Protein Kinase Cβ Inhibitors Attenuate Amphetamine‐Stimulated Behaviors Through Direct and Indirect Mechanisms in Different Brain Regions

Abstract

Amphetamines (AMPH) are a class of stimulants that elicit their behavioral effects through an increase in extracellular dopamine levels. Protein kinase Cβ (PKCβ) is necessary for the increase in extracellular dopamine levels and inhibition of PKCβ results in a decrease in AMPH‐stimulated dopamine release and AMPH‐stimulated locomotor activity. When PKCβ inhibitors are administered directly into the nucleus accumbens (NAc) of rats, the drugs act immediately to reduce AMPH's behavioral effects. However, when PKCβ inhibitors are administered into the lateral ventricles of rats, the drug must be administered 18 hrs prior to AMPH to alter AMPH's behavioral effects. In this study, we sought to assess the actions of the PKCβ inhibitors in distinct brain regions to better understand the mechanism of action and time course of the inhibitors. Male Sprague‐Dawley rats were administered 10 pmol of ruboxistaurin, a PKCβ‐selective inhibitor, directly into the NAc or the ventral tegmental area (VTA). Following a 30‐min or 18‐hr pretreatment time, rats were injected with 1 mg/kg AMPH (s.c.) and their locomotor activity was measured. In a separate group of rats, ventral striatal and VTA tissue were collected following an 18‐hr pretreatment of ruboxistaurin in the VTA and a 30‐min pretreatment of 1 mg/kg AMPH (s.c.). Levels of PKCβ and phosphorylated phosphoser41‐growth associated protein 43 (pGAP43), a PKC substrate, were evaluated via immunoblotting. An injection of ruboxistaurin into the NAc attenuated AMPH‐stimulated locomotor activity following a 30‐min pretreatment, but not an 18‐hr pretreatment. Conversely, an 18‐hr pretreatment of ruboxistaurin, but not a 30‐min pretreatment, in the VTA attenuated AMPH‐stimulated locomotor activity. PKCβ and pGAP43 levels were decreased in the VTA and pGAP43 levels were decreased in the ventral striatum. This suggests that an 18‐hr pretreatment of ruboxistaurin may result in a downregulation of PKCβ levels and a decrease in PKC activity, which could contribute to the decrease in AMPH‐stimulated locomotor activity at this timepoint. Furthermore, these studies demonstrate that PKCβ inhibitors act through at least two mechanisms; a direct and immediate mechanism at the NAc and an indirect mechanism at the VTA through regulation of PKCβ levels in the cell bodies. Future work will examine PKCβ levels and activity following a short or long pretreatment in the NAc.Support or Funding InformationFunded by NIH grant R01 DA11697, T32‐GM007767, Benedict and Diana Lucchesi Graduate Fellowship.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.