Developmental Tuning in a Spinal Nociceptive System: Effects of Neonatal Spinalization

Abstract

Recent studies indicate a modular organization of the nociceptive withdrawal reflex system. Each module has a characteristic receptive field, closely matching the withdrawal movement caused by its effector muscle. In the rat, the strength of the sensory input to each module is tuned during the first postnatal weeks, i.e., erroneous spinal connections are depressed, and adequate connections are strengthened. To clarify if this tuning is dependent on supraspinal structures, the effect of a complete neonatal spinal cord transection on the postnatal tuning of withdrawal reflexes was studied. The nociceptive receptive fields of single hindlimb muscles and compound withdrawal reflexes were examined in decerebrate unanesthetized and awake rats, respectively. Noxious thermal CO(2) laser stimulation was used to evoke reflex responses. Neonatal spinal cord transection resulted in a disrupted reflex organization in the adult rat, resembling that previously found in neonatal rats. The receptive fields of single hindlimb muscles exhibited abnormal distribution of sensitivity not matching the withdrawal action of the effector muscles. Likewise, the composite nocifensive movements, as documented in the awake rat, often resulted in erroneous movements toward the stimulus. It is concluded that withdrawal reflexes do not become functionally adapted in rats spinalized at birth. These findings suggest a critical role for supraspinal systems in the postnatal tuning of spinal nociceptive systems.

Developmental plasticity of coordinated action patterns in the perinatal rat

“…Sensory feedback from spontaneous movements expressed during the newborn period has been shown to be necessary for the correct development of this reflex (Petersson et al, 2003 Waldenström, Thelin, Thimansson, Levinsson, & Schouenborg, 2003). Although the spinal cord can generate spontaneous twitches and eventually houses the withdrawal reflex circuitry, a neonatal spinal transection leads to aberrant responses and the reflex circuit does not develop properly (Levinsson, Luo, Holmberg, & Schouenborg, 1999). Therefore, proper development and fine-tuning of the nociceptive withdrawal reflex is the product of spinal activity, sensory feedback from spontaneous movements, and supraspinal regulation of spinal mechanisms.…”

Postnatal Temporal, Spatial and Modality Tuning of Nociceptive Cutaneous Flexion Reflexes in Human Infants

“…Nevertheless, numerous anatomical and electrophysiological studies in rat pups have shown that the properties of nociceptive reflexes and their underlying dorsal horn nociceptive circuits differ in early postnatal life from those in adults [12], [16]–[18]. Most notably, withdrawal reflexes in rat pups have lower thresholds, in the innocuous range, and are greater in amplitude and duration than adult rats and the underlying dorsal horn neurons and reflex motoneurones have larger, disorganised cutaneous receptive fields [16], [19]–[22]. The changing properties of newborn rodent reflexes are due, at least in part, to the postnatal development of spinal sensory circuits.…”

Operant Conditioning of H-Reflex Can Correct a Locomotor Abnormality after Spinal Cord Injury in Rats

“…The spinal cord, like the rest of the CNS, undergoes activitydependent plasticity in development, during skill acquisition, and in response to trauma and disease (Goode and Van Hoven, 1982;Myklebust et al, 1982Myklebust et al, , 1986Casabona et al, 1990;Koceja et al, 1991;O'Sullivan et al, 1991;Nielsen et al, 1993;Straka and Dieringer, 1995;Levinsson et al, 1999;Wolpaw and Tennissen, 2001) (for review, see . The activity that induces spinal cord plasticity comes from peripheral sensory receptors via dorsal root input pathways and from the brain via descending pathways.…”