Fettah Abderrahman1, Boulain Marie1, Guilhemsang Lise2, Juvin Laurent1, Mallet Nicolas2, Barrière Grégory1 The intricate orchestration of motor control is governed by the cortico-basal ganglia- thalamocortical loops, with recent investigations highlighting the pivotal role of basal ganglia downstream projections to pedunculopontine nucleus (PPN) in regulating specific motor programs. Despite these advancements, the precise mechanisms through which the basal ganglia networks selectively control these functional motor modules remain incompletely elucidated. Our findings in mouse reveal that the substantia nigra pars reticulata (SNr) establishes dense connections with the pedunculopontine nucleus (PPN), positioning the PPN as a potential relay hub between basal ganglia (BG) outputs and reticular formation (RF) nuclei. In particular, we provide evidence that the PPN projects to distinct brainstem areas, including the lateral paragigantocellular nucleus (LPGi) and the lateral reticulospinal nucleus (LatRM) involved in locomotor and forelimb movements, respectively. We further confirmed that bilateral optogenetic activation of glutamatergic PPN neurons using Vglut2-Cre mice pauses various motor behaviors, including treadmill/overground locomotion, climbing, grooming, and feeding. In vivo electrophysiological recordings of glutamatergic PPN neurons in anaesthetized animals revealed different patterns of activity, highlighting functional heterogeneity within this cell population. Our ongoing investigations aim to better characterize the anatomo-functional heterogeneity within glutamatergic PPN neurons and their contribution to different motor behavior. This research provides valuable insights into the neural basis of movement selection.1. Univ. Bordeaux, CNRS, INCIA, UMR 5287, F-33000 Bordeaux, France 2. Univ. Bordeaux, CNRS, IMN, UMR 5293, F-33000 Bordeaux, France