Withdrawal from chronic ethanol exposure increases postsynaptic glutamate function of insular cortex projections to the rat basolateral amygdala
Introduction
Alcohol use disorder (AUD) is characterized by prolonged and excessive alcohol consumption. This type of chronic alcohol exposure produces neuroadaptations in brain circuits that regulate of emotional states (Gilpin and Koob, 2008; McCool, 2011; Valenzuela, 1997). In humans, withdrawal in alcohol-dependent patients significantly increases brain glutamate levels and significantly lowers brain GABA concentrations relative to healthy controls (Hermann et al., 2012; Tsai et al., 1998). Similarly, in rodent models of ethanol dependence, withdrawal increases glutamatergic synaptic function in the basolateral amygdala (BLA) which can contribute to increased anxiety-like behavior (Lack et al., 2007; McGinnis et al., 2019). The BLA serves as the primary input nuclei in the amygdala's emotional-related neural circuitry (Sah et al., 2003), receiving highly processed sensory information from cortical afferents arriving via the external capsule (EC) (Rainnie et al., 1991). We have previously reported using electrical stimulation that EC glutamatergic inputs onto BLA principal neurons undergo predominantly postsynaptic alterations characterized by increased AMPA receptor function following withdrawal (WD) from chronic intermittent ethanol (CIE) (Christian et al., 2012; Morales et al., 2018). However, EC afferents onto BLA neurons potentially arise from many different cortical regions; and, it is unclear if CIE/WD-induced postsynaptic changes can be localized to individual circuits.
The agranular insula cortex (AIC), a subdivision of the polymodal association cortex located on the ventrolateral surface of the rostral cerebral cortex, is reciprocally connected with the BLA via the EC (Allen et al., 1991; Matyas et al., 2014; McDonald and Mascagni, 1996). In addition to sensory inputs, the AIC integrates affective, anticipatory, and reward-related information arising from limbic regions (Maffei et al., 2012). Recent functional imaging studies in humans highlight the insula across many psychiatric and neurological disorders (Gogolla, 2017). A large body of evidence indicates that the AIC helps mediate fear and anxiety as well as addiction-related behaviors. For example, pharmacological inactivation of the AIC decreases both operant responding for alcohol and alcohol consumption (Pushparaj and Le Foll, 2015). Optogenetic inhibition of glutamatergic AIC inputs into the nucleus accumbens (NAc) reduces quinine-resistant alcohol intake, suggesting this pathway sustains aversion-resistant alcohol intake (Seif et al., 2013). Additionally, chemogenetic silencing of these AIC-NAc projections decreases alcohol intake in rats trained to self-administer alcohol (Jaramillo et al., 2018). Despite the mounting evidence that AIC circuits directly modulate AUD-related behaviors, very few studies have examined potential modulation of these circuits by ethanol itself. Notably, pharmacologically relevant concentrations of ethanol inhibit both AIC N-methyl-d-aspartate receptor (NMDAR)-mediated excitatory postsynaptic currents (EPSCs) and the induction of long-term depression (Shillinglaw et al., 2018). However, the effects of chronic ethanol exposure on downstream AIC projections, such as the AIC-BLA terminals, are yet to be examined.
Since AIC inputs arrive at the BLA via the EC and previous work shows that EC-BLA synapses undergo postsynaptic changes following withdrawal from chronic ethanol exposure, we hypothesized that AIC-BLA synapses would express a similar form of ethanol-induced plasticity. To test this hypothesis, we exposed rats to chronic, intermittent ethanol (CIE) using ethanol vapor chambers, a commonly used method for inducing dependence in rodent models of AUD (Gilpin et al., 2008). We have previously reported that varying durations of this type of ethanol exposure produce behavioral alterations indicative of a dependence-like phenotype including increased voluntary ethanol-self administration and increased anxiety-like behavior during withdrawal (Morales et al., 2015, 2018). Using a combination of electrophysiology and optically-evoked glutamatergic responses from AIC terminals in the BLA, we characterized the presynaptic and postsynaptic function of AIC-BLA synapses in CIE- and air-exposed animals.
Section snippets
Animals
Male Sprague-Dawley rats (100g) were purchased from Envigo (Indianapolis, IN) and given access to food and water ad libitum upon arrival. Rats were pair-housed in a humidity and temperature-controlled room and maintained on a reverse 12:12h light-dark cycle (lights off at 9 a.m.). At ~5 weeks of age, rats underwent surgery (N = 96); and rats that did not undergo surgery (N = 32) were aged ~8 weeks (250g) at arrival. All rats were aged ~10 weeks (300g) at the time of behavioral measures and
Neurons in the AIC make monosynaptic, glutamatergic synapses onto BLA principal neurons
Previous studies have shown that the AIC and BLA are reciprocally connected (Matyas et al., 2014; McDonald and Mascagni, 1996). Microinjection of Channelrhodopsin-eYFP into the dorsal and ventral aspects of the AIC (Fig. 1A) produced dense eYFP fluorescence in the BLA (Fig. 1B). Optically stimulating hChR2-expressing AIC terminals (Fig. 1C) produced EPSCs in BLA neurons that were abolished by the sodium channel blocker, TTX (1 μM, Fig. 1D); addition of the potassium channel inhibitor 4-AP
Discussion
In this study we examined the effects of chronic ethanol exposure and withdrawal on glutamate transmission in the AIC-BLA circuit. Using a combination of optogenetics and electrophysiology, we demonstrate that AIC terminals make monosynaptic glutamatergic synapses onto BLA principal neurons (Fig. 1). Following withdrawal from 10 days CIE (but not 7 days), AIC-BLA synapses express increased postsynaptic function represented by increased AMAPR-mediated, strontium-dependent asynchronous EPSC
CRediT authorship contribution statement
Molly M. McGinnis: Conceptualization, Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization, Funding acquisition. Brian C. Parrish: Formal analysis, Investigation. Brian A. McCool: Conceptualization, Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition.
Acknowledgements
This work was supported by the National Institutes of Health/National Institute on Alcohol Abuse and Alcoholism [T32 AA007565 and F31 AA025514 (MMM), R01 AA023999, R01 AA014445, R21 AA026572, and P50 AA026117 (BAM)].
References (44)
- et al.
Disruptions in serotonergic regulation of cortical glutamate release in primate insular cortex in response to chronic ethanol and nursery rearing
Neuroscience
(2012) - et al.
Ketamine-induced changes in rat behaviour: a possible animal model of schizophrenia. Test of predictive validity
Prog. Neuro-Psychopharmacol. Biol. Psychiatry
(2004) - et al.
Thalamic glutamatergic afferents into the rat basolateral amygdala exhibit increased presynaptic glutamate function following withdrawal from chronic intermittent ethanol
Neuropharmacology
(2013) - et al.
Pathway-specific feedforward circuits between thalamus and neocortex revealed by selective optical stimulation of axons
Neuron
(2010) - et al.
Short-term forms of presynaptic plasticity
Curr. Opin. Neurobiol.
(2011) The insular cortex
Curr. Biol.
(2017)- et al.
Translational magnetic resonance spectroscopy reveals excessive central glutamate levels during alcohol withdrawal in humans and rats
Biol. Psychiatr.
(2012) - et al.
Synaptic plasticity of NMDA receptors: mechanisms and functional implications
Curr. Opin. Neurobiol.
(2012) - et al.
Silencing the insular-striatal circuit decreases alcohol self-administration and increases sensitivity to alcohol
Behav. Brain Res.
(2018) - et al.
Chronic ethanol and withdrawal effects on kainate receptor-mediated excitatory neurotransmission in the rat basolateral amygdala
Alcohol
(2009)
Neural processing of gustatory information in insular circuits
Curr. Opin. Neurobiol.
Ethanol modulation of synaptic plasticity
Neuropharmacology
Chronic ethanol exposure increases voluntary home cage intake in adult male, but not female, Long-Evans rats
Pharmacol. Biochem. Behav.
Chronic intermittent ethanol exposure modulation of glutamatergic neurotransmission in rat lateral/basolateral amygdala is duration-, input-, and sex-dependent
Neuroscience
Involvement of the caudal granular insular cortex in alcohol self-administration in rats
Behav. Brain Res.
Adolescent alcohol exposure: are there separable vulnerable periods within adolescence?
Physiol. Behav.
Organization of visceral and limbic connections in the insular cortex of the rat
J. Comp. Neurol.
Structural changes in the insular cortex in alcohol dependence: a cross sectional study
Iran. J. Psychiatry
Decreased frequency but not amplitude of quantal synaptic responses associated with expression of corticostriatal long-term depression
J. Neurosci.
Chronic intermittent ethanol and withdrawal differentially modulate basolateral amygdala AMPA-type glutamate receptor function and trafficking
Neuropharmacology
Special K" drug on adolescent rats: oxidative damage and neurobehavioral impairments
Oxid Med Cell Longev
Chronic ethanol and withdrawal differentially modulate basolateral amygdala paracapsular and local GABAergic synapses
J. Pharmacol. Exp. Therapeut.
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