( Dopamine ( ( is ( ( a chemical ) ( in ( ( the brain ) ( that ( acts ( as ( ( a link ) ( to ( messages ( being ( sent ( to ( brain receptors ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Dopamine)) (VP (VBZ is) (NP (NP (DT a) (NN chemical)) (PP (IN in) (NP (NP (DT the) (NN brain)) (SBAR (WHNP (WDT that)) (S (VP (VBZ acts) (PP (IN as) (NP (NP (DT a) (NN link)) (PP (TO to) (NP (NP (NNS messages)) (VP (VBG being) (VP (VBN sent) (PP (TO to) (NP (NN brain) (NNS receptors)))))))))))))))) (. .)))
Dopamine is a chemical in the brain that acts as a link to messages being sent to brain receptors.
(ROOT (S (NP (NNP Addiction)) (VP (VBZ affects) (NP (NP (DT the) (JJ dopamine) (NNS receptors)) (PP (IN within) (NP (DT the) (NN brain))))) (. .)))