The mechanisms of the widespread production of phosphorylated HSP25 after fatiguing muscle stimulation

… Gould SA, Ballainvilliers, France). The heart rate (HR) and the percutaneous oxygen
141 saturation were continuously measured using the Mouse Ox apparatus (STARR
Life Sciences 142 Corporation, Oakmont, PA, USA). Animals … We already showed a widespread heat shock protein (HSP) response to fatigue of a single hindlimb muscle, responsible for a global adaptive response to an acute localized stress. We also demonstrated that the HSP response resulted from the activation of nerve afferents from the stimulated muscle. However, we did not examine the role played by the different muscle afferents as well as the efferent arm of HSP response. We here measured the changes in phosphorylated HSP25 (pHSP25) levels in resting hindlimb muscles, the diaphragm, kidney, and brain in response to a fatiguing stimulation of onetibialis anterior (TA) muscle which was repeated in five series of experiments: 1) intact muscle innervation, 2) during the selective procaine block of conduction in group IV muscle afferents, 3) after muscle nerve transection to suppress all the sensory messages, under pharmacological blockade of the 4) alpha adrenergic or 5) glutamatergic neurotransmission. The data showed that: 1) the pHSP25 response in hindlimb muscles resulted from the stimulation of both the groups III and IV muscle afferents while the pHSP25 response in the diaphragm, kidney, and brain resulted from the sole activation of the group IV fibres, 2) the blockade of alpha adrenergic, but not that of glutamatergic neurotransmission, suppressed the pHSP25 response in all the explored tissues except the brain. The present study highlights the role played by the groups III and IV muscle afferents in the fatigue-induced pHSP25 response and shows that the sympathetic nerve supply to the muscles and kidney represents the efferent arm of the pHSP25 activation. However, the pHSP25 changes in the brain cannot be explained by the pathways investigated here.