Increased Maternal Care Rescues Altered Reinstatement Responding Following Moderate Prenatal Alcohol Exposure

Long-term effects of low prenatal alcohol exposure on GABAergic interneurons of the murine posterior parietal cortex

BACKGROUND

Fetal alcohol spectrum disorders (FASDs) are characterized by a wide range of physical, cognitive, and behavioral impairments that occur throughout the lifespan. Prenatal alcohol exposure (PAE) can lead to adult impairments in cognitive control behaviors mediated by the posterior parietal cortex (PPC). The PPC plays a fundamental role in the performance of response tasks in both primates and rodents, specifically when choices between similar target and nontarget stimuli are required. Furthermore, the PPC is reciprocally connected with other cortical areas. Despite the extensive literature investigating the molecular mechanisms underlying PAE impairments in cognitive functions mediated by cortical areas, little is known regarding the long-term effects of PAE on PPC development and function. Here, we examined changes in the cellular organization of GABAergic interneurons and their function in PPC using behaviorally naïve control and PAE mice.

METHODS

We used a limited access model of PAE in which C57BL/6J females were exposed to a solution of 10% (w/v) ethanol and 0.066% (w/V) saccharin for 4 h/day throughout gestation. Using high-throughput fluorescent microscopy, we quantified the levels of GABAergic interneurons in the PPC of adult PAE and control offspring. In a separate cohort, we recorded spontaneous inhibitory postsynaptic currents (sIPSCs) using whole-cell patch clamp recordings from PPC layer 5 pyramidal neurons.

RESULTS

PAE led to a significant overall reduction of parvalbumin-expressing GABAergic interneurons in PAE mice regardless of sex. Somatostatin- and calretinin-expressing GABAergic interneurons were not affected. Interestingly, PAE did not modulate sIPSC amplitude or frequency.

CONCLUSIONS

These results suggest that impairments in cognitive control observed in FASD may be due to the significant reduction of parvalbumin-expressing GABAergic interneurons in the PPC. PAE animals may show compensatory changes in GABAergic function following developmental reduction of these interneurons.

Impaired cognitive control after moderate prenatal alcohol exposure corresponds to altered EEG power during a rodent touchscreen continuous performance task

Although it is well established that alcohol consumption during pregnancy can lead to lifelong difficulties in offspring, Fetal Alcohol Spectrum Disorders (FASD) remain a common neurodevelopmental syndrome. Translational behavioral tools that target similar brain circuits across species can facilitate understanding of these cognitive consequences. Touchscreen behavioral tasks for rodents enable easy integration of dura recordings of electroencephalographic (EEG) activity in awake behaving animals, with clear translational generalizability. Recently, we showed that Prenatal Alcohol Exposure (PAE) impairs cognitive control on the touchscreen 5-Choice Continuous Performance Task (5C-CPT) which requires animals to touch on target trials (hit) and withhold responding on non-target trials (correct rejection). Here, we extended these findings to determine whether dura EEG recordings would detect task-relevant differences in medial prefrontal cortex (mPFC) and posterior parietal cortex (PPC) corresponding with behavioral alterations in PAE animals. Replicating previous findings, PAE mice made more false alarm responses versus controls and had a significantly lower sensitivity index. All mice, regardless of sex or treatment, demonstrated increased frontal theta-band power during correct trials that followed an error (similar to post-error monitoring commonly seen in human participants). All mice showed a significant decrease in parietal beta-band power when performing a correct rejection versus a hit. PAE mice of both sexes showed a significantly larger decrease in parietal beta-band power when successfully rejecting non-target stimuli. These findings suggest that moderate exposure to alcohol during development can have long lasting effects on cognitive control, and task-relevant neural signals may provide a biomarker of impaired function across species.

Postnatal ethanol exposure impairs social behavior and operant extinction in the adult female mouse offspring

Fetal Alcohol Spectrum Disorder (FASD) comprises a group of neurodevelopmental deficits caused by alcohol exposure during pregnancy. Clinical studies suggest that while the male progeny experiences serious neurodevelopmental defects, female patients have more severe cognitive, social, and affective symptoms. Other than sex, dose, frequency, and timing of exposure determine the neurobehavioral outcomes in young and adult progeny. In this regard, human studies indicate that some individuals relapse during late-term gestational periods. In mice, this interval corresponds to the first 10 days after birth (postnatal, P0-P10). In our model of postnatal ethanol exposure (PEE^P0-P10), we tested whether adult female and male offspring show deficits in sociability, anxiety-like, reward consumption, and action-outcome associations. We report that female PEE^P0-P10 offspring have mild social impairments and altered extinction of operant responding in the absence of anxiety-like traits and reward consumption defects. None of these deficits were detected in the male PEE^P0-P10 offspring. Our data provide novel information on sex-specific neurobehavioral outcomes of postnatal ethanol exposure in female adult offspring.

Growth and behavioral differences in a C57BL/6J mouse model of prenatal alcohol exposure

BACKGROUND

Prenatal alcohol exposure (PAE) can produce behavioral deficits in the presence or absence of growth and morphological deficits. Here, we describe a murine PAE model having parallels to the clinical diagnosis of alcohol-related neurodevelopmental deficit (ARND).

METHODS

Pregnant C57BL/6J mice were gavaged with alcohol (ALC, 3 g/kg) or maltodextrin daily on embryonic days (E) E8.5 through E17.5. Blood alcohol levels were 211 ± 14 mg/dL at 30 min post-gavage. Offspring behavior was tested at adolescence.

RESULTS

ALC dams gained less weight during the alcohol exposure period (p = 0.035). ALC male and female pups weighed more than controls at P15 (p ≤ 0.001) and P22 (p ≤ 0.001), but not at P37, perhaps because their dams were pair-housed. During the training session for accelerating rotarod, control offspring trended to stay longer on the rotarod than did ALC offspring [F_(1,54) = 2.892, p = 0.095]. In the Y-maze, ALC offspring had a higher percent alternation than did controls [F_(1,54) = 16.577, p < 0.001], but activity level did not appear to differ. In the fear-conditioning test, there was no ALC effect in the training trial. In the contextual test, there was a group × minute effect for males [F_(4,120) = 2.94, p = 0.023], and ALC trended to freeze less than controls in minute 1 (p = 0.076) and froze less in minute 2 (p = 0.02). In the cue test, there was a trend for a group-sex interaction [F_(1,53) = 3.008, p = 0.089] on overall freezing, such that ALC males (p < 0.05) again froze less than control males, whereas ALC females (p < 0.05) froze more than control females.

CONCLUSIONS

This mouse model of PAE, using a repeated intermediate exposure, produces modest behavioral impairments that are consistent along the continuum of PAE models, including deficits in associative memory and hyper-responsivity. The lack of growth or morphological deficits suggests these mice may model aspects of ARND.

Corticostriatal Circuit Models of Cognitive Impairments Induced by Fetal Exposure to Alcohol

The term fetal alcohol spectrum disorder includes a group of diseases caused by fetal alcohol exposure (FAE). Patients with fetal alcohol spectrum disorder display heterogeneous socioemotional and cognitive deficits, particularly in the domain of executive function, that share symptoms with other neuropsychiatric disorders. Despite the availability of several preclinical models, the developmental brain defects causally linked to behavioral deficits induced by FAE remain poorly understood. Here, we first review the effects of FAE on corticostriatal development and its impact on both corticostriatal pathway function and cognitive abilities. We propose three non-mutually exclusive circuit models of corticostriatal dysfunctions to account for some of the FAE-induced cognitive deficits. One model posits that associative-sensorimotor imbalance causes hyper goal-directed behavior, and a second model implies that alteration of prefrontal-striatal behavioral suppression circuits results in loss of behavioral inhibition. A third model suggests that local striatal circuit deficits affect striatal neuronal ensemble function to impair action selection and performance. Finally, we discuss how preclinical approaches applied to these circuit models could offer potential rescue strategies for executive function deficits in patients with fetal alcohol spectrum disorder.

Alcohol exposure in utero disrupts cortico-striatal coordination required for behavioral flexibility

Deficits in behavioral flexibility are a hallmark of multiple psychiatric, neurological, and substance use disorders. These deficits are often marked by decreased function of the prefrontal cortex (PFC); however, the genesis of such executive deficits remains understudied. Here we report how the most preventable cause of developmental disability, in utero exposure to alcohol, alters cortico-striatal circuit activity leading to impairments in behavioral flexibility in adulthood. We utilized a translational touch-screen task coupled with in vivo electrophysiology in adult mice to examine single unit and coordinated activity of the lateral orbital frontal cortex (OFC) and dorsolateral striatum (DS) during flexible behavior. Prenatal alcohol exposure (PAE) decreased OFC, and increased DS, single unit activity during reversal learning and altered the number of choice responsive neurons in both regions. PAE also decreased coordinated activity within the OFC and DS as measured by oscillatory field activity and altered spike-field coupling. Furthermore, PAE led to sustained connectivity between regions past what was seen in control animals. These findings suggest that PAE causes altered coordination within and between the OFC and DS, promoting maladaptive perseveration. Our model suggests that in optimally functioning mice OFC disengages the DS and updates the newly changed reward contingency, whereas in PAE animals, aberrant and persistent OFC to DS signaling drives behavioral inflexibility during early reversal sessions. Together, these findings demonstrate how developmental exposure alters circuit-level activity leading to behavioral deficits and suggest a critical role for coordination of neural timing during behaviors requiring executive function.

Moderate prenatal alcohol exposure impairs cognitive control, but not attention, on a rodent touchscreen continuous performance task

A common feature associated with fetal alcohol spectrum disorders is the inability to concentrate on a specific task while ignoring distractions. Human continuous performance tasks (CPT), measure vigilance and cognitive control simultaneously while these processes are traditionally measured separately in rodents. We recently established a touchscreen 5-choice CPT (5C-CPT) that measures vigilance and cognitive control simultaneously by incorporating both target and nontargets and showed it was sensitive to amphetamine-induced improvement in humans and mice. Here, we examined the effects of moderate prenatal alcohol exposure (PAE) in male and female mice on performance of the 5-choice serial reaction time task (5-CSRTT), which contained only target trials, and the 5C-CPT which incorporated both target and nontarget trials. In addition, we assessed gait and fine motor coordination in behavioral naïve PAE and control animals. We found that on the 5-CSRTT mice were able to respond to target presentations with similar hit rates regardless of sex or treatment. However, on the 5C-CPT PAE mice made significantly more false alarm responses vs controls. Compared with control animals, PAE mice had a significantly lower sensitivity index, a measure of ability to discriminate appropriate responses to stimuli types. During 5C-CPT, female mice, regardless of treatment, also had increased mean latency to respond when correct and omitted more target trials. Gait assessment showed no significant differences in PAE and SAC mice on any measure. These findings suggest that moderate exposure to alcohol during development can have long lasting effects on cognitive control unaffected by gross motor alterations.

Alcohol exposure in utero disrupts cortico-striatal coordination required for behavioral flexibility

Deficits in behavioral flexibility are a hallmark of multiple psychiatric, neurological, and substance use disorders. These deficits are often marked by decreased function of the prefrontal cortex (PFC); however, the genesis of such executive deficits remains understudied. Here we report how the most preventable cause of developmental disability, in utero exposure to alcohol, alters cortico-striatal circuit activity leading to impairments in behavioral flexibility in adulthood. We utilized a translational touch-screen task coupled with in vivo electrophysiology in adult mice to examine single unit and coordinated activity of the lateral orbital frontal cortex (OFC) and dorsolateral striatum (DS) during flexible behavior. Prenatal alcohol exposure (PAE) decreased OFC, and increased DS, single unit activity during reversal learning and altered the number of choice responsive neurons in both regions. PAE also decreased coordinated activity within the OFC and DS as measured by oscillatory field activity and altered spike-field coupling. Furthermore, PAE led to sustained connectivity between regions past what was seen in control animals. These findings suggest that PAE causes altered coordination within and between the OFC and DS, promoting maladaptive perseveration. Our model suggests that in optimally functioning mice OFC disengages the DS and updates the newly changed reward contingency, whereas in PAE animals, aberrant and persistent OFC to DS signaling drives behavioral inflexibility during early reversal sessions. Together, these findings demonstrate how developmental exposure alters circuit-level activity leading to behavioral deficits and suggest a critical role for coordination of neural timing during behaviors requiring executive function.