Long-lasting increase in anxiety after electrolytic lesions of the pedunculopontine tegmental nucleus

This study examined the effect of electrolytic lesions of the pedunculopont ine tegmental nucleus (PPTg) on emotionality in rats. Rats with PPTg or sha m lesions were tested in the elevated plus-maze, the social interaction tes t, the open-field test, and the conditioned fear paradigm. Histology showed that lesions were concentrated on the caudal half of the PPTg. In the plus -maze; behavioral scores were biased toward increased "anxiety" on the 1st testing day. Five consecutive exposures to the apparatus led to marked habi tuation in sham-lesioned but not in PPTg-lesioned rats. On the 5th day, mos t indexes of emotionality indicated elevated anxiety in PPTg-lesioned rats. Increased anxiety was also found in PPTg-lesioned rats in the social inter action test. In the conditioned fear paradigm, movement suppression during the postconditioned stimulus period was found in both groups an the ist day of extinction but only in PPTg-lesioned rats on the 2nd extinction day, in dicating extinction was slower in PPTg-lesioned rats, Lesions of the caudal PPTg appear to produce long-lasting anxiety in rats.