Physiological and biochemical factors

These factors may mediate some of the effects of other aetiological influences; however, they are not of clinical utility at present.

• Overactivity of the sympathetic nervous system and increased secretion of adrenaline/noradrenaline (NA) are closely related to the physical manifestations of anxiety. ACTH and cortisol are also raised.

• Disordered activity of the limbic system of the brain, probably involving the inhibitory neurotransmitter gamma-amino-butyric acid (GABA); most anxiolytic drugs enhance GABA transmission. It is possible that the effects of GABA are brought about via influencing the 5-HT and NA systems.

• 5-HT release is increased in anxiety; 5-HT systems in the brainstem have been studied closely; reduction of receptor subtypes such as 5-HT1A has been postulated as linked to anxiety.

• NA release is increased in anxiety.

• Variation of symptoms with current physical status; for example, female patients usually describe an exacerbation in the premenstrual phase.

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