During social interactions, there is a tendency for people to mimic the gestures and mannerisms of others, which increases liking and rapport. Psychologists have extensively studied the antecedents and consequences of mimicry at the social level, but the neural basis of this behavior remains unclear. Many researchers have speculated that mimicry is related to activity in the human mirror system...

F344 and Lewis rats show different responses to opioids in several experimental paradigms. In this study we have used the specific mu-opioid agonist DAMGO to find out if these differences could be attributed to heterogeneity of mu-opioid receptors. The density of [H3]DAMGO binding sites was similar in the brain cortex and spinal cord of both strains, but DAMGO affinity for mu-opioid receptors w...

Novel bioactive opioid mimetic agonists containing 2',6'-dimethyl-l-tyrosine (Dmt) and a pyrazinone ring interact with mu- and delta-opioid receptors. Compound 1 [3-(4' -Dmt-aminobutyl)-6-(3'-Dmt-aminopropyl)-5-methyl-2(1H)pyrazinone] exhibited high mu-opioid receptor affinity and selectivity (K(i)mu = 0.021 nM and K(i)delta/K(i)mu = 1,519, respectively), and agonist activity on guinea pig ileu...

The role of central mu- and kappa-opioid receptors in the regulation of itch sensation was examined using pruritogen-induced mouse scratching behavior model. Intracerebroventricular administration of beta-funaltrexamine, a selective mu-opioid receptor antagonist, inhibited the scratching behavior induced by intradermal substance P, but subcutaneous administration of beta-funaltrexamine did not....

Sex differences in the experience of clinical and experimental pain have been reported. However, the neurobiological sources underlying the variability in pain responses between sexes have not been adequately explored, especially in humans. The endogenous opioid neurotransmitters and mu-opioid receptors are centrally implicated in responses to stress, in the suppression of pain, and in the acti...

1. When administered subcutaneously HS-599, a new didehydroderivative of buprenorphine (18,19-dehydrobuprenorphine), produced a long-lasting antinociceptive response in rats. Its potency exceeded twice that of buprenorphine. In the tail-flick test it acted as a full agonist but in the plantar test only as a partial agonist. Whereas the mu-opioid antagonists naloxone and naltrexone antagonized H...

The opioid system influences learning and memory processes. However, neural mechanisms underlying the modulation of hippocampal activity by opioid receptors remain largely unknown. Here, we compared how mu and delta receptors operate within the mouse CA1 network, and used knock-in mice expressing functional delta opioid receptors fused to the green fluorescent protein (DOR-eGFP) to determine ho...

Opioids modify sensory experience at many levels in the CNS. The mechanisms of this action, including the ways opioid receptors affect synaptic transmission, are not yet fully understood. Here we show that the selective activation of mu-opioid receptors suppressed inhibitory transmission between spinal cord dorsal horn neurons in vitro. mu-Opioid receptor activation reduced evoked inhibitory po...

Opioids modulate brain dopaminergic function in various experimental paradigms. This study used the rotational model of behavior in rats with unilateral 6-hydroxydopamine-induced lesions of the nigrostriatal pathway to investigate this interaction. Doses of two presynaptically acting dopaminergic drugs, amphetamine and cocaine, were coadministered with several doses of the mu opioid agonist, mo...

This study was to identify specific regions in kappa opioid receptors that accounted for binding selectivity of kappa ligands. Six chimeric mu/kappa receptors were constructed from cloned rat kappa and mu opioid receptors and transiently expressed in COS-1 cells. All six chimeric mu/kappa receptors bound [3H] diprenorphine with high affinities, indicating that these chimeras retain opioid recep...