Post-ischemic regional changes in acetylcholine synthesis following transient forebrain ischemia in gerbils

The synthesis rate of brain acetylcholine (ACh) was estimated 30 min and 5 days following transient forebrain ischemia performed by 10 min bilateral carotid occlusion in gerbils. ACh synthesis was evaluated from the conversion of radiolabeled choline (Ch) into ACh after an i.v. administration of [methyl-³H]Ch. Endogenous and labeled Ch and ACh were quantified by HPLC. The synthesis rate of ACh was significantly decreased following 30 min of recirculation. The reductions reached 55.4% in the hippocampus, 51.2% in the cerebral cortex and 44.4% in the striatum. Five days after ischemia, the values returned to normal in the cerebral cortex and in the striatum, while ACh synthesis remained selectively lowered (–30.4%, p<0.01) in the hippocampus. These cholinergic alterations may account for both early and delayed post-ischemic behavioral and mnesic deficits.     

EFFECT OF OXOTREMORINE ON THE APPARENT REGIONAL TURNOVER OF ACETYLCHOLINE IN MOUSE BRAIN

The effect of oxotremorine (1 mg kg^-1 i.p.) on the steady state concentration of acetylcholine (ACh) and choline (Ch) and the transformation of radioactive choline ([³H]Ch) was studied in different brain regions of the mouse following death by microwave irradiation of the head. Oxotremorine significantly increased the concentration of endogenous ACh in the cortex and hippocampus and of endogenous Ch in the cortex. Pretreatment with atropine (5 mg kg^-1 i.p.) prevented the increase in ACh. The biosynthesis of radioactive ACh ([³H]ACh) was decreased in all brain regions. Atropine (5 mg kg^-1) pretreatment counteracted this effect of oxotremorine (1 mg kg^-1), while methylatropine (5 mg kg^-1) had no effect except in the striatum. A calculation of the apparent turnover rate of ACh showed that oxotremorine (1 mg kg^-1) decreased the turnover in the cortex, hippocampus, midbrain. and striatum.     

Turnover Rate of Brain Acetylcholine Using HPLC Separation of the Transmitter

A simple, reliable method was developed for measuring brain acetylcholine (ACh) turnover using HPLC methodology. Mice were injected intravenously with [3H]choline ([3H]Ch), and the turnover rate of ACh was calculated from the formation of [3H]ACh. Ch and ACh were separated from phosphorylcholine and from other radioactive compounds using tetraphenylboron extraction and counterion/reverse-phase chromatography. Endogenous Ch and ACh were quantified electrochemically through hydrogen peroxide production in a postcolumn reactor containing covalently bonded ACh esterase and Ch oxidase. Labeled Ch and ACh were quantified in the same sample by collecting the chromatographic fractions for radioactive content determinations. The method is rapid, well adapted to large series, and highly reproducible, with recoveries of 72.1% for Ch and 79.3% for ACh. The turnover value in mouse cerebral hemispheres was 16.02 nmol g-1 min-1 and decreased to 9.94 nmol g-1 min-1 in mice treated with oxotremorine.     

REGIONAL BIOSYNTHESIS OF ACETYLCHOLINE IN BRAIN FOLLOWING FORCED ORAL CHRONIC BARBITONE TREATMENT TO RAT

Rats received a solution of sodium barbitone as their only drinking fluid for 33 and 42–44 weeks. In three groups (A3, A12 and A30) the barbitone solution was withheld and replaced by water 3, 12 and 30 days respectively before death. Two other groups consisted of animals drinking barbitone until death (B) and untreated controls (C). Abstinence convulsions were recorded by jiggle cages. Thirty nmol of tritium-labelled choline ([³H]Ch) were injected i.v. and the rats were killed by decapitation 1 min later. A significantly higher content of tritium-labelled acetylcholine ([³H]ACh) was found in the cerebellum + medulla oblongata + midbrain of rats receiving barbitone until death (group B) (+22%) and abstinent for 3 days (+54%) (group A3) compared with group C. The [³H]ACh content was also significantly increased in the hippocampus + cortex of rats abstinent for 3 days (+23%). In the striatum no significant effect on [³H]ACh content was found in any of the groups. The ratio [³H]ACh/[³H]Ch was significantly increased in the cerebellum + medulla oblongata + midbrain of rats in group B and A3 and in the hippocampus + cortex in group A3. These results might indicate an increased turnover of ACh. The effect of long-term barbitone treatment on the enzyme activities of brain choline acetyltransferase and acetylcholinesterase was also studied but no significant effect was found.     

Time course of decline of radiolabeled acetylcholine formed following intracerebroventricular administration of tritiated choline: Effects of oxotremorine and scopolamine

Rats were injected intracerebroventricularly with 5 Ci of [methyl-³H]choline. The time course of decline of the rediolabeled acetylcholine (ACh) formed was estimated in the ispilateral cerebral cortex and striatum. The [³H]ACh levels declined biphasically from the cerebral tissue. The initial decline proceeded rapidly, after which labeled ACh declined more slowly. Scopolamine (1 mg/kg, i.v.) caused a significant increase in the rat of [³H]ACh disappearance, which can be interpreted as an enhancement of ACh release. By contrast, oxotremorine (0.8 mg/kg, i.v.) markedly reduced the [³H]ACh disappearance. The results show that drug-induced changes in cholinergic neuronal activities can be estimated from the disappearance of radioactive ACh after labeling the endogenous transmitter through intracerebroventricular administration of labeled choline.     

Modification of [3H]MK801 Binding to Rat Brain NMDA Receptors after the Administration of a Convulsant Drug and an Adenosine Analogue: A Quantitative Autoradiographic Study

Specific [³H]MK801 binding to rat brain NMDA receptors after the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied by means of a quantitative autoradiographic method. MP administration (150 mg/kg, i.p.) caused significant decreases in [³H]MK801 binding in several hippocampus subareas and layers, mainly in CA1 and CA3 at seizure (11–27%) and postseizure (8–16%) and in cerebral occipital cortex at seizure (18–22%). In nucleus accumbens, a rise was observed at postseizure (44%) and a tendency to increase at seizure (24%). CPA (2mg/kg, i.p.) decreased ligand binding in hippocampus (CA1, CA2, CA3) (17–22%) and in occipital cerebral cortex (18–24%). When CPA was administered 30 minutes before MP (which delayed seizure onset) and rats were sacrified at seizure, decreases in [³H]MK801 binding in several layers of CA1 and CA3 of hippocampus (11–27%) and in CA1, CA2, CA3 (24–35%) after CPA+MP postseizure, and an increase in CA2 after CPA and CPA+MP postseizure (20–34%), were observed. A drop was found in the occipital subarea (18–24%) after CPA and in the frontal and occipital subarea after CPA+MP postseizure (24–34%) while no changes were observed in any treatment involving the other cerebral cortex regions, thalamic nuclei, caudate putamen and olfactory tubercle. These results show that [³H]MK801 binding changes according to drug treatment and the area being studied, thus indicating a different role in seizure activity.     

Choline and acetylcholine metabolism in rat neostriatal slices

Choline (Ch) uptake and release and acetylcholine (ACh) synthesis and release have been studied by gas chromatography mass spectrometry (GCMS) in slices of rat neostriatum in vitro to assess the effects of depolarization by 25 mM K+ and the influence of elevated concentrations of Ch in the incubation medium. During the first 60 min after preparation, 25 mM K+ increased ACh release by 182% and reduced ACh levels by 40%. The rate of ACh synthesis was unchanged. After a 1-h equilibration period, the rate of ACh synthesis was considerably less (2.41 nmol mg-1 h-1, compared to 9.78 nmol mg-1 h-1). Exposure to 25 mM K+ during the second hour increased the rate to 6.47 nmol mg-1 h-1. During the first 10 min of exposure to 25 mM K+, ACh synthesis was reduced, regardless of incubation. Increasing concentrations of external [2H4]Ch apparently favored initial rates of net ACh synthesis, since the rank order of initial net ACh synthesis rates is the same as the rank order of external [2H4] Ch concentration under both normal and depolarized conditions. However, the only significant effect of external [2H4]Ch on ACh metabolism was that it increased ACh release during the initial 10 min, when the preparation was depolarized with K+. The efflux of endogenous [2H0]Ch was increased initially (10 min) and slowed over a 60-min period by 25 mM K+, and increased when [2H4]Ch in the medium was increased. Changes in ACh synthesis and release were dependent upon the time exposure of slices to high K+, and the results suggest that Ch favors initial rates of ACh synthesis, but that Ch influences ACh release primarily under conditions of stress (i.e., depolarization).     

The effect of heptyl-physostigmine,a new cholinesterase inhibitor,on the central cholinergic system of the rat

Heptyl-physostigmine (Heptyl-Phy; MF-201) is a new carbamate derivative of physostigmine (Phy) with greater lipophilicity and longer inhibitory action on cholinesterase (ChE) activity than the parent compound. Following single dose administration of 5 mg/kg heptyl-Phy i.m., maximal whole brain acetylcholinesterase (AChE) inhibition (82%) if reached at 60 min. Inhibition of plasma BuChE butyrylcholinesterase (BuChE) remains close to the steady state level (60%) between 120 and 360 min. At 360 min, whole brain AChE activity is still 67% inhibited compared to controls. Inhibition of AChE activity displays brain regional differences which are more significant at 360 min. At this time point, AChe activity in cerebellum is only 40% inhibited while frontal cortex and medial septum are still 80% inhibited. Increases in acetycholine (ACh) levels also show regional differences, however, there is no direct relationship between AChE inhibition and ACh increase. The electrically evoked [³H]ACh release in cortical slices was inhibited only by the highest concentration of heptyl-Phy tested (10^–4M). At this concentration ChE activity was 97% inhibited in vitro. In conclusion, our results demonstrate that heptyl-Phy compares favorably to other reversible cholinesterase inhibitors (ChEI), particularly to Phy as far as producing a more long-lasting inhibition of AChE and a more prolonged increase of ACh in brain with less severe side effects. Therefore, it represents an interesting candidate for cholinomimetic therapy of Alzheimer disease (AD).Dept. of Pharmacology, Shanghai Institute of Materia Medica Chinese Academy of Sciences Shanghai 20031 China.Special issue dedicated to Dr. Paola S. Timiras     

KINETICS OF PLASMA CHOLINE IN RELATION TO TURNOVER OF BRAIN CHOLINE AND FORMATION OF ACETYLCHOLINE1

—[²H₄]Ch (2 μmol kg^-1 min^-1) was infused into both anaesthetized and conscious rats to study the kinetics of plasma and brain choline (Ch) and brain acetylcholine (ACh). A larger amount of endogenous Ch was found to leave the brain than enter, even in conscious animals. [²H₄]Ch was taken up into the brain where a portion was converted to [²H₄]ACh. Upon stopping the infusion, however, more [²H₄]Ch was found to leave than enter, indicating a source capable of generating Ch in brain which is labelled by infusion for 32 min. There appears, however, to be more than one source of Ch in the brain since the post mortem increase is not labelled following prolonged infusion. Thus, the brain Ch pool appears to be continually diluted by the sources within the brain to the extent of 93 per cent. During the infusion of [²H₄]Ch, the total levels of brain Ch and ACh did not increase. The brain Ch and ACh specific activities rose exponentially and appear to approach an asymptote at about 4 h. The source or sources of Ch within the brain produce Ch at a rate of 26·3 nmol g^-1 min^-1. The turnover of free Ch in the rat brain is 28·4 nmol g^-1 min^-1.     

Relation of brain regional physostigmine concentration to cholinesterase activity and acetylcholine and choline levels in rat

The relationship between physostigmine (Phy) concentration, acetylcholine (ACh), choline (Ch) and cholinesterase (ChE) activity was examined in whole rat brain after the administration of [³H]Phy (650 g/kg i.m.). Cholinesterase inhibition was found to be inversely related to Phy levels. Maximal inhibition (80%) was seen at 5 min and by 2 hrs ChE activity had returned to control levels. Acetylcholine levels in whole brain peaked at 30 min at a concentration (80 nmol/g) 2.3 times higher than controls (33 nmol/g). Choline levels were not significantly altered. The regional distribution of Phy concentration and ChE activity was studied in six areas of the brain following i.m. administration of three different dosages of [³H]Phy. Physostigmine concentration and ChE activity showed a dose dependency in each area examined except in SP (medial septum). Striatum (ST) showed the greatest relative increase of ACh up to 30 min, when compared to other areas. Choline levels were not changed in any area with the exception of ST at 5 min where a decrease was seen. There was a relationship between ChE activity, Phy concentration and ACh levels in all areas examined with exception of the medulla oblongata (MO). Our results indicate that even though ChE was inhibited practically uniformly in all brain areas, the percent increase with respect to control animals and the relative increase of ACh varied widely from area to area. This finding has clinical implications in cases in which cholinomimetic therapy is used to elevate ACh levels in specific brain areas which show a cholinergic deficit.Special issue dedicated to Prof. Eduardo De Robertis.     

Certain aspects of acetylcholine metabolism in teleost retina

Acetylcholine (ACh) synthesis and release from isolated superfused retina of the teleostEugerres plumieri has been studied under different physiological conditions. The retinas were superfused with Krebs-Ringer solutions containing [¹⁴C]choline and the extracellular space of 32% was determined by [³H]inulin. The retina accumulates choline (Ch) from the superfusion medium and this process is mediated by a high affinity transport system with aK _m of 1.82 M. The incorporated Ch is mainly utilized for the synthesis of ACh. The ACh content of the light-adapted retina is not significantly different from that of a dark-adapted one. However, the release of [¹⁴C]ACh from the light-adapted retina was 52% higher as compared to the release from the dark-adapted retina. Flicker stimulation induced a larger increase in ACh release, than from either light or dark adapted retina, proportional to flicker frequency. The results suggest that changes in ACh utilization were related to the function of cellular units responsible for light changes transduction rather than light detection.In partial fulfillment of a MSc degree.     

Choline Uptake and Acetylcholine Synthesis in Synaptosomes: Investigations Using Two Different Labeled Variants of Choline

Abstract: Using sequential incubations in media of different K⁺ composition, we investigated the dynamics of choline (Ch) uptake and acetylcholine (ACh) synthesis in rat brain synaptosomal preparations, using two different deuterated variants of choline and a gas chromatographic-mass spectrometric (GC-MS) assay for ACh and Ch. Synaptosomes were preincubated for 10 min in a Krebs medium with or without high K⁺ and with 2 μM-[²H₉]Ch. At the end of the preincubation all variants of ACh and Ch were measured in samples of the pellet and medium. In the second incubation (4 min) samples of synaptosomes were resuspended in normal or high K⁺ solutions containing [²H₄]Ch (2 μM) and all variants of ACh and Ch were measured in the pellet and medium at the end of this period. This protocol allowed us to compare the effects of preincubation in normal or high K⁺ solution on the metabolism during a second low or high K⁺ incubation of a [²H₉]Ch pool accumulated during the preincubation period. Moreover, we were able to compare and contrast the effects of this protocol on [²H₉]Ch metabolism versus [²H₄]Ch metabolism. The most striking result we obtained was that [²H₉]Ch that had been retained by the synaptosomes after the preincubation was not acetylated during a subsequent incubation in normal or high K⁺ media. This result suggests that if an intraterminal pool of Ch is involved in ACh synthesis, the size of this pool is below the limits of detection of our assay. We have confirmed the observation that a prior depolarizing incubation results in an enhanced uptake of Ch during a second incubation in normal K⁺ Krebs. Moreover, Ch uptake is stimulated by prior incubation under depolarizing conditions relative to normal preincubation when the second incubation is in a high K⁺ solution. These results are discussed in terms of current models of the regulation of ACh synthesis in brain.     

Evidence for the Involvement of Docosahexaenoic Acid in Cholinergic Stimulated Signal Transduction at the Synapse

[4,5-³H]Docosahexaenoic acid ([³H]DHA) or [9,10-³H]palmitic acid ([³H]PAM) was infused intravenously for 5 min to awake, adult male rats before and after treatment with arecoline (15 mg/kg, i.p.), a cholinergic agonist. Animals were killed 15 min post-infusion, the brains were rapidly removed and subcellular fractions were obtained after sucrose density centrifugation. In control animals, [³H]DHA and [³H]PAM were incorporated into the synaptosomal fractions, representing 50%–60% of total membrane label. Most remaining membrane label (30%–40%) was in the microsomal fraction. Both fractions contained the synaptic marker synaptophysin. The remaining 10% of radioactivity was in the myelin and mitochondrial fractions. Arecoline significantly increased [³H]DHA entry into the synaptosomal fractions by 100% and into the microsomal fraction by 50%. In these fractions 60%–65% of the [³H]DHA was in phospholipid, the rest corresponding to free fatty acid and diacylglycerol. In contrast, arecoline did not change [³H]PAM incorporation into any brain fraction. These results demonstrate that plasma [³H]DHA incorporation is selectively increased into synaptic membrane phospholipids of the rat brain in response to cholinergic activation. The increased incorporation of DHA but not of PAM into synaptic membranes in response to cholinergic stimulation indicates a primary role for DHA in phospholipid mediated signal transduction at the synapse involving activation of phospholipase A₂ and/or C.     

Effect of L-DOPA pretreatment on invivo protein synthesis in various rat brain regions

A single dose of L-dihydroxyphenylalanine (L-DOPA, 500 mg/kg, i.p.) that caused massive disaggregation of brain polysomes also suppressed the incorporation of [³H] lysine into trichloracetic acid (TCA)-precipitable proteins of cortex, cerebellum, hypothalamus, brainstem and striatum. The magnitude of this inhibition of [³H] protein synthesis was similar in all brain regions studied, and was not related to changes in the specific activity of the precursor amino acid.     

Measurement of Acetylcholine Turnover Rate in Brain: An Adjunct to a Simple HPLC Method for Choline and Acetylcholine

Abstract: An existing method for measuring acetylcholine (ACh) and choline (Ch) is shown to be useful formeasuring the turnover rate of ACh in mouse brain. Methl-[3H]Ch is injected into mice. They are killed atdifferent times by microwave irradiation and Ch and AChextracted and separated by reverse-phase HPLC. Ch andACh are converted to hydrogen peroxide by a post-column enzyme reaction. Hydrogen peroxide, which isdirectly related to the tissue content of Ch or ACh, isdetermined electrochemically. The fractions that corre-spond to the detector response for Ch and ACh are col-lected for the measurement of radioactivity. In this wayspecific radioactivities of endogenous Ch and ACh areestimated in the same sample. We used the specific ra-dioactivity values determined by this procedure to esti-mate the turnover of ACh for striatum, cerebral cortex, and hippocampus of the mouse.     

Inhibition of choline efflux results in enhanced acetylcholine synthesis and release in the guinea-pig corticocerebral synaptosomes.

Synthesis and release of [3H]acetylcholine ([3H]ACh) were measured in synaptosomes from the guinea pig cerebral cortex after preloading with [3H]choline ([3H]Ch). We demonstrate here that inhibition of choline (Ch) efflux results in an increase in acetylcholine (ACh) synthesis and release. Our findings are as follows: (1) inhibition of [3H]Ch efflux by hemicholinium-3 (HC-3) (100 microM), increased the levels of both the released (116% of control) and the residing (115% of control) [3H]ACh. (2) The muscarinic agonist, McN-A-343 (100 microM), which was previously shown to inhibit Ch efflux, also increased the released (121% of control) and the residing (109% of control) [3H]ACh. (3) Omission of Na+ ions (which are required for Ch transport) from the incubation medium had similar effects to those observed with McN-A-343 and HC-3. These results suggest inverse relationships between Ch efflux on one hand, and ACh synthesis and release on the other hand. (4) Depolarization with 50 mM K+, or with the K+ channel blocker, 4-aminopyridine (100 microM), also increased the total level of [3H]ACh (113 and 107% of nondepolarized synaptosomes, respectively). However, whereas conditions that inhibit Ch transport such as HC-3, McN-A-343 and "no sodium" increased both the residing and the released [3H]ACh depolarization with high K+ or 4-aminopyridine reduced the residing (79 and 87% of control, respectively) and increased only the released [3H]ACh (182 and 148% of control, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of mefluidide on growth,development, and cell wall digestibility of sorghum

Application of mefluidide (N-[2,4-dimethyl-5-([(trifluoromethyl)sulfonyl]amino) phenyl]acetamide) inhibits plant development in perennial grasses. This study examined the effect of mefluidide on the morphological development and digestibility of sorghum. In the greenhouse, 5.9 × 10^–5 g active ingredient (a.i.) plant^–1 applied at the seedling, eight-leaf and boot stages reduced mean plant height 70%, 59%, and 2%, respectively. Heights were also reduced 14%, 15% and 35% by 5.9 × 10^–8, 5.9 × 10^–7 and 5.9 × 10^–6 gram a.i. plant^–1 applied at the eight-leaf stage. Field application of 0.26 or 0.52 kg ha^–1 mefluidide at either the eight-leaf or flagleaf stage reduced mean plant height of all cultivars. Basal tiller numbers increased 319% 28 d, and dry matter production was reduced 65% 42 d following mefluidide application at the eight-leaf stage. Treated stems were 34% higher and treated leaves were 7% higher in cellulase dry matter digestibility than control plants following mefluidide application at the eight-leaf stage. These results indicate that mefluidide application to vegetative stages in sorghum may enhance the forage value of the plants while it inhibits normal plant growth.     

Acetylcholine synthesis by chick spinal cord neurons in dissociated cell culture

Acetylcholine (ACh) synthesis was examined in cultures of chick spinal cord cells to follow the development of the cholinergic neurons. The cells, prepared from 4-day-old embryonic chick spinal cords, were grown either alone in dissociated cell cultures (SC cultures) or with chick myotubes (SC-M cultures). ACh synthesis was measured by incubating the cultures in [³Hcholine and using high-voltage paper electrophoresis to quantitate the amount of [³H]ACh present in cell extracts prepared from the labeled cultures. The amount of [³H]ACh synthesized in SC-M cultures was strictly proportional to the number of spinal cord cells used to prepare the cultures, and was linear with the time of incubation in [³H]choline for periods up to 1 hr. Maximal rates of synthesis were observed with [³H]choline concentrations in excess of 100 μM. Such rates for 1-week-old SC-M cultures were approximately 10–20 pmoles of [³H]ACh/hr/10⁵ spinal cord cells. Studies on the stability of the intracellular [³H]ACh revealed the presence of a major pool with a half-time of 20–30 min. A second, small pool decayed more rapidly. No detectable [³H]ACh was spontaneously released from the cells, suggesting that most of the decay represented intracellular degradation. Development of cholinergic neurons as monitored by [³H]ACh synthesis continued over a 2-week period in SC-M cultures and paralleled general cell growth. When examined at 1 week, SC-M cultures had about a 50% greater capacity for [³H]ACh synthesis and 60% more choline acetyltransferase activity than did SC cultures. No difference was observed in the stability of the [³H]ACh formed for the two types of cultures at 1 week, and no further difference was observed in the rates of [³H]ACh synthesis at 2 weeks. Growth of SC cultures in medium containing different amounts of chick embryo extract (2–10%) or in medium with fetal calf serum (10%) instead of extract produced only small differences in the measured rates of [³H]ACh synthesis. Thus chick spinal cord cells can undergo some of the early stages of cholinergic development in cell culture without sustained contact with skeletal myotubes, one of the normal postsynaptic target cells for the cholinergic neuron population. No absolute requirement for muscle factors was revealed under these conditions, although such factors may have been provided by other cell types in the spinal cord population or may have been present in other additions to the culture medium.     

Decrease of Acetylcholine Release from Cortical Slices in Aged Rats: Investigations into Its Reversal by Phosphatidylserine

The release of total acetylcholine (ACh) and [3H]ACh was investigated in electrically stimulated cortical slices prepared from 4- and 18-month-old male Wistar rats. The slices were prelabeled with [3H]choline ([3H]Ch) and perfused with Krebs solution containing physostigmine. Total ACh was measured and the nature of the tritium efflux identified by HPLC. The total tritium content in the slices at the end of the incubation period was half as great in the old as in young rats. A linear relationship was found between stimulation frequencies (2, 5, and 10 Hz) and fractional [3H]ACh release in both young and old rats. In the latter the release was significantly smaller. At 10 Hz stimulation frequency the ratio between the two 2-min stimulation periods, S2/S1, was higher in the 18-month-old rats than in the young rats. Specific activity of the evoked ACh release was significantly smaller in S2 than in S1 in 4-month-old rats only. These findings indicate that the young synthetize ACh from endogenous unlabeled Ch more than older rats. In 18-month-old rats both the evoked total ACh and [3H]ACh release, expressed as picograms per minute, showed an approximately 50% decrease in both S1 and S2 stimulation periods, with no significant difference in specific activity. Phosphatidylserine (PtdSer) administration (15 mg/kg, i.p. daily) for 1 week to 18-month-old rats prevented the reduction in total evoked ACh release but not the reduction in evoked [3H]ACh release. The specific activity of ACh release was therefore significantly smaller than that of the young and untreated old rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Examination of the Role of Central Cholinergic Mechanisms in the Therapeutic Effects of HI-6 in Organophosphate Poisoning

Abstract: In atropine-pretreated rats, HI-6 (125 mg/kg i.p.) raised the LD₅₀ of Soman (subcutaneous) 5.7 times. Addition of HI-6 (25 μg i.c. v.) failed to enhance this protection further. HI-6 (intraperitoneal) also protected animals from intracerebroventricular Soman. HI-6, administered intracerebroventricularly either alone or in combination with intraperitoneal HI-6, failed to increase protection, nor did it reactivate Soman-inhibited acetylcholinesterase (AChE) in several brain areas. HI-6 (125 or 62.5 mg/kg i.p.) protected rats from Sarin lethality, but only the higher dose significantly altered the brain AChE activity. Furthermore, HI-6 (intraperitoneal) failed to block the Soman-induced increase in acetylcholine (ACh) or choline (Ch) levels in any of the brain areas examined. These data indicate that HI-6 is a very beneficial therapy against Soman, but that no definitive central anticholinergic activity of the compound could be found to explain its protective effects. It is possible that HI-6 acts by noncholinergic central mechanisms, or that it produces its beneficial effects outside the CNS. Furthermore, brain AChE activity does not appear to be indicative of protective effects of this oxime. ACh or Ch levels in this study were not good parameters to predict the outcome of Soman poisoning.