A survey of spinal dorsal horn neurones encoding the spatial organization of withdrawal reflexes in the rat

Behavioral choices in invertebrates are mediated by a combination of shared and specialized circuitry, including neurons that are inhibited during competing behaviors. Less is known, however, about the neural mechanisms of behavioral choice in vertebrates. The spinal cord can appropriately select among several types of limb movements, including limb withdrawal (flexion reflex), scratching, and locomotion, and thus is conducive to examination of vertebrate mechanisms of behavioral choice. Flexion reflex can interrupt and reset the rhythm of scratching and locomotion, suggesting that a combination of shared and specialized circuitry contributes to these behaviors, but little is known about the interneurons involved. Here, I used in vivo intracellular recording and dye injection to identify a group of spinal interneurons that are strongly activated during fictive flexion reflex but inhibited during fictive scratching and fictive swimming. These flexion-selective interneurons are typically rhythmically hyperpolarized during fictive scratching and fictive swimming. This hyperpolarization can be maximal during the ipsilateral hip flexor bursts of rhythmic limb motor patterns, although these cells are strongly activated during the ipsilateral hip flexor bursts of fictive flexion reflex. Thus, these interneurons are relatively specialized for fictive limb withdrawal, rather than contributing to the hip flexor phase of multiple types of limb movements. These flexion-selective cells are physiologically and morphologically distinguishable from a recently described group of spinal interneurons (transverse interneurons) that are strongly activated during both fictive flexion reflex and fictive scratching. Thus, spinal interneurons with distinct behavioral roles may to some extent be morphologically distinguishable.

Section: Morphological Comparisons To Dorsal Horn Cells In Other Studiesmentioning

confidence: 59%

Spinal Interneurons That Are Selectively Activated during Fictive Flexion Reflex

Berkowitz¹

2007

“…A receptive field, divided into four areas of differing sensitivity [85-100% (referred to as receptive field focus), 60 -85%, 30 -60%, and 0 -30% of maximal response] was then delineated. The areas of differing sensitivity were delineated with the aid of computer-generated isoresponse lines (Kriging algorithm and contour program, software from Golden, Inc., Golden, CO; "Grid" and "Topo" programs; also see Schouenborg et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

“…These findings may suggest that each individual reflex pathway receives cutaneous input from a given skin area, and that the adult distribution of input strength from this area is the result of a postnatal tuning process. The location and extent of this area could be determined by the spatial relation between the reflex interneurons (Schouenborg et al, 1995) and the location of the primary afferent terminations in the spinal cord dorsal horn (Molander and Grant, 1986).…”

Section: Adaptation Of Withdrawal Reflex Pathways To Altered Input-oumentioning

confidence: 99%

Developmental Adaptation of Rat Nociceptive Withdrawal Reflexes after Neonatal Tendon Transfer

Holmberg

Schouenborg

et al. 1997

Nociceptive withdrawal reflexes (NWRs) were studied in adult rats in which the movement patterns produced by single muscles had been altered by neonatal tendon transfer. NWRs evoked by cutaneous noxious mechanical and thermal (CO 2 -laser) stimulation were recorded using electromyography in a decerebrate spinal preparation. The sensitivity distribution within the receptive fields of the NWRs of the extensor digitorum longus and the peronei muscles exhibited changes corresponding to the altered movement patterns. No detectable change of NWRs was found in normal muscles whose receptive fields overlapped that of the modified muscle. Furthermore, NWRs of muscles that regained an essentially normal function after neonatal tendon transfer did not differ from normal. It is proposed that a developmental experience-dependent mechanism, which takes into account the hindlimb movement pattern caused by contraction of single muscles, underlies the functionally adapted organization of adult NWRs.

“…Instead, termination patterns of different cutaneous fibers in the adult rat lumbar spinal cord appear to be closely related to the locations and receptive fields of the reflex sensorimotor circuits (Levinsson et al, 2002). In the withdrawal reflex circuits, pools of reflex encoding interneurons located in the deep part of the dorsal horn, in turn, are related to the sequence of motor neurons in the ventral horn (Schouenborg et al, 1995). In adult mammals, the nociceptive withdrawal reflex system is functionally organized into modules (Schouenborg, 2003); each module controls a single or a few synergistic muscles and transforms sensory input from a receptive field into appropriate motor activity.…”

Section: Introductionmentioning

confidence: 98%

Action-Based Body Maps in the Spinal Cord Emerge from a Transitory Floating Organization

Granmo¹,

Petersson²,

Schouenborg³

2008

Self Cite

101

During development primary afferents grow into and establish neuronal connections in the spinal cord, thereby forming the basis for how we perceive sensory information and control our movements. In the somatosensory system, myriads of primary afferents, conveying information from different body locations and sensory modalities, get organized in the dorsal horn of the spinal cord so that spinal multisensory circuits receive topographically ordered information. How this intricate pathfinding is brought about during development is, however, largely unknown. Here we show that a body representation closely related to motor patterns emerges from a transitory floating and plastic organization through profound activity-dependent rewiring, involving both sprouting and elimination of afferent connections, and provide evidence for cross-modality interactions in the alignment of the multisensory input. Thus, far from being inborn and stereotypic, the dorsal horn of the spinal cord now appears to be a highly adaptive brain-body interface.