Diseases of the neuromuscular junction (NMJ) include a large spectrum of
acquired and inherited disorders mainly characterized by fluctuating muscle
weakness and fatigability of ocular, bulbar or limb muscles. Remarkable
progress has been made in our understanding of the pathogenesis of these
disorders in recent years.
Drugs Acting on Motor Systems
spinal disorders. Benzodiazepines enhance the effectiveness of the inhibitory transmitter GABA (p. 226) at GABAA receptors. Baclofen stimulates GABAB receptors. !2-Adrenoceptor agonists such as clonidine and tizanidine probably act presynaptically to inhibit release of excitatory amino acid transmitters. The convulsant toxins, tetanus toxin (cause of wound tetanus) and strychnine diminish the efficacy of interneuronal synaptic inhibition mediated by the amino acid glycine (A).
This chapter will concentrate on the mechanisms by which drugs alter neurotransmission
of relevance to the treatment of psychiatric disorders.
■ The major site of action for drugs used in psychiatry is the synapse and in particular
those utilising amines or amino acids as neurotransmitters.
■ The majority of the drugs act either presynaptically to influence levels of the
neurotransmitter in the synaptic cleft, or by altering the functional state of the