Neuropeptide receptors in developing and adult rat spinal cord: An in vitro quantitative autoradiography study of calcitonin gene‐related peptide, neurokinins, μ‐opioid, galanin, somatostatin, neurotensin and vasoactive intestinal polypeptide receptors

Abstract

A number of neuroactive peptides including calcitonin gene-related peptide (CGRP), substance P, neurokinin B, opioids, somatostatin (SRIF), galanin, neurotensin and vasoactive intestinal polypeptide (VIP) have been localized in adult rat spinal cord and are considered to participate either directly and/or indirectly in the processing of sensory, motor and autonomic functions. Most of these peptides appear early during development, leading to the suggestion that peptides, in addition to their neurotransmitter/neuromodulator roles, may possibly be involved in the normal growth and maturation of the spinal cord. To provide an anatomical substrate for a better understanding of the possible roles of peptides in the ontogenic development of the cord, we investigated the topographical profile as well as variation in densities of [125I]hCGRP alpha, [125I]substance P/neurokinin-1 (NK-1), [125I]eledoisin/neurokinin-3 (NK-3), [125I]FK 33-824 ([D-Ala2, Me-Phe4, Met(O)ol5]enkephalin)/mu-opioid, [125I]galanin, [125I]T0D8-SRIF14 (an analog of somatostatin); [125I]neurotensin and [125I]VIP binding sites in postnatal and adult rat spinal cord using in vitro quantitative receptor autoradiography. Receptor binding sites recognized by each radioligand are found to be distributed widely during early stages of postnatal development and then to undergo selective modification to attain their adult profile of distribution during the third week of postnatal development. The apparent density of various receptor sites, however, are differently regulated depending on the lamina and the stage of development studied. For example, the density of mu-opioid binding sites, following a peak at postnatal day 4 (P4), declines gradually in almost all regions of the spinal cord with the increasing age of the animal. [125I]substance P/NK-1 binding sites, on the other hand, show very little variation until P14 and then subsequently decrease as the development proceeds. In the adult rat, most of these peptide receptor binding sites are localized in relatively high amounts in the superficial laminae of the dorsal horn. To varying extents, moderate to low density of various peptide receptor binding sites are also found to be present in the ventral horn, intermediolateral cell column and around the central canal. Taken together, these results suggest that each receptor-ligand system is regulated differently during development and may each uniquely be involved in cellular growth, differentiation and in maturation of the normal neural circuits of the spinal cord. Furthermore, the selective localization of various receptor binding sites in adult rat spinal cord over a wide variety of functionally distinct regions reinforces the neurotransmitter/modulator roles of these peptides in sensory, motor and autonomic functions associated with the spinal cord.

Potent Spinal Analgesia Elicited through Stimulation of NTS2 Neurotensin Receptors

“…This distribution is considerably more widespread than that of NTS1 receptors, as described using either receptor autoradiography or immunohistochemistry. By autoradiography, high-affinity (i.e., NTS1) NT receptors were localized to lamina II of the dorsal horn, and most prominently in the deeper inner segment III (Ninkovic et al, 1981;Young and Kuhar, 1981;Uhl, 1982;Faull et al, 1989;Kar and Quirion, 1995). Likewise, by immunohistochemistry, a very dense plexus of NTS1-immunoreactive fibers was detected in the substantia gelatinosa of the dorsal horn, and NTS1-immunoreactive nerve cell bodies were observed in the deeper part of layer II (Fassio et al, 2000).…”

“…Indeed, whereas neurons expressing NTS1 mRNA had been reported in DRG neurons (Zhang et al, 1995) and high concentrations of NTS1 binding sites, and NTS1-immunoreactive nerve cell bodies and fibers had been detected in the substantia gelatinosa of the dorsal horn (Ninkovic et al, 1981;Kar and Quirion, 1995;Fassio et al, 2000), nothing was known about the distribution of NTS2 receptors in these two areas. Likewise, recent studies using knock-down strategies had suggested that NTS1 receptors may be implicated in spinal antinociception (Tyler et al, 1998;Pettibone et al, 2002), but whether NTS2 receptors were also involved in this process was still an open question.…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…Anatomical mapping of VPAC1-R and VPAC2-R mRNAs indicates that the two receptor transcripts have completely different and apparently complementary dis- Cauvin et al, 1991;Yashpal et al, 1991;Kar and Quirion, 1995 The symbols provide a semi-quantitative evaluation of the density of PACAP binding sites: ϩϩϩ, high density; ϩϩ, moderate density; ϩ, low density; -, no binding sites.…”

Preferential synaptic relationships between substance P-immunoreactive boutons and neurokinin 1 receptor sites in the rat spinal cord

“…The distribution of the NK-1r in the spinal cord has been studied extensively by using radioactive ligand binding and, more recently, immunocytochemistry. The former approach has shown a close match between the distribution of SP immunoreactivity and NK-1r binding sites in the superficial laminae of the dorsal horn (6,7). In contrast, studies using two different antibodies against the NK-1r have shown a conspicuous lack of NK-1r immunostaining in lamina II (8)(9)(10), an area that is abundantly innervated by SP.…”