Neuropeptidergic and autonomic control of the vasculature of the rat knee joint revealed by laser Doppler perfusion imaging

Abstract

SUMMARYAn imaging technique (laser Doppler perfusion imaging, LDI), based on measurement of backscattered Doppler-broadened laser radiation, was used to provide two-dimensional images of perfusion in the exposed rat knee joint capsule. In control animals, frequency-dependent constriction of knee joint blood vessels occurred during electrical stimulation of sympathetic nerve fibres whilst dose-dependent vasodilatation of these vessels was elicited by direct application of the sensory neuropeptide substance P (SP) to the capsule. Intra-articular injection of the neurotoxic agent capsaicin did not affect vasoconstrictor responses when tested 5-7 days later, but substantially reduced dilator responses to SP. These findings indicate that capsaicin is selectively neurotoxic for sensory unmyelinated fibres but not sympathetic postganglionic fibres 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 flow is heterogeneous.

Leukocyte trafficking and pain behavioral responses to a hydrogen sulfide donor in acute monoarthritis

“…Changes in synovial blood flow to the medial aspect of the knee joint were measured using a Moor laser Doppler imager (LDI; Moor Instruments, Axminster, UK), as previously described (12,17). This technique is based on the principal that laser photons of a known wavelength undergo Doppler shifting when encountering circulating erythrocytes.…”

In vivo effects of CB2 receptor‐selective cannabinoids on the vasculature of normal and arthritic rat knee joints

“…Animals were allowed to recover for 1 week prior to the blood flow experiments. Sham‐injected animals were not tested as an intra‐articular injection of sterile saline has been shown to have no effect on synovial blood flow or vasoreactivity ( Karimian et al , 1995 ).…”

“…Knee joint blood flow was measured by laser Doppler perfusion imaging (LDI) as previously described ( Karimian et al , 1995 ; McDougall et al , 1995 ). The technique involved placing a laser Doppler perfusion imager (MoorLDI V.2; Moor Instruments Ltd., Devon, UK) 30 cm above the exposed rat knee and angling the scanner head to avoid reflectance artefact.…”

“…TRPV1 channels are non‐selective cation channels expressed on the axon terminals of a subgroup of primary afferent neurons ( Caterina et al , 1997 ; Szallasi, 2002 ). In joints, activation of TRPV1 channels by local capsaicin treatment leads to inflammatory changes, including increased synovial blood flow ( Karimian et al , 1995 ; Varga et al , 2005 ). Interestingly, the CB 1 receptor agonist arachidonyl‐2‐chloroethylamide has also been shown to act on TRPV1 channels to cause synovial hyperaemia in the rat knee ( Baker and McDougall, 2004 ).…”

Involvement of sympathetic efferents but not capsaicin-sensitive afferents in nociceptin-mediated dual control of rat synovial blood flow

“…Relative changes in knee joint perfusion were ascertained by a laser Doppler imager (Moor Instruments, Axminster, UK) using previously described protocols that have been validated for rat knee joint perfusion studies (23). The technique involves a low-power (2 mW) red laser beam (wavelength ϭ 633 nm) scanning over the surface of a tissue of interest in a raster pattern.…”