Figure 1. THC exposure during P5–P16 induces neurochemical deficits in CA1 hippocampal neurons.

(A) Experimental paradigm in CCK^BAC/DsRed and Cck^BAC/DsRedGad1^gfp/+ mice. Daily injections had an average volume of 100 μL, but final volume was adjusted to the individual body weight; n = 3–8 mice/genotype/treatment (n = 3–4 mice/treatment for Cck^BAC/DsRedGad1^gfp/+ line). (B) Schematic outline of the dorsal hippocampus, with red circles denoting the localization of DsRed⁺ neurons. (C) Representative images from DsRed⁺/GFP⁺ hippocampi after vehicle or THC treatment. Vertical bar over the pyramidal layer shows the general approach to measure cell spread within. Solid arrowheads point to DsRed⁺/GFP⁺ interneurons in control, whereas open arrowheads denote residual cells upon THC exposure. Arrows point to small-diameter DsRed⁺ neurons at the deep stratum lacunosum moleculare (slm; see also Supplemental Figure 3A). (D) High-resolution image of pyramidal cells in hippocampal CA1, with vertical bar illustrating a vector to measure cell spread (left) with quantitative data (right). (E) DsRed⁺/GFP⁺ neurons in slm. Arrows point to small-diameter DsRed⁺ signal. (F and G) The density of DsRed⁺ (F) but not GFP⁺ neurons (G) significantly decreased in nonpyramidal layers of the CA1 subfield (qualifying as interneurons by location) after THC treatment. (H) Likewise, the density of DsRed⁺/GFP⁺ interneurons in strata alveus/oriens (but not of the GFP⁺ neuronal contingent) became significantly reduced upon THC treatment. (I) Similar changes were seen in stratum lacunosum moleculare. (J) Representative photomicrograph showing the distribution of Pvalb⁺/GFP⁺ interneurons in nonpyramidal CA1. (K) THC-induced dose-dependent changes in Pvalb⁺ interneuron density in stratum oriens. Note that THC treatment did not affect the probability of Pvalb and GFP colocalization. (L) Histochemical detection of Sst⁺ interneurons in the hippocampus. (M) THC induced dose-dependent changes in the density of but not the probability of colocalization with GFP for Sst⁺ interneurons. Cell counts were normalized to a surface area of 1 mm². Data were expressed as mean ± SD; *P < 0.05, **P < 0.01, ***P < 0.001 (versus control; 1-way ANOVA followed by Bonferroni’s post hoc test). Scale bars: 120 μm (C), 25 μm (D and E), 10 μm (J and L). str., striatum; alv, str. alveus; dg, dentate gyrus; or, str. oriens; PFA, paraformaldehyde; pyr, str. pyramidale; rad, str. radiatum.