Expression patterns of Arc mRNA after renewal of appetitive behavior in female rats.

Renewal of appetitive behavior depends on the gonadal hormonal state of the female rat. In this experiment the effect of female rat estrous cycle stage on renewal of appetitive behaviors is replicated and extended upon to understand how endogenous hormonal states around the estrous cycle drive renewal at the neuronal population level. Estrous cycle stage (i.e., proestrus (P, high hormone) or metestrus/diestrus (M/D, low hormone)) was considered during two important learning and behavioral expression windows: at extinction training and during LTM/renewal testing. First, rats in P during context-dependent extinction training but in some other stage of the estrous cycle during long-term memory and renewal testing (Different) were shown to exhibit more renewal of conditioned foodcup (but not conditioned orienting) behavior compared to rats in other estrous cycle groups. Next, cellular compartment analysis of temporal activity using fluorescence in situ hybridization (catFISH) was used to examine immediate early gene activity of Arc mRNA in neuronal populations after distinct context-stimulus exposures (i.e., extinction and acquisition test contexts). Arc mRNA expression patterns were examined in the prefrontal cortex (PFC), amygdala, hippocampus (HPC), and paraventricular nucleus of the thalamus. P-different rats showed differential neuronal population activity in the infralimbic cortex of the PFC, the lateral amygdaloid nucleus, and both CA1 and CA3 regions of the dorsal HPC. In each region P-different rats exhibited more co-expression and less specificity of Arc mRNA compared to other hormonal groups, indicating that renewal of appetitive foodcup behavior induces Arc mRNA in overlapping neuronal populations in female rats.

Rapid appetitive transitions are sculpted by amygdala to accumbens pathways

Foraging, pursuit, and predation rapidly transition into behavioral quiescence during reward capture and consumption. While appetitive-consummatory dissociations are embedded at both psychological and neural levels, the mechanisms controlling switches or transitions between appetitive seeking and consummatory behaviors remain poorly understood. Here we identify the BLA→AcbSh pathway as critical to these transitions by showing that this pathway inhibits the appetitive seeking response in the presence of consummatory demands. Using an appetitive cue-discrimination task in male rats, we show that reward delivery is a significant driver of seeking inhibition and that a BLA→AcbSh pathway mediates this inhibition. This role in suppressing seeking responses during periods of consumption was not due to a general suppression of behavior because responding to other cues during the same test was unaffected. Moreover, it was specific to the BLA→AcbSh pathway, because the contribution of the BLA→AcbC pathway to appetitive switching was distinct and modest. State-dependent silencing of BLA→AcbSh revealed that the modulation of seeking before and after reward delivery are co-dependent. Finally, we found that BLA terminals in AcbSh have functional connectivity to LH-projecting AcbSh neurons, thereby identifying a BLA→AcbSh→LH pathway as a putative route for the rapid regulation of appetitive behaviors. Taken together, these findings suggest that the BLA→AcbSh pathway is a core component of an appetitive switching system, recruited under conditions requiring rapid or dynamic shifts in appetitive behavior, and that this pathway enables these shifts by actively inhibiting seeking.

The interaction between lifetime depression severity and BMI is related to altered activation pattern in the right inferior frontal gyrus during food anticipation

ABSTRACTBackgroundDepression and obesity often co-occur but the underlying neural mechanisms for this bidirectional link are not well understood. Using fMRI, we examined how the relationship between Body Mass Index (BMI) and dimensional lifetime depression severity was associated with brain activation during food anticipation and pleasant/unpleasant rating.Methods90 participants (48 healthy controls, 42 with unipolar depression (UD), 69 female, age=28.5±6.6) were fMRI-scanned while performing the Food and Object Cued Encoding task consisting of food/object anticipation and food/object pleasant/unpleasant rating phases.ResultsThe analysis across all participants revealed a significant BMI-by-lifetime depression severity interaction on RIFG activation during food anticipation (p<0.0125). Most symptomatic and overweight/obese individuals with UD showed decreased right inferior frontal gyrus (RIFG) activation during food anticipation, while less symptomatic and/or normal-weight individuals with UD showed increased RIFG activation during food anticipation. RIFG activation during food anticipation was negatively correlated with RIFG activation during pleasant/unpleasant rating (r= -0.63, p<0.001). Individuals with UD who showed higher RIFG activation for food items during pleasant/unpleasant rating reported liking or wanting those food items less than those with lower RIFG activation (p<0.05).ConclusionsThe IFG is involved in emotion regulation and response inhibition necessary to control appetitive behavior. Greater RIFG activation during pleasant/unpleasant rating of food coupled with low ratings of food liking and wanting could be associated with inhibition of cognitive and emotional response to food in UD. This process may be cognitively challenging and stressful thus putting affected individuals with UD at risk for weight gain and worsening of depression.

An endogenous opioid circuit determines state-dependent appetitive behavior

Mu-opioid peptide receptor (MOPR) stimulation alters respiration, analgesia, and reward behavior, and can induce addiction and drug overdose. Despite its evident importance, the endogenous mechanisms for MOPR regulation of appetitive behavior have remained unknown. Here we report that endogenous MOPR regulation of appetitive behavior in mice acts through a specific dorsal raphe to nucleus accumbens projection. MOPR-mediated inhibition of raphe terminals is necessary and sufficient to determine appetitive behavioral state while select enkephalin-containing NAc ensembles are engaged prior to reward consumption, suggesting that local enkephalin release is the source of endogenous MOPR ligand. Selective modulation of NAc enkephalin neurons and CRISPR-Cas9-mediated disruption of enkephalin substantiate this finding. These results isolate a fundamental endogenous opioid circuit for state-dependent appetitive behavior and suggest alternative mechanisms for opiate modulation of reward.

Dissecting the localization of Tilapia tilapinevirus in the brain of the experimentally infected Nile tilapia (Oreochromis niloticus)

Tilapia tilapinevirus or tilapia lake virus (TiLV) is an emerging virus that inflicts significant mortality on farmed tilapia globally. Previous studies reported detection of the virus in multiple organs of the infected fish; however, little is known about the in-depth localization of the virus in the central nervous system. Herein, we determined the distribution of TiLV in the entire brain of experimentally infected Nile tilapia. In situ hybridization (ISH) using TiLV-specific probes revealed that the virus was broadly distributed throughout the brain. The strongest positive signals were dominantly detected in the forebrain (responsible for learning, appetitive behavior, and attention) and the hindbrain (involved in controlling locomotion and basal physiology). The permissive cell zones for viral infection were observed mostly to be along the blood vessels and the ventricles. This indicates that the virus may productively enter into the brain through the circulatory system and widen broad regions, possibly through the cerebrospinal fluid along the ventricles, and subsequently induce the brain dysfunction. Understanding the pattern of viral localization in the brain may help elucidate the neurological disorders of the diseased fish. This study revealed the distribution of TiLV in the whole infected brain, providing new insights into fish-virus interactions and neuropathogenesis.

Relationship of estrogen synthesis capacity in the brain with obesity and self-control in men and women

Gonadal hormones are linked to mechanisms that govern appetitive behavior and its suppression. Estrogens are synthesized from androgens by the enzyme aromatase, highly expressed in the ovaries of reproductive-aged women and in the brains of men and women of all ages. We measured aromatase availability in the amygdala using positron emission tomography (PET) with the aromatase inhibitor [11C]vorozole in a sample of 43 adult, normal-weight, overweight, or obese men and women. A subsample of 27 also completed personality measures to examine the relationship between aromatase and personality traits related to self-regulation and inhibitory control. Results indicated that aromatase availability in the amygdala was negatively associated with body mass index (BMI) (in kilograms per square meter) and positively correlated with scores of the personality trait constraint independent of sex or age. Individual variations in the brain’s capacity to synthesize estrogen may influence the risk of obesity and self-control in men and women.