title: Neural substrates underlying fear-evoked freezing: the periaqueductal grey-cerebellar link.
abstract: The central neural pathways involved in fear-evoked behaviour are highly conserved across mammalian species, and there is a consensus that understanding them is a fundamental step towards developing effective treatments for emotional disorders in man. The ventrolateral periaqueductal grey (vlPAG) has a well-established role in fear-evoked freezing behaviour. The neural pathways underlying autonomic and sensory consequences of vlPAG activation in fearful situations are well understood, but much less is known about the pathways that link vlPAG activity to distinct fear-evoked motor patterns essential for survival. In adult rats, we have identified a pathway linking the vlPAG to cerebellar cortex, which terminates as climbing fibres in lateral vermal lobule VIII (pyramis). Lesion of pyramis input-output pathways disrupted innate and fear-conditioned freezing behaviour. The disruption in freezing behaviour was strongly correlated to the reduction in the vlPAG-induced facilitation of α-motoneurone excitability observed after lesions of the pyramis. The increased excitability of α-motoneurones during vlPAG activation may therefore drive the increase in muscle tone that underlies expression of freezing behaviour. By identifying the cerebellar pyramis as a critical component of the neural network subserving emotionally related freezing behaviour, the present study identifies novel neural pathways that link the PAG to fear-evoked motor responses.
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK School of Biological Sciences, University of Bristol, Bristol, BS8 1UG, UK.
authors.forename: Stella
authors.initials: S
authors.lastname: Koutsikou
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Crook
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Emma V
authors.initials: EV
authors.lastname: Earl
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: J Lianne
authors.initials: JL
authors.lastname: Leith
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Watson
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK b.m.lumb@bristol.ac.uk.
authors.forename: Bridget M
authors.initials: BM
authors.lastname: Lumb
authors.affiliation: School of Physiology and Pharmacology, Medical Sciences Building University of Bristol, Bristol, BS8 1TD, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Apps
mesh_terms: D000818:Animals; D002531:Cerebellum / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D046352:Freezing Reaction, Cataleptic / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D010487:Periaqueductal Gray / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000502:physiology*