RECONSTRUCTION OF FLEXOR EXTENSOR ALTERNATION DURING FICTIVE ROSTRAL SCRATCHING BY 2-SITE STIMULATION IN THE SPINAL TURTLE WITH A TRANSVERSE SPINAL HEMISECTION/

Analyses of fictive scratching motor patterns in the spinal turtle wit h transverse hemisection provided support for the concept of bilateral shared spinal cord circuitry among neurons responsible for generating left-and right-side rostral, pocket, and caudal fictive scratching. R hythmic bursts of hip flexor activity, the hip extensor deletion varia tion of fictive rostral scratching, were elicited by ipsilateral stimu lation in the rostral scratch receptive field of a spinal turtle [tran section at the segmental border between the second (D2) and third (D3) postcervical spinal segments] with a contralateral transverse hemisec tion one segment anterior to the hindlimb enlargement (at the D6-D7 se gmental border). In addition, other sites were stimulated in this prep aration: (1) contralateral sites in a rostral, pocket, or caudal scrat ch receptive field or (2) ipsilateral sites in a caudal scratch recept ive field. A reconstructed fictive rostral scratch motor pattern of rh ythmic alternation between hip flexor and hip extensor activation was produced by simultaneous stimulation of one site in the ipsilateral ro stral scratch receptive field and another site in one of the other scr atch receptive fields. This reconstructed rostral scratch motor patter n resembled the normal rostral scratch motor pattern produced by one-s ite rostral scratch stimulation of a spinal turtle (D2-D3 transection) with no additional transections. The observation of a reconstructed r ostral scratch motor pattern produced by two-site stimulation in the s pinal turtle with transverse hemisection supports the concept that hip extensor circuitry activated by stimulation of other scratch receptiv e fields is shared with circuitry activated by ipsilateral rostral scr atch receptive field stimulation.