Projected fiber systems dopaminergic

Consistent with these observations, there is some evidence that caffeine may act, in part, on dopaminergic fibers that project into the medial forebrain bundle. Other psychostimulants also appear to act on this system, which may be at least one of the neural mechanisms involved in the development of dependence.271 Further work has suggested a parallel between caffeine and another highly addictive drug, alcohol. Many of the same factors that enter into the development of alcoholism may also influence the development of dependence on caffeine.272... 

The EOPs have been directly implicated in the pathophysiology of TS syndrome. Haber and co-workers (1986) reported decreased levels of dynorphin A(l-17) immunoreactivity in striatal fibers projecting to the GP in postmortem material from a small number of Tour-ette s patients. This observation, coupled with the neu-roanatomic distribution of dynorphin, its broad range of motor and behavioral effects, and its modulatory interactions with striatal dopaminergic systems, suggest that dynorphin might have a key role in the patho-biology of TS. However, subsequent studies have failed to confirm these initial observations (van Wattum et al., 1999). 

---