Pharmacology of organophosphates.

The cholinergic nerve fibers, which employ acetylcholine (ACh) as a neurohumoral transmitter, and the results of their activation are listed. The reactions between the enzyme acetylcholinesterase (AChE), its natural substrate, ACh, and the various types of inhibitors are described. The limited therapeutic uses of the anticholinesterase (anti-ChE) agents are considered. The toxicological effects encountered when the anti-ChE agents are employed as insecticides or as chemical warfare (CW) agents are discussed. Certain anti-ChE agents produce also a delayed neurotoxic effect which is apparently unrelated to the inhibition of AChE.

The George B. Koelle symposium on the cholinergic synapse.

The George B. Koelle Symposium on the Cholinergic Synapse described the early development of the importance of ACh as a transmitter at both cholinergic synapses of the CNS, ganglion and neuromuscular junction. While a great deal is known about the function of cholinergic transmission at the neuromuscular junction, the integrated role of cholinergic, nicotinic and muscarinic receptors in the overall process of CNS functions, i.e., behavior, motor control, abstract thinking, memory and speech remains as a challenge for future investigation. The architecture of the cholinergic synapse appears to be a dynamic process involving ARIA, Agrin and the various forms of ACh esterase. The regulation of gene expression and site directed localization of postsynaptic cholinergic receptor proteins during the life cycle involves the dynamic interactions of these agents with the postsynaptic membrane and postsynaptic gene express. The last two papers at the symposium dealt with the chemistry of the nicotinic receptor regulated channel involved in ACh binding and the consequent cationic channel conductional changes.

Effects of glycyl-L-glutamine and methylprednisolone on maintenance of acetylcholinesterase of transected rat sciatic nerves.

Under anesthesia with sodium pentobarbital, the sciatic nerves of rats were transected bilaterally, and a catheter was inserted into the central end of the left renal artery. After an initial flush, an Alzet pump was attached to the catheter, containing various concentrations of glycyl-L-glutamine (Gly-Gln), methylprednisolone sodium succinate (MePred), or both. Rats were sacrificed at intervals of 2, 4, or 6 days; the peripheral portions of the sciatic nerves were excised, homogenized, and centrifuged, and the supernates were assayed for acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, EC 3.1.1.7) and protein. Significantly higher contents of AcChoEase over untreated transected controls were obtained (i) at 4 days posttransection in rats infused with 0.015 M Gly-Gln and (ii) at 6 days posttransection in rats infused with MePred at 3.0 mg.kg-1.hr-1 after an initial dose of 120 mg/kg with or without Gly-Gln.

Glycyl-L-glutamine opposes the fall in choline acetyltransferase in the denervated superior cervical ganglion of the cat.

Intracarotid infusion of 3 microM glycyl-L-glutamine was found to oppose the fall in the choline acetyl-transferase content of the preganglionically denervated cat superior cervical ganglion; this same effect has been demonstrated previously for acetylcholinesterase content. Because choline acetyltransferase, in contrast to acetylcholinesterase, occurs exclusively in the preganglionic axons and their terminals, this finding raises the possibility that glycyl-L-glutamine opposes postsectional axonal degeneration.

Effect of glycyl-L-glutamine on the rate of regeneration of acetylcholinesterase in the rat gastrocnemius muscle after diisopropyl phosphorofluoridate administration.

Rats were given glycyl-L-glutamine (Gly-Gln) by intraaortic infusion with Alzet osmotic pumps during the 48-hr period following the intraaortic administration of diisopropyl phosphorofluoridate (DFP) (10 mumol/kg). The infusion of 1.2 mumol of Gly-Gln per 24 hr resulted in a significant increase in the acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, EC 3.1.1.7) activity of the gastrocnemius muscles over that of rats that received DFP only. At a total dose of 3.6 mumol per 24 hr, a diminished result was obtained; at 0.36 mumol per 24 hr, no effect was detectable. These findings, together with earlier ones, suggest that the neurotrophic effect of Gly-Gln or a similar endogenous factor on AcChoEase synthesis is a general phenomenon at sites of cholinergic transmission.

Histochemical demonstration of neurotoxic esterase.

We developed a histochemical method for localizing neurotoxic esterase (NTE), defined as the phenylvalerate (PV)-hydrolyzing esterase that is resistant to 40 microM paraoxon (A) but inactivated by paraoxon plus 50 microM mipafox (B). NTE is considered to be the target enzyme in the production of organophosphorus ester-induced delayed neurotoxicity (OPIDN). Cryostat sections were incubated in a medium containing alpha-naphthyl valerate and 6-benzamido-4-methoxy-m-toluidine diazonium chloride (fast violet B) after treatment with the above-mentioned inhibitors, leading to formation of an aqueous insoluble precipitate at sites of enzymatic activity. NTE activity was estimated as staining detectable in A but not in B. In the central nervous system (CNS) of chicken, NTE appeared to be present primarily in the somata of most neurons, but at sites indistinguishable from those of the other inhibitor-resistant and -sensitive alpha-naphthyl valerate-hydrolyzing esterases. It could not be distinguished in the CNS of cat, probably because it constitutes less than 3% of the total PV-hydrolyzing activity in the CNS of that species.

Maintenance by glycyl-L-glutamine in vivo of molecular forms of acetylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat.

The 24-hr intracarotid infusion of plasma-treated glycyl-L-glutamine (3 microM) produced significant enhancement of the monomeric G1 and tetrameric G4 forms of acetylcholinesterase of the cat superior cervical ganglion 48 hr after denervation, in comparison with denervated, noninfused controls. No significant effect of glycyl-L-glutamine could be demonstrated 4 or 6 days after denervation. These findings are consistent with the conclusion, drawn from a previous in vitro study, that glycyl-L-glutamine acts at a stage prior to the aggregation of the G1 form into higher polymers to maintain the acetylcholinesterase content of denervated ganglia. It is proposed that the dipeptide may regulate the transcription of the DNA for acetylcholinesterase to its corresponding mRNA.

Effects of glycyl-L-glutamine in vitro on the molecular forms of acetylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat.

Normal and preganglionically denervated cat superior cervical ganglia were sectioned and cultured for 24 or 48 hr, with or without preliminary inactivation of acetylcholinesterase, and in the presence or absence of 10(-5) M glycyl-L-glutamine. They were then homogenized, and the molecular forms of acetylcholinesterase were analyzed by sucrose gradient sedimentation. We observed an increased proportion of the globular monomeric G1 form, and to a lesser extent of the dimeric G2 and tetrameric membranous G4 forms, of acetylcholinesterase in the glycyl-L-glutamine-treated compared with the control cultures. There was only a small increase in the total acetylcholinesterase activity and no significant variation in the activity of the metabolic enzyme lactate dehydrogenase. It therefore seems likely that glycyl-L-glutamine, or the endogenous neurotrophic factor, maintains acetylcholinesterase in the preganglionically denervated ganglia in vivo by specifically increasing the biosynthesis of the monomeric G1 form, but not that of other proteins; these trophic factors do not seem to promote the polymerization of G1 into the more complex G2 and G4 forms.

Distributions of molecular forms of acetylcholinesterase and butyrylcholinesterase in nervous tissue of the cat.

We analyzed the activities of acetylcholinesterase and butyrylcholinesterase, and of the metabolic enzymes enolase and lactate dehydrogenase, in the superior cervical ganglion, ciliary ganglion, dorsal root ganglion, stellate ganglion, and caudate nucleus of the cat; we found that these tissues possess very different levels of enzymic activities. The proportions of the alpha alpha, alpha gamma, and gamma gamma enolase isozymes are also quite variable. We particularly studied the molecular forms of acetylcholinesterase and butyrylcholinesterase, in normal tissues and in preganglionically denervated SCG, in comparison with earlier histochemical findings. The results are consistent with the premise that the G1 (globular monomer) forms of both enzymes are located in the cytoplasm, the G4 (globular tetramer) forms are at the plasma membranes, and the A12 (collagen-tailed, asymmetric dodecamer) form of acetylcholinesterase is at synaptic sites.

Direct neurotrophic action of glycyl-L-glutamine in the maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat.

Intracarotid infusion of glycyl-L-glutamine (Gly-Gln) was shown previously to oppose the fall in the acetylcholinesterase and butyrylcholinesterase contents of the cat superior cervical ganglion (SCG) that otherwise follows preganglionic denervation. However, its effect was demonstrable only on the vascularly remote left SCG but not on the directly infused right SCG. Accordingly, it was concluded that a metabolite of Gly-Gln, formed in the blood, is an active neurotrophic factor. Glycyl-L-glutamic acid and L-glutamic acid were subsequently found to have a similar but less marked effect on both SCG. In the present study an alternative explanation has been tested: that Gly-Gln must combine slowly with some component of plasma to enable it to penetrate the ganglion cells and exert its neurotrophic effect. Findings are consistent with the latter proposal.

L-glutamic acid, a neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat.

In continuation of previous studies, the intraarterial fusion of L-glutamic acid for 24 hr was found to oppose the decrease in acetylcholinesterase and butyrylcholinesterase in the superior cervical ganglion of the cat that otherwise occurs 48 hr after preganglionic denervation. The combination of glutamic acid and gamma-aminobutyric acid, in concentrations that were inactive individually, likewise produced the same neurotrophic effect. Inactive in this respect were glycine plus L-glutamine, pyroglutamic acid, gamma-aminobutyric acid, and L-aspartic acid. The possible mechanisms and implications of these findings are discussed.

Glycyl-L-glutamine, a precursor, and glycyl-L-glutamic acid, a neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat in vivo.

L. W. Haynes and M. E. Smith have reported [(1985) Biochem. Soc. Trans. 13, 174-175] that glycyl-L-glutamine (Gly-Gln) increases the A12 and G4 forms of acetylcholinesterase (AcChoEase) in cultured embryonic rat skeletal muscle. Since Gly-Gln meets the criteria established for the neurotrophic factor (NF) in extracts of central nervous system/sciatic nerves that maintains AcChoEase and butyrylcholinesterase (BtChoEase) in the denervated cat superior cervical ganglion (SCG) in vivo, it was tested by the latter procedure. Solutions of Gly-Gln (10(-7)-10(-3) M) in 0.9% NaCl solution were infused for 24 hr via the right common carotid artery of cats with preganglionically denervated SCG, following ligation of the external carotid and lingual arteries. At 48 hr postdenervation, the AcChoEase and BtChoEase contents of the right SCG were within the range of similarly treated controls infused with 0.9% NaCl solution; the AcChoEase and BtChoEase contents of the left SCG, where the infused solutions arrived by way of a much more circuitous route, were significantly elevated at concentrations of Gly-Gln of 10(-5) M and higher. This suggested that the neurotrophic effect on the left SCG was produced by a metabolite of Gly-Gln. Accordingly, glycine, L-glutamine, and glycyl-L-glutamic acid (Gly-Glu) were then tested. Glycine and L-glutamine were inactive; Gly-Glu, 10(-6)-10(-5) M, exerted a significantly positive neurotrophic effect at both the right and left SCG; at 10(-4) M, the effect was absent. The method employed currently for preparation of extracts of SCG for assay of AcChoEase, BtChoEase, and protein contents (homogenization of scissor-minced ganglia in water) was compared with homogenization in molar NaCl/1% Triton X-100. Values obtained by the former procedure, in comparison with the latter, were 91% +/- 7% for AcChoEase and 83% +/- 7% for BtChoEase, expressed as substrate hydrolyzed per mg of protein per min.

Partial characterization of the neurotrophic factor for maintenance of acetylcholinesterase and butyrylcholinesterase in the preganglionically denervated superior cervical ganglion of the cat in vivo.

In continuation of previous reports, it was found that the neurotrophic factor (NF) of the central nervous system of the cat for the maintenance of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7; AcChoEase) in the denervated cat superior cervical ganglion is a heat-stable compound of low molecular weight (less than 1,000) and that it is probably a peptide. Acetylcholine and nerve growth factor were eliminated as the NF; cyclic AMP produced an effect similar to that of the NF. The NF is probably not present in significant amounts in liver or skeletal muscle; it appears to be present in small intestine. It does not modify the AcChoEase content of the nondenervated cat superior cervical ganglion. Possible mechanisms of action of the NF are discussed.

Electron microscope localization of acetylcholinesterase and butyrylcholinesterase in the ciliary ganglion of the cat.

Ciliary ganglia (CG) of cats were stained for acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) by the bis-(thioacetoxy) aurate (I), or Au(TA)2, method for examination by electron microscopy. Acetylcholinesterase was localized along the axolemmas of the preganglionic fibers and their terminals and on the plasmalemmas of the perikarya and dendrites of the ganglion cells, as in the cat superior cervical ganglion (SCG). In contrast to the SCG, AChE was also found in significant amounts in the rough endoplasmic reticulum of the CG cells and dendrites, and in varying but high concentrations in channels of extracellular space in the complex capsular region surrounding the perikarya and dendrites. Butyrylcholinesterase was confined chiefly to the dendritic and perikaryonal plasma membranes of the ganglion cells, as in the SCG. Lysosomes and mitochondria were stained chiefly for non-cholinesterase enzymes, as indicated by the physostigmine-treated controls. The significance of these distributions is discussed.