The effects of alcohol and cannabinoid exposure during the brain growth spurt on behavioral development in rats

Abstract

Cannabis is the most commonly used illicit drug among pregnant women. Moreover, over half of pregnant women who are consuming cannabis are also consuming alcohol; however, the consequences of combined prenatal alcohol and cannabis exposure on fetal development are not well understood. The current study examined behavioral development following exposure to ethanol (EtOH) and/or CP-55,940 (CP), a cannabinoid receptor agonist. From postnatal days (PD) 4-9, a period of brain development equivalent to the third trimester, Sprague-Dawley rats received EtOH (5.25 g/kg/day) or sham intubation, as well as CP (0.4 mg/kg/day) or vehicle. All subjects were tested on open field activity (PD 18-21), elevated plus maze (PD 25), and spatial learning (PD 40-46) tasks. Both EtOH and CP increased locomotor activity in the open field, and the combination produced more severe overactivity than either exposure alone. Similarly, increases in thigmotaxis in the Morris water maze were caused by either EtOH or CP alone, and were more severe with combined exposure, although only EtOH impaired spatial learning. Finally, developmental CP significantly increased time spent in the open arms on the elevated plus maze. Overall, these data indicate that EtOH and CP produce some independent effects on behavior, and that the combination produces more severe overactivity in the open field. Importantly, these data suggest that prenatal cannabis disrupts development and combined prenatal exposure to alcohol and cannabis may be particularly damaging to the developing fetus, which has implications for the lives of affected individuals and families and also for establishing public health policy.

Keywords: behavior; cannabinoid; development; ethanol; teratology.

FIGURE 1

Timeline of drug exposure, behavioral testing, and tissue collection

FIGURE 2

Developmental EtOH reduced body weight, an effect that persisted throughout early adulthood. CP exposure exacerbated the EtOH growth reductions up to PD 25. *** = EtOH + CP < EtOH + Vehicle and EtOH + < + Sham; ** = EtOH < Sham

FIGURE 3

EtOH exposure during the third trimester equivalent increased overall locomotor activity in the open-field chamber (a, total distance traveled summed across days) and slowed habituation within sessions (b, total distance per bin averaged across days). Similarly, subjects exposed to EtOH showed less habituation of rearing across days compared to their Sham counterparts (c). CP exposure also increased locomotor activity and reduced habituation of locomotor activity (a,b) and rearing across testing (d). * = CP + Sham > Vehicle + Sham; ** = EtOH sig differs from Sham

FIGURE 4

Both developmental EtOH and CP exposure separately increased locomotor activity in the center of the chamber (a). The combination of CP and EtOH significantly impaired habituation during sessions (b) and both EtOH and CP reduced habituation across days (c). However, only developmental EtOH exposure significantly increased the time spent in the center of the chamber (d,e). *** = EtOH + CP > all other groups, EtOH > Sham; ** = EtOH > Sham; * = CP > Vehicle

FIGURE 5

CP exposure during the 3rd trimester equivalent increased the total time spent on the open arms of the elevated plus maze, driven by a significant CP-related increase among sham-intubated subjects (a). In contrast, EtOH exposure decreased the time spent grooming (c) and the number of rearing (d) behaviors on the maze. No groups differed in overall activity on the plus maze (b). * = CP > Vehicle; ** = EtOH < Sham

FIGURE 6

Developmental EtOH exposure impaired performance on the Morris water maze spatial learning task, leading to increased path lengths to find the platform (a), as well as less precise direction of swimming toward the target (increased heading angle; b), whereas EtOH and CP separately increased thigmotaxis during acquisition (c). Only developmental EtOH exposure significantly impaired spatial memory during the probe test, reducing time spent in the target platform area (d). ** EtOH differs sig from sham; *CP > Vehicle

FIGURE 7

Developmental EtOH exposure reduced total brain weights (a) as well as forebrain (b) and cerebellum weights (c), whereas CP exposure had no long-lasting effects on brain weights. ** = EtOH < Sham