The Spinal Neurons Exhibit an ON-OFF and OFF-ON Firing Activity Around the Onset of Fictive Scratching Episodes in the Cat

Carlos A Cuellar,Rodolfo Delgado-Lezama,Braniff De La Torre Valdovinos,Rafael Ornelas-Kobayashi,Nayeli Huidobro,Elias Manjarrez

doi:10.3389/fncel.2018.00068

Abstract

In a previous report, we found neurons with ON-OFF and OFF-ON firing activity in the obex reticular formation during scratching. The aim of the present study was to examine whether the spinal neurons also exhibit this type of activity in relation to the “postural stage” of fictive scratching in the cat. We found that the extensor and intermediate scratching neurons exhibit an ON-OFF firing rate; conversely, the flexor neurons show an OFF-ON activity, relative to every scratching episode. These patterns of spiking activity are similar to those found in neurons from the obex reticular formation during scratching. Our findings provide support to the following hypotheses. First, there is a possible functional link between supraspinal and spinal, ON-OFF and OFF-ON neuronal groups. Second, the fictive goal-directed motor action to maintain the fictive “postural stage” of the hindlimb during fictive scratching is associated with the neuronal tonic activity of the OFF-ON spinal neurons, whereas the ON-OFF spinal neurons are associated with an extensor tone that occurred prior the postural stage.

Highlights

In cats, the mechanical stimulation of receptive fields from the neck and the pinna produces scratching behavior
We observed that the sustained firing activity of both extensor and intermediate neurons returns after the end of the scratching episode
We found that the “extensor and intermediate” neurons exhibit opposite firing activity compared to “flexor” neurons during fictive scratching, i.e., ON-OFF vs. OFF-ON

Summary

Introduction

The mechanical stimulation of receptive fields from the neck and the pinna produces scratching behavior. In 1906, Sherrington showed that the scratching is a stereotyped and relatively simple motor pattern that can be studied to provide insights into the organization of the spinal circuitry that generates rhythmic motor output (Sherrington, 1910). Subsequent studies showed that the scratching could be useful to study the spinal networks known as central pattern generators (CPGs) (Brown, 1911). Many stereotyped motor patterns are produced by the CPG (Grillner, 1981; Berkowitz and Stein, 1994; Whelan, 1996; Kiehn and Kjaerulff, 1998; Orlovsky et al, 1999; Kiehn, 2006). An animal preparation that exhibits “fictive scratching” could be obtained after the section of motoneuron axons or when the muscles are removed or paralyzed. Many spinal interneurons and motoneurons are involved in this “fictive goal-directed motor action” of

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