The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Jan 2011
Comparative StudyDown-regulation of synaptic GluN2B subunit-containing N-methyl-D-aspartate receptors: a physiological brake on CA1 neuron α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hyperexcitability during benzodiazepine withdrawal.
A significant link was previously established between benzodiazepine withdrawal anxiety and a progressive increase in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) potentiation in hippocampal CA1 neurons from rats withdrawn up to 2 days from 1-week oral administration of the benzodiazepine flurazepam (FZP). Despite AMPAR current potentiation, withdrawal anxiety was masked by a 2-fold reduction in CA1 neuron N-methyl-D-aspartate receptor (NMDAR) currents since preinjection of an NMDA antagonist restored NMDAR currents and unmasked anxiety in 2-day FZP-withdrawn rats. In the current study, GluN subunit levels in postsynaptic density (PSD)-enriched subfractions of CA1 minislices were compared with GluN2B-mediated whole-cell currents evoked in CA1 neurons in hippocampal slices from 1- and 2-day FZP-withdrawn rats. ⋯ Because AMPA (1 μM) preincubation of slices from 1-day FZP-withdrawn rats induced depression of GluN2B subunit-mediated currents, depression of NMDAR currents was probably secondary to AMPAR potentiation. CA1 neuron NMDAR currents were depressed ∼50% after 2-day withdrawal and offset potentiation of AMPAR-mediated currents, leaving total charge transfer unchanged between groups. Collectively, these findings suggest that a reduction of GluN2B-containing NMDAR may serve as a homeostatic feedback mechanism to modulate glutamatergic synaptic strength during FZP withdrawal to alleviate benzodiazepine withdrawal symptoms.
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J. Pharmacol. Exp. Ther. · Dec 2010
A transmembrane amino acid in the GABAA receptor β2 subunit critical for the actions of alcohols and anesthetics.
Alcohols and inhaled anesthetics enhance the function of GABA(A) receptors containing α, β, and γ subunits. Molecular analysis has focused on the role of the α subunits; however, there is evidence that the β subunits may also be important. The goal of our study was to determine whether Asn265, which is homologous to the site implicated in the α subunit (Ser270), contributes to an alcohol and volatile anesthetic binding site in the GABA(A) receptor β(2) subunit. ⋯ We found that potentiation by butanol, octanol, or isoflurane in the N265C mutant was nearly abolished after the application of OMTS, suggesting that an alcohol and volatile anesthetic binding site at position 265 of the β(2) subunit was irreversibly occupied by octanethiol and consequently prevented butanol or isoflurane from binding and producing their effects. OMTS did not affect modulation or direct activation by pentobarbital, but there was a partial reduction of allosteric modulation by flunitrazepam and alphaxalone in mutant α(1)β(2)(N265C)γ(2S) receptors after OMTS was applied. Our findings provide evidence that Asn265 may contribute to an alcohol and anesthetic binding site.
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J. Pharmacol. Exp. Ther. · Dec 2010
Tolerance to the antinociceptive effect of morphine in the absence of short-term presynaptic desensitization in rat periaqueductal gray neurons.
Opioids activate the descending antinociceptive pathway from the ventrolateral periaqueductal gray (vlPAG) by both pre- and postsynaptic inhibition of tonically active GABAergic neurons (i.e., disinhibition). Previous research has shown that short-term desensitization of postsynaptic μ-opioid receptors (MOPrs) in the vlPAG is increased with the development of opioid tolerance. Given that pre- and postsynaptic MOPrs are coupled to different signaling mechanisms, the present study tested the hypothesis that short-term desensitization of presynaptic MOPrs also contributes to opioid tolerance. ⋯ However, short-term desensitization of MOPr inhibition of eIPSCs was not observed in either saline- or morphine-pretreated rats. Reducing the number of available MOPrs with the irreversible opioid receptor antagonist, β-chlornaltrexamine decreased maximal MOPr inhibition with no evidence of desensitization, indicating that the lack of observed desensitization is not caused by receptor reserve. These results demonstrate that tolerance to the antinociceptive effect of morphine is associated with a decrease in presynaptic MOPr sensitivity or coupling to effectors, but this change is independent of short-term MOPr desensitization.
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J. Pharmacol. Exp. Ther. · Dec 2010
The novel pyrrolidine nor-lobelane analog UKCP-110 [cis-2,5-di-(2-phenethyl)-pyrrolidine hydrochloride] inhibits VMAT2 function, methamphetamine-evoked dopamine release, and methamphetamine self-administration in rats.
Both lobeline and lobelane attenuate methamphetamine self-administration in rats by decreasing methamphetamine-induced dopamine release via interaction with vesicular monoamine transporter-2 (VMAT2). A novel derivative of nor-lobelane, cis-2,5-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-110), and its trans-isomers, (2R,5R)-trans-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-111) and (2S,5S)-trans-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-112), were evaluated for inhibition of [(3)H]dihydrotetrabenazine binding and [(3)H]dopamine uptake by using a rat synaptic vesicle preparation to assess VMAT2 interaction. Compounds were evaluated for inhibition of [(3)H]nicotine and [(3)H]methyllycaconitine binding to assess interaction with the major nicotinic receptor subtypes. ⋯ At high concentrations, UKCP-110 also increased extracellular dihydroxyphenylacetic acid. It is noteworthy that UKCP-110 decreased the number of methamphetamine self-infusions, while having no effect on food-reinforced behavior or the methamphetamine stimulus cue. Thus, UKCP-110 represents a new lead in the development of novel pharmacotherapies for the treatment of methamphetamine abuse.
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J. Pharmacol. Exp. Ther. · Dec 2010
The novel triple reuptake inhibitor JZAD-IV-22 exhibits an antidepressant pharmacological profile without locomotor stimulant or sensitization properties.
Triple reuptake inhibitors (TRIs) that block the dopamine transporter (DAT), norepinephrine transporter, and serotonin transporter are being developed as a new class of antidepressant that may have better efficacy and fewer side effects compared with traditional antidepressants. We describe a novel TRI, 2-[4-(4-chlorophenyl)-1-methylpiperidin-3-ylmethylsulfanyl]-1-(3-methylpiperidin-1-yl)-ethanone (JZAD-IV-22), that inhibits all three monoamine transporters with approximately equal potency in vitro. (+/-)-1-(3,4-dichlorophenyl)-3-azabicyclo-[3.1.0]hexane hydrochloride (DOV 216,303), a TRI shown to be an effective antidepressant in a clinical trial, shows reuptake inhibition similar to that of JZAD-IV-22 in vitro. Furthermore, both JZAD-IV-22 and DOV 216,303 increase levels of dopamine, norepinephrine, and serotonin in the mouse prefrontal cortex when administered by peripheral injection. ⋯ These results demonstrate that JZAD-IV-22 is a TRI with antidepressant-like activity similar to that of DOV 216,303. The striking feature that distinguishes the two TRIs is that locomotor sensitization, a common underlying feature of drugs of abuse, is seen with DOV 216,303 but is completely lacking in JZAD-IV-22. These findings may have implications for the potential for abuse liability in humans.