Prenatal alcohol and cannabis exposure can have opposing and region‐specific effects on parvalbumin interneuron numbers in the hippocampus

BACKGROUND: We have recently shown that alcohol and cannabis can interact prenatally, and in a recent review paper we further identified Parvalbumin-positive (PV) interneurons in the hippocampus as a potential point of convergence for these teratogens. METHODS: A 2 (EtOH, Air) x 2 (THC, Vehicle) design was used to expose pregnant Sprague-Dawley rats to either EtOH or air, in addition to either THC or the inhalant vehicle solution, from gestational days 5–20. Immunohistochemistry was performed to detect parvalbumin-positive interneurons in one male and one female pup from each litter at post-natal day (PND) 70. RESULTS: Significant between-group, and sub-region specific, effects were found in the dorsal CA1 subfield, as well as the ventral DG. In the dorsal CA1 subfield, there was an increase in the number of PV interneurons in both the EtOH and EtOH + THC groups, but only a possible decrease with THC alone. There were fewer changes in interneuron numbers overall in the DG, however, a sex difference was found, and a decrease in the number of PV interneurons in the THC exposed group was observed in the male ventral DG. There was also an increase in cell layer volume between the EtOH + THC group and control group in the DG, and an increase from the control and THC group to the EtOH group in the CA1 region. CONCLUSIONS: Prenatal alcohol and prenatal THC exposure differentially affect parvalbumin interneuron numbers in the hippocampus, indicating that both individual and combined exposure can impact the balance of excitation and inhibition in a structure critically involved in learning and memory processes.