Postsynaptic receptors definition

As previously noted, all currently available antidepressants enhance monoamine neurotransmission by one of several mechanisms. The most common mechanism is inhibition of the activity of SERT, NET, or both monoamine transporters (Table 30-2). Antidepressants that inhibit SERT, NET, or both include the SSRIs and SNRIs (by definition), and the TCAs. Another mechanism for increasing the availability of monoamines is inhibition of their enzymatic degradation (the MAOIs). Additional strategies for enhancing monoamine tone include binding presynaptic autoreceptors (mirtazapine) or specific postsynaptic receptors (5-HT antagonists and mirtazapine). Ultimately, the increased availability of monoamines for... 

Caveats include minor differences in size and shape from muscle to muscle, and fixation artifacts that can eliminate staining, especially presynaptically. In general, defects in the presynaptic terminal, such as partial retraction, are reflected less-precise definition in the postsynaptic receptors. 

NEUROTRANSMITTERS Transmitters may produce minimal effects on bioelectric properties, yet activate or inactivate biochemical mechanisms necessary for responses to other circuits. Alternatively, the action of a transmitter may vary with the context of ongoing synaptic events— enhancing excitation or inhibition, rather than operating to impose direct excitation or inhibition. Each chemical substance that fits within the broad definition of a transmitter may therefore require operational definition within the spatial and temporal domains of a specific ceU-ceU circuit. Those same properties may not necessarily be generalized to other cells contacted by the same presynaptic neurons differences in operation may relate to differences in postsynaptic receptors and the mechanisms by which an activated receptor produces its effects. 

The majority of these compounds are agonists or partial agonists. Pure antagonists, devoid of any agonistic activity at presynaptic receptors (somatodendritic autoreceptors) or postsynaptic receptors were identified only very recently (for details of the definition of agonists, partial agonists and antagonists, see [6]). 

Some of the depressant behavioral effects of hallucinogens may involve inhibitory postsynaptic 5-HT receptors. For example, depressant effects of hallucinogens on startle and locomotor activity may result from activation of these receptors, since 5-HT itself has similar effects. Studies on supersensitivity are lacking, however, and, again, the absence of selective antagonists prevents definitive conclusions. 

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