV+ interneurons evoked place preference while suppressing them resulted in conditioned place aversion (CPA). Activation of PV+interneurons during place conditioning increased Fos expression in SPNs in the direct pathway (dSPNs) and impaired lithium chloride-induced CPA. Activation of dSPNs and SPNs in the indirect pathway (iSPNs) induced CPP and CPA, respectively; conversely, suppression of dSPNs or iSPNs induced CPA or CPP. In addition, activation or suppression of calretinin-expressing (CR) GABAergic interneurons did not induce place preference or aversion. These data suggest that PV+ interneurons can bidirectionally determine the emotional valence through their regulation of accumbal SPN activities and raise the possibility that manipulation of PV+ interneuron activity may have the potential to alter emotional valence and treat related mental disorders.

Cues that predict the availability of food rewards influence motivational states and elicit food-seeking behaviors. If a cue no longer predicts food availability, animals may adapt accordingly by inhibiting food seeking responses. Sparsely activated sets of neurons, coined neuronal ensembles, have been shown to encode the strength of reward-cue associations. While alterations in intrinsic excitability have been shown to underlie many learning and memory processes, little is known about these properties specifically on cue-activated neuronal ensembles. We examined the activation patterns of cue-activated orbitofrontal cortex (OFC) and nucleus accumbens (NAc) shell ensembles using wild-type and Fos-GFP mice following appetitive conditioning with sucrose and extinction learning. We also investigated the neuronal excitability of recently activated, GFP+ neurons in these brain areas using whole-cell electrophysiology in brain slices. Exposure to a sucrose cue elicited activation of neurons in both the NAc shell and OFC. In the NAc shell, but not the OFC, these activated GFP+ neurons were more excitable than surrounding GFP- neurons. Following extinction, the number of neurons activated in both areas was reduced and activated ensembles in neither area exhibited altered excitability. These data suggest that learning-induced alterations in the intrinsic excitability of neuronal ensembles is regulated dynamically across different brain areas. Furthermore, we show that changes in associative strength modulate the excitability profile of activated ensembles in the NAc shell.SIGNIFICANCE STATEMENTSparsely distributed sets of neurons called 'neuronal ensembles' encode learned associations about food and cues predictive of its availability. Widespread changes in neuronal excitability have been observed in limbic brain areas after associative learning, but little is known about the excitability changes that occur specifically on neuronal ensembles that encode appetitive associations. Here we reveal that sucrose cue exposure recruited a more excitable ensemble in the nucleus accumbens, but not orbitofrontal cortex compared to their surrounding neurons. This excitability difference was not observed when the cue's salience was diminished following extinction learning. These novel data provide evidence that the intrinsic excitability of appetitive memory-encoding ensembles is differentially regulated across brain areas and dynamically adapts to changes in associative strength.

Repetitive behaviors are diagnostic for autism spectrum disorder (ASD) and commonly observed in other neurodevelopmental disorders. Currently, there are no effective pharmacological treatments for repetitive behavior in these clinical conditions. This is due to the lack of information about the specific neural circuitry that mediates the development and expression of repetitive behavior. Our previous work in mouse models has linked repetitive behavior to decreased activation of the subthalamic nucleus, a brain region in the indirect and hyperdirect pathways in the basal ganglia circuitry. The present experiments were designed to further test our hypothesis that pharmacological activation of the indirect pathway would reduce repetitive behavior. We used a combination of adenosine A1 and A2A receptor agonists that have been shown to alter the firing frequency of dorsal striatal neurons within the indirect pathway of the basal ganglia. This drug combination markedly and selectively reduced repetitive behavior in both male and female C58 mice over a six-hour period, an effect that required both A1 and A2A agonists as neither alone reduced repetitive behavior. The adenosine A1 and A2A receptor agonist combination also significantly increased the number of Fos transcripts and Fospositive cells in dorsal striatum. Fos induction was found in both direct and indirect pathway neurons suggesting that the drug combination restored the balance of activation across these complementary basal ganglia pathways. The adenosine A1 and A2A receptor agonist combination also maintained its effectiveness in reducing repetitive behavior over a 7-day period. These findings point to novel potential therapeutic targets for development of drug therapies for repetitive behavior in clinical disorders.

Abstract