Reversiblephosphorylation,afundamentalregulatorymechanismrequiredformanybiologicalprocessesincludingmemoryformation,iscoordinated bytheopposingactionsofproteinkinasesandphosphatases.TypeIproteinphosphatase(PP1),inparticular,hasbeenshowntoconstrainlearningand memory formation. However, how PP1 might be regulated in memory is still not clear. Our previous work has elucidated that PP1 inhibitor-2 (I-2) is an endogenousregulatorofPP1inhippocampalandcorticalneurons(Houetal.,2013).Contrarytoexpectation,ourstudiesofcontextualfearconditioning andnovelobjectrecognitioninI-2heterozygousmicesuggestthatI-2isamemorysuppressor.Inaddition,lentiviralknock-downofI-2intheratdorsal hippocampus facilitated memory for tasks dependent on the hippocampus. Our data indicate that I-2 suppresses memory formation, probably via negatively regulating the phosphorylation of cAMP/calcium response element-binding protein (CREB) at serine 133 and CREB-mediated gene expression in dorsal hippocampus. Surprisingly, the data from both biochemical and behavioral studies suggest that I-2, despite its assumed action as a PP1 inhibitor, is a positive regulator of PP1 function in memory formation.

No abstract

Repeated use of opioids can lead to the development of analgesic tolerance and dependence. Additionally, chronic opioid exposure can cause a paradoxical emergence of heightened pain sensitivity to noxious stimuli, termed hyperalgesia, which may drive continued or escalated use of opioids to manage worsening pain symptoms. Opioid-induced hyperalgesia has traditionally been measured in rodents via reflex-based assays, including the von Frey method. To better model the cognitive/motivational dimension of pain in a state of opioid dependence and withdrawal, we employed a recently developed non-reflex-based method for measuring pain avoidance-like behavior in animals (mechanical conflict avoidance test). Adult male Wistar rats were administered an escalating dose regimen of morphine (opioid-dependent group) or repeated saline (control group). Morphine-dependent rats exhibited significantly greater avoidance of noxious stimuli during withdrawal. We next investigated individual relationships between pain avoidance-like behavior and alterations in protein phosphorylation in central motivation-related brain areas. We discovered that pain avoidance-like behavior was significantly correlated with alterations in phosphorylation status of protein kinases (ERK, CaMKII), transcription factors (CREB), presynaptic markers of neurotransmitter release (Synapsin), and the rate-limiting enzyme for dopamine synthesis (TH) across specific brain regions. Our findings suggest that alterations in phosphorylation events in specific brain centers may support cognitive/motivational responses to avoid pain.

The prefrontal cortex (PFC) represents and executes the highest forms of goal-directed behavior, and has thereby attained a central neuroanatomical position in most pathophysiological conceptualizations of motivational disorders, including alcohol use disorder (AUD). Excessive, intermittent exposure to alcohol produces an allostatic dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis along with heightened forebrain glucocorticoid signaling that can damage PFC architecture and function. Negative affective states intimately associated with the transition to alcohol dependence result not only from a dysregulated HPA axis, but also from the inability of a damaged PFC to regulate subcortical stress and reinforcement centers, including the ventral striatum and amygdala. Several cognitive symptoms commonly associated with severe AUD, ranging from poor risk management to the cognitive/affective dimension of pain, are likely mediated by altered function of key anatomical elements that modulate PFC executive function, including contributions from the cingulate cortex and insula. Future therapeutic strategies for severe AUD should focus on attenuating the deleterious effects of excessive stress hormone activity on cognitive/affective and motivational behaviors gated by the PFC.