Intraspinal stretch receptor neurons mediate different motor responses along the body in lamprey

Abstract

In lampreys, stretch receptor neurons (SRNs) are located at the margins of the spinal cord and activated by longitudinal stretch in that area caused by body bending. The aim of this study was a comprehensive analysis of motor responses to bending of the lamprey body in different planes and at different rostrocaudal levels. For this purpose, in vitro preparation of the spinal cord isolated together with notochord was used, and responses to bending were recorded from SRNs, as well as from motoneurons innervating the dorsal (dMNs) and ventral (vMNs) parts of a myotome. It was found that SRNs were activated on the convex (stretched) side of the preparation during bending both in the yaw and in the pitch plane. By contrast, responses of motoneurons depended on the site and plane of bending. In the yaw plane, concave responses to bending of rostral segments and convex responses to bending of mid-body segments prevailed. In the pitch plane, convex responses in dMNs and concave responses in vMNs to bending in mid-body segments prevailed. These spinal reflexes could contribute to feedback regulation of locomotor body undulations and to the control of body configuration during locomotion. After a longitudinal split of the spinal cord, only convex responses in motoneurons were present, suggesting an important role of contralateral networks in determining the type of motor response. Stimulation of the brainstem changed the type of motor response to bending, suggesting that these spinal reflexes can be modified by supraspinal signals in accordance with different motor behaviors.

The role of mechanical resonance in the neural control of swimming in fishes

“…Edge cells, the proprioceptor in lampreys, for example, have axons that extend away from the point of local curvature, primarily in the rostral direction (Rovainen, 1982). Moreover, the impact of edge cells on the CPG seems to differ along the body, with rostral edge cells entraining the CPG at a phase almost 180° different from the effect of caudal edge cells (Tytell and Cohen, 2008; Hsu et al, 2013). …”

Supraspinal control of spinal reflex responses to body bending during different behaviours in lampreys

“…These methods for bending the preparation were similar to those described in our previous study (Hsu et al . a ), which demonstrated that bending activated SRNs causing spinal reflexes.…”

“…A similar result was obtained in the isolated spinal cord (Hsu et al . a ). This finding suggests that, first, networks underlying concave responses to bending in the rostral segments could be selectively activated and thus contribute to the behaviours like steering during FFS that require large amplitude bending in the rostral part of the body (Fagerstedt & Ullén, ; Saitoh et al .…”

“…As shown in our previous study (Hsu et al . a ), the effect of bending at a specific site decays with the increase of the distance between the bending and recording site. So, in the present study, the sites of VR recording depended on the site of preparation bending.…”

“…Recently, in an in vitro spinal cord preparation, we have found two types of spinal reflex responses to passive lateral bending, with activation of motoneurons (MNs) either on the convex side or on the concave side (Hsu et al . a ).…”