DAF-2c signaling promotes taste avoidance after starvation in Caenorhabditis elegans by controlling distinct phospholipase C isozymes

Previously, we reported that DAF-2c, an axonal insulin receptor isoform in Caenorhabditis elegans, acts in the ASER gustatory neuron to regulate taste avoidance learning, a process in which worms learn to avoid salt concentrations experienced during starvation. Here, we show that secretion of INS-1, an insulin-like peptide, after starvation conditioning is sufficient to drive taste avoidance via DAF-2c signaling. Starvation conditioning enhances the salt-triggered activity of AIA neurons, the main sites of INS-1 release, which potentially promotes feedback signaling to ASER to maintain DAF-2c activity during taste avoidance. Genetic studies suggest that DAF-2c–Akt signaling promotes high-salt avoidance via a decrease in PLCβ activity. On the other hand, the DAF-2c pathway promotes low-salt avoidance via PLCε and putative Akt phosphorylation sites on PLCε are essential for taste avoidance. Our findings imply that animals disperse from the location at which they experience starvation by controlling distinct PLC isozymes via DAF-2c.

Effects of Buprenorphine on the Memory and Learning Deficit Induced by Methamphetamine Administration in Male Rats

Little is known about the effects of methamphetamine (Meth) and buprenorphine (Bup) on memory and learning in rats. The aim of this investigation was to examine the impact of Meth and Bup on memory and learning. Fourteen male Wistar rats weighing 250–300 g were assigned to four groups: Sham, Meth, Bup, and Meth + Bup and were treated for 1 week. Spatial learning and memory, avoidance learning, and locomotion were assessed using the Morris water maze, passive avoidance learning, and open field tests, respectively. Meth and Bup impaired spatial learning and memory in rats. Co-administration of Meth + Bup did not increase the time spent in the target quadrant compared to Meth alone in the MWM. The Bup and Meh + Bup groups were found with an increase in step-through latency (STLr) and a decrease in the time spent in the dark compartment (TDC). Meth and Bup had no effects on locomotor activity in the open field test. Bup showed a beneficial effect on aversive memory. Since Bup demonstrates fewer side effects than other opioid drugs, it may be preferable for the treatment of avoidance memory deficits in patients with Meth addiction.

Paternal Aggression in Early-Life Impairs the Spatial Memory and Passive Avoidance Learning in Adulthood of Male Rats: The Possible Role of DRD2

Negative early-life experiences (e.g., having an aggressive father) can leave long-lasting impacts on the behavior. However, it is not clear if they influence learning and memory. In this study, we investigated the influences that the presence of an aggressive father had on the level of passive avoidance learning and spatial memory. We also studied the changes in the dopamine receptor D2 (DRD2) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) gene expression in the hippocampus. Then, we evaluated if a DRD2 antagonist (Sulpiride, 0.125, 0.25, or 0.5 µg/rat) could modulate these changes. We found that the subjects exposed to early-life stress made by aggressive fathers had impaired passive avoidance learning and spatial memory than those with normal fathers. Treatment with Sulpiride improved passive avoidance learning and spatial memory in rats with aggressive fathers. The rats with aggressive fathers also had higher expression of the DRD2 gene in their hippocampus than those with normal fathers, while the PGC-1α gene expression was not different among groups. Treatment with Sulpiride (0.125, 0.25, or 0.5 µg/rat) reduced the DRD2 gene expression in those with aggressive fathers to the normal level in those with normal fathers. These data suggest that living in a shared place with an aggressive father, even without any physical contact, can detrimentally affect passive avoidance learning and spatial memory which is accompanied by the increased expression of the DRD2 gene. Also, Sulpiride as a dopaminergic antagonist could reverse this process.

Overnight fasting affects avoidance learning and relief

Prolonged fasting influences threat and reward processing, two fundamental systems underpinning adaptive behaviors. In animals, overnight fasting sensitizes the mesolimbic-dopaminergic activity governing avoidance, reward, and fear-extinction learning. Despite evidence that overnight fasting may also affect reward and fear learning in humans, effects on human avoidance learning have not been studied yet. Here, we examined the effects of 16h-overnight fasting on instrumental avoidance and relief from threat omission. To this end, 50 healthy women were randomly assigned to a fasting (N=25) or a re-feeding group (N=25) and performed an Avoidance-Relief Task. We found that fasting decreases unnecessary avoidance during signaled safety; this effect was mediated via a reduction in relief pleasantness during signaled absence of threat. A fasting-induced reduction in relief was also found during fear extinction learning. We conclude that fasting optimizes avoidance and safety learning. Future studies should test whether these effects also hold for anxious individuals.

Different brain systems support the aversive and appetitive sides of human pain-avoidance learning

Both unexpected pain and unexpected pain absence can drive avoidance learning, but whether they do so via shared or separate neural and neurochemical systems is largely unknown. To address this issue, we combined an instrumental pain-avoidance learning task with computational modeling, functional magnetic resonance imaging (fMRI) and pharmacological manipulations of the dopaminergic (100 mg levodopa) and opioidergic (50 mg naltrexone) systems (N=83). Computational modeling provided evidence that untreated participants learned more from received than avoided pain. Our dopamine and opioid manipulations negated this learning asymmetry by selectively increasing learning rates for avoided pain. Furthermore, our fMRI analyses revealed that pain prediction errors were encoded in subcortical and limbic brain regions, whereas no-pain prediction errors were encoded in frontal and parietal cortical regions. However, we found no effects of our pharmacological manipulations on the neural encoding of prediction errors. Together, our results suggest that human pain-avoidance learning is supported by separate threat- and safety-learning systems, and that dopamine and endogenous opioids specifically regulate learning from successfully avoided pain.

Divergent encoding of active avoidance behavior in corticostriatal and corticolimbic projections

Active avoidance behavior, in which an animal performs an action to avoid a stressor, is crucial for survival and may provide insight into avoidance behaviors seen in anxiety disorders. Active avoidance requires the dorsomedial prefrontal cortex (dmPFC), which is thought to regulate avoidance via downstream projections to the striatum and amygdala. However, the endogenous activity of projection-defined dmPFC subpopulations during active avoidance learning remains unexplored. Here we utilized fiber photometry to record from the dmPFC and its downstream projections to the dorsomedial striatum (DMS) and the basolateral amygdala (BLA) during active avoidance learning in mice. We examined neural activity during conditioned stimulus (CS) presentations, active avoidance, and cued freezing. Both prefrontal projections showed learning-related increases in activity during CS onset throughout active avoidance training. The dmPFC as a whole showed increased activity during avoidance and decreased activity during cued freezing. Finally, dmPFC-DMS and dmPFC-BLA projections showed divergent encoding of active avoidance behavior, with the dmPFC-DMS projection showing increased activity and the dmPFC-BLA showing decreased activity during active avoidance. Our results identify differential prefrontal encoding of active and passive coping behaviors in the same behavioral paradigm and demonstrate divergent encoding of active avoidance in projection-specific dmPFC subpopulations.