Cholinergic Parameters Research Articles

Changes in cholinergic parameters associated with failure of conotruncal septation in embryonic chick hearts after neural crest ablation.

Cells from the neural crest over occipital somites migrate to the heart, where they give rise to parasympathetic postganglionic neurons as well as ectomesenchymal elements which contribute to conotruncal septation. With a microcautery needle, the neural crest over occipital somites was ablated bilaterally in chicken embryos at an early stage of development. Histological examination on incubation day 15 revealed conotruncal malformations, involving malformation or absence of the conotruncal septum in all embryos. Two peaks of embryo mortality were observed. One peak (incubation days 6-8) occurred at the same time as conotruncal septal closure; the second peak (incubation days 11-13) was concurrent with the onset of functional parasympathetic innervation. A disruption of parasympathetic innervation was indicated by: (1) a decrease in acetylcholinesterase staining, (2) a decrease (27%) in the number of ganglion cells in the conotruncus, (3) decreases in the acetylcholine content of atrium (31%) and ventricle (39%), and (4) a decrease (21%) in muscarinic acetylcholine receptor density on incubation day 15. Radiolabeled ligand-binding studies revealed no change in the affinity of cardiac muscarinic receptors for [3H]methylscopolamine (KD = 0.17-0.21 nM). Agonist-binding affinity and sensitivity to guanine nucleotides were similarly unaffected. The reasons for the limited extent of the parasympathetic lesion are unclear, but may involve recruitment of precursor cells from other regions of the neural crest, partial regeneration of the neural crest following surgical removal, or an alteration in the contribution of incoming sympathetic or preganglionic parasympathetic elements. No such plasticity was associated with neural crest contributions to the structural development of the conotruncus. Malformations were observed in all lesioned embryos.

Effects of lead tetraacetate on various cholinergic parameters in vitro

Effects of lead tetraacetate on various cholinergic parameters in vitro

Is acetylcholine release from striatal nerve endings regulated by muscarinic autoreceptors?

The presence in cholinergic nerve endings of muscarinic autoreceptors regulating the release of acetylcholine elicited by depolarizing stimuli was investigated in different areas of the rat brain. Synaptosomes prepared from cerebral cortex, hippocampus or corpus striatum were prelabeled with [ 3H]choline and the inhibitory effect of exogenous acetylcholine on the Ca 2+-dependent release of [ 3H]acetylcholine evoked by 15 mM KCl was analyzed by superfusion. While acetylcholine was equally active in reducing its own release in hippocampus and cortex, it was much less effective in striatal synaptosomes. In contrast the values of several presynaptic cholinergic parameters ([ 3H]choline uptake, [ 3H]acetylcholine synthesis and release) were the highest in the striatum. Since experiments with slices showed that autoregulation of acetylcholine release through muscarinic receptors appeared to occur as efficiently in the striatum as in the two other areas, the present results suggest that in the striatum the autoregulation of acetylcholine release may not necessarily require the activation of autoreceptors located on cholinergic nerve terminals.

Calcium-dependent [3H]acetylcholine release and muscarinic autoreceptors in rat cortical synaptosomes during development.

A number of presynaptic cholinergic parameters (high affinity [3H]choline uptake, [3H]acetylcholine synthesis, [3H]acetylcholine release, and autoinhibition of [3H]acetylcholine release mediated by muscarinic autoreceptors) were comparatively analyzed in rat brain cortex synaptosomes during postnatal development. These various functions showed a differential time course during development. At 10 days of age the release of [3H]acetylcholine evoked by 15 mM KCl from superfused synaptosomes was Ca2+-dependent but insensitive to the inhibitory action of extrasynaptosomal acetylcholine. The muscarinic autoreceptors regulating acetylcholine release were clearly detectable only at 14 days, indicating that their appearance may represent a criterion of synaptic maturation more valuable than the onset of a Ca2+-dependent release.

Effects of a carbamate insecticide (propoxur) on brain cholinergic system in mice.

Effects of an anticholinesterase insecticide, propoxur (Pr), on various cholinergic parameters in brain tissue were investigated in ICR mice. Adult female mice were administered subcutaneously with Pr singly (10 mg/kg) or consecutively (5 mg/kg/day) for 10 days. In order to examine the effects of Pr on cholinergic system of forebrain, mice were killed 10, 60, 180 and 360 min after a single injection or 24 hr after the end of a consecutive injection of Pr (saline as control). Pr caused 78 and 56% increase in acetylcholine (ACh) content of forebrain at 10 and 60 min, 50 to 26% decrease in acetylcholinesterase (AChE) activity over a period of 10 and 180 min, 20% decrease in high affinity choline uptake by crude synaptosomal preparation of cerebral cortex at 10 and 60 min, and 40% decrease in 3H-quinuclidinyl benzilate (QNB) to brain homogenate at 10 min after a single injection. A consecutive administration of Pr caused 34% and 40% decreases in high affinity choline uptake and 3H-QNB binding, respectively, but no appreciable changes in ACh content and AChE activity. Neither a single nor a consecutive administration of Pr caused any change in choline acetyl transferase activity. In order to examine behavioral effects of Pr, mice were tested for openfield behavior (0FB) and rotarod (RR) performance. The RR dysfunction was observed 10 min after a single injection and 4 to 10 days after the beginning of consecutive injection of Pr. 0FB decreased only 10 min after a single injection of Pr. These results suggest that Pr has also some effects on cholinergic sytem other than AChE in brain tussue. Some changes in behavior roughly correlated with those in the cholinergic system.

Cholinergic activity in hippocampus in chronic alcoholism

Evidence indicates that hippocampus and cholinergic mechanisms play a role in memory function. Animal studies have indicated an effect of prolonged ethanol treatment on cholinergic parameters. It is well known that chronic alcoholics often have a disturbed memory function. In this postmortem study the cholinergic activity in the hippocampus was studied in 20 chronic alcoholics and 14 controls. Of the alcoholics, 13 were classified as ‘intoxicated alcoholics’ and 7 as ‘sober alcoholics’, i.e., without ethanol in blood and urine at the time of death. To study both pre- and postsynaptic effects, the enzyme choline acetyltransferase (ChAT, presynaptic marker) as well as muscarine- and nicotinelike receptor binding sites were measured. There was a lower, although not significant, activity in ChAT in the hippocampus of the chronic alcoholics as compared to the controls. The lowest ChAT activity was found in the group of ‘sober alcoholics’, however it was not statistically significant. In the chronic alcoholics there was a trend towards lower numbers of muscarine-like binding sites reaching significance for the oldest group of alcoholics (59–68 years; −30%; p < 0.01) in comparison to controls. The combination of the normal aging process with degenerative nerve cell changes and alcohol abuse might lead to the more pronounced decrease in muscarinic binding sites found for the older alcoholics.

Atropine modulates changes in striatal muscarinic receptor binding sites in barbital abstinence in the rat.

We have previously reported that cholinergic mechanisms in the brain are involved in tolerance and physical dependence as expressed in the abstinence after 30–40 weeks forced chronic treatment with barbital to rats (for reviews see Nordberg &amp; Wahlström 1980, 1981a). In the first part of the abstinence period the turnover of acetylcholine (ACh) seems to be increased in different areas of the brain since both decreased content of endogenous ACh and increased biosynthesis of ACh have been recorded (Nordberg &amp; Wahlström 1977, 1979). These changes have been observed at peak abstinence when there is a maximal tolerance to hexobarbital and a maximal number of spontaneous convulsions. Some changes in cholinergic parameters may prevail in late abstinence as illustrated by reduced content of endogenous ACh in the striatum which is still present after 80 days of abstinence (Nordberg &amp; Wahlström 1981b). The muscarinic receptors also undergo changes in the abstinence (Nordberg et al. 1980). In the striatum an increased number of binding sites has been measured on day 0 to 3 in the abstinence. Increases, but with different time courses, are seen also in other brain areas (Nordberg &amp; Wahlström 1982).

Effects of immobilization and cold exposure on the turnover rate of acetylcholine in rat brain areas

The effect of two ‘Stressors’, immobilization and cold exposure, on the turnover rate of acetylcholine in various brain areas has been determined. Neither short term (10 min) nor long term (1 24 h) immobilization stress modifies the acetylcholine or choline concentrations or the turnover rate of acetylcholine in various rat brain areas. Cold exposure reduces the turnover rate of acetylcholine in the hypothalamus and modifies some of the other cholinergic parameters (e.g. choline content or fractional rate constant for acetylcholine efflux) in all areas studied. These results suggest that cholinergic neurons may be involved in thermoregulation but may not necessarily be involved in the phenomenon of immobilization stress.

Regional distribution of cholinergic parameters within the rat striatum

The topographical distribution of choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake was studied in 21 separate areas of the rat striatum. The areas of the nucleus chosen represented dorsolateral, dorsomedial, ventrolateral and ventromedial regions along the rostrocaudal aspect of the striatum, such that a three-dimensional distribution of the cholinergic parameters could be obtained. Within any given rostrocaudal section, no significant dorsoventral differences were noted for any of the cholinergic parameters. On the other hand, marked differences were found in a comparison of the medial and lateral striatum. Choline acetyltransferase, muscarinic receptor binding and high affinity choline uptake were more concentrated in the lateral striatum than the medial striatum, and the magnitude of this medio-lateral disparity increased from rostral to caudal regions of the nucleus. The lateral striatum exhibited no significant rostrocaudal variations in the cholinergic parameters; however, the medial portion of the striatum did exhibit differences along its rostrocaudal extent, with the rostral-most sections being enriched relative to the more caudal sections. These results suggest that the cholinergic system in the striatum is heterogeneously distributed within this nucleus, with the lateral portion possessing a greater cholinergic innervation than the medial portion. They further suggest that future neurochemical studies of cholinergic alterations in the striatum should include a consideration of the possibility of regional effects within the nucleus rather than treating the striatum as a homogeneous tissue.

Distribution of choline acetyltransferase, acetylcholinesterase, muscarinic receptor binding, and choline uptake in discrete areas of the rat medulla oblongata.

Quantitative measurements were made of choline acetyltransferase (CAT) activity, acetylcholinesterase (AChE) activity and cholinergic muscarinic receptor binding ([3H]QNB) in eight areas of a cross-section of the rat medulla oblongata. A fourth cholinergic parameter, high-affinity choline uptake, was measured in three groups of these areas. CAT, AChE and [3H]QNB binding were found to be highest in the hypoglossal nucleus and the dorsal motor nucleus of the vagus; the lowest value was in the area which contains the inferior olive and the corticospinal tract. The distribution of AChE and CAT activities varied approximately 7- to 10-fold among the eight regions examined, whereas that of the muscarinic receptor varied only about 4-fold. The Na+-dependent high-affinity choline uptake varied approximately 20-fold from the region with the lowest activity (inferior olivary nucleus and corticospinal tract) to that with the highest activity (tissue areas containing the dorsal motor nucleus, hypoglossal nucleus of the solitary tract and nucleus cuneatus). The four cholinergic parameters are statistically correlated throughout all the areas of the medulla which were studied.

Lack of effect of repeated electroconvulsive shock on [3H]spiroperidol and [2H]5-hydroxytryptamine binding and cholinergic parameters in rat brain.

Repeated electroconvulsive shock (ECS) administered on alternate days for 10 days produced no changes in rat striatal [3H]spiroperidol binding measured 24 h after the last shock compared to anaesthetised controls. Similarly, there was no change in while brain specific [3H]5-HT binding. Sodium-dependent high affinity [3H]choline uptake (HAUC) and ChAT were also unaltered in striatal and hippocampal samples following repeated ECS. Acute administration of Pentylenetetrazol did produce an increase in hippocampal HAUC immediately postictally. However, ECS (Xl) did not change HAUC measured 1 h postictally. An effect of halothane on HAUC was noted in these experiments indicating the importance of an evaluation of anaesthetic effects in ECS studies.

Effects of MK-771, A TRH analog, on pentobarbital-induced alterations of cholinergic parameters in discrete regions of rat brain

MK-771 ( l-pyro-2-aminoadipyl-histidyl-thiazolidine-4-carboxamide) was administered intraventricularly to conscious and pentobarbital-narcotized rats. In the conscious rats MK-771 did not affect the regional levels of acetylcholine (ACh) or the rate of sodium-dependent high-affinity choline uptake (HACU). MK-771 was found to antagonize pentobarbital-induced elevations of ACh levels in the cortex, hippocampus and striatum. MK-771 also reversed the depressant effects of pentobarbital on the HACU of the cortex and hippocampus. Striatal HACU was unaltered by the administration of pentobarbital or the combination of pentobarbital and MK-771.

Effect of gonadal hormones on luteinizing hormone in plasma and on choline acetyltransferase activity and acetylcholine levels in discrete nuclei of the rat brain.

In order to assess the possible involvement of central cholinergic mechanisms in the feedback actions of gonadal hormones, the activity of choline acetyltransferase (ChAT) and the concentration of acetylcholine (ACh) were measured in microdissected brain nuclei of male and female rats after castration and gonadal hormone replacement. Castration of male rats significantly elevated plasma levels of LH and also increased ChAT activity and ACh level in the medial preoptic nucleus. Castration also increased ChAT activity but not ACh concentration in the posteromedial amygdala. In the rostral part of the nucleus tractus diagonalis and in the ventral tegmental area. ACh concentrations were elevated by castration, but ChAT activity was unaffected. Daily administration of testosterone propionate (TP) to castrated males attenuated the postcastration rise of plasma LH and also partially prevented the increases of ACh in the medial preoptic and rostral tractus diagonalis nuclei and of ChAT in the posteromedial amygdala. In addition, TP treatment significantly decreased ChAT acivity in the rostral nucleus tractus diagonalis. Treatment of ovariectomized female rats with estradiol benzoate lowered plasma levels of LH, but did not affect cholinergic parameters. Administration of progesterone to estrogen-primed females produced a surge in plasma LH and decreased the activity of ChAT and the concentration of ACh in the periventricular nucleus. Such treatment also reduced ChAT activity in the caudal nucleus tractus diagonalis and decreased ACh levels in the ventral tegmental area. The combined estradiol/progesterone treatment elevated ChAT activity in the supraoptic nucleus. These results demonstrate that cholinergic activity in several discrete brain regions known to be targets for testicular and ovarian hormones is altered by gonadectomy and gonadal hormone treatment and suggest involvement of cholinergic systems in the feedback effects of estadiol, progesterone and testosterone.

Effects of methylmercury chloride on various cholinergic parameters in vitro.

The effects of methylmercury chloride and other mercury compounds on cholinergic parameters were studied in vitro. Methylmercury chloride (MMC) and phenylmercury acetate inhibited choline acetyltransferase (ChA) with 20 microM of I50, and mercury nitrate (MN) with 100 microM of I50. All the three compounds had little effect on cholinesterase activity. MMC inhibited a high affinity choline uptake with 41 microM of Ki, as well as a low affinity choline uptake with 250 microM of Ki. MMC did not affect a spontaneous and potassium-stimulated ACh release from brain tissue slices incubated in eserinized Krebs-Ringer's solution up to the concentration of 100 microM. It was shown that the organic mercury compounds, such as methylmercury, were potent inhibitors of the choline uptake systems, as well as ChA activity.

Effect of pretreatment under various cationic conditions on acetylcholine content and choline transport in rat whole brain synaptosomes.

AbstractThe effects of different ionic environments were measured on the concentration of acetyl‐choline (ACh) from synaptosomes and their effect on subsequent high affinity choline (Ch) transport and ACh synthesis after resuspension of the synaptosomes in the normal Krebs medium. KCl (40 mM) was used to induce ACh release and reduce synaptosomal ACh content. The effects of Na+ omission, Ca2+ omission, and high Mg2+ on spontaneous (KC1: 4.75 mM) and potassium induced (KC1: 40 mM) ACh release and other cholinergic parameters are presented. The high affinity transport of Ch was more highly correlated with the reciprocal of the ACh level (r= 0.934, P= 9.7 × 10‐4) than with the ACh release rate during preincubation (r= 0.792, P= 3.4 × 10‐2). The results are consistent with the view that the consequences of the various ionic conditions on Ch transport and ACh synthesis are dependent on their effects on intrasynaptosomal ACh levels and only secondarily on synaptosomal ACh release.

Striatal lesions with kainic acid: neurochemical characteristics

Stereotaxic injection of 2.5 μg of kainic acid, a rigid analogue of glutamate, into the rat striatum caused a 70% reduction in the striatum of the cholinergic parameters, choline acetyltransferase, acetylcholine and synaptosomal uptake of choline and a similar reduction in the GABAergic parameters, glutamic acid decar☐ylase, γ-aminobutyric acid (GABA) and synaptosomal uptake of GABA. In contrast, the striatal content of dopamine and the synaptosomal uptake of dopamine were unchanged, and the activity of tyrosine hydroxylase was significantly increased. Significant changes in the activity of neurotransmitter synthesizing enzymes were demonstrable within 6 h after injection of 2.5 μg of kainic acid and maximal effects occurred at 48 h; the activities of choline acetyltransferase and glutamic acid decar☐ylase remained depressed up to 21 days after injection. The kinetic characteristics of striatal tyrosine hydroxylase were altered 48 h after injection with a two-fold increase in the V max for tyrosine and a three-fold reduction in K m for the pteridine cofactor. In contrast to the effects of kainic acid, the injection of copper sulfate, a non-specific toxin, caused a proportionate reduction in the dopaminergic as well as the cholinergic and GABAergic presynaptic markers. The kainate lesion caused an 85% decrement in the activity of dopamine-sensitive adenylate cyclase, a 40% reduction in the specific binding of [ 3H]quinuclidinyl benzilate and a 195% increase in the specific binding of [ 3H]GABA in the striatum. The morphology of the kainate injected striatum was markedly altered with nearly a complete loss of intrinsic neurons, increased number of glial cells but intact internal capsule fibers. Intracerebral injection of nanomolar quantities of kainic acid appears to cause degeneration of neurons with cell bodies near the injection site while sparing axons terminating in or passing through the region.

Amphetamine-haloperidol interactions in rat striatum: Failure to correlate behavioral effects with dopaminergic and cholinergic dynamics

Previous reports have suggested that the hyperactivity and stereotype produced by amphetamine (AMP) and the catalepsy produced by haloperidol (HAL) are mediated by striatal dopaminergic mechanisms. In the present study, we have measured the behavioral effects of AMP, and HAL, and their effects on striatal dopaminergic function, using both an index of pre-synaptic activity (synaptosomal dopamine (DA) synthesis) and a parameter which we suggest will reflect post-synaptic dopaminergic function (sodium-dependent, high affinity choline uptake). Administration of 2 mg/kg AMP produces hyperactivity and causes a decrease in DA biosynthesis, both of which are blocked by 0.75 mg/kg HAL. AMP (5 mg/kg) produced stereotypy, further decreases DA biosynthesis and causes a decrease in choline uptake, consistent with stimulation of DA receptors. However, while pretreatment with 3 mg/kg HAL completely blocked the stereotypy induced by 5 mg/kg AMP, it failed to reverse the effects of this dose in either DA biosynthesis or choline uptake. These data suggest that either 5 mg/kg AMP affects striatal dopaminergic and cholinergic parameters by a mechanism independent of HAL sensitive receptors, or the stereotypy produced by high doses of AMP are not related to striatal dopaminergic and cholinergic function.

Lack of Influence of the Phase of Estrus Cycle or Treatment with Steroid Contraceptive Drugs on Cholinergic Parameters in Mouse and Rat Brain

Acetylcholine and choline levels were found not to fluctuate with the phase of the estrus cycle in the cerebral hemispheres, deincephalon and mesencephalon in the rat and mouse. Choline acetyltransferase activity was not altered in these brain areas in the mouse while in the rat there was a small but significant decrease in the cerebral hemispheres during proestrus (p less than 0.01), and in the mesencephalon during estrus (p less than 0.05), both with respect to diestrus. Chronic 30-day treatment with steroid contraceptive drug combinations (lynestrenol, 5 mg/kg+ mestranol, 0.3 mg/kg; lynestrenol, 2.5 mg/kg+ mestranol, 0.15 mg/kg; norethindrone, 4 mg/kg+ mestranol, 0.2 mg/kg; norethynodrel, 4 mg/kg+ mestranol, 0.06 mg/kg) did not alter cholinergic parameters in the brain areas of these two species except for minor changes in rare instances.

Effect of acute and chronic treatment with dichlorvos on rat brain cholinergic parameters

The activity of acetylcholinesterase in rat brain was decreased by 70% 1 hr after oral administration of dichlorvos (DDVP, O,O-dimethyl- O-2,2-dichlorvinyl-phosphate) in a dose corresponding to 50% of the LD50; after 14 days of administration of 5% of the LD50, the activity decreased by 45%. In neither case was the activity of whole brain choline acetyltransferase or the contents of acetylcholine and choline altered. However, in the cerebral hemispheres, and especially the corpus striatum, acetylcholine was considerably increased without a concomitant change in choline.

Lack of effect of intraventricular 6-hydroxydopamine pretreatment on rat striatal cholinergic parameters

Lack of effect of intraventricular 6-hydroxydopamine pretreatment on rat striatal cholinergic parameters