Sex Effects of Marijuana on Brain Structure and Function

Background

Tetrahydrocannabinol (Δ⁹-THC), the primary ingredient in marijuana, exerts its effects across several neurological and biological systems that interact with the endocrine system. Thus, differential effects of Δ⁹-THC are likely to exist based on sex and hormone levels.

Methods

We reviewed the existing literature to determine sex-based effects of Δ⁹-THC on neural structure and functioning.

Results

The literature demonstrates differences in male and female marijuana users on brain structure, reward processing, attention, motor coordination, and sensitivity to withdrawal. However, inconsistencies exist in the literature regarding how marijuana affects men and women differentially, and more work is needed to understand these mechanisms. While extant literature remains inconclusive, differentiation between male and female marijuana users is likely due to neurological sexual dimorphism and differential social factors at play during development and adulthood.

Conclusions

Sex has important implications for marijuana use and the development of cannabis use disorders and should be considered in the development of prevention and treatment strategies.

fMRI study of neural sensitization to hedonic stimuli in long-term, daily cannabis users

Although there is emergent evidence illustrating neural sensitivity to cannabis cues in cannabis users, the specificity of this effect to cannabis cues as opposed to a generalized hyper‐sensitivity to hedonic stimuli has not yet been directly tested. Using fMRI, we presented 53 daily, long‐term cannabis users and 68 non‐using controls visual and tactile cues for cannabis, a natural reward, and, a sensory‐perceptual control object to evaluate brain response to hedonic stimuli in cannabis users. The results showed an interaction between group and reward type such that the users had greater response during cannabis cues relative to natural reward cues (i.e., fruit) in the orbitofrontal cortex, striatum, anterior cingulate gyrus, and ventral tegmental area compared to non‐users (cluster‐threshold z = 2.3, P < 0.05). In the users, there were positive brain‐behavior correlations between neural response to cannabis cues in fronto‐striatal‐temporal regions and subjective craving, marijuana‐related problems, withdrawal symptoms, and levels of THC metabolites (cluster‐threshold z = 2.3, P < 0.05). These findings demonstrate hyper‐responsivity, and, specificity of brain response to cannabis cues in long‐term cannabis users that are above that of response to natural reward cues. These observations are concordant with incentive sensitization models suggesting sensitization of mesocorticolimbic regions and disruption of natural reward processes following drug use. Although the cross‐sectional nature of this study does not provide information on causality, the positive correlations between neural response and indicators of cannabis use (i.e., THC levels) suggest that alterations in the reward system are, in part, related to cannabis use. Hum Brain Mapp 37:3431–3443, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Total retinal volumetric blood flow rate in diabetic patients with poor glycemic control

Total retinal volumetric blood flow rate was measured in 12 normal subjects and 18 poorly controlled diabetic patients with background diabetic retinopathy. Maximum or center-line erythrocyte velocity (Vmax) was assessed by bidirectional laser Doppler velocimetry in four to five major retinal veins of one eye of each subject. Venous diameter (D) was measured from monochromatic fundus photographs. Total venous cross-section and measured total retinal volumetric blood flow in the diabetic patients were significantly larger than normal (P = 0.001 and P = 0.02, respectively). A positive linear correlation was found between Vmax and D in normal and diabetic eyes. Volumetric blood flow rate, Q, varied with D at a power of 2.87 in normal eyes. Total volumetric blood flow correlated with total venous cross-section. It was found that Q in the temporal retina was significantly larger than in the nasal retina in normal subjects (P = 0.0008) and diabetic patients (P = 0.0002). A significant difference in Q was observed between the superior and inferior retina in diabetic patients (P = 0.03) but not in normal subjects. The retinal vascular regulatory response to 100% oxygen breathing was reduced (P = 0.019) in diabetic patients and correlated with the level of background diabetic retinopathy. A close estimate of total volumetric blood flow may be obtained from blood flow measurement in one major retinal vein and the determination of total venous cross-section. This may be important for clinical studies in which measurements of all individual retinal veins may not be feasible.