Among TH(+) VTA neurons, 33% (13/39) were inhibited and only 10% (4/39) were excited by deltorphin II. MOR agonist DAMGO, DPDPE and deltorphin II produced either a predominant K+ dependent hyperpolarization or a Cav2.1 mediated depolarization in different neurons. In some neurons Nandrolone propionate DPDPE and deltorphin II produced opposite responses. Excitation, inhibition, Nandrolone propionate or no effect by DAMGO did not predict the response to DPDPE or deltorphin II, arguing against a MOR-DOR conversation generating DOR subtypes. However, in a subset of VTA neurons the DOR antagonist TIPP-augmented DAMGO responses; we also observed DPDPE or deltorphin II responses augmented by the MOR selective antagonist CTAP. These findings directly support the presence of two impartial, stable forms of the DOR, and show that MOR and DOR can interact in some neurons to alter downstream signaling. the potency and efficacy of a MOR agonist and vice-versa at G protein dependent pathways (Gomes et al., 2000, 2011), presumably by enabling the heterodimers to switch from G protein impartial to G protein dependent signaling. This type of conversation at the neuronal Nandrolone propionate level would complicate the interpretation of data from behavioral pharmacology experiments that use receptor selective antagonists, since it raises the possibility that an antagonist will not just block activation of the intended receptor, but may also increase the efficacy or potency of an endogenous peptide acting at a heterodimer receptor partner. Further evidence for functional MOR-DOR heterodimers is usually that synthetic bivalent compounds that combine MOR agonist and DOR antagonist actions show enhanced MOR analgesia and reduced MOR tolerance, dependence, and incentive (Daniels et al., 2005). The atomic spacing between the MOR agonist and DOR Mouse monoclonal to CD106 antagonist components of the bivalent molecule is critical (must be greater than 22 ?), suggesting that this ligands action depends on MOR and DOR binding sites being a specific and relatively short distance from each other. Another possibility is that the behavioral differences observed in response to DOR subtype pharmacologies is usually generated by functional selectivity or biased agonism. That is, structurally unique DOR selective ligands induce different conformational changes in the same receptor that favor activation of one or another intracellular signaling pathway, thereby imposing different effects around the circuit. The first evidence that such ligand-directed alternate signaling is possible was exhibited in studies of the 2-adrenergic receptor (Drake et al., 2008). Also, as heterodimerized receptors transmission through alternative mechanisms, a heterodimer-selective ligand (Fujita et al., 2014; Gomes et al., 2013) would appear to be a biased agonist. Splice variants may also lead to different pharmacologies (Pasternak, 2001), however it is usually unknown if DOR splice variants are expressed in neurons and have functional consequences. While each of these possibilities for functional diversity depends upon ligand-receptor and receptor-receptor conversation within a single cell, to date, there has been no direct demonstration that this pharmacological differences between DOR1 and DOR2 ligands at the behavioral level can be explained by different molecular interactions at the single neuron level. DOR1 activation in the ventral tegmental area (VTA) increases dopamine release in the nucleus accumbens (NAc) (Devine et al., 1993a, 1993b). Although DPDPE does not induce a conditioned place preference when infused into the VTA (Mitchell et al., 2014), animals will self-administer DPDPE directly into the VTA, suggesting that, like MOR activation, DOR1 activation in the VTA has a positive motivational effect (Devine and Wise, 1994). However, in long term alcohol drinking rats, while the MOR selective antagonist CTAP reduces alcohol consumption, the DOR selective antagonist TIPP-increases it (Margolis et al., 2008a). These complex behavioral effects of selective DOR ligands in the VTA and the evidence of MOR-DOR competitive conversation contrast with the limited quantity of electrophysiologic studies investigating actions of selective DOR agonists. For instance, an early study with a small sample size (3 neurons) found.