Periadolescent ethanol vapor exposure persistently reduces measures of hippocampal neurogenesis that are associated with behavioral outcomes in adulthood

Abstract

Excessive alcohol consumption is prevalent among adolescents and may result in lasting neurobehavioral consequences. The use of animal models to study adolescent alcohol exposure has the advantage of allowing for the control necessary in order to evaluate the effects of ethanol on the brain and separate such effects from genetic background and other environmental insults. In the present study the effects of moderate ethanol vapor exposure, during adolescence, on measures of neurogenesis and behavioral measures were evaluated at two different times following ethanol withdrawal, in adulthood. The two groups of Wistar rats were both exposed to intermittent ethanol vapor (14 hrs on/10 hrs off/day) for 35–36 days from PD 23-PD 58 (average blood ethanol concentration (BEC): 163 mg%). In the first group, after rats were withdrawal from vapor they were subsequently assessed for locomotor activity, conflict behavior in the open field, and behaviors in the forced swim test and then sacrificed at 72 days of age. The second group of rats were withdrawn from vapor and injected for 5 days with Bromo-deoxy-Uridine (BrdU). Over the next 8 weeks they were also assessed for locomotor activity, conflict behavior in the open field, and behaviors in the forced swim test and then sacrificed at 113/114 days of age. All rats were perfused for histochemical analyses. Ethanol vapor exposed rats displayed hypoactivity in tests of locomotion and less anxiety-like and/or more “disinhibitory” behavior in the open field conflict. Quantitative analyses of immunoreactivity revealed a significant reduction in measures of neurogenesis, progenitor proliferation, as indexed by doublecortin (DCX), Ki67, and increased markers of cell death as indexed by cleaved caspase-3, and Fluoro-Jade at 72 days, and decreases in doublecortin (DCX), and increases in cleaved caspase-3 at 114 days in the ethanol vapor exposed rats. Progenitor survival, as assessed by BrdU+, was reduced in the vapor exposed animals that were sacrificed at 114 days. The reduction seen in DCX labeled in cell counts was significantly correlated with hypoactivity at 24 hours after withdrawal as well as less anxiety-like and/or more “disinhibitory” behavior in the open field conflict test at 2 and 8 weeks following termination of vapor exposure. These studies demonstrate that behavioral measures of disinhibitory behavior correlated with decreases in neurogenesis are all significantly and persistently impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

Adolescent Alcohol Exposure Reduces Behavioral Flexibility, Promotes Disinhibition, and Increases Resistance to Extinction of Ethanol Self-Administration in Adulthood

“…We suggest that the observation of increases in entries and time spent in the open arms is consistent with an increase in impulsivity. This is also consistent with a recent report using a modified open field conflict task in which it was observed that adult AIE exposed rats displayed more disinhibitory behavior compared to non-alcohol exposed control rats (Ehlers et al , 2013a). As with the EPM, the possibility that the rats were exhibiting less anxiety-like behavior on this task cannot be excluded.…”

Chronic intermittent ethanol exposure during adolescence: Effects on social behavior and ethanol sensitivity in adulthood

“…For instance, early adolescents demonstrate more pronounced ethanol-induced damage in anterior cortical regions than their older counterparts following 4 days of exposure to high ethanol daily doses of 9–10 g/kg (Crews, Braun, Hoplight, Switzer, & Knapp, 2000), and repeated (Ehlers, Liu, Wills, & Crews, 2013) as well as acute adolescent exposure to ethanol has been reported to effectively inhibit neurogenesis in these immature animals (Crews, Mdzinarishvili, Kim, He, & Nixon, 2006). Alterations are also evident in the glutamatergic (Guerri & Pascual, 2010; Pascual, Boix, Felipo, & Guerri, 2009) and gamma-aminobutyric acid systems (Falco, Bergstrom, Bachus, & Smith, 2009; Fleming, Acheson, Moore, Wilson, & Swartzwelder, 2012) – neural systems that play a substantial role in modulation of social behavior (Morales, Varlinskaya, & Spear, 2013a,b; Silvestre, Nadal, Pallarés, & Ferré, 1997; Siviy, Line, & Darcy, 1995) and anxiety-like behavioral alterations (Atack, 2005; Möhler, 2012; Trincavelli, Da Pozzo, Daniele, & Martini, 2012).…”

Neuroimmune Basis of Alcoholic Brain Damage

“…Interestingly, adult hippocampal neurogenesis is resilient, recovering over a 30-day period from the 4-day binge alcohol model (Nixon & Crews, 2004) and a 7-week chronic prolonged relapsing model of alcohol dependence, whereas the ventricular neurogenesis is persistently reduced (Hansson et al, 2010). In contrast, in models of underage drinking (e.g., adolescent intermittent ethanol (AIE) treatment), hippocampal neurogenesis is persistently inhibited into adulthood (Broadwater, Liu, Crews, & Spear, 2013; Ehlers, Liu, Wills, & Crews, 2013). AIE exposure reductions in neurogenesis were found to be associated with more “disinhibitory” behavior in the open field conflict test at 2 and 8 weeks following termination of vapor exposure (Ehlers, Liu, et al, 2013).…”

“…In contrast, in models of underage drinking (e.g., adolescent intermittent ethanol (AIE) treatment), hippocampal neurogenesis is persistently inhibited into adulthood (Broadwater, Liu, Crews, & Spear, 2013; Ehlers, Liu, Wills, & Crews, 2013). AIE exposure reductions in neurogenesis were found to be associated with more “disinhibitory” behavior in the open field conflict test at 2 and 8 weeks following termination of vapor exposure (Ehlers, Liu, et al, 2013). Similarly, AIE exposure of rats found reduced hippocampal volumes assessed using MRI consistent with those found in alcoholism (Ehlers, Oguz, Budin, Wills, & Crews, 2013).…”