The overall aim of this project is to develop and implement a new magnetic resonance spectroscopy (MRS) technique for measuring brain metabolites in adolescent chronic marijuana smokers and matched healthy control subjects, in order to investigate the effects of chronic marijuana exposure during this critical phase of brain development. It is well established that the primary psychoactive compound within marijuana, (9-tetrahydrocannabinol (THC), activates the cannabinoid type-1 (CB1) receptor located on glutamate and (-amino butyric acid (GABA) neuron and axon terminals. CB1 receptors decrease glutamate or GABA release through the inhibition of Ca2+ currents and modulation of K+ channel gating. Both glutamate and GABA play pivotal roles in cortical remodeling throughout adolescence. However, the MRS approaches currently available to measure these metabolites are limited by poor reliability as a result highly metabolite-selective MRS approaches that measure only a subset of biochemical compounds are often adopted. Improved quantification of the perturbation of GABAergic and glutamatergic tone induced by chronic marijuana exposure is needed to understand its impact on the developing brain. We propose to apply in vivo localized two-dimensional (2D) proton (1H) MRS to study neurochemical alterations in 26 adolescent chronic marijuana smokers and 26 matched controls. We will develop and implement 2D 1H MRS methods in order to enhance the effective spectral resolution by separating all metabolite proton MR signals over a 2D surface. All 2D 1H MRS datasets will be fitted using prior knowledge fitting (ProFit), a spectral fitting algorithm that iteratively fits the whole 2D surface using individual 2D metabolite basis spectra. A significant advantage of the proposed 2D 1H MRS method used in combination with ProFit is the concomitant quantification of GABA and glutamate with a significantly higher level of precision than conventional 1D 1H MRS methods. A further important advantage of this approach will be the simultaneous and reliable measure of brain glutamine, an astrocytic precursor that is central to glutamatergic and GABAergic neurotransmission. Importantly, additional metabolic information concerning N-acetyl aspartate, choline-containing compounds, total creatine and myo-inositol is retained albeit with higher precision using 2D 1H MRS and ProFit. We believe the newly advanced MRS methods proposed would allow us to examine the biochemical changes associated with heavy cannabis use at level not previously possible and will produce findings with important implications for early intervention and treatment.
Adolescent cannabis consumption is widespread and constitutes a significant public health concern. The proposed study will implement a new magnetic resonance spectroscopy (MRS) method to examine the impact of chronic cannabis use on brain chemistry during adolescent brain maturation. Findings from this research will lead to an improved understanding of the effects of adolescent cannabis use during this vulnerable period of brain development and have the potential to aid in the identification of more effective prevention and treatment strategies.
| Prescot, Andrew P; Shi, Xianfeng; Choi, Changho et al. (2014) In vivo T(2) relaxation time measurement with echo-time averaging. NMR Biomed 27:863-9 |
