Editing Chemical synapse (section)

===Homosynaptic plasticity=== <!--Homotropic modulation redirects here-->
{{Main|Homosynaptic plasticity}}
[[Homosynaptic plasticity]] (or also homotropic modulation) is a change in the synaptic strength that results from the history of activity at a particular synapse.  This can result from changes in presynaptic calcium as well as feedback onto presynaptic receptors, i.e. a form of [[autocrine signaling]]. Homosynaptic plasticity can affect the number and replenishment rate of vesicles or it can affect the relationship between calcium and vesicle release. Homosynaptic plasticity can also be postsynaptic in nature. It can result in either an increase or decrease in synaptic strength.

One example is neurons of the [[sympathetic nervous system]] (SNS), which release [[noradrenaline]], which, besides affecting postsynaptic receptors, also affects presynaptic [[α2-adrenergic receptors]], inhibiting further release of noradrenaline.<ref name=Rang>{{cite book |author1=Rang, H.P. |author2=Dale, M.M. |author3=Ritter, J.M. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |page=129 |isbn=978-0-443-07145-4 |edition=5th}}</ref> This effect is utilized with [[clonidine]] to perform inhibitory effects on the SNS.