In Vivo Observation of Structural Changes in Neocortical Catecholaminergic Projections in Response to Drugs of Abuse

Abstract

Catecholaminergic (dopamine and norepinephrine) projections to the cortex play an important role in cognitive functions and dysfunctions including learning, addiction, and mental disorders. While dynamics of glutamatergic synapses have been well studied in such contexts, little is known regarding catecholaminergic projections, owing to lack of robust methods. Here we report a system to monitor catecholaminergic projections in vivo over the timeframes that such events occur. GFP expression driven by tyrosine hydroxylase promoter in a transgenic mouse line enabled us to perform two-photon imaging of cortical catecholaminergic projections through a cranial window. Repetitive imaging of the same axons over 24 h revealed the highly dynamic nature of catecholaminergic boutons. Surprisingly, administration of single high dose methamphetamine induced a transient increase in bouton volumes. This new method opens avenues for longitudinal in vivo evaluation of structural changes at single release sites of catecholamines in association with physiology and pathology of cortical functions.

Significance Statement This work demonstrates a novel approach for longitudinal two-photon in vivo monitoring of catecholaminergic projections in the neocortex using a tyrosine hydroxylase promoter-GFP transgenic mouse. Using this method, we revealed the highly dynamic nature of the catecholaminergic projections over 24 h period, and a transient morphologic change of these axons in response to a drug of abuse, Methamphetamine (MAP). To our knowledge, this is the first observation of such MAP induced morphologic change of catecholamine axons in vivo. In the future, this new method can be extended to observe structural changes associated with cortical development, learning, and mental disorders, in which catecholamine projections to the cortex are known to play a key role.