DECIPHERING PERSISTENT PREFRONTAL CORTEX KYNURENIC ACID ALTERATIONS AND MOLECULAR SHIFTS IN ADULT MICE FOLLOWING ADOLESCENT THC EXPOSURE

Background: Adolescent THC use represents a risk factor for cognitive deficits in psychiatric disorders emerging in adulthood among individuals initiating cannabis consumption during adolescence (D’Souza et al., 2020). Importantly, adolescent THC exposure induces severe persistent cognitive impairments and disrupts glutamatergic and GABAergic neurotransmission in the rat prefrontal cortex (PFC; Zamberletti et al., 2014). These neurochemical changes correlate with a sustained long-term elevation of kynurenic acid (KYNA) in the PFC, a key tryptophan degradation metabolite via the kynurenine pathway (KP), believed to be implicated in the developmental pathogenesis of several psychiatric disorders, including schizophrenia (SZ). Because not all cannabis users display the harmful THC-induced impairments, it is likely that certain individuals possess underlying pre-existing genetic susceptibilities susceptible to THC exposure (Levine et al., 2017; Hasin, 2018). Mice with a targeted knockout of kynurenine 3-monooxygenase (KMO), a KP enzyme indirectly regulating KYNA synthesis (Giorgini et al., 2013), exhibit elevated KYNA concentrations relative to wild-type (WT) counterparts, thereby offering a potent developmental model to investigate the specific contributions of PFC KYNA signaling in the dysfunction induced by the exposure to THC during adolescence. Methods: Male and female C57BL6/J (a well characterized mouse strain with respect to the behavioral effects of THC; Wise et al., 2011) WT (i.e. Kmo + /+; N = 12, 6 males, 6 females) and HET (i.e. Kmo + /-; N = 12, 6 males, 6 females) were chronically treated with vehicle or ascending doses of THC (2.5 mg/kg; 5 mg/kg; 10 mg/kg i.p.), twice a day from postnatal day (PD) 35 to 45 (see Zamberletti et al., 2014 for protocol validation). Extracellular KYNA and GABA levels have been measured by in vivo microdialysis in the PFC of adult (PND 75) mice. On day 1 after the surgery, after three stable basal values were obtained, the effects of a challenge of L-kynurenine (i.e. the biological precursor of KYNA (10 mg/kg i.p) mimicking a translationally relevant “second hit”, on extracellular KYNA and GABA levels were measured. Results: In vivo microdialysis showed that basal PFC KYNA levels were higher in both male and female HET mice (P < 0.05), while basal PFC GABA was elevated only in female HET (P < 0.05) compared to WT animals. Adolescent THC produced a sustained rise in PFC KYNA in male WT mice (P < 0.05), without affecting GABA levels. L-kynurenine (10 mg/kg, i.p.) significantly increased PFC KYNA levels in all groups (P < 0.01), with a smaller increase in HET than WT (P < 0.05) and was not affected by adolescent THC treatment. L-kynurenine did not alter PFC GABA, although THCtreated HET showed a trend to a decrease. In addition, prepulse inhibition is being assessed in HET and WT mice exposed to adolescent THC, molecular profiling via RT-PCR is under way, and preliminary proximity ligation assays are being conducted to probe potential protein interactions. Conclusions: The present study revealed that the use of cannabinoids early in life can induce a malfunction of the KP in male, but not female, WT mice. This observation mirrors earlier findings reported in male rat models. Moreover, elevated cerebral KYNA following targeted KMO downregulation correlates with distinct altered sensitivity to THC-driven shifts in prefrontal cortex KYNA and GABA concentrations across HET and WT mice. Elaboration of the mechanisms underlying these changes can be expected to provide useful information regarding the etiology of adolescent THC-induced risk of neuropsychiatric illnesses in adulthood.