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D J Jenden

Publications and source records attributed to D J Jenden.

At least 19 recordsLinked to original sources
PubMed1996

In vivo 1H MRS choline: correlation with in vitro chemistry/histology.

We correlated the in vivo 1H Magnetic Resonance Spectroscopy (MRS) concentration of the choline peak (CHO) with in vitro chemical measures of choline-containing compounds and a histological grade of cellularity in 18 patients with neoplastic and infectious brain lesions. Gas-chromatography-mass-spectrometry (GCMS) was used to measure the concentrations of free choline (Cho), glycerophosphocholine (GPCho), phosphocholine (PCho) and phosphatidylcholine (PtdCho) from biopsies in the same area where MRS was performed. Cellular density, free Cho, PCho and GPCho were the strongest determinants of 1H MRS CHO while PtdCho was not. Just as the 1H MRS 2.0 peak reflects both the concentration of n-acetyl-l-aspartate and neuronal density, the 1H MRS 3.2 peak reflects the concentration of water-soluble choline-containing compounds and cellular density.

Brain↗
PubMed1996

Regulation of acetylcholine synthesis in the presence of hemicholinium mustard.

High affinity choline uptake (HACU) is a critical element in the synthetic pathway for acetylcholine (ACh), and is known to demonstrate activity-dependent regulation in vivo and in vitro. However, little is known about this important sodium-dependent transport protein at the biochemical level, and about the nature of its interaction with the ACh synthetic enzyme ChAT. Hemicholinium mustard (HCM), an irreversibly binding analog of hemicholinium-3 (HC3), was used to create a preparation with HACU that is completely inhibited in order to investigate the immediate source of Ch for ACh synthesis. Rat brain synaptosomes were pre-incubated with HCM and washed before transport incubations of increasing length (0-6 min) were carried out. The contribution of endogenous and extracellular (tracer) Ch to the ACh level was measured at each time point using a gas chromatography mass spectrometry (GCMS) system that allows quantitative measurement of endogenous (unlabelled; [2Ho]) Ch as well as tracer (deuterium-labelled; [2H4]) Ch. The hypothesis was that if an endogenous intraterminal Ch pool can be used for ACh synthesis, an increase in unlabelled ACh across time would be observed. In neither HCM-treated nor control synaptosomes was an increase observed in intraterminal (pellet) unlabelled ACh. To test the effects of high tissue demand, in other experiments synaptosomes were depolarized with addition of 40 mM KCl to the buffer after HCM treatment; again, no significant increase in intraterminal unlabelled ACh was observed across time. These experiments demonstrate that endogenous unlabelled Ch does not contribute to ACh synthesis, even when HACU is inactivated, and under conditions of high demand.

Acetylcholine↗
PubMed1996

Elevation of cerebrospinal fluid choline levels by nicotinamide involves the enzymatic formation of N1-methylnicotinamide in brain tissue.

Nicotinamide administration can elevate plasma and brain choline levels and produce a marginal increase in striatal acetylcholine levels in the rat. We now report that subcutaneous nicotinamide produces a substantial and long-lasting rise in cisternal cerebrospinal fluid (CSF) levels of choline in free-moving rats, possibly through the enzymatic formation of N1-methylnicotinamide (NMN) in brain. CSF choline levels peaked 2 hours after nicotinamide administration and were accompanied by increases in striatal, cortical, hippocampal and plasma choline levels. The enzymatic formation of [3H]NMN in rat brain was evaluated by incubating aliquots of rat brain cytosol with unlabelled nicotinamide and the methyl donor [3H]S-adenosylmethionine. High performance liquid chromatography and radiochemical detection demonstrated that [3H]NMN was specifically formed by a brain cytosolic enzyme. The production of [3H]NMN was dependent on exogenous nicotinamide and could be prevented by denaturing the cytosol. The metabolism of nicotinamide to NMN in rat brain may explain the rise in CSF choline levels since NMN, a quaternary amine, can inhibit choline transport at the choroid villus and reduce choline clearance.

Acetylcholine↗
PubMed1996

The influence of aging on whole body choline release and clearance.

We have confirmed that hypoxia elicits a substantial rise in blood choline levels in young adult rats. An intravenous infusion of tracer quantities of [2H4]-Ch, serial measurements of blood [2H0]-Ch and [2H4]-Ch, and a simple pharmacokinetic model were used to assess the bidirectional flux of choline between the central pool and peripheral pools before, during and after a period of imposed hypoxia, in rats ranging from 56 to 780 days of age. The results indicate that the age-dependence of the hypercholinemic response to hypoxia is predominantly due to an increase in the amount of choline released in response to hypoxia, and that changes in its clearance are relatively unimportant.

Aging↗
PubMed1996

Cholinergic control of cerebral blood flow in stroke, trauma and aging.

Enhancing the availability of endogenous acetylcholine by inhibition of cholinesterase with physostigmine, eptastigmine or soman at sub-toxic doses increases cerebral blood flow (CBF) and the response of this variable to changes in PaCO2. These effects are not correlated with metabolic activation, suggesting that the function of the cholinergic vasodilation is not merely to supply metabolic substrates. Since choline (Ch) can exchange between blood and the brain extracellular milieu the stage is set for possible feedback interactions between ACh synthesis and CBF. A negative feedback of CBF on ACh synthesis under conditions of a negative arteriovenous (A-V) difference for Ch across cerebral capillaries may contribute to stabilize GBF in ischemia. Eptastigmine and physostigmine significantly improve perfusion in experimental models of focal cerebral ischemia and traumatic brain injury respectively. During the short periods of time in which the A-V difference for Ch across the brain is positive, a positive feedback between cerebral free Ch and CBF may enhance the ability of the brain to recover Ch from the circulation for synthesis of membrane phospholipids. A loss of cholinergic cerebrovascular control may thus impair the survival of all cells within the CNS and contribute to the pathophysiology of dementia. Perhaps the view that the loss of cholinergic cells is the end point of Alzheimer's dementia could be modified to state that a cholinergic deficit may be the starting point of a decline in cerebral phospholipid turnover and cell membrane renewal that could lead to a generalized deterioration of cerebral function.

Acetylcholine↗
PubMed1996

In vivo proton magnetic resonance spectroscopy of the normal aging human brain.

The effect of age on brain metabolite concentrations was evaluated using localized proton magnetic resonance spectroscopy. This technique allows in vivo measurements of N-acetyl compounds (NA), total creatine (CR), choline-containing compounds (CHO), myo-inositol (MI), glutamate and glutamine (GLX), as well as the percentage of cerebrospinal fluid (CSF) and the brain water content within the brain region studied. Frontal gray matter and frontal white matter brain regions were examined in 36 normal healthy volunteers (19-78 years of age). Using a rigorous absolute quantitation method, with an external reference and atrophy correction, we found relatively stable concentrations of NA, a neuronal marker. In contrast, CR, CHO, MI, and the percentage of CSF increased in the gray matter with age. However, the brain water content decreased significantly with age (r = -0.72; p < 0.0001). No significant age-related changes in metabolite concentrations, CSF or brain water content were observed in the white matter regions. These findings demonstrate that biochemical alterations are associated with aging in the frontal gray matter. There might be an increase in the brain density as indicated by increased metabolite concentrations and decreased brain water content with aging.

Adult↗
PubMed1995

Effects of hypoxia and hypercapnia on whole body release and clearance of choline.

We have recently demonstrated an increase in arterial blood choline (Ch) concentration in normocapnic hypoxia and apnea. This could be due to enhanced release of free Ch from tissues, to decreased Ch clearance, or both. The present investigations was undertaken to determine the individual contributions of these processes to the whole body balance of Ch, using an intravenous infusion of tracer quantities of [2H4]Ch to assess the bidirectional flux between the central pool and peripheral pools. Rats were subjected to normocapnic hypoxia or hypercapnia; release and clearance of Ch were calculated using a simple model. Hypoxia caused an increase in Ch production and a decrease in Ch clearance. At severe levels of hypoxia, Ch clearance was essentially zero. Hypoxia was attended by progressive acidosis that was related to the magnitude of the hypoxic challenge. To determine the possible effects of acidosis per se on the variables measured, respiratory acidosis with normoxia was provoked by controlled administration of CO2. Under these conditions, parallel decreases in Ch production and Ch clearance were observed.

Acidosis↗
PubMed1995

Choline deficiency: a cause of hepatic steatosis during parenteral nutrition that can be reversed with intravenous choline supplementation.

Patients receiving long-term total parenteral nutrition (TPN) develop hepatic steatosis as a complication. Our previous studies have shown this to be caused, at least in part, by choline deficiency. We studied four patients (1 man, 3 women) aged 50 +/- 13 years who had low plasma-free choline concentrations 4.8 +/- 1.7 (normal, 11.4 +/- 3.7 nmol/mL). The patients had received TPN for 9.7 +/- 4.7 years. They received parenteral nutrition solutions containing choline chloride (1 to 4 g/d) for 6 weeks. Abdominal computed tomography (CT) was performed at baseline, biweekly during the choline supplementation, and 4 weeks after discontinuation of choline. During choline administration, the plasma-free choline concentration increased into the normal range within 1 week in all four patients and remained at or above the normal range for all 6 weeks, but decreased back to baseline when choline supplementation was discontinued. Hepatic steatosis resolved completely, as estimated by CT. Liver density increased from -14.2 +/- 22.3 Hounsfield units (HU) to 8.4 +/- 10.3 HU at week 2 (P = .002); 9.6 +/- 10.7 HU at week 4 and 13.1 +/- 7.3 HU at week 6, as determined by the liver-spleen CT number difference obtained by the subtraction of the average spleen CT number (in HU) from the average liver CT number. This improvement continued up to 4 weeks after choline supplementation (13.8 +/- 2.8 HU). Hepatic steatosis was shown to have recurred in one patient after 10 weeks of return to choline-free parenteral nutrition. The hepatic steatosis associated with parenteral nutrition can be ameliorated, and possibly prevented, with choline supplementation. Therefore, choline may be an essential nutrient for patients who require long-term parenteral nutrition.

Adult↗
PubMed1994

Cysteine string proteins: a potential link between synaptic vesicles and presynaptic Ca2+ channels.

Presynaptic calcium channels are key regulators of neurotransmitter release. Oocyte expression studies suggest that cysteine string proteins are essential subunits or modulators of these channels. Subcellular fractionation revealed that cysteine string proteins copurify with synaptic vesicles. An average vesicle had eight protein monomers with both the amino and carboxyl termini detected on the cytoplasmic face. Thus, docked synaptic vesicles may regulate presynaptic calcium channels and neurotransmitter release.

Animals↗
PubMed1994

Choline pharmacokinetics during intermittent intravenous choline infusion in human subjects.

A study of choline pharmacokinetics was undertaken in four patients receiving long-term total parenteral nutrition. On consecutive days, 7, 14, 28, and 56 mmol choline chloride were intravenously infused over a 12-hour period in each subject. The choline concentration was determined in plasma at baseline, 1/4, 1, 3, 6, and 12 hours, and 3 and 12 hours after the infusion ended, and in daily 24-hour urine collections. Analysis of variance showed the data fit a two-compartment model in which elimination from the central compartment was saturable significantly better than a one-compartment model in all four subjects (p < 10(-8) in all cases), and significantly better than a nonsaturating model in three of the four subjects (p = 1.0 x 10(-9), 7.5 x 10(-6), 9.4 x 10(-11), respectively). The model allowed estimates of the rate constant for choline elimination at ambient levels, first-order rate constants for transfer between central and peripheral compartments, the dissociation constant for the saturable elimination process, the apparent volume of distribution in the central compartment, the steady-state volume of distribution, and the quantities of choline in the central compartment and in the readily exchangeable pool.

Adult↗
PubMed1993

Sleep-wake disturbances in an animal model of chronic cholinergic insufficiency.

Rats reared on a diet in which choline is replaced with N-aminodeanol (NADE), undergo > 50% replacement of brain acetylcholine with acetylated NADE, a false cholinergic transmitter. We examined amounts of sleep and wakefulness in 7 littermate pairs of rats fed either NADE-substituted, or a choline control diet for > 100 days after weaning. During the lights-on portion of the 12/12 h light/dark cycle, NADE rats spent more time awake, and less time in both non-REM and REM sleep compared to littermate controls. Average durations of waking episodes were significantly increased in NADE rats. During the 12 h dark period, there were no between-group differences in sleep-waking amounts. Behavioral hyper-responsiveness which interferes with sleep onset, combined with reduced activity in brainstem cholinergic mechanisms involved in REM sleep generation may underlie daytime sleep-waking disturbances in NADE rats.

Acetylation↗
PubMed1993

Cholinergic mechanisms in startle and prepulse inhibition: effects of the false cholinergic precursor N-aminodeanol.

We examined the effects of cholinergic deficiency on prepulse inhibition (PPI) of the acoustic startle. Rats treated with a choline-free diet that contained the false cholinergic precursor N-aminodeanol showed great deficit in PPI. This deficit does not appear to be secondary to an increase of stereotyped behaviors. Startle threshold was also greatly reduced, as these rats startled to the 70-dB prepulse and the baseline startle amplitude was increased by 60% over the control rats. Arecoline (4 mg/kg) partially reversed the deficit in PPI. This improvement persisted beyond the period of drug treatment. On the other hand, scopolamine (1 mg/kg) reduced PPI in the control rats. These results suggest that cholinergic systems play a major role in both the elicitation and prepulse inhibition of startle.

Acoustic Stimulation↗
PubMed1992

Incomplete reversibility of an experimentally induced hypocholinergic state: biochemical and physiological, but not behavioral, recovery.

In previous reports, we described the experimental development of a hypocholinergic state in rats following the total replacement of dietary choline by an artificial isostere, N-aminodeanol (NADe). NADe shares most of the physicochemical and biochemical characteristics of choline (Ch) but is utilized less efficiently in pathways leading to the formation of both acetylcholine and phospholipids. This experimental model mimics many of the features of human degenrative dementias. We now discuss the behavioral and physiological effects of restoring a normal diet after the hypocholinergic state has become well established. The procedure by which that state was induced has been described in detail in earlier publications. After replacing Ch in the diets of weanling rats for 270 days, NADe replaced 70-85% of the phospholipid-bound Ch in plasma, brain, and peripheral tissue. When dietary NADe was removed and Ch was restored in the diet, NADe disappeared and plasma and erythrocyte (RBC) choline levels returned to normal within 30-60 days. Quinuclidinyl benzilate (QNB) binding showed that muscarinic receptors continued to be depressed in animals remaining on the NADe diet, but returned to control levels in the reversal group. There were no differences in cholinesterase activity among the three treatments. Choline acetyltransferase activity returned to control levels, while continuing to be lower in the NADe animals. Liver lipids were elevated in the latter and not significantly different in the control and reversal groups. Among physiological functions, body weight increased more rapidly in the reversal group than in animals continuing on the NADe diet. Brain weights of the reversal animals were significantly greater than those of animals not reversed, but less than controls. Core body temperatures did not differ from controls at any time during the reversal period. Behaviorally, nociceptive thresholds indicative of sensory-reflexive and sensory-perceptual responses remained significantly below normal, that is, a hyperalgesic state. Reversal animals also remained hyperactive and displayed memory significantly poorer than those on the normal diet, that is, no improvement over animals continuing on NADe. In general, the results suggest that behavioral losses induced by NADe reflect persisting changes in the CNS, despite essentially complete recovery of biochemical parameters. The changes may be morphological or be associated with adaptive changes in other neurochemical events in the CNS.

Animals↗
PubMed1992

Pharmacological stimulation reveals recombinant human nerve growth factor-induced increases of in vivo hippocampal cholinergic function measured in rats with partial fimbrial transections.

The present study determined the effects of chronic recombinant human nerve growth factor administration [1 microgram given intracerebroventricularly q.i.d. (every other day) for three weeks] on in vivo hippocampal cholinergic function in adult rats with unilateral partial fimbrial transections. Partial fimbrial transections did not significantly alter the levels of endogenous acetylcholine or [2H4]acetylcholine in the hippocampus due to functional compensation by surviving cholinergic terminals. In animals chronically treated with nerve growth factor, the levels of endogenous choline, endogenous acetylcholine, [2H4]choline and [2H4]acetylcholine accumulated in the hippocampus on the lesioned side were not significantly different from those on the contralateral unlesioned side or from values measured in animals treated with cytochrome c, a control protein. However, changes in cholinergic parameters induced by the partial lesions or recombinant human nerve growth factor treatment became manifest when animals were challenged using pharmacological agents such as pentylenetetrazole or pilocarpine given after lithium chloride pretreatment. First, in nerve growth factor-treated animals administered the general stimulant pentylenetetrazole (10 mg/kg) 2 min prior to measuring in vivo cholinergic parameters, we observed a significant increase in the hippocampal content of [2H4]choline in both lesioned and unlesioned hippocampi. The magnitude of the increase was significantly higher on the lesioned compared to the unlesioned side. Although chronic recombinant human nerve growth factor treatment induced increases of hippocampal [2H4]choline levels, there were no concomitant increases in the level of [2H4]acetylcholine. Second, in nerve growth factor-treated animals administered lithium chloride (3 mmol/kg) 20 h prior to pilocarpine (30 mg/kg), we observed a significant enhancement of the content of endogenous acetylcholine in the hippocampus of the lesioned side. Partial fimbrial transections also reduced in vitro cholinergic parameters reflecting endogenous acetylcholine levels in hippocampal slices. The content of endogenous acetylcholine in the slices was decreased by approximately 50% and chronic nerve growth factor treatment significantly elevated this value to approximately non-lesioned control values. Similarly, reductions in spontaneous and veratridine-evoked release of endogenous acetylcholine induced by partial fimbrial transections were counteracted by recombinant human nerve growth factor treatment. These findings demonstrate that chronic recombinant human nerve growth factor treatment effectively enhances the in vivo and in vitro synthesis, storage and release of endogenous acetylcholine. The results from the in vivo studies suggest that recombinant human nerve growth factor-induced differences in functional performance of hippocampal neurons may only be manifest during behavioral and/or pharmacological stimulation.

Acetylcholine↗
PubMed1992

Effects of hypoxia on choline exchange among organs.

Cerebral blood flow (CBF) and the arteriovenous (A-V) difference for choline (Ch) across brain, lung, splanchnic territory, liver, kidney, and lower limb were studied in anesthetized, mechanically ventilated rats subjected to 10-20-min periods of hypoxia induced by lowering the inspired O2 concentration to 13%. A large, time-dependent increase in arterial blood Ch concentration occurred during hypoxia. This phenomenon coincided with a net rate of uptake of Ch by the brain during hypoxia (0.81 +/- 0.24 nmol/min, n = 10; p less than 0.05), which contrasted with a net rate of loss of Ch by this organ during the control period that preceded hypoxia (-0.20 +/- 0.08 nmol/min, n = 10; p less than 0.05). During hypoxia, lungs and splanchnic territory showed negative A-V differences for Ch levels (net Ch loss), whereas brain, liver, kidney, and lower limb showed positive A-V differences for Ch levels (net Ch uptake). Ch output from lungs was already detected at 5 min within the period of hypoxia and reversed rapidly after restoration of normal oxygenation. On the other hand, Ch output from the splanchnic territory became evident only 10 min after commencement of hypoxia and outlasted this experimental condition. It is concluded that extracerebral production of Ch during hypocapnic hypoxia raises the arterial concentration of this molecule and, by reversing the gradient across cerebral capillaries, prevents the cerebral loss of Ch in this condition.

Animals↗
PubMed1992

Characterization of the irreversible inhibition of high-affinity choline transport produced by hemicholinium mustard.

The inhibition of high-affinity choline transport by hemicholinium mustard (HCM), an alkylating analogue of hemicholinium-3, was examined in rat brain synaptosomes and guinea pig myenteric plexus. In synaptosomes, 50% high-affinity choline transport inhibition occurs with an HCM concentration of 104 nM (4-min incubation). A 10-min preincubation with 10 microM HCM results in essentially complete (greater than 95%) inactivation that persists after washing. Low-affinity choline transport in synaptosomes is unaffected by HCM inhibition at all concentrations examined (1-50 microM). Time course experiments indicate that the maximum irreversible inhibition (58%) seen after a 1-min preincubation with 500 nM HCM decreases to 46% inhibition after a 15-min preincubation; however, analysis of variance reveals that this difference is not significant. HCM inhibition of acetylcholine release from myenteric plexus-longitudinal muscle preparations persists for at least 2 h after removal of drug from the incubation bath; this inactivation can be prevented by coincubation with a high choline concentration during treatment with the mustard. In contrast, inhibition produced by the parent compound hemicholinium-3 is largely reversed by washing in both preparations examined. The observed potency and selectivity of HCM suggest its usefulness as a covalent probe for high-affinity choline transport.

Acetylcholine↗