A neurochemical target at which cannabinoids interact to have global effects on behavior is brain noradrenergic circuitry. Acute and repeated administration of a cannabinoid receptor synthetic agonist is capable of increasing multiple indices of noradrenergic activity. This includes cannabinoid-induced 1) increases in norepinephrine (NE) release in the medial prefrontal cortex (mPFC); 2) desensitization of cortical alpha 2-adrenoceptor-mediated effects; 3) activation of c-Fos in brainstem locus coeruleus (LC) noradrenergic neurons; and 4) increases in anxiety like behaviors. In the present study, we sought to examine adaptations in adrenoceptor expression and function under conditions of cannabinoid receptor type 1 (CB1r) deletion using knockout (KO) mice and compare these to wild type (WT) controls. Electrophysiological analysis of alpha 2-adrenoceptor-mediated responses in mPFC slices in WT mice showed a clonidine-induced a2-adrenoceptor-mediated increase in mPFC cell excitability coupled with an increase in input resistance. In contrast, CB1r KO mice showed an alpha 2-adrenoceptor-mediated decrease in mPFC cell excitability. We then examined protein expression levels of alpha 2- and beta 1-adrenoceptor subtypes in the mPFC as well as TH expression in the locus coeruleus (LC) of mice deficient in CB1r. Both alpha 2- and inadrenoceptors exhibited a significant decrease in expression levels in CB1r KO mice when compared to WT in the mPFC, while a significant increase in TH was observed in the LC. To better define whether the same cortical neurons express alpha 2A-adrenoceptor and CB1r in mPFC, we utilized high-resolution immunoelectron microscopy. We localized alpha 2A-adrenoceptors in a knock-in mouse that expressed a hemoagglutinin (HA) tag downstream of the alpha 2A-adrenoceptor promoter. Although the alpha 2A-adrenoceptor was often identifiedpre-synaptically, we observed co-localization of CB1r with alpha 2-adrenoceptors post-synaptically in the same mPFC neurons. Finally, using receptor binding, we confirmed prior results showing that alpha 2A-adrenoceptor is unchanged in mPFC following acute or chronic exposure to the synthetic cannabinoid receptor agonist, WIN 55,212-2, but is increased, following chronic treatment followed by a period of abstinence. Taken together, these data provide convergent lines of evidence indicating cannabinoid regulation of the cortical adrenergic system. (C) 2017 Elsevier Inc. All rights reserved.