Buspirone

🧬 Receptor activityPHDC

Mechanism of actionPH

The therapeutic action of buspirone in generalized anxiety disorders is thought to be mainly derived from its interaction with two major 5-HT_1A receptor subtypes that are involved in the brain's anxiety and fear circuitry to enhance the serotonergic activity in these brain areas. Buspirone acts as a full agonist at presynaptic 5-HT_1A receptors, or 5-HT_1A autoreceptors, expressed at dorsal raphe while acting as a partial agonist at the postsynaptic 5-HT_1A receptors expressed on hippocampus and cortex. 5-HT_1A receptors function as inhibitory autoreceptors by being expressed on the soma or dendrites of serotonergic neurons or mediate postsynaptic actions of 5-HT by being highly expressed on the corticolimbic circuits. They are inhibitory G-protein coupled receptors that couple to Gi/Go proteins. When activated, presynaptic 5-HT_1A autoreceptors causes neuron hyperpolarization and reduces the firing rate of the serotonergic neuron, thereby decreasing extracellular 5-HT levels in the neuron's projection areas. Activated postsynaptic 5-HT_1A receptors promote hyperpolarization to released 5-HT on pyramidal neurons. The anxiolytic action of buspirone is mainly thought to arise from the interaction at presynaptic 5-HT_1A autoreceptors. Acting as a potent agonist in these receptors, buspirone initially causes activation of these autoreceptors and inhibition of 5-HT release. It is proposed that buspirone induces desensitization of somatodendritic autoreceptors over time, which may explain the delayed onset of action of the drug. Desensitization of the autoreceptors ultimately results in heightened excitation of serotonergic neurons and enhanced 5-HT release. Buspirone also displays a weak affinity for serotonin 5HT2 receptors and acts as a weak antagonist on dopamine D2 autoreceptors, although there is not much evidence that the action at these receptors contribute to the anxiolytic effect of buspirone. It acts as an antagonist at presynaptic dopamine D3 and D4 receptors and may bind to alpha-1 adrenergic receptors as a partial agonist.

PharmacodynamicsPH

The clinical effect of buspirone in alleviating the symptoms of generalized anxiety disorders typically takes 2 to 4 weeks to achieve. The delayed onset of action of buspirone suggests that the therapeutic effectiveness in generalized anxiety may involved more than its molecular mechanism of action at the 5-HT_1A receptors, or buspirone may induce adaptations of 5-HT_1A receptors. Buspirone was not shown to alter the psychomotor or cognitive function in healthy volunteers, and the risk of developing sedation is relatively low compared to other anxiolytics, such as benzodiazepines. Unlike benzodiazepines and barbiturates used in anxiety disorders, buspirone is not associated with a risk for developing physical dependence or withdrawal, or any significant interaction with central nervous system depressants such as ethanol. This is due to the lack of effects on GABA receptors. Buspirone also does not exhibit any anticonvulsant or muscle-relaxing properties, but may interfere with arousal reactions due to its inhibitory action on the aactivity of noradrenergic locus coerulus neurons. Despite its clinical effectiveness in generalized anxiety, buspirone demonstrated limited clinical effectiveness on panic disorders, severe anxiety, phobias, and obsessive compulsive disorders. The clinical effectiveness of the long-term use of buspirone, for more than 3 to 4 weeks, has not demonstrated in controlled trials but there were no observable significant adverse events in patients receiving buspirone for a year in a study of long-term use.

Pharmacokinetics

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