Induction of the high-affinity nerve growth factor receptor on embryonic chicken sensory nerve cells by elevated potassium

Chronic pain is associated with increased TrkA immunoreactivity in spinoreticular neurons

Repetitive noxious stimulation leads to permanent adaptive changes of central pathways involved in the genesis and integration of nociception. Several classes of neurotrophic factors that affect brain plasticity are also involved in the regulation of sensory functions in adulthood. To investigate a putative role of nerve growth factor (NGF) in central plasticity linked to chronic pain, modifications in immunoreactivity (IR) for the high-affinity NGF receptor, TrkA, were studied at spinal levels in a rat model of inflammatory chronic pain, adjuvant-induced arthritis (AIA). We report a specific increase in the number of TrkA-IR profiles in laminae V-VI at lumbar levels L3 and L4 in arthritic rats. Tract tracing using FluoroGold injections in the ventrobasal complex of the thalamus and in the brainstem showed that these increased TrkA-IR profiles are spinoreticular neurons. Dual labeling with calcitonin gene-related peptide or substance P showed that TrkA-IR neurons were mainly located in projection fields of small- to medium-sized primary afferent fibers, which convey nociceptive inputs. These results suggest that TrkA-containing neurons of the spinal dorsal horn participate in the first central relay of transmission of nociceptive information to supraspinal centers. Enhanced numbers of TrkA-IR neurons during AIA strongly support the hypothesis of a participation of NGF in adaptive mechanisms of central nociceptive pathways observed in chronic pain states.

Nerve growth factor and serum differentially regulate development of the embryonic otic vesicle and cochleovestibular ganglion in vitro

The preceding paper (P. Bernd and J. Represa, 1989, Dev. Biol. 134) describes the characterization and localization of nerve growth factor (NGF) receptors in inner ear primordia, the otic vesicle (OV) and cochleovestibular ganglion (CVG), obtained from 72-hr (stage 19-20) quail embryos. The studies described in this paper investigated whether NGF serves as a mitogen, a survival factor, and/or a differentiation factor in this system. Explants of isolated OV and CVG were maintained for 24 hr in serum-free medium alone (M-199), M-199 containing serum, M-199 containing NGF, or M-199 containing both serum and NGF. [3H]Thymidine was also present for the entire culture period. Both OV and CVG incorporated greater amounts of [3H]thymidine in the presence of serum or NGF, and their combined effect was additive. NGF's effects were dose dependent, saturable, and specific (blocked by anti-NGF). NGF caused little or no morphological differentiation of OV and no increase in protein levels, in contrast to OV grown in the presence of serum. CVG had both cochlear and vestibular portions present in all cases, but the apparent size and protein content of CVG was increased in the presence of either serum or NGF. Effects of serum and NGF were completely, but reversibly, blocked by amiloride, suggesting that the Na+-H+ exchange system had been activated. In order to determine whether increases in [3H]thymidine incorporation were due to increased cell survival or perhaps to an increase in proliferation, explants were initially grown for a 24-hr period in serum-free medium, followed by reactivation for an additional 24 hr in medium containing serum and/or NGF. It is likely that cells requiring either serum or NGF for survival would die during a 24-hr period in their absence. Our results revealed that the level of [3H]thymidine incorporation in OV was the same after reactivation. In the case of CVG, only NGF treatment yielded similar results; [3H]thymidine incorporation was lower in CVG reactivated with serum. It appears, therefore, that serum has probable proliferative effects upon OV and CVG, as well as survival effects for CVG. NGF, however, does not appear to affect survival in either OV or CVG, so that increases in [3H]thymidine incorporation in response to NGF are most likely due to proliferative effects upon OV or CVG, at least at this embryonic stage.

Characterization and localization of nerve growth factor receptors in the embryonic otic vesicle and cochleovestibular ganglion

We have investigated the possibility that nerve growth factor (NGF) may play a role in the development of the inner ear. Primordia of the inner ear, the otic vesicle (OV) and cochleovestibular ganglion (CVG), were isolated from 72-hr (stage 19-20) quail embryos and examined for the presence of NGF receptors. Quantitative binding studies revealed that both OV and CVG exhibited specific 125I-NGF binding; levels of nonspecific binding were 6 to 26% of total binding. Scatchard analysis yielded a linear plot, indicating the presence of a single class of NGF receptor. The average binding constant (Kd) was 8.0 nM for OV and 8.6 nM for CVG, corresponding to the low affinity (site II) NGF receptor. Examination of light microscopic radioautographs indicated that most of the specific 125I-NGF binding was located in the ventromedial wall of the OV, with little or no binding in the lateral wall and endolymphatic primordia. These studies were corroborated by microdissection of OV, in which 70% of the radioactivity was found to be localized in the medial half of the OV. In CVG, specific 125I-NGF binding was more concentrated in the cochlear portion of the ganglion, with silver grains primarily over areas containing support cells and immature neurons. Quantitative binding studies with isolated cochlear and vestibular ganglia obtained from 144-hr (stage 29-30) quail embryos revealed that the cochlear ganglion exhibited three times more specific 125I-NGF binding than the vestibular ganglion. The presence of NGF receptors on OV and CVG suggests that these structures are responsive to and/or dependent upon NGF. The following paper (J. Represa and P. Bernd, 1989, Dev. Biol. 134) examines the question of whether NGF serves either as a mitogen, a survival factor, or a differentiation factor in this system.

Interaction of nerve growth factor with murine alpha-macroglobulin

The murine nerve growth factor, when injected i.v. or, combined in vitro with plasma, was found largely associated with the mouse alpha-macroglobulin (a homologue of human alpha 2-macroglobulin). The nerve growth factor-alpha-macroglobulin complex produced is sufficiently stable to resist separation by gel filtration in 1.0 M sodium chloride, polyacrylamide gel electrophoresis, and immunoprecipitation by antibodies against alpha-macroglobulin. As determined by equilibrium binding studies and computer generated Scatchard analysis, alpha-macroglobulin apparently possesses two types of binding sites with the apparent dissociation constants of 1.2 x 10(-6) and 2.9 x 10(-9) M, respectively, saturable by 3.7 and 0.03 moles of nerve growth factor. Hence, about one mole of nerve growth factor is bound to each of the four subunits of alpha-macroglobulin. Nerve growth factor can be readily dissociated from alpha-macroglobulin in sodium dodecyl sulfate gel electrophoresis in the absence of a reductant. Procedures that affect the proteinase-binding or methylamine- activities of alpha-macroglobulin do not affect the binding of nerve growth factor, and the binding is unaffected by the presence of zinc ions or EDTA. Hence, nerve growth factor is noncovalently associated with alpha-macroglobulin at a site separate from that of the proteinase-, methylamine-, and zinc-binding sites of alpha-macroglobulin. Mouse alpha-macroglobulin can protect the nerve growth factor from inactivation by trypsin. Even in the presence of trypsin, alpha-macroglobulin-nerve growth factor complexes still can stimulate the neurite outgrowth by dorsal root ganglia of 9-day-old chicken embryos. Since alpha-macroglobulin can specifically and noncovalently carry nerve growth factor, one important role of this alpha-macroglobulin in the circulation and extracellular spaces may be to protect the nerve growth factor from proteinase inactivation.

Induction of the high-affinity nerve growth factor receptor on embryonic chicken sensory nerve cells by elevated potassium

Culture medium with elevated K+ has been shown to enhance the survival of neurons isolated from several different regions of the nervous system. Nerve growth factor binds to binding sites on sensory and sympathetic neurons through two sites, one of high-affinity (Kd1 approximately 3 X 10(-11) M) and the other of low-affinity (Kd2 approximately 2 X 10(-9) M). Equilibrium binding data generated on dissociated cells derived from E9 chicken embryo dorsal root ganglia, has shown that there is a two-fold increase in the number of high affinity (type I) receptors, with no effect on the affinity, when cells are incubated for 2 hours in buffer containing 59 mM K+. There does not appear to be a significant change in the affinity or the number of low-affinity binding sites. This two-fold increase in type I receptors is dependent on temperature, Ca+2, and active protein synthesis. There does not appear to be an intracellular pool of the type I receptor sufficient to account for this increase. The induction is not observed on sensory nerve cells cultured in 59 mM K+ for 24 hours, either in the presence or absence of nerve growth factor. Additionally, the induction in the number of type I receptors requires that both nerve growth factor and K+ be present simultaneously. Taken in total, this data suggests that there may be a critical period in which the sensory neurons require nerve growth factor exposure to respond. Evidence is presented which indicates that nerve growth factor responsive cells are able to elicit neurites after an acute exposure to nerve growth factor of as little as 4 hours. Finally, there is an approximate two-fold decrease in the concentration of nerve growth factor needed to elicit maximal fiber outgrowth, consistent with the two-fold increase in the number of type I receptors.

Characteristics of partially purified nerve growth factor receptor

Receptors for the nerve growth factor protein (NGF) have been isolated from three cell types [embryonic chicken sensory neurons (dorsal root sensory ganglia; DRG), rat pheochromocytoma (PC12) and human neuroblastoma (LAN-1) cells] and have been shown to be similar with respect to equilibrium dissociation constants. The present results demonstrate that there are multiple molecular weight species for NGF receptors from DRG neurons and PC12 cells. NGF receptors can be isolated from DRG as four different molecular species of 228, 187, 125, and 112 kilodaltons, and PC12 cells as three molecular species of 203, 118, and 107 kilodaltons. The NGF receptors isolated from DRG show different pH-binding profiles for high- and low-affinity binding. High-affinity binding displays a bell-shaped pH profile with maximum binding between pH 7.0 and 7.9, whereas low-affinity binding is constant between pH 5.0 and 9.1, with a twofold greater binding at pH 3.6. At 22 degrees C, the association rate constant was found to be 9.5 +/- 1.0 X 10(6) M-1 s-1. Two dissociation rate constants were observed. The fast dissociating receptor has a dissociation rate constant of 3.0 +/- 1.5 X 10(-2) s-1, whereas the slow dissociating receptor constant was 2.4 +/- 1.0 X 10(-4) s-1. The equilibrium dissociation constants calculated from the ratio of dissociation to association rate constants are 2.5 X 109-11) M for the high-affinity receptor (type I) and 3.2 X 10(-9) M for the low-affinity receptor (type II). These values are the same as those determined by equilibrium experiments on the isolated receptors.(ABSTRACT TRUNCATED AT 250 WORDS)