Ionic Selectivity of Mechanically Activated Channels in Spider Mechanoreceptor Neurons

Milenkovic N, Wetzel C, Moshourab R, Lewin GR. Speed and temperature dependences of mechanotransduction in afferent fibers recorded from the mouse saphenous nerve. J Neurophysiol 100: 2771-2783, 2008. First published September 24, 2008 doi:10.1152/jn.90799.2008. Here we have systematically characterized the stimulus response properties of mechanosensitive sensory fibers in the mouse saphenous nerve. We tested mechanoreceptors and nociceptors with defined displacement stimuli of varying amplitude and velocity. For each sensory afferent investigated we measured the mechanical latency, which is the delay between the onset of a ramp displacement and the first evoked spike, corrected for conduction delay. Mechanical latency plotted as a function of stimulus strength was very characteristic for each receptor type and was very short for rapidly adapting mechanoreceptors (Ͻ11 ms) but very long in myelinated and unmyelinated nociceptors (49 -114 ms). Increasing the stimulus speed decreased mechanical latency in all receptor types with the notable exception of C-fiber nociceptors, in which mean mechanical latency was not reduced Շ100 ms, even with very fast ramp stimuli (2,945 m/s). We examined stimulus response functions and mechanical latency at two different temperatures (24 and 32°C) and found that stimulus response properties of almost all mechanoreceptors were not altered in this range. A notable exception to this rule was found for C-fibers in which mechanical latency was substantially increased and stimulus response functions decreased at lower temperatures. We calculated Q 10 values for mechanical latency in C-fibers to be 5.1; in contrast, the Q 10 value for conduction velocity for the same fibers was 1.4. Finally, we examined the effects of short-term inflammation (2-6 h) induced by carrageenan on nociceptor and mechanoreceptor sensitivity. We did not detect robust changes in mechanical latency or stimulus response functions after inflammation that might have reflected mechanical sensitization under the conditions tested.

Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Speed and Temperature Dependences of Mechanotransduction in Afferent Fibers Recorded From the Mouse Saphenous Nerve

Milenkovic¹,

Wetzel²,

Moshourab³

et al. 2008

“…For current-and voltage-clamp experiments a "hypodermis preparation" was used: the hypodermis membrane was detached from the cuticle with the VS-3 neurons attached and placed on a poly-L-lysine (1 mg/ml) coated coverslip in a recording chamber as described previously (Sekizawa et al 1999). Preparations were continuously superfused with spider saline [in mM: 223 NaCl, 6.8 KCl, 8 CaCl 2 , 5.1 MgCl 2 , 5 sucrose, and 10 HEPES, pH 7.8 (Höger et al 1997)]. All chemicals were purchased from Sigma (Oakville, ON, Canada) if not otherwise indicated.…”

Section: Experimental Animals and Preparationsmentioning

confidence: 99%

Contributions of Voltage- and Ca²⁺-Activated Conductances to GABA-Induced Depolarization in Spider Mechanosensory Neurons

Panek

Höger²,

French³

et al. 2008

Self Cite

“…The hypodermis membrane with the VS-3 slit sense organ was detached from the cuticle and attached to a coverslip coated with 1 mg/ml poly-L-lysine (Sigma P5899) and then placed in a recording chamber as described previously in detail (Sekizawa et al 1999). The preparation was superfused continuously with spider saline [in mM: 223 NaCl, 6.8 KCl, 8 CaCl 2 , 5.1 MgCl 2 , 5 sucrose, and 10 HEPES, pH 7.8 (Höger et al 1997)] using a BPS-4 solution exchange system and PR10 pressure regulator (ALA Scientific, New York, NY). The drugs were injected either using the solution exchange system or manually with a syringe and a needle.…”

Section: Electrophysiologymentioning

confidence: 99%

Distribution and Function of GABA_BReceptors in Spider Peripheral Mechanosensilla

Panek

Meisner

Torkkeli

2003

Self Cite

. The mechanosensilla in spider exoskeleton are innervated by bipolar neurons with their cell bodies close to the cuticle and dendrites attached to it. Numerous efferent fibers synapse with peripheral parts of the mechanosensory neurons, with glial cells surrounding the neurons, and with each other. Most of these efferent fibers are immunoreactive to ␥-aminobutyric acid (GABA), and the sensory neurons respond to agonists of ionotropic GABA receptors with a rapid and complete inhibition. In contrast, little is known about metabotropic GABA B receptors that may mediate longterm effects. We investigated the distribution of GABA B receptors on spider leg mechanosensilla using specific antibodies against 2 proteins needed to form functional receptors and an antibody that labels the synaptic vesicles on presynaptic sites. Both anti-GABA B receptor antibodies labeled the distal parts of the sensory cell bodies and dendrites but anti-GABA B R1 immunoreactivity was also found in the axons and proximal parts of the cell bodies and some glial cells. The fine efferent fibers that branch on top of the sensory neurons did not show GABA B receptor immunoreactivity but were densely labeled with anti-synapsin and indicated synaptic vesicles on presynaptic locations to the GABA B receptors. Intracellular recordings from sensory neurons innervating the slit sensilla of the spider legs revealed that application of GABA B receptor agonists attenuated voltageactivated Ca 2ϩ current and enhanced voltage-activated outward K ϩ current, providing 2 possible mechanisms for controlling the neurons' excitability. These findings support the hypothesis that GABA B receptors are present in the spider mechanosensilla where their activation may modulate information transmission.