Effects of posttraining damage to the pedunculopontine tegmental nucleus on conditioned stimulus transfer in two-way active avoidance in rats.

The effects of posttraining excitotoxic lesions of the pedunculopontine tegmental nucleus (PPTg) on two-way active avoidance after changing the conditioned stimulus (CS) used during prelesion training were examined. Prelesion training was carried out with either a tone or a light as the CS, and this CS was changed during postlesion training. Replacing the tone with a light reduced the performance of control and lesioned rats, but the degree of reduction was higher in the latter. Replacing the light with a tone had slight detrimental effects in lesioned rats but not in controls. Thus, posttraining PPTg lesions slowed down the reacquisition of shuttle-box avoidance under conditions of CS transfer, an effect that may be attributable to disruption of attention and/or gating of sensory stimuli.

Effects of pre-training pedunculopontine tegmental nucleus lesions on delayed matching- and non-matching-to-position in a T-maze in rats.

Lesions of the pedunculopontine tegmental nucleus (PPTg) can impair spatial learning tasks, but it is not clear whether those detrimental effects depend on the specific training conditions (for example, number of response choices available) or are secondary to enhanced anxiety. In the present work, rats with either bilateral excitotoxic (ibotenate) lesions of the PPTg (lesion group) or with vehicle infusions (control group) were tested in an elevated plus-maze, in order to measure anxiety-like behaviours and spontaneous locomotion. Subsequently, they were trained in a delayed matching-to-position (DMTP) task in a T-maze (a two-response choice task). After reaching a predefined learning criterion, or after a maximum of 30 training sessions, the animals were trained in a delayed non-matching-to-position (DNMTP) task. Lesioned animals made less grooming episodes, stretch-attend postures and closed arm entries than controls in the elevated plus-maze, suggesting slightly lower anxiety levels. None of the lesioned rats reached the learning criterion for the DMTP, and overall accuracy levels were significantly lower in those rats, compared to controls. In the DNMTP task, lesioned animals showed lower accuracy levels and higher side bias than controls in some of the sessions, but there were no significant differences between the two groups in the proportion of animals reaching the learning criterion. It is concluded that spatial learning deficits induced by damage to the PPTg are not secondary to enhanced anxiety. Instead, those deficits seem to be influenced by several conditions that modify task demands, the number of response choices being only one of such conditions.

Effects of pedunculopontine tegmental nucleus lesions on emotional reactivity and locomotion in rats.

Bilateral damage to the pedunculopontine tegmental nucleus (PPTg) has been found to impair several learning tasks; however, it is not clear whether this effect could be at least partially attributable to changes in the rat emotional reactivity and/or spontaneous locomotion. Therefore, the present work has tested the effects of bilateral electrolytic lesions of the PPTg on the behaviour of rats in the elevated plus-maze and the open field test. Because the behaviour of rats in learning and emotional tasks can be sensitive to routine experimental manipulations, we also have tested the effects of brief pre-surgical handling procedures on anxiety-like behaviours and locomotion in both lesioned and control rats. Lesions of the pedunculopontine tegmental nucleus (1). did not have any effects on spontaneous locomotor activity and (2). did not increase emotional reactivity. In fact, there was a slight bias towards a reduction in anxiety-like behaviours in lesioned rats, as evidenced by a significant increase in the number of open arm entries. Pre-surgical handling induced a slight decrease of emotional reactivity and a slight increase of exploratory activity. We conclude that damage to the pedunculopontine tegmental nucleus is not accompanied by either an enhancement of emotional reactivity or by an altered spontaneous locomotion.