Benzodiazepines elicit five principle pharmacological effects –namely: anxiolytic (anxiety-reducing)/ sedative; hypnotic (sleep-inducing); muscle relaxant and anticonvulsant. They may be prescribed to mediate one or more of these effects. They are also used during alcohol detoxification and to reduce hyperexcitability and/ or aggression during acute psychotic episodes. Additionally at high doses, some benzodiazepines also have amnesic effects which are useful for surgical procedures.
These effects (and associated adverse effects) arise from the action of benzodiazepines on the main inhibitory neurotransmitter Gamma-Amino Butyric Acid (GABA).
GABA is a chemical that occurs naturally in the body and transmits inhibitory signals from nerve cells (neurons) throughout the central nervous system (CNS), to target cells that exert its actions. These signals are transmitted across small gaps between nerve and target cells called synapses. It causes a reduction in the excitability of neurons and is also responsible for the regulation of muscle tone in humans.
Both benzodiazepines and GABA bind to postsynaptic GABAA receptors causing a decrease in the activity of nerve cells that regulate movement (motor neurons).
Benzodiazepines bind to the gamma subunit of GABAA receptors which increases the opening of the chloride channels. Increased movement of chloride ions through these channels increases the postsynaptic membrane’s resistance to excitation.
Benzodiazepines share a common basic chemical structure and the addition of different chemical groups to this structure gives rise to their specific properties.
The affinity of each benzodiazepine to water affects how quickly they begin to act after being taken and how long they continue to act for. Less water soluble benzodiazepines (such as diazepam and midazolam) begin to act more quickly than those that are more water soluble (such as lorazepam and alprazolam) but also tend to be shorter-acting.