RESUMO
Selection of GC rats for the predisposition to cataleptic freezing has increased not only the frequency, intensity, and duration of freezing, but also the proportion of irritable or "nervous" rats with enhanced anxiety, defensive behavior with vocalization, jerky running, and jumpiness. An increased amplitude of the startle reflex is a correlate of this "nervousness." The results of the comparison of some behavioral characters in the nervous and freezing GC rats, as well as in F1 and F2 offspring from homogeneous crosses between nervous and freezing GC rats suggest that cataleptic freezing and nervousness are two poles of the same bipolar catatonic reaction. They have a common mechanism, with the alternative or preferential expression of one particular form of the reaction is determined by the external and internal environments or the set of modifier genes in the given individual.
