The effects of pituitary-derived melanocortin peptides are primarily attributed to ACTH-mediated adrenocortical glucocorticoid production. Identification of a widely distributed receptor for ACTH/MSH peptides, the melanocortin-5 receptor (MC5-R), suggested non-steroidally mediated systemic effects of these peptides. Targeted disruption of the MC5-R produced mice with a severe defect in water repulsion and thermoregulation due to decreased production of sebaceous lipids. High levels of MC5-R was found in multiple exocrine tissues, including Harderian, preputial, lacrimal, and sebaceous glands, and was also shown to be required for production and stress-regulated synthesis of porphyrins by the Harderian gland and ACTH/MSH-regulated protein secretion by the lacrimal gland. These data show a requirement for the MC5-R in multiple exocrine glands for the production of numerous products, indicative of a coordinated system for regulation of exocrine gland function by melanocortin peptides.

Locomotor activity is a polygenic trait that varies widely among inbred strains of mice (). To characterize the role of D2 dopamine receptors in locomotion, we generated F2 hybrid (129/Sv x C57BL/6) D2 dopamine receptor (D2R)-deficient mice by gene targeting and investigated the contribution of genetic background to open-field activity and rotarod performance. Horizontal activity of D2R-/- mice was approximately half that of drug-naive, strain-matched controls but was significantly greater than haloperidol-treated controls, which were markedly hypokinetic. Wild-type 129/SvEv and C57BL/6 mice with functional D2 receptors had greater interstrain differences in spontaneous activity than those among the F2 hybrid mutants. Incipient congenic strains of D2R-deficient mice demonstrated an orderly gene dosage reduction in locomotion superimposed on both extremes of parental background locomotor activity. In contrast, F2 hybrid D2R-/- mice had impaired motor coordination on the rotarod that was corrected in the congenic C57BL/6 background. Wild-type 129/SvEv mice had the poorest rotarod ability of all groups tested, suggesting that linked substrain 129 alleles, not the absence of D2 receptors per se, were largely responsible for the reduced function of the F2 hybrid D2R-/- and D2R+/- mice. Neurochemical and pharmacological studies revealed unexpectedly normal tissue striatal monoamine levels and no evidence for supersensitive D1, D3, or D4 dopamine receptors in the D2R-/- mice. However, after acute monoamine depletion, akinetic D2R+/- mice had a significantly greater synergistic restoration of locomotion in response to SKF38393 and quinpirole compared with any group of D2R+/+ controls. We conclude that D2R-deficient mice are not a model of Parkinson's disease. Our studies highlight the interaction of multiple genetic factors in the analysis of complex behaviors in gene knock-out mice.

Dopamine secreted from hypophysial hypothalamic neurons is a principal inhibitory regulator of pituitary hormone secretion. Mice with a disrupted D2 dopamine receptor gene had chronic hyperprolactinemia and developed anterior lobe lactotroph hyperplasia without evidence of adenomatous transformation. Unexpectedly, the mutant mice had no hyperplasia of the intermediate lobe melanotrophs. Aged female D2 receptor -/- mice developed uterine adenomyosis in response to prolonged prolactin exposure. These data reveal a critical role of hypothalamic dopamine in controlling pituitary growth and support a multistep mechanism for the induction and perpetuation of lactotroph hyperplasia, involving the lack of dopamine signaling, a low androgen/estrogen ratio, and a final autocrine or paracrine "feed-forward" stimulation of mitogenesis, probably by prolactin itself.

Although dopaminergic transmission has been strongly implicated in alcohol self-administration, the involvement of specific dopamine receptor subtypes has not been well established. We studied the ethanol preference and sensitivity of D2-receptor-deficient mice to directly evaluate whether dopamine D2 receptors contribute to alcohol (ethanol) consumption. We report a marked aversion to ethanol in these mice, relative to the high preference and consumption exhibited by wild-type littermates. Sensitivity to ethanol-induced locomotor impairment was also reduced in these mutant mice, although they showed a normal locomotor depressant response to the dopamine D1 antagonist SCH-23390. These data demonstrate that dopamine signaling via D2 receptors is an essential component of the molecular pathway determining ethanol self-administration and sensitivity.

Presynaptic D 2 dopamine (DA) autoreceptors, which are well known to modulate DA release, have recently been shown to regulate DA transporter (DAT) activity. To examine the effects of D 2 DA receptor deficiency on DA release and DAT activity in dorsal striatum, we used mice genetically engineered to have two (D 2 ϩ/ϩ ), one (D 2 ϩ/Ϫ ), or no (D 2 Ϫ/Ϫ ) functional copies of the gene coding for the D 2 DA receptor. In vivo microdialysis studies demonstrated that basal and K ϩ -evoked extracellular DA concentrations were similar in all three genotypes. However, using in vivo electrochemistry, the D 2 Ϫ/Ϫ mice were found to have decreased DAT function, i.e., clearance of locally applied DA was decreased by 50% relative to that in D 2 ϩ/ϩ mice. In D 2 ϩ/ϩ mice, but not D 2 Ϫ/Ϫ mice, local application of the D 2 -like receptor antagonist raclopride increased DA signal amplitude, indicating decreased DA clearance. Binding assays with the cocaine analogue [ 3 H]WIN 35,428 showed no genotypic differences in either density or affinity of DAT binding sites in striatum or substantia nigra, indicating that the differences seen in DAT activity were not a result of decreased DAT expression. These results further strengthen the idea that the D 2 DA receptor subtype modulates activity of the striatal DAT. Key Words: D 2 dopamine autoreceptorGene knockout mice-Dopamine uptake-In vivo microdialysis-In vivo electrochemistry-Striatum. J. Neurochem. 72, 148 -156 (1999).Dopaminergic neurotransmission in the CNS plays a key role in the control of motor, cognitive, and reward processes. Dopaminergic neurotransmission is a complex and tightly controlled process that involves synthesis, storage, release, receptor binding, subsequent activation of signal transduction systems, and termination of the action of the neurotransmitter. Extracellular levels of dopamine (DA) within the striatum are thought to largely depend on a balance between vesicular release of DA and reuptake of the released DA through the DA transporter (DAT). Multiple mechanisms have been identified for the short-and long-term regulation of DA release, whereas relatively little is known about mechanisms by which DAT may be acutely regulated.One well-characterized mechanism by which DA release can be modulated is via DA autoreceptors. DA receptors are divided into two general classes, the D 1 -like family, composed of the D 1 and D 5 receptor subtypes, and the D 2 -like family, composed of the D 2 , D 3 , and D 4 subtypes (see Sokoloff and Schwartz, 1995). Release-modulating DA autoreceptors belong to the D 2 -like family (see Langer, 1997). Studies using in vitro slice techniques, synaptosomes, and in vivo microdialysis have provided strong evidence that activation of these terminal autoreceptors with D 2 -like receptor agonists inhibits DA release within the rodent striatum (Dwoskin and Zahniser, 1986;Altar et al., 1987;Westerink and de Vries, 1989). D 2 DA receptors have been localized on dopaminergic axon terminals (Sesack et al., 1994), and at least a subpopul...

Brain dopamine (DA) systems are involved in the modulation of the sensorimotor gating phenomenon known as prepulse inhibition (PPI). The class of D2-like receptors, including the D2, D3, and D4 receptor subtypes, have all been implicated in the control of PPI via studies of DA agonists and antagonists in rats. Nevertheless, the functional relevance of each receptor subtype remains unclear because these ligands are not specific. To determine the relevance of each receptor subtype, we used genetically altered strains of "knock-out" mice lacking the DA D2, D3, or D4 receptors. We tested the effects of each knock-out on both the phenotypic expression of PPI and the disruption of PPI produced by the indirect DA agonist d-amphetamine (AMPH). No phenotypic differences in PPI were observed at baseline. AMPH significantly disrupted PPI in the D2 (+/+) mice but had no effect in the D2 (-/-) mice. After AMPH treatment, both DA D3 and D4 receptor (+/+) and (-/-) mice had significant disruptions in PPI. These findings indicate that the AMPH-induced disruption of PPI is mediated via the DA D2 receptor and not the D3 or D4 receptor subtypes. Uncovering the neural mechanisms involved in PPI will further our understanding of the substrates of sensorimotor gating and could lead to better therapeutics to treat gating disorders, such as schizophrenia.

Cationic and anionic electrospray mass spectra were measured for equine myoglobin, lactalbumin and hen egg white lysozyme from acidic and basic solutions. Both positive and negative ions were detected from all solutions in which the proteins were soluble. This was observed in both nebulization-assisted and thermally assisted electrospray. As in other studies, the distribution of the charge states reflected functional groups in the proteins, and also folding or extension of the protein.

Neuropeptide B (NPB) and neuropeptide W (NPW) have been recently identified as ligands for the G protein-coupled receptor (GPR) 7 and GPR8. The precise in vivo role of this neuropeptidereceptor pathway has not been fully demonstrated. In this paper, we report that NPB-deficient mice manifest a mild adult-onset obesity, similar to that reported in GPR7-null mice. NPB-deficient mice also exhibit hyperalgesia in response to inflammatory pain. Hyperalgesia was not observed in response to chemical pain, thermal pain, or electrical stimulation. NPB-deficient mice demonstrated intact behavioral responses to pain, and learning from the negative reinforcement of electrical stimulation was unaltered. Baseline anxiety was also unchanged as measured in both the elevated plus maze and time spent immobile in a novel environment. These data support the idea that NPB is a factor in the modulation of responses to inflammatory pain and body weight homeostasis.body weight ͉ G protein-coupled receptor 7 ͉ neuropeptide W ͉ obesity