The periaqueductal grey matter (PAG) is a key structure in the expression of behavioural responses to pain and fear; however the motor pathways that mediate these crucial survival behaviours are poorly understood. Previous anatomical studies have suggested connections between the PAG and the cerebellum, a hindbrain motor structure which has recently also been implicated in emotional function and the expression of survival behaviours, such as freezing behaviour. This thesis provides evidence of a possible anatomical pathway between these two structures, and describes investigations into a possible function of this connection. In sodium pentobarbital anaesthetised rats, cerebellar cortical field potentia Is were recorded in response to electrical stimulation in the PAG. Stimulation at both "IPAG and dlPAG sites was found to evoke bilateral climbing fibre field potentia Is in lateral regions of cerebellar vermallobule VIII. Fos expression was significantly increased in the fastigial nucleus A module in animals that underwent stereotaxic procedures, compared to anaesthetic control animals. Animals that received noxious pinches of the snout also tended to display greater numbers of Fos labelled neurons in this region. Animals that underwent excitation of the vlPAG with dl-homocysteic acid (DLH) displayed significantly fewer Fos labelled neurons in the A module than saline injected animals. This may reflect a vlPAG mediated depression of the noxious input to the cerebellum originating from stereotaxic and surgical procedures employed during the experiment. The functional significance of the PAG-Iobule VIII connection was investigated by lesioning connections to/from lateral lobule VIII using CTb-saporin. On average, lesioned animals displayed significantly reduced freezing behaviour during presentation of an aversively conditioned auditory tone. The animals that displayed the greatest reduction in freezing also displayed significantly fewer Fos labelled neurons in the caudal vIPAG. This suggests that vermallobule VIII supports neuronal activation of the caudal vlPAG during exposure to conditioned fear stimuli.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633195 |
| Date | January 2014 |
| Creators | Crook, Jonathan James |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0015 seconds