Abstracts

Rationale: Previously we demonstrated that cannabidiol (CBD) applied extradural to the injured region followed by oil injection reduced lesion volume and restored vestibulomotor and cognitive clinical functions following traumatic brain injury (TBI). To determine whether an optimal ratio of CBD:THC from flower extract of cannabis has superior behavioral and neuroprotective effects than hemp CBD lacking THC (CBD₀), five medicinally available extracts at different CBD:THC ratio concentrations (300:1, 10:1, 1:1, 1:20, 1:100) were compared with CBD₀ following TBI.

Methods: A controlled weight drop was used to induce cortical contusion injury (CCI). Multiple behavioral tests were conducted. Brains were evaluated histologically with hematoxylin and eosin and immunohistochemically with NeuN, GFAP, and parvalbumin (PV).


Results: Notable weight loss and slower weight gain recovery was observed with THC dominant cannabis, THC_100:1. Neuroscores and vestibulomotor performance were restored to a greater degree within a range of CBD:THC at 300:1 to 10:1 ratios. High THC with low CBD concentrations (1:20-100) resulted in early onset to spontaneous seizures post-TBI. In the alternating T-maze, TBI, CBD₀, CBD_1:1, and THC_100:1 treated groups had lowest spontaneous alternation rates whereas CBD_10:1 had the highest. In contrast, the CBD_300:1 treated animals had the best performance on novel object recognition task, while TBI or THC_100:1 treatment led to the least amount of time with the novel object. Although CBD₀ treated rats spent more time with objects than the TBI group, the amount of time spent was equal with novel and familiar objects thereby lacking recognition discrimination. In the forced swim test (FST), reduced floating was observed with CBD dominant extracts; immobility time was highest in the TBI group and lowest in the THC_100:1 treated group < THC_20:1< CBD₀. In the elevated plus maze, (EPM), the CBD₀ group spent the most time in closed arms. Both tests suggest reduced anxiety level was THC dependent. Histological analyses showed the CBD₃₀₀, CBD_10:1 and THC_20:1 treated groups had the most hippocampal sparing, whereas the THC_100:1 treated group was similar to the TBI group. All cannabis extracts showed lower injured cell counts compared to the TBI group with CBD_10:1 and THC_20:1 groups having the most protection and the THC_100:1 group having the least. Reduction in fast spiking inhibitory PV interneuron labeling was observed not only within the motor cortex and hippocampus on the side of contusion but also within the contralateral hippocampus. PV cortical and hippocampal cell counts were remarkably low after THC dominant treatments but largely restored with CBD dominant extracts. Reduced GFAP labeling was highest with CBD dominant cannabis supporting its role against inflammation.

Conclusions: Preservation of PV interneurons by CBD dominant treatment indicates that CBD was responsible for their rescue to reduce excitability. In contrast, further loss of PV expression with THC dominant treatment supports their proconvulsant effect. Thus, an optimal concentration ratio of CBD:THC (300-10:1) is critical for neuroprotection and recovery of locomotor and cognitive functions following TBI.

Funding: none