Elsevier

Behavioural Brain Research

Volume 293, 15 October 2015, Pages 203-207
Behavioural Brain Research

Short communications
Involvement of the caudal granular insular cortex in alcohol self-administration in rats

https://doi.org/10.1016/j.bbr.2015.07.044Get rights and content

Highlights

  • CGIC inactivation reduced operant responding for alcohol under a fixed ratio-3 schedule.

  • CGIC inactivation increased the amount of alcohol left unconsumed by the rats.

  • Altogether, CGIC inactivation reduced intake of 12% alcohol in rats.

Abstract

Animal models of substance abuse have established a role for the caudal granular insular cortex (CGIC) in drug taking behaviour for several addictive substances, yet nothing has thus far been reported for alcohol. The current research was undertaken to examine the involvement of the CGIC in a rat model of alcohol self-administration. We investigated the inactivating effects of local infusions of a γ-aminobutyric acid agonist mixture (baclofen/muscimol) into the CGIC on alcohol self-administration under a fixed ratio-3 (FR-3). This inactivation of the CGIC decreased operant responding for alcohol along with a corresponding decrease in oral alcohol intake. Our results demonstrate the involvement of the CGIC in alcohol taking behaviour and suggest future studies examine the differential involvement of the various subregions of the insular cortex in various aspects of alcohol consumption.

Introduction

The insular cortex has been a region of great interest in addiction research since Naqvi et al. observed that stroke-induced damage to this region disrupts addiction to cigarette smoking [1]. The insular cortex, or insula, is responsible for interoception or the physiological condition of the body [2]. Understandably, insular activity has been observed in neuroimaging studies of anxiety, cognition, conscious urges, anxiety, pain, cognition, mood and substance abuse while animal models have also demonstrated a role for the insular cortex in behavioural aspects of multiple addictive substances (see [3] for review).

The granular, dysgranular, and agranular corticies are the three structurally and functionally distinct subregions that comprise the insula [4]. The caudal granular insular cortex (CGIC) integrates nociceptive [5] and unimodal viscerosensory [6] afferents from the thalamus along with those from the somatosensory cortex. It also primarily sends efferent projections back to those areas as well as to the caudate-putamen [7]. Through the dysgranular insular subregion, information initially integrated in the CGIC is relayed and further integrated before reaching the rostral agranular insular cortex (RAIC) [8]. Importantly, the granular insular cortex is the only insular subregion lacking projections to nuclei within the amygdala [8].

Recent findings by Seif et al. have established a role for glutamatergic neurons, projecting from the rostral agranular insular cortex (RAIC) to the nucleus accumbens, in quinine or electric footshock-based aversion-resistant alcohol intake but not for alcohol intake in the absence of such deterrents [9]. To our knowledge, no studies have yet to examine a role for the CGIC in alcohol self-administration. Thus, the current study examined whether the CGIC was involved in alcohol self-administration behavior, as we have previously observed for nicotine. The same intracranial manipulations used previously were used in the current study: bilateral infusions of γ-aminobutyric acid (GABA) receptor agonists, baclofen and muscimol.

Section snippets

Methods and results

Naive male Long-Evans rats (Charles River, Lachine, QC) weighing 300–325 g at the start of experiments were maintained on ∼20 g of rat chow daily and ad libitum water while in their home cages. Animals were single-housed in a temperature-controlled room on a 12 h reverse light cycle with all behavioral testing occurring during the dark phase.

Alcohol solution for oral self-administration was prepared by diluting 95% ethanol in tap water. A mixture of baclofen and muscimol (0.3 and 0.03 nmol/side,

Discussion

The results presented here demonstrate that inactivation of the CGIC is capable of attenuating operant responding for alcohol, as well as its overall intake, under an FR-3 schedule of reinforcement. Overall, these results appear similar to our prior findings with nicotine [11] and suggest that the CGIC may thus play a similar role in the self-administration of both drugs. An interesting finding was the increase in amount of wasted alcohol (i.e. mL of alcohol earned by the rat through operant

Conflicts of interest

Authors have none to declare.

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