Periadolescent ethanol exposure reduces adult forebrain ChAT+IR neurons: correlation with behavioral pathology

Abstract

Substance abuse typically begins in adolescence; therefore, the impact of alcohol during this critical time in brain development is of particular importance. Epidemiological data indicate that excessive alcohol consumption is prevalent among adolescents and may have lasting neurobehavioral consequences. Loss of cholinergic input to the forebrain has been demonstrated following fetal alcohol exposure and in adults with Wernicke-Korsakoff syndrome. In the present study, immunohistochemistry for choline acetyltransferase (ChAT) was determined to assess forebrain cholinergic neurons (Ch1–4), and behavioral changes following periadolescent alcohol exposure. Wistar rats were exposed to intermittent ethanol vapor (14 hrs on/10 hrs off/day) for 35 days from PD 22-PD 57 (average blood alcohol concentration (BAC): 163 mg%). Rats were withdrawn from vapor and assessed for locomotor activity, startle response, conflict behavior in the open field, and immobility in the forced swim test, as adults. Rats were then sacrificed at day 71/72 and perfused for histochemical analyses. Ethanol vapor exposed rats displayed: increased locomotor activity 8 hrs after the termination of vapor delivery for that 24 hr period at day 10 and day 20 of alcohol vapor exposure, significant reductions in the amplitude of their responses to prepulse stimuli during the startle paradigm at 24 hrs withdrawal, and at two weeks following withdrawal, less anxiety-like and/or more “disinhibitory” behavior in the open field conflict, and more immobility in the forced swim test. Quantitative analyses of ChAT immunoreactivity revealed a significant reduction in cell counts in the Ch1–2 and Ch3–4 regions of the basal forebrain in ethanol vapor exposed rats. This reduction in cell counts was significantly correlated with less anxiety-like and/or more “disinhibitory” behavior in the open field conflict test. These studies demonstrate that behavioral measures of arousal, affective state, disinhibitory behavior and ChAT+IR, are all significantly impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

Adolescent binge ethanol exposure alters specific forebrain cholinergic cell populations and leads to selective functional deficits in the prefrontal cortex

“…Our AIE model was based on the characterization of adolescence that begins in the rat at PD 28 (Spear, 2000). Although other researchers have suggested that adolescence begins at a later time point, for example PD35 (Semple et al, 2013), our AIE model is consistent with previous research that has demonstrated adolescent specific deficits following EtOH exposure during PD28-PD55 (Ehlers et al, 2011; Broadwater and Spear, 2013; Vetreno et al, 2014; Vetreno and Crews, 2012). Additionally, our AIE model encompasses the peri-adolescent, early, mid and late adolescent periods that are in accordance with both Spear (2000) and Semple (2013).…”

“…Although AIE leads to decreased neurogenesis within the hippocampus (Geil et al, 2014; Vetreno and Crews, 2015; Sakharkar et al, 2016), AIE’s detrimental effects on spatial memory are inconclusive (Risher et al, 2013; Swartzwelder et al, 2015; Beaudet et al, 2016). Following AIE, there is also a significant loss in the number of cholinergic neurons within the medial septum/diagonal band (MS/DB), which projects to the hippocampus, and the Nucleus basalis of Meynert (NbM) that projects to the cortex (Ehlers et al, 2011; Vetreno et al, 2014; Boutros et al, 2015). These effects are age-specific; there is no difference in cholinergic populations following adult binge exposure models (Vetreno et al, 2014).…”

Effects of ethanol exposure during adolescence or in adulthood on Pavlovian conditioned approach in Sprague-Dawley rats

“…For example, Ehlers, Criado, Wills, Liu, & Crews (2011) found an increase in locomotor activity and a decrease in cholinergic neurons in Ch1–4 nuclei of the basal forebrain after adolescent ethanol exposure. There is also evidence of neuroinflammation and myelin disruption within the prefrontal cortex after chronic adolescent ethanol exposure in rats (Bava, Jacobus, Thayer, & Tapert, 2013; Pascual, Pla, Miñarro, & Guerri, 2013).…”

Ontogeny and adolescent alcohol exposure in Wistar rats: open field conflict, light/dark box and forced swim test

“…These data were then compared to previously published behavioral data (Ehlers et al, 2011, 2013a,b) on adult rats (PD70-107) that were exposed to 5 weeks of ethanol vapor or control (air) conditions during adolescence.…”

“…It has been demonstrated that chronic intermittent exposure to ethanol vapor during adolescence (14 hours exposure/10 hours no exposure, daily, over a 5-week period) can cause: increases in voluntary ethanol drinking, reductions in the size of the hippocampus as imaged by diffusion tensor imaging, reductions in measures of hippocampal neurogenesis, increases in the latency of the P300 component of the event-related potential, signs of behavioral disinhibition in the light/dark box and open field conflict test, immobility in the forced swim test, and reductions in cholinergic tone in the basal forebrain (see Criado and Ehlers, 2013; Ehlers et al, 2011, 2013a,b, 2014). …”