Examination Questions on Sedatives, Hypnotics, and Antiepilepsy Agents: Understanding GABA and GABAA Receptor Complexes

Examination Questions: Sedative and Hypnotics, and Antiepilepsy agents 1. What is the chemical name of GABA? a. The amino acid derivative, ? -aminobutyrate, also called 4-aminobutyrate, (GABA) is a well-known inhibitor of presynaptic transmission in the CNS. 2. Explain: the structure of GABAA receptor complex and location of Benzodiazepine’s and barbiturate’s binding sites on GABAA receptors. a. The GABAA receptor complex have chloride channels associated with in the receptor (influx of Cl cause hyperpolarization causing CNS depression) b. In this isoform, the two binding sites for GABA are located between adjacent ? and ? 2 subunits, and the binding pocket for benzodiazepines (the BZ site of the GABAA receptor) is between an ? 1 and the ? 2 subunit. i.? 1 subunits in GABAA receptors mediate sedation, amnesia, and ataxic effects of benzodiazepine 3. Describe the difference in the action of barbiturates at lower and higher dose on GABAA receptors a. BZ increase synaptic inhibition of GABA b. They enhance GABAergic effects without directly activating GABAA receptor by opening of chloride channels but by increasing frequency of chloride opening events and enhancing chloride ion conductance. . Barbiturates increase the duration of the GABA-gated chloride channel openings d. At high concentrations, the barbiturates may also be GABA-mimetic, directly activating chloride channels. e. Barbiturates are less selective in their actions than benzodiazepines, because they also depress the actions of the excitatory neurotransmitter glutamic acid via binding to the AMPA receptor (can cause full surgical anesthesia and pronounced central depressant effects – low margin of safety). f.

If GABA is not present, benzodiazepines cannot produce their effects (they can increase the frequency but cannot initiate; only GABA opens the channels). 4. Name GABAA and GABAB receptor agonist a. GABAA is the major inhibitory neurotransmitter in spinal cord, hypothalamus, hippocampus, substantia nigra, cerebellar cortex and cerebral cortex b. GABAA containing ? 1 subunit agonist: zolpidem, zaleplon, and eszopiclone 5. Describe how Clorazepate produces its effect following oral administration a.

Diazepam and the active metabolite of clorazepate is more rapidly absorbed than other commonly used benzodiazepines. b. Clorazepate, a prodrug, is converted to its active form, desmethyldiazepam (nordiazepam), by acid hydrolysis in the stomach. 6. Explain why benzodiazepines cross biological membranes freely and distribute rapidly in various organ systems including brain and placenta. a. Most of hypnotics and sedatives are lipid soluble and thus have rapid onset of central nervous system effects. b.

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All sedative-hypnotics cross the placental barrier during pregnancy (NOT TO BE USED DURING PREGNANCY). 7. Explain the mechanism of action of Flumazenil a. Competitive antagonists with high affinity for the BZ binding site b. It blocks many of the actions of benzodiazepines, zolpidem, zaleplon, and eszopiclone c. Flumazenil is approved for use in reversing the central nervous system depressant effects of benzodiazepine overdose and to hasten recovery in anesthetic and diagnostic procedures. 8. Name short-acting benzodiazepines a. Short-acting agents (t1/2

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