ONTOGENY AND CHARACTERIZATION OF [I-125] BOLTON HUNTER-ELEDOISIN BINDING-SITES IN RAT SPINAL-CORD BY QUANTITATIVE AUTORADIOGRAPHY

The distribution and characteristics of [I-125]Bolton Hunter-eledoisin binding sites in rat lumbar spinal cord were studied during postnatal development by in vitro receptor autoradiography. At three, six, and 10 days of age, specific [I-125]eledoisin binding was distributed throughout the dorsal and ventral horns of the spinal cord. In contrast, from day 24 onwards, specific binding of [I-125]eledoisin was confined to superficial layers of the dorsal horn, with negligible amounts of specific binding in the ventral horn. [I-125]Eledoisin binding to neonatal (three day) and adult (eight to 12 weeks) spinal cord sections was characterized using tachykinin agonists. In both dorsal and ventral horns of neonatal spinal cord, the rank order of potency of agonists indicated that the majority (64%) of specific [I-125]eledoisin binding was to neurokinin-3 binding sites. The identity of the non-neurokinin-3 sites labelled by [I-125]eledoisin remains to be determined. In adult rat spinal cord, [I-125]eledoisin appeared to bind exclusively to neurokinin-3 binding sites. These results suggest that major changes take place in the localization of neurokinin-3 receptors during postnatal ontogeny of the rat spinal cord. These changes may reflect an important role for tachykinins in neuronal plasticity of the developing spinal cord.