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pharmacology and biology, outstanding contributions to the field of neuroscience, drug development, and the treatment of drug abuse. In gratitude for 40 years of fruitful collegial interaction and advancements with our friend.

Chronic stress is a risk factor for Major depressive disorder (MDD), and in rodents, it recapitulates human behavioral, cellular and molecular changes. In MDD and after chronic stress, neuronal dysfunctions and deficits in GABAergic signaling are observed and responsible for symptom severity. GABA signals predominantly through GABAA receptors (GABAA-R) composed of various subunit types that relate to downstream outcomes. Activity at α2-GABAA-Rs contributes to anxiolytic properties, α5-GABAA-Rs to cognitive functions, and α1-GABAA-Rs to sedation. Therefore, a therapy aiming at increasing α2and α5-GABAA-Rs activity, but devoid of α1-GABAA-R activity, has potential to address several symptomologies of depression while avoiding side effects. This study investigated the activity profiles and behavioral efficacy of two molecules enantiomers of each other (GL-II-73 and GL-I-54), separately and as a racemic mixture (GL-RM), and potential disease-modifying effects on neuronal morphology. Results confirm GL-I-54 and GL-II-73 exert positive allosteric modulation at the α2-, α3-, α5-GABAA-Rs and α5-containing GABAA-Rs, respectively, and have anti-depressant and pro-cognitive effects independently.Using unpredictable chronic mild stress (UCMS) in male and female mice (n=12/group), we show that acute and chronic administration of GL-RM combined the anti-depressant and pro-cognitive effects of each enantiomer, although at lower doses avoiding sedation. Morphology studies showed reversal of spine density loss caused by UCMS after chronic GL-RM treatment at apical and basal dendrites of the PFC and CA1. Together, these results support using a racemic mixture with combined α2-, α3-, α5-GABAA-R profile to reverse chronic stress-induced mood symptoms, cognitive deficits, and with anti-stress neurotrophic effects.

The imidazodiazepine, (5‐(8‐ethynyl‐6‐(pyridin‐2‐yl)‐4H‐benzo [f]imidazole[1,5‐α][1,4]diazepin‐3‐yl) oxazole or KRM‐II‐81) is a new α2/3‐selective GABAkine (gamma aminobutyric acid A receptor potentiator) with anticonvulsant, anxiolytic, and antinociceptive activity in preclinical models. Reducing metabolism was utilized as a means of potentially extending the half‐life of KRM‐II‐81. In vitro and in vivo studies were conducted to evaluate metabolic liabilities. Incubation of KRM‐II‐81 in hepatocytes revealed sites of potential metabolism on the oxazole and the diazepine rings. These sites were targeted in the design of a deuterated analog (D5‐KRM‐II‐81) that could be evaluated as a potentially longer‐acting analog. In contrast to computer predictions, peak plasma concentrations of D5‐KRM‐II‐81 in rats were not significantly greater than those produced by KRM‐II‐81 after oral administration. Furthermore, brain disposition of KRM‐II‐81 was higher than that of D5‐KRM‐II‐81. The half‐life of the two compounds in either plasma or brain did not statistically differ from one another but the tmax for D5‐KRM‐II‐81 occurred slightly earlier than for KRM‐II‐81. Non‐metabolic considerations might be relevant to the lack of increases in exposure by D5‐KRM‐II‐81. Alternative sites of metabolism on KRM‐II‐81, not targeted by the current deuteration process, are also possible. Despite its lack of augmented exposure, D5‐KRM‐II‐81, like KRM‐II‐81, significantly prevented seizures induced by pentylenetetrazol when given orally. The present findings introduce a new orally active anticonvulsant GABAkine, D5‐KRM‐II‐81.

We dedicate this work to Professor Jan Bergman for his outstanding contributions to heterocyclic and organic chemistry as a whole