Pro-opiomelanocortin (POMC)-derived peptides (the melanocortins adrenocorticotropin, alpha-, beta- and gamma-melanocyte stimulating hormone; and the endogenous opioid beta-endorphin) have a diverse array of biological activities, including roles in pigmentation, adrenocortical function and regulation of energy stores, and in the immune system and the central and peripheral nervous systems. We show here that mice lacking the POMC-derived peptides have obesity, defective adrenal development and altered pigmentation. This phenotype is similar to that of the recently identified human POMC-deficient patients. When treated with a stable alpha-melanocyte-stimulating hormone agonist, mutant mice lost more than 40% of their excess weight after 2 weeks. Our results identify the POMC-null mutant mouse as a model for studying the human POMC-null syndrome, and indicate the therapeutic use of peripheral melanocortin in the treatment of obesity.

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Whereas tissue injury increases spinal dynorphin expression, the functional relevance of this upregulation to persistent pain is unknown. Here, mice lacking the prodynorphin gene were studied for sensitivity to non-noxious and noxious stimuli, before and after induction of experimental neuropathic pain. Prodynorphin knock-out (KO) mice had normal responses to acute nonnoxious stimuli and a mild increased sensitivity to some noxious stimuli. After spinal nerve ligation (SNL), both wild-type (WT) and KO mice demonstrated decreased thresholds to innocuous mechanical and to noxious thermal stimuli, indicating that dynorphin is not required for initiation of neuropathic pain. However, whereas neuropathic pain was sustained in WT mice, KO mice showed a return to baselines by post-SNL day 10. In WT mice, SNL upregulated lumbar dynorphin content on day 10, but not day 2, after injury. Intrathecal dynorphin antiserum reversed neuropathic pain in WT mice at post-SNL day 10 (when dynorphin was upregulated) but not on post-SNL day 2; intrathecal MK-801 reversed SNL-pain at both times. Opioid (, ␦, and ) receptor density and G-protein activation were not different between WT and KO mice and were unchanged by SNL injury. The observations suggest (1) an early, dynorphinindependent phase of neuropathic pain and a later dynorphindependent stage, (2) that upregulated spinal dynorphin is pronociceptive and required for the maintenance of persistent neuropathic pain, and (3) that processes required for the initiation and the maintenance of the neuropathic pain state are distinct. Identification of mechanisms that maintain neuropathic pain appears important for strategies to treat neuropathic pain.

Mutant mice homozygous for 'retinal degeneration slow' (rds/rds) are characterized phenotypically by abnormal development of photoreceptor outer segments in the retina, followed by gradual degeneration of photoreceptors. This process of degeneration is complete by one year, with preservation of all other retinal cells. The biochemical defect that leads to the mutant phenotype is not known. Our strategy for cloning the rds gene was based upon three previously reported observations. First, the rds locus maps to chromosome 17. Second, experimental rds/rds----+/+ and rds/+----+/+ tetra-parental mice manifest patchy photoreceptor changes in the retina, suggesting that the wild-type rds locus is expressed within cells of the photoreceptor lineage. Finally, the process of degeneration is specific to photoreceptors. On the basis of these observations, we predicted that the rds mRNA is encoded by a gene on chromosome 17 and is normally expressed exclusively within photoreceptors in the retina. We here present evidence that this is the case.

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