Adolescent cannabidiol treatment produces antidepressant-like effects without compromising long-term cognition in rats

Abstract

Background: Recent preclinical studies have shown sex-dependent antidepressant-like responses of cannabidiol in adolescence, which were dependent on biological sex, early-life stress, and dose. In particular, cannabidiol (10 mg/kg) induced acute and sustained antidepressant-like responses in adolescent male rats, while it lacked efficacy in females. This follow-up study aimed at further characterizing cannabidiol's effects in adolescence, in an attempt to overcome female unresponsiveness, while also evaluating its long-term safety profile in adulthood.

Methods: Groups of adolescent rats of both sexes were treated (ip) with cannabidiol (10, 30, 60 mg/kg) or vehicle (1 ml/kg) for 7 days. Acute (30 min post-injection) and repeated (24 h post-treatment) antidepressant-like responses were measured in the forced-swim test. Brains were collected to evaluate several neurochemical correlates in the hippocampus (CBR1, CBR2, BDNF, and cell proliferation) after adolescent cannabidiol exposure (acute and repeated). Some rats were left undisturbed until adulthood, when long-term effects on cognition were measured in the Barnes maze (short- and long-term memory) or affective-like responses in the forced-swim test. Data was analyzed with two-way ANOVAs (independent variables: sex and treatment).

Results: While the dose of 10 mg/kg of cannabidiol induced antidepressant-like effects in adolescent rats, higher doses had no effect in adolescent rats of both sexes. No changes were observed in any of the hippocampal neuroplasticity markers evaluated. Adolescent cannabidiol exposure did not induce long-term changes in cognitive performance or affective-like behavior.

Conclusions: Overall, our data suggest that adolescent cannabidiol treatment produces dose-dependent antidepressant-like effects of moderate magnitude without compromising long-term cognition in rats.

Keywords: Adolescence; Antidepressant; Biological sex; Cannabidiol; Hippocampus; Neuroplasticity.

Fig. 1

Experimental design. (A) Objective (1) Characterization of the antidepressant-like response of cannabidiol (CBD) as measured under the stress of the forced-swim test (FST) in adolescent rats of both sexes. Doses tested: 10, 30, and 60 mg/kg, ip; acute effects as measured 30 min post-acute dose; repeated effects as measured 24 h after 7 doses (1 dose/day). (B) Objective (2) Potential drug targets: neurochemical markers evaluated in the hippocampus of adolescent rats of both sexes following CBD treatment. Doses tested: 10, 30, and 60 mg/kg, ip; 30 min post-acute treatment and 24 h post-repeated treatment. Cell proliferation (i.e., Ki-67), cannabinoid (CB) receptors, and BDNF (brain-derived neurotrophic factor) as a neuroplasticity marker. (C) Objective (3) Long-term effects in adulthood. Short- and long-term memory in the Barnes maze and behavioral despair in the FST

Fig. 2

Antidepressant-like effects of cannabidiol in adolescence. (A-B) Validating the effective dose of 10 mg/kg of cannabidiol (CBD, ip) after an (A) acute dose (30 min post-treatment), or a (B) repeated treatment (7 doses, 1 dose per day; 24 h post-treatment) as measured under the stress of the forced-swim test (FST) in adolescent rats of both sexes. (A) Groups of treatment: Acute effects (30 min post-treatment): male-C (n = 15); male-CBD-10 (n = 16); female-C (n = 14); female-CBD-10 (n = 14). (B) Groups of treatment: Repeated effects (24 h post-treatment): male-C (n = 23); male-CBD-10 (n = 25); female-C (n = 13); female-CBD-10 (n = 15). (C-D) Testing new doses (30 or 60 mg/kg, ip.) of cannabidiol (ip) after an C acute dose (30 min post-treatment), or a (D) repeated treatment (7 doses, 1 dose per day; 24 h post-treatment). (C-D) Groups of treatment: male-C (n = 7); male-CBD-30 (n = 8); male-CBD-60 (n = 7); female-C (n = 7); female-CBD-30 (n = 8); female-CBD-60 (n = 8). Note that the same rats were assessed following the acute and repeated treatment. (A-D) Data represent mean ± SEM of the time spent immobile (s). Individual values are shown for each rat (symbols). Two-way ANOVAs (independent variables: sex, treatment). Post-hoc comparisons through Dunnett’s test when appropriate: **p < 0.05 vs. male-C

Fig. 3

Potential drug targets: neurochemical markers evaluated in the hippocampus of adolescent male and female rats following cannabidiol treatment. Doses tested: 10, 30 and 60 mg/kg, ip. The right hippocampus was used to determine target protein content through western blot analyses after an (A) acute (30 min post-treatment) and (B) repeated (24 h post-treatment) treatment of cannabidiol (CBD). Representative images of selected western blots are shown for cannabinoid (CB) receptor 1 (CB1R) and 2 (CB2R), brain-derived neurotrophic factor (BDNF), and β-actin. (C) The left hippocampus was cryostat-cut and used to quantify by immunohistochemistry the number of Ki-67 + cells per area of dentate gyrus (mm²), as a marker of cell proliferation, exclusively following the repeated treatment of CBD. Representative images of Ki-67 + cells (brown labeling in the blue granular layer) taken with a light microscope using a 10x objective lens are shown for each treatment condition, together with the magnified window at 63x. Scale bar: 30 μm. The results of the experiments evaluating these drug targets in hippocampal samples of adolescent rats of both sexes treated in adolescence with cannabidiol are summarized in Table 1

Fig. 4

Long-term effects of adolescent cannabidiol treatment on cognitive performance in adult male and female rats. Time spent (s) in 3 consecutive trials (T1, T2, T3) and 2 test sessions (spaced 24 h) to complete the Barnes maze in adult (A) male and (B) female rats. Data represent mean ± SEM of the time (s) spent to complete the Barnes maze. Note that a time-limit is present for trials (180 s) and test sessions (90 s). Two-way repeated measures ANOVAs were performed to assess the effects across time (independent variables: test day and treatment Group). (C,D) Individual values are shown within treatment bars for each rat (symbols) for test sessions 10 min and 24 h. A grid line represents the maximum amount of time available to resolve the maze (90 s). Two-way ANOVAs, with sex and treatment as independent variables, were performed