EEG-ß/γ spectral power elevation in rat: a translatable biomarker elicited by GABA(Aα2/3)-positive allosteric modulators at nonsedating anxiolytic doses.

Benzodiazepine drugs, through interaction with GABA(Aα1), GABA(Aα2,3), and GABA(Aα5) subunits, modulate cortical network oscillations, as reflected by a complex signature in the EEG power spectrum. Recent drug discovery efforts have developed GABA(Aα2,3)-subunit-selective partial modulators in an effort to dissociate the side effect liabilities from the efficacy imparted by benzodiazepines. Here, we evaluated rat EEG and behavioral end points during dosing of nine chemically distinct compounds that we confirmed statistically to selectively to enhance GABA(Aα2,3)-mediated vs. GABA(Aα1) or GABA(Aα5) currents in voltage clamped oocytes transfected with those GABA(A) subunits. These compounds were shown with in vivo receptor occupancy techniques to competitively displace [(3)H]flumazenil in multiple brain regions following peripheral administration at increasing doses. Over the same dose range, the compounds all produced dose-dependent EEG spectral power increases in the ß- and and γ-bands. Finally, the dose range that increased γ-power coincided with that eliciting punished over unpunished responding in a behavioral conflict model of anxiety, indicative of anxiolysis without sedation. EEG γ-band power increases showed a significant positive correlation to in vitro GABA(Aα2,3) modulatory intrinsic activity across the compound set, further supporting a hypothesis that this EEG signature was linked specifically to pharmacological modulation of GABA(Aα2,3) signaling. These findings encourage further evaluation of this EEG signature as a noninvasive clinical translational biomarker that could ultimately facilitate development of GABA(Aα2,3)-subtype-selective drugs for anxiety and potentially other indications.

Development and SAR of functionally selective allosteric modulators of GABAA receptors.

Positive modulators at the benzodiazepine site of α2- and α3-containing GABA(A) receptors are believed to be anxiolytic. Through oocyte voltage clamp studies, we have discovered two series of compounds that are positive modulators at α2-/α3-containing GABA(A) receptors and that show no functional activity at α1-containing GABA(A) receptors. We report studies to improve this functional selectivity and ultimately deliver clinical candidates. The functional SAR of cinnolines and quinolines that are positive allosteric modulators of the α2- and α3-containing GABA(A) receptors, while simultaneously neutral antagonists at α1-containing GABA(A) receptors, is described. Such functionally selective modulators of GABA(A) receptors are expected to be useful in the treatment of anxiety and other psychiatric illnesses.

Developing dual functional allosteric modulators of GABA(A) receptors.

Positive modulators at benzodiazepine sites of α2- and α3-containing GABA(A) receptors are believed to be anxiolytic. Negative allosteric modulators of α5-containing GABA(A) receptors enhance cognition. By oocyte two-electrode voltage clamp and subsequent structure-activity relationship studies, we discovered cinnoline and quinoline derivatives that were both positive modulators at α2-/α3-containing GABA(A) receptors and negative modulators at α5-containing GABA(A) receptors. In addition, these compounds showed no functional activity at α1-containing GABA(A) receptors. Such dual functional modulators of GABA(A) receptors might be useful for treating comorbidity of anxiety and cognitive impairments in neurological and psychiatric illnesses.

Reversal of ketamine-induced working memory impairments by the GABAAalpha2/3 agonist TPA023.

BACKGROUND: Ketamine has been used to model cognitive and behavioral symptoms of schizophrenia. Current hypotheses state that inadequate glutamatergic transmission in schizophrenia leads to a deficiency in gamma-aminobutyric acid (GABA)ergic inhibitory mechanisms and treatment with a GABA type A receptor subunits alpha2/alpha3 (GABA(Aalpha2/3)) modulator improved working memory performance in a preliminary study in patients. Here, we used ketamine to impair spatial working memory and disrupt behavior to examine the capacity for the GABA(Aalpha2/3) agonist 7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023) to reverse these symptoms. METHODS: Rhesus monkeys received TPA023 (.7, 2.0, and 5 mg/kg; by mouth) or vehicle 45 minutes before ketamine (1.0-1.7 mg/kg; intramuscular) or saline in a semirandomized Latin square design. Behavioral observations were acquired at approximately 5 minutes, and spatial delayed response performance was tested at 15 minutes postinjection. RESULTS: Ketamine produced a profound impairment in spatial working memory in association with the emergence of hallucinatory-like behaviors. TPA023 at all doses blocked ketamine's cognitive-impairing ability but did not influence the behavioral symptoms. CONCLUSIONS: Acute GABA(Aalpha2/3) agonist administration reverses the working memory deficits induced by ketamine in primates. This finding indicates that the consequences of N-methyl-D-aspartate deficiency on the function of prefrontal circuits involved in working memory can be completely overcome by acute enhancement of GABA signaling.

Parkin suppresses wild-type alpha-synuclein-induced toxicity in SHSY-5Y cells.

Current hypotheses concerning the mechanism of neuronal cell death in Parkinson's disease (PD) and related synucleopathies propose a functional interaction between parkin and alpha-synuclein (alphaS). Recently parkin was shown to suppress mutant alphaS-induced toxicity in primary neurons, providing a basis for an association between these proteins and neuronal loss [Neuron 36 (2000) 1007-1019]. We have asked if a similar association could be made between wild-type (wt) alphaS and parkin. We examined inducible over-expression of alphaS in SHSY-5Y cells through adenoviral infection under conditions which produce cellular toxicity through a reduction in ATP levels. We demonstrate that parkin suppresses toxicity induced by mutant (A53T) and wt alphaS. Parkin over-expression was also associated with the appearance of higher molecular weight alphaS-immunoreactive bands by Western blot analysis. These data, consistent with a protective role for parkin, extend previous findings to include a functional association between parkin and the wt form of alphaS.