Nonmuscle myosin IIB as a therapeutic target for the prevention of relapse to methamphetamine use.

Memories associated with drug use increase vulnerability to relapse in substance use disorder (SUD), and there are no pharmacotherapies for the prevention of relapse. Previously, we reported a promising finding that storage of memories associated with methamphetamine (METH), but not memories for fear or food reward, is vulnerable to disruption by actin depolymerization in the basolateral amygdala complex (BLC). However, actin is not a viable therapeutic target because of its numerous functions throughout the body. Here we report the discovery of a viable therapeutic target, nonmuscle myosin IIB (NMIIB), a molecular motor that supports memory by directly driving synaptic actin polymerization. A single intra-BLC treatment with Blebbistatin (Blebb), a small-molecule inhibitor of class II myosin isoforms, including NMIIB, produced a long-lasting disruption of context-induced drug seeking (at least 30 days). Further, postconsolidation genetic knockdown of Myh10, the heavy chain of the most highly expressed NMII in the BLC, was sufficient to produce METH-associated memory loss. Blebb was found to be highly brain penetrant. A single systemic injection of the compound selectively disrupted the storage of METH-associated memory and reversed the accompanying increase in BLC spine density. This effect was specific to METH-associated memory, as it had no effect on an auditory fear memory. The effect was also independent of retrieval, as METH-associated memory was disrupted 24 h after a single systemic injection of Blebb delivered in the home cage. Together, these results argue for the further development of small-molecule inhibitors of NMII as potential therapeutics for the prevention of SUD relapse triggered by drug associations.

Narp immunostaining of human hypocretin (orexin) neurons: loss in narcolepsy.

OBJECTIVE: To investigate whether neuronal activity-regulated pentraxin (Narp) colocalizes with hypocretin (Hcrt or orexin) in the normal human brain and to determine if Narp staining is lost in the narcoleptic human brain. BACKGROUND: Human narcolepsy is characterized by a loss of the peptide hypocretin in the hypothalamus. This loss could result from the degeneration of neurons containing hypocretin or from a more specific loss of the ability of these neurons to synthesize Hcrt. Narp has been found to colocalize with hypocretin in the rat hypothalamus. METHODS: We investigated the distribution of Narp in three normal and four narcoleptic human postmortem brains using immunohistochemistry with an antibody to Narp. Colocalization studies of Narp and hypocretin were also performed in two normal brains using immunohistochemistry with an antibody to Narp and an antibody to hypocretin. RESULTS: We found that Narp colocalizes with hypocretin in the lateral hypothalamic area (LHA), the dorsomedial hypothalamus (DMH), the dorsal hypothalamic area (DHA), and the posterior hypothalamic area (PHA) of the normal human. The number of Narp-positive neurons was reduced by 89% in these areas of the narcoleptic hypothalamus. In contrast, Narp staining in the paraventricular (Pa) and supraoptic nuclei (SO) of the human hypothalamus did not differ between normal and narcoleptic brains. CONCLUSIONS: This finding supports the hypothesis that narcolepsy results from the specific loss of hypocretin neurons. Loss of hypothalamic Narp may contribute to the symptoms of narcolepsy.