Distribution and Function of GABABReceptors in Spider Peripheral Mechanosensilla

Open Access
Publisher Website
Google Scholar
Abstract
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 γ-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 GABABreceptors that may mediate long-term effects. We investigated the distribution of GABABreceptors 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-GABABreceptor antibodies labeled the distal parts of the sensory cell bodies and dendrites but anti-GABABR1 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 GABABreceptor immunoreactivity but were densely labeled with anti-synapsin and indicated synaptic vesicles on presynaptic locations to the GABABreceptors. Intracellular recordings from sensory neurons innervating the slit sensilla of the spider legs revealed that application of GABABreceptor agonists attenuated voltage-activated Ca2+current and enhanced voltage-activated outward K+current, providing 2 possible mechanisms for controlling the neurons' excitability. These findings support the hypothesis that GABABreceptors are present in the spider mechanosensilla where their activation may modulate information transmission.