NEUROPEPTIDERGIC AND AUTONOMIC CONTROL OF THE VASCULATURE OF THE RAT KNEE-JOINT REVEALED BY LASER-DOPPLER PERFUSION IMAGING

An imaging technique (laser Doppler perfusion imaging, LDI), based on measurement of backscattered Doppler-broadened laser radiation, was us ed to provide two-dimensional images of perfusion in the exposed rat k nee joint capsule. In control animals, frequency-dependent constrictio n of knee joint blood vessels occurred during electrical stimulation o f sympathetic nerve fibres whilst dose-dependent vasodilatation of the se vessels was elicited by direct application of the sensory neuropept ide substance P (SP) to the capsule. Intra-articular injection of the neurotoxic agent capsaicin did not affect vasoconstrictor responses wh en tested 5-7 days later, but substantially reduced dilator responses to SP. These findings indicate that capsaicin is selectively neurotoxi c for sensory unmyelinated fibres but not sympathetic postganglionic f ibres and is also capable of modifying receptor-mediated effects of SP . LDI is a useful method for mapping tissue perfusion, particularly in structures such as joints where the spatial distribution of blood flo w is heterogeneous.