Are all Autoreceptors Downregulated by their Respective Endogenous Ligands?
Autoreceptors - are receptors of the presynaptic terminal.
α2 adrenoreceptors receptors are down-regulated due to repeated exposure.

Pharmacodynamic tolerance begins when the cellular response to a substance is reduced with repeated use. A common cause of pharmacodynamic tolerance is high concentrations of a substance constantly binding with the receptor, desensitizing it through constant interaction

This is a common occurrence - not just for autoreceptors but receptors in general.
But for your interest here is one for dopamine autoreceptors (Pay-wall).