The pattern of Fos-like immunoreactivity expressed within the nucleus of the solitary tract is associated with individual variation in the taste quality of a stimulus

Neuronal activity in the anterior paraventricular nucleus of thalamus positively correlated with sweetener consumption in mice

Although the brain can discriminate between various sweet substances, the underlying neural mechanisms of this complex behavior remain elusive. This study examines the role of the anterior paraventricular nucleus of the thalamus (aPVT) in governing sweet preference in mice. We fed the mice six different diets with equal sweetness for six weeks: control diet (CD), high sucrose diet (HSD), high stevioside diet (HSSD), high xylitol diet (HXD), high glycyrrhizin diet (HGD), and high mogroside diet (HMD). The mice exhibited a marked preference specifically for the HSD and HSSD. Following consumption of these diets, c-Fos expression levels in the aPVT were significantly higher in these two groups compared to the others. Utilizing fiber photometry calcium imaging, we observed rapid activation of aPVT neurons in response to sucrose and stevioside intake, but not to xylitol or water. Our findings suggest that aPVT activity aligns with sweet preference in mice, and notably, stevioside is the sole plant-based sweetener that elicits an aPVT response comparable to that of sucrose.

Escalation of alcohol intake is associated with regionally decreased insular cortex activity but not changes in taste quality

BACKGROUND

Intermittent access to ethanol drives persistent escalation of intake and rapid transition from moderate to compulsive-like drinking. Intermittent ethanol drinking may facilitate escalation of intake in part by altering aversion-sensitive neural substrates, such as the insular cortex (IC), thus driving greater approach toward stimuli previously treated as aversive.

METHODS

We conducted a series of experiments in rats to examine behavioral and neural responses associated with escalation of ethanol intake. First, taste reactivity analyses quantified the degree to which intermittent brief-access ethanol exposure (BAEE) alters sensitivity to the aversive properties of ethanol. Next, we determined whether pharmacological IC inhibition facilitated ethanol escalation. Finally, given that the IC is primary gustatory cortex, we employed psychophysical paradigms to assess whether escalation of ethanol intake induced changes in ethanol taste. These paradigms measured changes in sensitivity to the intensity of ethanol taste and whether escalation in intake shifts the salient taste quality of ethanol by measuring the degree to which the taste of ethanol generalized to a sucrose-like ("sweet") or quinine-like ("bitter") percept.

RESULTS

We found a near-complete loss of aversive oromotor responses in ethanol-exposed relative to ethanol-naïve rats. Additionally, we observed significantly lower expression of ethanol-induced c-Fos expression in the posterior IC in exposed rats relative to naïve rats. Inhibition of the IC resulted in a modest, but statistically reliable increase in the acceptance of higher ethanol concentrations in naïve rats. Finally, we found no evidence of changes in the psychophysical assessment of the taste of ethanol in exposed, relative to naïve, rats.

CONCLUSIONS

Our results demonstrate that neural activity within the IC adapts following repeated presentations of ethanol in a manner that correlates with reduced sensitivity to the aversive hedonic properties of ethanol. These data help to establish that alterations in IC activity may be driving exposure-induced escalations in ethanol intake.