Patterns of FOS Expression in the Spinal Cord and Periaqueductal Grey Matter of 6OHDA-Lesioned Rats

Abstract

A less well-known feature of Parkinson disease is that up to 40% of patients experience distinct sensory disturbances, including hyperalgesia and chronic pain. There is a limited understanding of the neural mechanisms that generate these symptoms, however. This study explores the patterns of Fos expression (a well-known marker for changes in cell activity) in the spinal cord and periaqueductal grey matter (PaG), two major sensory (nociceptive) centers, of hemiparkinsonian rats. The medial forebrain bundle (mfb; major tract carrying dopaminergic nigrostriatal axons) was injected with either 6OHDA or saline (controls). A week later, some rats were subjected to mechanical stimulation (pinching) of the hindpaw for 2 h, whereas others received no stimulation. Thereafter, brains were processed using routine tyrosine hydroxylase (marker for dopaminergic cells) or Fos immunocytochemistry. In the PaG, there were many more Fos⁺ cells in the 6OHDA-lesioned than in the Control group, in both the stimulation and, in particular, the non-stimulation cases. In the spinal cord, there were also more Fos⁺ cells in the 6OHDA-lesioned than in the Control group, but in the stimulation cases only. Overall, the results show distinct changes in Fos expression in the spinal cord and PaG of 6OHDA-lesioned rats, suggesting a substrate for some of the abnormal sensory (nociceptive) circuits that may be evident in parkinsonian cases.

Keywords:

• cell activity
• mechanical stimulation
• pain
• Parkinson disease

ABBREVIATIONS
6OHDA:	=	6 hydroxydopamine
cp:	=	cerebral peduncle
DAB:	=	3,3prime;-diaminobenzidine tetrahydrochloride
GABA:	=	gaminobutyric acid
NS:	=	non-stimulation
NTBS:	=	nickel-Tris-buffered saline
PaG:	=	periaqueductal grey matter
PBS:	=	phosphate buffered saline
S:	=	stimulation
SNc:	=	substantia nigra pars compacta
TH:	=	tyrosine hydroxylase
VTA:	=	ventral tegmental area