(S (S (SBAR (IN Because) (S (BASENP (NN prolactin)) (VP (VBZ regulates) (NP (BASENP (DT the) (NNS levels)) (PP (IN of) (NP (BASENP (NNS precursors)) (PP (IN of) (BASENP (NNS oligodendrocytes))))))))) (COMMA ,) (S (BASENP (DT the) (NNS scientists)) (VP (VBD hypothesized) (SBAR (IN that) (S (BASENP (NN prolactin) (NNS levels)) (VP (VBD were) (ADJP (JJ responsible) (PP (IN for) (NP (BASENP (DT the) (NNS differences)) (PP (IN in) (BASENP (NN damage)))))))))))) (PERIOD .))