Cholinergic receptors in human hippocampus-- regional distribution and variance with age

Reduced number of [3H]nicotine and [3H]acetylcholine binding sites in the frontal cortex of Alzheimer brains

Nicotinic cholinergic receptors were measured in human frontal cortex using [3H]nicotine and [3H]acetylcholine (in the presence of atropine) as receptor ligands. A parallel marked reduction in number of [3H]nicotine (52%; P less than 0.01) and [3H]acetylcholine (-55%; P less than 0.05) binding was found in the frontal cortex of Alzheimer brains (AD/SDAT) when compared to age-matched control brains. As a comparison the number of muscarinic receptors was quantified using [3H]quinuclidinyl benzilate and found to be significantly increased (+23%; less than 0.01) in AD/SDAT compared to controls.

Calmodulin regulation of the cholinergic receptor in the rat heart during ontogeny and senescence

The contents of calmodulin and cholinergic muscarinic receptor binding sites in the hearts of fetal, adult and aged rats have been examined. A biphasic pattern of calmodulin development was observed. A relatively high level of calmodulin appeared on gestational days 14-15 followed by a steady but significant decrease at birth and during the first week of postnatal life. The level of calmodulin then increased significantly during the first month followed by a decrease at 6 and 26 months of age. Calmodulin contents were significantly higher in the atrium than in the ventricle in the age groups of 1-26 months. The number of [3H]QNB binding sites showed a steady increase during the gestational periods studied, reaching a peak at 9 days after birth and followed by a significant (P less than 0.05) decline at 6 and 26 months of age. A good correlation between the levels of [3H]QNB binding and calmodulin was observed from day 9 of the postnatal period to 26 months of age. In the presence of calcium, calmodulin induced a dose-dependent receptor binding loss in the hearts of postnatal, young adult and aged rats under phosphorylating conditions. These findings support the suggestion that calmodulin may regulate cholinergic functions during ontogeny and senescence.

Muscarinic receptor subtypes in hippocampus in Alzheimer's disease and mixed dementia type

The relative proportion of super-high, high and low affinity agonist binding sites was measured in the hippocampus from individuals with dementia of the Alzheimer type (AD/SDAT), mixed (AD-MID) type and controls, using labelled quinuclidinyl benzilate ([3H]QNB) competing with unlabelled carbachol. A significant reduced number of [3H]QNB binding sites was obtained in dementia groups. A significant decrease in the proportion of super-high affinity agonist (V1) binding sites was found in the AD-MID group compared to controls while no change was found in the AD/SDAT group. The affinity constant (K1) for the V1 site was also significantly lower in the AD-MID group compared to controls.

A muscarinic receptor type in human lymphocytes: a comparison of 3H-QNB binding to intact lymphocytes and lysed lymphocyte membranes

Human blood lymphocytes from normal blood donors exhibited specific binding of the muscarinic antagonist 3H-quinuclidinyl benzilate (3H-QNB). The 3H-QNB binding to intact viable lymphocytes as well as to lysed lymphocyte membranes "P2" was saturable and displaceable by both muscarinic agonists and antagonists. For the lysed lymphocyte membranes "P2" a single binding site with a Bmax of 109 pmol/g protein and a Kd of 15 nM was obtained. Intact viable lymphocytes also showed one binding site with a Kd of 24 nM and a Bmax of 1556 pmol/g protein. The higher Bmax value might be explained in terms of uptake of the ligand when using intact cells or through loss of binding sites when using lysed lymphocyte membranes "P2". IC50 values were lower by a factor of 10(2) for atropine and scopolamine and by 10(4) for pirenzepine when lysed lymphocyte membranes "P2" were used instead of intact viable lymphocytes.

In vitro activation of amphibian dermal melanocytes by nicotine

Epidemiologic investigations have shown that nicotine could be a factor causing oral melanin pigmentation in man. Nicotine was therefore tested on amphibian skin melanocytes. Cell reactions were registered by spectrophotometry, in vitro light microscopy, photomicrography and light and electron microscopy. It was found that dermal melanocytes in the toad Bufo bufo and the frog Rana arvalis were activated by nicotine and that this activation was not mediated via beta-adrenergic receptors in melanocytes.

Characterization and localization of serotonin receptors in human brain postmortem

Saturation binding experiments, quantitative autoradiography and computerized densitometric techniques were used to study serotonin S1 and S2 receptor distribution in the human brain, using [3H]serotonin and [3H]ketanserin, respectively. The two ligands exhibited saturable binding to sites very similar in affinity and pharmacology to the S1 and S2 receptors in rat brain. The highest densities of S1 receptors appeared over the hippocampus and layer I of the cortex. S2 receptors were highest in layer IV of the cortex. Analysis of ligand binding to coronal sections through a whole hemisphere allows quantification of receptors in very discrete regions--such as the individual layers of the cortex--and has the advantage of simultaneous visualization of receptors in many different regions which are represented on a single section. Gross similarities but also important differences are found between serotonin receptor distribution in rat and human, stressing the importance of performing these kind of experiments on human brains if they are to be used for the study of diseases and drug action in human subjects.

Histamine in dorsal and ventral hippocampus. II. Effects of H1 and H2 histamine antagonists on exploratory behavior in male rats

The effects on Hole-Board behavior of histamine (HA) microinjected into different parts of the hippocampus and the effects of pyrilamine (PYR, an H1-histamine antagonist), ranitidine (RAN, an H2-histamine antagonist) or alpha-fluoromethyl-histidine (alpha-FMH, an irreversible inhibitor of the HA synthetizing enzyme) injected into the hippocampus on behavior were studied. Forty five nMol of HA were injected stereotaxically into the dorsal or ventral hippocampus. Five min later, Hole-board behavior was measured. It was observed that HA inhibited locomotion and rearing only in the rats injected into the ventral hippocampus. In other experiments, animals were microinjected into the ventral hippocampus with 135 nMol of PYR or RAN in 1 microliter of saline solution. Ten min later, they were microinjected with 45 nMol of HA. Hole-board exploratory activity was measured 5 min thereafter. Results showed that both PYR and RAN were effective in counteracting the inhibitory effect of HA on locomotor activity, but only RAN was able to block the inhibitory action of HA on rearing behavior. Head-dipping frequency was not affected by these treatments. In rats microinjected with 20 nMol of alpha-FMH, increased scores of locomotion were observed but the other behaviors (head-dipping frequency, grooming and rearing) were not affected. The present results support the hypothesis that HA in hippocampus may be exerting a regulatory role on behavior by interaction with H1 and H2 receptors.

Extraneural cholinergic markers in Alzheimer's and Parkinson's disease

Muscarinic and nicotinic binding sites were analysed in lymphocytes from patients with Alzheimer's disease, Multi-infarct dementia, Parkinson's disease and age- matched controls. A significant decrease in the number of both muscarinic and nicotinic binding sites was obtained in lymphocytes from Alzheimer patients while in Parkinson patients a significant decrease was found only in the nicotinic binding sites. Using butyrylthiocholine as substrate, no change was observed in cholinesterase activity in plasma from Alzheimer patients, whereas a significant decrease in plasma cholinesterase activity was found in Parkinson patients.

Cholinergic receptors in aging and Alzheimer's disease

Although Alzheimer's disease (AD) is a disorder involving multiple neurotransmitter systems, the basal forebrain cholinergic system (Ch system) is severely and consistently affected in this condition. In both animals and man, the nature of age-associated alterations in the Ch system is unclear. In addition, available studies of cholinergic receptors in AD and aging are not consistent. In normal aging, the density of muscarinic cholinergic receptors (MCR) is reported to be either unchanged or decreased. In AD, increased, unchanged, or decreased densities have been reported. Recently, a subtype of MCR (M2), thought to be located presynaptically, has been reported to be reduced in neocortex and amygdala. In both AD and aging, nicotinic cholinergic receptors (NCR) have not been adequately studied. Our recent studies using [3H] acetylcholine and [3H] nicotine have demonstrated a reduction in NCR in AD. Possible explanations for some of the inconsistent findings are discussed, and directions for future studies are suggested.

Memory function and brain biochemistry in normal aging and in senile dementia

One might argue that the decrease in the number of brain cells as a function of age could be the source of the functional age deficits in memory performance. However, this possibility seems less likely since the actual loss of neurons up to advanced age is relatively small. There are no good estimates of the loss of synapses. Golgi staining of cortical neurons would indicate that there is a loss with higher age. So far, however, the most convincing data of marked loss with age appear at the biochemical level. Most human data fail to demonstrate a decrease in cholinergic and serotonergic activity as a function of normal aging, although there is a loss of corresponding receptors. In AD/SDAT, however, there is a marked damage to these systems. Conceivably, acetylcholine may be providing informational rather than tone setting or balancing influence on memory function. This may explain the failure of cholinomimetic drugs to improve memory in AD/SDAT due to their inability to supply the informational properties of normal neuronal transmission. The catecholamines, noradrenaline and dopamine are both lost in normal aging and to a much higher degree in AD/SDAT. Animal data show that noradrenaline deficiency results in scattered attention. Such a pattern might also exist in the intact aged and through guidance by means of instructions, contextual cues, and a richer TBR information, the elderly are being forced to attend. This may promote and supersede the normal functions of the noradrenaline system by directions from external rather than internal influences, conceivably by potentiating the remaining noradrenaline neurons. The cortical motor areas are relatively spared from neuro-degenerative changes in normal aging and in AD/SDAT and this might provide a neuroanatomical basis for the elderly's and mildly to moderately demented patients' success in memory performance when motor action is involved. The role of dopamine in motor function and its stability with age in hippocampus may also provide a neurochemical basis for the preservation of memory when the subjects are allowed to act physically during encoding.

Different interactions of steric isomers of hexobarbital to muscarinic agonist and antagonist binding sites in brain

The interaction between the racemate, or the steric isomers of hexobarbital, and the binding of [3H]oxotremorine or [3H]quinuclidinylbenzilate to muscarinic binding sites was studied in different parts of the rat brain. In concentrations clearly within those reached when inducing anesthesia, hexobarbital displaced both the agonist and the antagonist from their binding sites. (-)-R-hexobarbital, which is least potent as an anesthetic, was most potent as a displacer. In most brain regions, the agonist was more readily displaced than the antagonist by both isomers of hexobarbital.

Cholinergic drug effects and brain muscarinic receptor binding in aged rats

Muscarinic systems are significantly altered in the brains of laboratory animals and man as a result of normal aging. Cholinergic neurotransmission in cerebral cortex and hippocampus is also severely impaired in a major age-related neurological disorder, Alzheimer's disease. The objective of these studies was to assess specific 3H-quinuclidinyl benzilate (3H-QNB) binding to brain muscarinic receptors in young, adult and senescent Fischer 344 rats, and to relate receptor changes to differences in the pharmacologic actions of cholinergic drugs. Muscarinic receptor density declined with advanced age in the frontal cortex, corpus striatum and hypothalamus, but no age-related changes in receptor affinity were observed. Specific binding of 3H-QNB in hippocampus was not significantly altered. In contrast, the in vivo effects of oxotremorine (hypothermia and antinociception) were markedly enhanced in aged rats, whereas scopolamine-induced locomotor activity was reduced. Hence, senescent rats were more sensitive to the pharmacologic actions of a cholinergic agonist, but less responsive than young rats to a muscarinic antagonist. These seemingly contradictory results of binding experiments and pharmacological studies could be due, in part, to changes in subtypes of brain muscarinic receptors with advanced age. Alternatively, the age-related differences in cholinergic drug effects may reflect a decreased ability of the senescent animal to adapt to changes in its environment.

Effects of DDT on muscarine- and nicotine-like binding sites in CNS of immature and adult mice

Immature (10 days of age) and adult (60 days of age) mice were given a single peroral administration of 0.5 mg p,p'-DDT/kg body wt. or a fat emulsion vehicle. The mice were killed 24 h or 7 days post-treatment and the muscarine- and nicotine-like binding sites were measured in the cerebral cortex and in the cerebellum using [3H]quinuclidinyl benzilate ([3H]QNB) and [3H]alpha-bungarotoxin ([3H]alpha-BTX), respectively, as ligands. A significant decrease in the [3H]QNB binding to the muscarine-like receptors in the cerebral cortex was seen in the 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT)-treated adults after 7 days. The effects on the muscarine-like receptors appeared to be different in the immature mice compared to the adults, showing an increase between 24 h and 7 days post-treatment in the immature and a decrease in the adults. No change was seen on the nicotine-like receptors.

Evidence for Multiple Muscarinic Receptor Subtypes in Human Brain

Pirenzepine, a compound with selective antimuscarinic activity, was used to distinguish muscarinic acetylcholine receptor subtypes in normal human brain. Hill coefficients and IC50 values derived from the inhibition of specific [3H]L-quinuclidinyl benzilate receptor binding suggest the presence of two muscarinic binding sites, differing both in affinity for pirenzepine and in tissue distribution.

Quantitative light microscopic autoradiographic localization of cholinergic muscarinic receptors in the human brain: brainstem

We have investigated the localization of muscarinic cholinergic receptors in the brainstem of eight patients free of neurological disease following quantitative autoradiography of microtome sections of postmortem tissue labeled in vitro with N-[3H]methyl scopolamine as a ligand. Receptor densities were quantified by microdensitometry with the aid of a computer assisted image analysis system. Our results reveal a heterogeneous distribution of receptor sites. High concentrations of muscarinic cholinergic receptor sites were associated with many nuclei and areas of the brainstem including the nucleus facialis (VII), hypoglossus (XII), ambiguus, the motor trigeminal nucleus (V), the nucleus solitarius, the nucleus of the lateral lemniscus, the superior and inferior colliculi, the sensory trigeminal nucleus (substantia gelatinosa), the pontine nuclei, the parabrachial nuclei, some tegmental nuclei and the periaqueductal gray matter. Very high concentrations of N-[3H]methyl scopolamine binding sites were also localized in the ventral tegmental area, the nucleus paranigralis and the nucleus ovalis. Receptor densities varied between individual brains although the relative distribution of the densities in the different nuclei was the same for all of the brains examined. Most of the brainstem nuclei containing muscarinic cholinergic receptors were enriched in high affinity agonist binding sites as shown by characteristic displacement of the ligand with carbachol. Exceptions were the substantia nigra, the nucleus olivaris inferior and the substantia gelatinosa of the fifth nerve. Receptor density values and pharmacological characteristics obtained in the cortex and basal ganglia in our cases are in good agreement with previously reported values in humans, using conventional biochemical methods. This indicates that procedures used in the autoradiographic technique are not detrimental to the pharmacological characteristics and densities of muscarinic cholinergic receptors. Our results thus clearly show the feasibility of using these techniques for the localization and quantification of muscarinic cholinergic receptors in human brain postmortem material. Furthermore, our findings indicate the potential involvement of the muscarinic cholinergic effect of acetylcholine in the normal function of many brainstem centers, including motor and sensory nuclei, visual and auditory relay nuclei and cardiovascular and respiratory-related nuclei.

Muscarinic binding sites in small homogenates and in autoradiographic sections from rat and human spinal cord

Binding of labelled L- quinuclidinylbenzylate was studied in cryosections and homogenates of human and rat spinal cord. For the cryosections an autoradiographic method was used. With both techniques a higher density of muscarinic binding sites was found in rat than in human spinal cord. In the autoradiographs very high densities of muscarinic binding sites were observed in the motor neurone area and in the apical part of the dorsal horn. The latter high density region was not always found in homogenates from dissected tissue samples. The autoradiographic technique has a better resolution for detecting discrete regional variations in the receptor content of the spinal cord.

Expression of muscarinic binding sites in primary human brain tumors

The expression of muscarinic binding sites was examined in a collection of primary brain tumors of different cellular origins and various degrees of dedifferentiation, as compared to control specimens. Eleven gliogenous tumors were examined, all of which contained substantial amounts of muscarinic binding sites. Most of the other tumor types examined did not display detectable binding of [3H]N-methyl-4-piperidyl benzilate ([3H]4NMPB). Scatchard analysis indicated the existence of homogeneous antagonist sites in both normal forebrain and glioblastoma multiforme, with Kd values of 1.2 nM and 0.9 nM, respectively. The density of muscarinic binding sites varied between tumors from different patients, and also between specimens prelevated from different areas of the same tumor. This variability, as well as the average density of binding sites, appeared to be larger in highly malignant tumors than in less malignant ones. In contrast, the density of muscarinic receptors from control specimens was invariably high, but within the same order of magnitude. To test whether the muscarinic binding activity in the brain tumors is correlated to other cholinoceptive properties, cholinesterase activity was also examined. Individual data for density of [3H]4NMPB binding sites were then plotted against corresponding values of cholinesterase activity. The pattern of distribution of these values was clearly different in tumor specimens, when compared to that observed in samples derived from non-malignant brain. Our observations indicate that human brain cells of gliogenous origin are capable of expressing muscarinic binding sites, and that, if a correlation exists between muscarinic receptors and cholinesterase levels in gliogenous tumors, it differs from that of non-malignant brain tissue.

Neurotransmitter receptors in the central nervous system and aging: pharmacological aspect (review)

The present review is concerned with the modern ideas about age-related changes of neurotransmitter receptors in the central nervous system and the possible ways of their pharmacological regulation. Based on the experimental data, attention has been paid to substantiation of the degree of maintenance of the receptor reactions in the CNS during aging in response to various pharmacological manipulations. Finally, the concept about an important role of the disturbances of neurotransmitter processes and their receptor link in the mechanisms of aging of the brain has been postulated.

Increased muscarinic cholinergic receptors in prefrontal cortices of medicated schizophrenics

Alterations in 3H-quinuclidinyl benzilate binding sites associated with muscarinic cholinergic receptors were investigated in orbito-frontal and medial frontal cortices from 12 schizophrenics, 6 on-drug and 6 off-drug cases, and from 10 controls. Significantly lower affinities of the sites were found in both areas of schizophrenics than controls. An increase in receptor number was shown only in the orbito-frontal cortex from schizophrenics. On-drug group of schizophrenics did, however, show a significant increase in receptor number and a significant decrease in affinity in both areas, while there were no significant differences in any binding parameters of off-drug schizophrenics from controls. Also in the caudate the similar results were obtained. It is, thus, concluded that alterations in muscarinic cholinergic receptors of schizophrenic patients result from long-term medication with antimuscarinic actions.

Postmortem changes in binding to the muscarinic receptor from human cerebral cortex

The effects of storage at 4 degrees C on the antagonist and agonist binding properties of the muscarinic acetylcholine receptor from fresh surgical and frozen autopsy samples from human cerebral cortex were studied. The number of L-[3H]3-quinuclidinyl benzilate binding sites and their affinities were stable up to 51 h, both when stored as pieces of intact nonfrozen tissue and as a homogenate. The agonist binding properties as measured by the ability of the muscarinic agonist carbachol to compete with L-[3H]3-quinuclidinyl benzilate were also stable up to 51 h when the tissue was stored in the form of pieces. The affinity for carbachol decreased when the tissue was stored as a homogenate. The frozen autopsy samples showed no significant differences in binding properties in comparison with fresh neurosurgical tissue.

Cholinergic receptor binding and autoradiography in brains of non-neurological and senile dementia of Alzheimer-type patients

Muscarinic and nicotinic cholinergic receptor distribution was studied by dry-mount autoradiography in brains obtained postmortem from patients with senile dementia of Alzheimer-type (SDAT) and non-neurological controls. Sections were incubated with either [N-methyl-3H]scopolamine, ([3H]NMS) or [125I]alpha-bungarotoxin, ([125I]alpha-BTX). No significant difference in the affinity and number of muscarinic and nicotinic receptors was found in hippocampus, frontal, temporal and cingulate cortex between SDAT patients and non-neurological controls. However, some SDAT cases showed diffuse instead of laminar [3H]NMS labeling in cortical regions. The labeling pattern was not affected by the presence of neuritic plaques and neurofibrillary tangles.

Muscarinic receptor compensation in hippocampus of Alzheimer patients

The activity of the acetylcholine synthesizing enzyme choline acetyltransferase (ChAT) (presynaptic marker) and number of muscarine-like receptor binding sites have been measured in the hippocampus from eight individuals with senile dementia of Alzheimer type (SDAT) and ten controls. A negative correlation (r = 0.80; p less than 0.05) was found between the ChAT activity and the number of muscarine-like receptors in the SDAT group but not in the controls. The findings might indicate an ongoing compensatory receptor mechanism as a response to changes in presynaptic cholinergic activity.

Changes in cholinergic activity in human hippocampus following chronic alcohol abuse

Cholinergic mechanisms in the hippocampus seem to play a role in memory function. Since it is well known that chronic alcoholics often have a disturbed memory function, the cholinergic activity of the hippocampus has been measured in 20 chronic alcoholics and 14 controls, post-mortem. Of the alcoholics, 13 were classified as "intoxicated" alcoholics and 7 as "sober" alcoholics, i.e., without ethanol in blood or urine at the time of death. A lower, although not significantly lower activity of the enzyme choline acetyltransferase (ChAT, presynaptic marker) was measured in the hippocampus of the chronic alcoholics as compared to the control group. A trend towards a lower number of muscarine-like binding sites was also observed for the alcoholic group, but was only significant for the oldest group of alcoholics (59-68 years; -30%; p less than 0.01) in comparison to controls. No significant change in the number of nicotine-like binding sites was found. A normal aging process with degenerative nerve cell changes might, in combination with an excessive intake of ethanol, lead to the more pronounced decrease in muscarine-like binding sites found for the older alcoholics.

Age-differences in choline acetyltransferase activities and muscarinic receptor binding in brain regions of C57BL/6J mice

Muscarinic receptor binding and choline acetyltransferase, (ChAT, EC.2.3.1.6.) activity were assayed in four brain regions of C57BL/6J mice of four ages (4, 12, 18, and 24 months). In the cerebellum, there were no age differences in either of the cholinergic markers. However, significant age differences were noted in the Vmax for ChAT and in the Bmax for [3H]quinuclidinyl benzilate ( [3H]QNB) in the cortex, striatum and hippocampus. Increases were noted in Vmax of the synthetic enzyme in all three regions and for Bmax in the hippocampus. Bmax for [3H]QNB decreased in the cortex and striatum. The high- and lower-affinity muscarinic binding constants, the percentage of muscarinic binding to high affinity sites determined by carbamylcholine displacement of [3H]QNB, as well as the affinities of ChAT for acetyl coenzyme A and choline chloride showed no age differences in any brain region.

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 nicotine-like 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 less than 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.

Changes in the mechanisms of hormone and neurotransmitter action during aging: current status of the role of receptor and post-receptor alterations. A review

Alterations in responsiveness to hormones and neurotransmitters during aging appear to be due to changes at both the receptor and post-receptor levels. Although many such observations have now been independently confirmed, disagreement over the extent and/or importance of receptor alterations exists in a number of cases. Receptors do not appear to change with age in certain systems, but only a few reports have actually been able to localize particular post-receptor alterations responsible for changes in response. This review attempts to catalogue studies in these areas which have been carried out to date, and discusses possible reasons for discrepancies as well as future research directions.

Muscarinic agonist receptor subtypes in aging rat brain

Whole brain homogenates from rats aged 6 months (young) and 24 months (old) showed a decline with age of the pre-synaptic cholinergic marker, choline acetyltransferase, and also of total specific binding sites for the muscarinic antagonist L(-)quinuclidinyl benzilate (L-QNB). However, neither the proportion nor the inhibition constants of high and low affinity muscarinic agonist binding sites (defined by displacement of L-QNB binding with carbachol) changed with age. These findings may be relevant to the central cholinergic deficit reported to be associated with cognitive impairment in aging man.

Changes in populations of cholinergic binding sites in brain after chronic exposure to barbital in rats

Male rats were treated with barbital in their drinking fluid for about 40 weeks (daily dose 200 mg/kg). The treatment was stopped on day 0 and the number of muscarinic binding sites was measured in 3 brain parts (striatum; cortex and hippocampus; medulla oblongata and midbrain) during the abstinence with labeled quinuclidinyl benzilate (QNB) as ligand. Nicotine-like binding sites were quantified in the cortex with labeled tubocurarine. An increased number of QNB-binding sites was found in the striatum during the early part of the abstinence (days 0--3), found by another increase later in the abstinence (days 12--21). In the cortex preparation a variable increase in QNB binding was measured from days 2--9 of the abstinence, whereas in the midbrain preparation the QNB binding was found to be increased only on day 9 in comparison to controls. A change in the proportion between high and low affinity muscarinic binding sites (measured by agonist-antagonist competition) was found in the cortex preparation during the period when the QNB binding was increased. Prior to the maximum abstinence convulsions the QNB binding was higher in rats without recorded spontaneous convulsions in comparison to rats with convulsions. A negative correlation between the time after the last convulsion and the number of QNB binding sites was observed in data from rats where the maximum convulsions had occurred before sacrifice. In addition, a negative relationship between the number of muscarine- and nicotine-like binding sites was found in the cortex during days 5--9 of the abstinence.

Pre- and postsynaptic muscarinic receptors in surgical samples from human cerebral cortex

The present study was carried out using fresh surgical material from human cerebral cortex of patients who were not medicated with atropine or other drugs known to affect the cholinergic system. The concentration of [3H]L-quinuclidinyl benzilate binding sites was 0.45 /+- 0.05 pmol/mg protein and the Kd-value of the receptor-[3H]L-QNB-complex was 0.038 /+- 0.005 nM. Agonist binding was studied by varying the concentration of carbamylcholine (10(-8) to 10(-2) M) in the presence of a constant concentration (0.2nM) of [3H]L-quinuclidinyl benzilate. The data revealed the existence of two populations of binding sites for carbamylcholine with different affinities and capacities. Presynaptic muscarinic receptors were studied in slices of the cerebral cortex, which were loaded with [3H]choline. The muscarinic antagonist, atropine (10(-6) and 10(-7) M) acting at the presynaptic muscarinic receptors enhanced the release of [3H] acetylcholine. It was also shown that muscarinic stimulation leads to elevation of cyclic GMP levels in the human cerebral cortical slices.

Studies on the neuromuscular junction with a special preference to nicotinic receptors in normal delivering cows and cows suffering from parturient paresis

Acetylcholine synthesizing (ACh-s) activity, and binding of 3H-alpha-bungarotoxin (3H-Btx) and 3H-d-tubocurarine (3H-TC) were analysed in gluteus media muscle from normal cows and from cows suffering from parturient paresis, both at parturition and 3 months later. At parturition, the ACh-s activity was 50% lower in the muscle of paretic cows than in non-paretic cows. No difference was found in the number of 3H-Btx and 3H-TC binding sites at parturition, while 3 months after parturition the numbers of 3H-TC and 3H-Btx binding sites were significantly higher in normal than in paretic cows. These significant differences in the number of receptors and a possible underlying receptor regulation defect might be a plausible etiological factor for the disease parturient paresis.