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There are two different types of adrenoreceptor – the α and β receptors. The α receptors are further classified into α1 and α2 subtypes and α2 receptors are widely distributed throughout the body and are found in adrenergic neurons, blood vessels, the pancreas and in smooth muscle.

Benzodiazepines bind to the gamma sub-unit of the GABA-A receptor, causing an allosteric (structural) modification of the receptor that results in an increase in GABA A receptor activity.

The action of noradrenaline at the synapse is terminated by its re-uptake across the pre-synaptic membrane. This is an energy dependent process.

Antagonist binding to the α2 noradrenaline receptor induces noradrenaline release.

Noradrenaline binding to α2 noradrenaline receptor inhibits noradrenaline release. The α2 noradrenaline receptor is coupled to inhibitory G-proteins.

Competitive antagonists shift the dose-effect curve for an agonist, but this effect can eventually be overcome by enough agonist concentration.