Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, PC20
Electrophysiological mapping of novel periaqueductal grey - cerebellar pathways
J. Leith1, B. M. Lumb1, R. Apps1
1. Department of Physiology & Pharmacology, University of Bristol, Bristol, United Kingdom.
The midbrain periaqueductal grey (PAG) is hypothesised to coordinate behavioural strategies that are dynamically activated under different environmental conditions (Lovick & Bandler, 2005). Stimulation of the ventrolateral (VL) PAG is associated with antinociception, hypotension, bradycardia, and immobility, together termed passive coping (Keay & Bandler, 2001). The sensory and autonomic consequences of PAG activation have received much attention, however the interaction of the PAG with motor control centres necessary to evoke distinct effects on movement remains poorly understood. The aim of this study was therefore to examine whether a functional link exits between the VL-PAG and the cerebellum, the largest sensorimotor structure in the brain, by examining local field potentials and single unit activity in the cerebellar cortex evoked by electrical stimulation of the VL-PAG. Experiments were carried out in pentobarbitone-anaesthetised (60mg/kg i.p.) adult male Wistar rats (n=7). Craniotomies were performed to allow access to the PAG with a bipolar stimulating electrode and to the posterior cerebellum with a recording electrode. Electrical stimulation of the VL-PAG evoked a distinct field potential on the cerebellar cortical surface. The response had a mean onset latency of 14.5±0.2ms (mean±s.e.m.), and was localised to vermal lobule VIII, distributed bilaterally. The evoked response displayed features typical of climbing fibre fields. In some experiments, single unit recordings were also made from the cerebellar cortex of vermal lobule VIII and VL-PAG stimulation elicited complex spike activity in Purkinje cells at a latency similar to the evoked field. These experiments therefore indicate that a neural pathway exists that links the VL-PAG with the cerebellum via the inferior olive climbing fibre system. We suggest that this novel PAG-cerebellar link may be involved in coordinating behavioural responses associated with VL-PAG function.
Where applicable, experiments conform with Society ethical requirements