Hyperalgesia induced in the rat by the amino-terminal octapeptide of nerve growth factor.

Nerve growth factor (NGF) in the mouse submandibular gland undergoes cleavage of its amino-terminal octapeptide when salivation is induced by epinephrine. The significance of this event is uncertain; cleaved NGF demonstrates bioactivity and no function has been attributed to the octapeptide produced (NGF-OP; Ser-Ser-Thr-His-Pro-Val-Phe-His). Enzyme inhibition studies indicating structural relatedness of NGF-OP and bradykinin (BK) prompted us to determine whether NGF-OP would elicit BK-like actions. We found that like BK, NGF-OP induced a decrease in mechanical nociceptive threshold (i.e., produced hyperalgesia) in the hairy skin of the rat. This effect was dose-dependent and sequence-specific; like BK it was attenuated by sympathectomy and indomethacin pretreatment. However, NGF-OP actions appeared to be distinct from those for BK in that tissue injury was required for NGF-OP to induce hyperalgesia. Furthermore, we found no evidence that NGF-OP bound to or activated BK receptors. Our data indicate that NGF-OP is a distinct mediator of hyperalgesia. We suggest that NGF-OP alters pain threshold in the injured target regions of NGF-responsive neurons.

beta-NGF-endopeptidase: structure and activity of a kallikrein encoded by the gene mGK-22.

Mouse nerve growth factor (NGF) is cleaved at a histidine-methionine bond to release an NH2-terminal octapeptide (NGF1-8). The enzyme responsible, beta-NGF-endopeptidase, is structurally and functionally similar to gamma-NGF and epidermal growth factor-binding protein (EGF-BP) and cleaves mouse low molecular weight kininogen to produce bradykinin-like activity. These data have suggested that, like gamma-NGF and EGF-BP, beta-NGF-endopeptidase is a mouse glandular kallikrein. Evidence for a physiological role for NGF1-8 encouraged studies to further characterize the structure and function of this enzyme. Purified beta-NGF-endopeptidase migrated as a single band on isoelectric focusing and reducing SDS-polyacrylamide gels. As was expected, it removed NGF1-8 from NGF. Interestingly, enzymatic activity on an artificial substrate, and on NGF, was inhibited by NGF1-8 and by bradykinin. These studies further supported the view that beta-NGF-endopeptidase acts on both NGF and kininogen. The first 30 NH2-terminal amino acids of beta-NGF-endopeptidase were sequenced. This analysis demonstrated that the enzyme is encoded by the gene designated mGK-22 (Evans et al., 1987). The sequence of this gene corresponds to that of EGF-BP type A (Anundi et al., 1982; Drinkwater et al., 1987), and so studies were performed to determine whether or not beta-NGF-endopeptidase participates in EGF complex formation. Chromatographic and kinetic data gave no evidence that beta-NGF-endopeptidase is an EGF-binding protein. Our studies suggest that contamination of high molecular weight (HMW) EGF preparations with beta-NGF-endopeptidase erroneously led to earlier designation of the product of mGK-22 as an EGF-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental regulation of nerve growth factor and its receptor in the rat caudate-putamen.

In prior studies, nerve growth factor (NGF) administration induced a robust, selective increase in the neurochemical differentiation of caudate-putamen cholinergic neurons. In this study, expression of NGF and its receptor was examined to determine whether endogenous NGF might serve as a neurotrophic factor for these neurons. The temporal pattern of NGF gene expression and the levels of NGF mRNA and protein were distinct from those found in other brain regions. NGF and high-affinity NGF binding were present during cholinergic neurochemical differentiation and persisted into adult-hood. An increase in NGF binding during the third postnatal week was correlated with increasing choline acetyltransferase activity. The data are consistent with a role for endogenous NGF in the development and, possibly, the maintenance of caudate-putamen cholinergic neurons.

Intraventricular NGF infusion in the mature rat brain enhances sympathetic innervation of cerebrovascular targets but fails to elicit sympathetic ingrowth.

The ability of peripheral axons to regenerate long distances in the peripheral nervous system (PNS) is well documented; however, examples of axonal elongation within the adult mammalian central nervous system (CNS) are rare. One example of axonal growth in the mature brain is the sprouting of sympathetic axons into the hippocampal formation following disruption of the septohippocampal pathway. A current hypothesis is that elevated hippocampal NGF levels, secondary to loss of retrograde transport by septal neurons, elicits sympathetic ingrowth, In this study, we sought to determine whether elevation of hippocampal NGF activity without septal denervation is sufficient to elicit sympathetic sprouting. Forty-one female rats were infused for two weeks with NGF or cytochrome C in the right lateral ventricle through cannulae connected to an osmotic minipump. In some animals the brains were sectioned and stained for acetylcholinesterase (AChE) activity and norepinephrine histofluorescence; in others, CNS tissue was assayed for nerve growth factor (NGF) content with a two-site ELISA. A Farrand microspectrophotometer was used to measure the intensity of catecholamine fluorescence around the internal carotid artery. The average fluorescence intensity of the sympathetic innervation of the internal carotid artery in the NGF-injected animals was over twice that of vehicle-injected rats indicating that the infused NGF was both accessible to the sympathetic axons and biologically active. However, in none of the cases with elevated hippocampal NGF levels were sympathetic axons observed within the hippocampal formation or any other brain region. These results suggest that simple elevation of brain NGF, while perhaps necessary, is insufficient to permit the growth of sympathetic axons into the mature mammalian CNS.