Characterisation of a Peripheral Neuropathic Component of the Rat Monoiodoacetate Model of Osteoarthritis

Joint degeneration observed in the rat monoiodoacetate (MIA) model of osteoarthritis shares many histological features with the clinical condition. The accompanying pain phenotype has seen the model widely used to investigate the pathophysiology of osteoarthritis pain, and for preclinical screening of analgesic compounds. We have investigated the pathophysiological sequellae of MIA used at low (1 mg) or high (2 mg) dose. Intra-articular 2 mg MIA induced expression of ATF-3, a sensitive marker for peripheral neuron stress/injury, in small and large diameter DRG cell profiles principally at levels L4 and 5 (levels predominated by neurones innervating the hindpaw) rather than L3. At the 7 day timepoint, ATF-3 signal was significantly smaller in 1 mg MIA treated animals than in the 2 mg treated group. 2 mg, but not 1 mg, intra-articular MIA was also associated with a significant reduction in intra-epidermal nerve fibre density in plantar hindpaw skin, and produced spinal cord dorsal and ventral horn microgliosis. The 2 mg treatment evoked mechanical pain-related hypersensitivity of the hindpaw that was significantly greater than the 1 mg treatment. MIA treatment produced weight bearing asymmetry and cold hypersensitivity which was similar at both doses. Additionally, while pregabalin significantly reduced deep dorsal horn evoked neuronal responses in animals treated with 2 mg MIA, this effect was much reduced or absent in the 1 mg or sham treated groups. These data demonstrate that intra-articular 2 mg MIA not only produces joint degeneration, but also evokes significant axonal injury to DRG cells including those innervating targets outside of the knee joint such as hindpaw skin. This significant neuropathic component needs to be taken into account when interpreting studies using this model, particularly at doses greater than 1 mg MIA

Loss of the inactive myotubularin-related phosphatase Mtmr13 leads to a Charcot–Marie–Tooth 4B2-like peripheral neuropathy in mice

Charcot–Marie–Tooth disease type 4B (CMT4B) is a severe, demyelinating peripheral neuropathy characterized by slowed nerve conduction velocity, axon loss, and distinctive myelin outfolding and infolding. CMT4B is caused by recessive mutations in either myotubularin-related protein 2 (MTMR2; CMT4B1) or MTMR13 (CMT4B2). Myotubularins are phosphoinositide (PI) 3-phosphatases that dephosphorylate phosphatidylinositol 3-phosphate (PtdIns3P) and PtdIns(3,5)P2, two phosphoinositides that regulate endosomal–lysosomal membrane traffic. Interestingly, nearly half of the metazoan myotubularins are predicted to be catalytically inactive. Both active and inactive myotubularins have essential functions in mammals and in Caenorhabditis elegans. MTMR2 and MTMR13 are active and inactive PI 3-phosphatases, respectively, and the two proteins have been shown to directly associate, although the functional significance of this association is not well understood. To establish a mouse model of CMT4B2, we disrupted the Mtmr13 gene. Mtmr13-deficient mice develop a peripheral neuropathy characterized by reduced nerve conduction velocity and myelin outfoldings and infoldings. Dysmyelination is evident in Mtmr13-deficient nerves at 14 days and worsens throughout life. Thus, loss of Mtmr13 in mice leads to a peripheral neuropathy with many of the key features of CMT4B2. Although myelin outfoldings and infoldings occur most frequently at the paranode, our morphological analyses indicate that the ultrastructure of the node of Ranvier and paranode is intact in Mtmr13-deficient nerve fibers. We also found that Mtmr2 levels are decreased by ≈50% in Mtmr13-deficient sciatic nerves, suggesting a mode of Mtmr2 regulation. Mtmr13-deficient mice will be an essential tool for studying how the loss of MTMR13 leads to CMT4B2

Schooling and swimming behaviors of Hyla semilineata tadpoles (Anura, Hylidae)

The schooling behavior of Hyla semilineata Spix, 1824 tadpoles is described. Experiments were carried out both in the natural environment and under controlled conditions to quantify the constant movement of these tadpoles. Bullfrog tadpoles (Rana catesbeiana Shaw, 1802), similar in size to the H. semilineata larvae, were used as controls in the experiments. Hyla semilineata tadpoles remained stationary for one sixth of the time that the bullfrog tadpoles did and the number of individuals of H. semilineata moving at any given moment was about seven times greater. The schooling behavior and constant swimming behavior of these tadpoles may enhance the effect of their warning coloration