Selective extracellular stimulation of individual neurons in ganglia

Abstract

Selective control of individual neurons could clarify neural functions and aid disease treatments. To target specific neurons, it may be useful to focus on ganglionic neuron clusters, which are found in the peripheral nervous system in vertebrates. Because neuron cell bodies are found primarily near the surface of invertebrate ganglia, and often found near the surface of vertebrate ganglia, we developed a technique for controlling individual neurons extracellularly using the buccal ganglia of the marine mollusc Aplysia californica as a model system. We experimentally demonstrated that anodic currents can selectively activate an individual neuron and cathodic currents can selectively inhibit an individual neuron using this technique. To define spatial specificity, we studied the minimum currents required for stimulation, and to define temporal specificity, we controlled firing frequencies up to 45 Hz. To understand the mechanisms of spatial and temporal specificity, we created models using the NEURON software package. To broadly predict the spatial specificity of arbitrary neurons in any ganglion sharing similar geometry, we created a steady-state analytical model. A NEURON model based on cat spinal motorneurons showed responses to extracellular stimulation qualitatively similar to those of the Aplysia NEURON model, suggesting that this technique could be widely applicable to vertebrate and human peripheral ganglia having similar geometry.

Preparing the Periphery for a Subsequent Behavior: Motor Neuronal Activity during Biting Generates Little Force but Prepares a Retractor Muscle to Generate Larger Forces during Swallowing inAplysia

“…To extracellularly record from a motor neuron, an extracellular glass electrode was gently pressed onto the sheath above the neuron's soma (Lu et al, 2008;McManus et al, 2012, their Fig. 5).…”

Extracellularly Identifying Motor Neurons for a Muscle Motor Pool in <em>Aplysia californica</em>

“…Note that it is still possible to activate neurons that are not at the surface via extracellular stimulation. However, our model 5 has showed that the stimulation may lose specificity when the target neuron is deeper than the neighboring neurons. When the neuron is deeper, the electrode-to-soma distance will be greater and higher current will be needed to activate this neuron, which may be high enough to activate other surface neurons nearby.…”

“…To locate a candidate neuron, use the manipulator to gently press the tip of the extracellular glass electrode down onto the sheath over the center of the neuron soma 5 (Figure 3), which is the best location for stimulation and recording selectivity 5 . Since the threshold current for activating a neuron increases linearly with electrode-to-soma distance 5 , the stimulation selectivity will become worse when the electrode is moved away from the center of the target neuron toward a neighboring neuron. 3.…”

“…Since most extracellular amplifiers do not allow simultaneous stimulation and recording in a channel, set the channel used to stimulate and record the soma (the soma channel) to stimulation mode and apply a brief anodic current (e.g. 6 msec for Aplysia neurons 5 ) to the soma (Figures 4A, 5A; note arrows 1 in both figures), starting from a low current (e.g. 200 μA), and gradually increasing the current until the neuron bursts.…”

“…mollusks), analysis of motor pools is done using intracellular techniques 1,2,3,4 . Recently, we developed a technique to extracellularly stimulate and record individual neurons in Aplysia californica 5 . We now describe a protocol for using this technique to uniquely identify and characterize motor neurons within a motor pool.…”