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

Neurotransmitter receptor localization: from autoradiography to imaging mass spectrometry

Autoradiography is used to determine the anatomical distribution of biological molecules in human tissue and experimental animal models. This method is based on the analysis of the specific binding of radiolabeled compounds to locate neurotransmitter receptors or transporters in fresh frozen tissue slices. The anatomical resolution obtained by quantification of the radioligands has allowed the density of receptor proteins to be mapped over the last 40 years. The data yielded by autoradiography identify the receptors at their specific microscopic localization in the tissues and also in their native microenvironment, the intact cell membrane. Furthermore, in functional autoradiography, the effects of small molecules on the activity of G protein-coupled receptors are evaluated. More recently, autoradiography has been combined with membrane microarrays to improve the high-throughput screening of compounds. These technical advances have made autoradiography an essential analytical method for the progress of drug discovery. We include the future prospects and some preliminary results for imaging mass spectrometry (IMS) as a useful new method in pharmacodynamic and pharmacokinetic studies, complementing autoradiographic studies. IMS results could also be presented as density maps of molecules, proteins, and metabolites in tissue sections that can be identified, localized, and quantified, with the advantage of avoiding any labeling of marker molecules. The limitations and future developments of these techniques are discussed here.

Effect of lumbar epidural administration of neostigmine on lower urinary tract function

BACKGROUND

Neostigmine is cholinomimetic and is used for postoperative analgesia. Its urodynamics effects on voiding function have not been elucidated.

MATERIALS AND METHODS

Adult patients without bothersome voiding symptoms planned for rigid cystoscopy under local anesthesia were enrolled. They underwent multichannel urodynamics (filling cystometry and pressure-flow study) before and 30 min after lumbar epidural administration of Neostigmine (2 microg/kg).

RESULTS

Indications for cystoscopy were check examination for follow up of carcinoma urinary bladder (n = 3), staging for carcinoma cervix (5), and removal of ureteral stent (4). Patients' mean age was 51.9 +/- 11.7 years and international Prostatic symptom score 2.34 +/- 3.41. A trend of decreased maximum cystometric capacity (MCC) was observed after Neostigmine (413.50 +/- 142.45 ml vs. 357.00 +/- 145.62 ml; P = 0.056) without any change in end-filling pressure. Five patients developed detrusor overactivity (DO) and one had increase in its amplitude (P = 0.031). Four patients developed rhythmic rectal contractions and one had increase in its amplitude (P = 0.219). There was no difference in any of the voiding parameters. Mean Visual Analog Pain Score (VAS scale 0-10) during cystoscopy for this group was significantly lower than that in a similar group of patients who did not receive Neostigmine prior to rigid cystoscopy (1.16 +/- 0.94 vs. 4.57 +/- 1.45; P = 0.0001). The drug was well tolerated in majority of the patients.

CONCLUSION

Epidural Neostigmine is effective in providing analgesia during diagnostic rigid cystoscopy. It leads to development of DO and decrease in bladder capacity without any effect on voiding function. These findings may help clinicians to use it for transurethral procedure-related pain relief without apprehension of voiding difficulty.

Cholinergic modulation of nociceptive responses in vivo and neuropeptide release in vitro at the level of the primary sensory neuron

Muscarinic acetylcholine receptors (mAChRs) have been widely reported as pharmacological targets for the treatment of pain. However, most of these efforts have focused on CNS mAChRs and their role in modulating nociception at the level of the spinal cord. The present study examines the contribution of peripheral mAChRs in trigeminal nociceptive pathways using a combination of in vivo and in vitro approaches. In the formalin model of orofacial nociception in rats, a peri-oral co-injection of the M2 agonist arecaidine dose-dependently inhibited phase 2 nocifensive behavior up to approximately 50% at 5 nmol. This effect was blocked by co-treatment with the mAChR antagonist atropine and was not seen when arecaidine was administered under the skin of the back, a site distant from that of the formalin injection. In vitro superfusion of isolated rat buccal mucosa with the non-selective mAChR agonist muscarine or arecaidine led to a concentration-dependent inhibition of capsaicin-evoked CGRP release to 39% (EC50=255 nM) and 28% (EC50=847 nM) of control values, respectively. Both responses were blocked by the non-selective mAChR antagonist atropine or the M2 antagonist gallamine. Further, the endogenous ligand ACh produced a bi-phasic response, potentiating evoked CGRP release to 195% of control (EC50= 918nM) and inhibiting evoked CGRP release to 45% of control (EC50=255 microM), effects that were shown to be mediated by nAChRs and mAChRs, respectively. Finally, combined in situ hybridization/immunofluorescence demonstrated that m2 mRNA was present in 20% of trigeminal ganglion neurons between 30 and 60 microm in diameter and that 5-9% of these also expressed CGRP or VR1 immunoreactivity. These results show that activation of peripheral M2 receptors produces antinociception in vivo and the inhibition of nociceptor activity in vitro. While histological analyses at the level of the trigeminal neuronal cell bodies leave open the question of whether the effects of M2 agonists are direct or indirect, these data indicate that primary sensory neuronal M2 receptors may represent a viable peripheral target for the treatment of pain and inflammation.

Intrathecal clonidine reduces hypersensitivity after nerve injury by a mechanism involving spinal m4 muscarinic receptors

alpha2-Adrenergic agonists reduce mechanical and thermal hypersensitivity in animals with nerve injury and effectively treat neuropathic pain in humans. Previous studies indicate a reliance of alpha2-adrenergic agonists in this setting on spinal cholinergic activation and stimulation of muscarinic receptors. The subtype(s) of muscarinic receptors in the spinal cord that produces antinociception in normal animals is controversial, and those involved in reducing hypersensitivity and interacting with alpha2-adrenergic systems after nerve injury are unstudied. To examine this, the left L5 and L6 spinal nerves were tightly ligated in rats, resulting in reduction in withdrawal threshold to punctate mechanical stimuli. Intrathecal clonidine, 15 micro g, returned the withdrawal threshold to normal. Using highly specific m1 and m4 antagonists, we observed no reduction in the effect of clonidine by the m1 antagonist, but inhibition of clonidine's effect by the m4 antagonist. Western analysis revealed no difference in quantitative expression of m1 and m4 receptor protein in the dorsal spinal cord of spinal nerve-injured animals compared with sham-operated controls, suggesting this interaction with m4 receptors does not reflect an increase in receptor expression.

IMPLICATIONS

Neuraxial clonidine is an effective adjunct in the treatment of neuropathic pain and increases acetylcholine concentrations in cerebrospinal fluid in humans. These data in animals suggest that spinal m4 type muscarinic receptors are important to the effect of clonidine in treating hypersensitivity to touch after nerve injury.

High 3H-vesamicol binding in ALS motor neurons--autoradiographic visulalization of hyperactivities?

OBJECTIVES

To evaluate if increased metabolic demand in remaining motor neurons in ALS spinal cord sections can be visualized by 3H-vesamicol binding.

MATERIAL AND METHODS

As a presumed marker of the vesicular acetylcholine transporter, 3H-vesamicol was applied in quantitative autoradiography in cervical spinal cord sections from 11 ALS patients and 4 control cases. The regional binding was compared to that of the muscarinic ligand 3H-QNB.

RESULTS

Our results demonstrate the same magnitude of H-vesamicol binding in the ventral horn of ALS spinal cord as compared to controls, despite the profound loss of motor neurons in that specific area in ALS. The specificity of 3H-vesamicol binding for the cholinergic transporter is high in the motor neuron area, and sigma-sites constitute a minor proportion.

CONCLUSION

The lack of decrease in 3H-vesamicol binding in postmortem ALS spinal cord sections probably reflects an upregulated synthesis of vesicular membranes in remaining and hyperactive motor neurons in vivo.

Receptor localization in the mammalian dorsal horn and primary afferent neurons

The dorsal horn of the spinal cord is a primary receiving area for somatosensory input and contains high concentrations of a large variety of receptors. These receptors tend to congregate in lamina II, which is a major receiving center for fine, presumably nociceptive, somatosensory input. There are rapid reorganizations of many of these receptors in response to various stimuli or pathological situations. These receptor localizations in the normal and their changes after various pertubations modify present concepts about the wiring diagram of the nervous system. Accordingly, the present work reviews the receptor localizations and relates them to classic organizational patterns in the mammalian dorsal horn.

Spinal cholinergic and monoamine receptors mediate the antinociceptive effect of morphine microinjected in the periaqueductal gray on the rat tail, but not the feet

The antinociceptive effects of morphine (5 micrograms) microinjected into the ventrolateral periaqueductal gray were determined using both the tail flick and the foot withdrawal responses to noxious radiant heating in lightly anesthetized rats. Intrathecal injection of appropriate antagonists was used to determine whether the antinociceptive effects of morphine were mediated by alpha 2-noradrenergic, serotonergic, opioid, or cholinergic muscarinic receptors. The increase in the foot withdrawal response latency produced by microinjection of morphine in the ventrolateral periaqueductal gray was reversed by intrathecal injection of the cholinergic muscarinic receptor antagonist atropine, but was not affected by the alpha 2-adrenoceptor antagonist yohimbine, the serotonergic receptor antagonist methysergide, or the opioid receptor antagonist naloxone. In contrast, the increase in the tail flick response latency produced by morphine was reduced by either yohimbine, methysergide or atropine. These results indicate that microinjection of morphine in the ventrolateral periaqueductal gray inhibits nociceptive responses to noxious heating of the tail by activating descending neuronal systems that are different from those that inhibits the nociceptive responses to noxious heating of the feet. More specifically, serotonergic, muscarinic cholinergic and alpha 2-noradrenergic receptors appear to mediate the antinociception produced by morphine using the tail flick test. In contrast, muscarinic cholinergic, but not monoamine receptors appear to mediate the antinociceptive effects of morphine using the foot withdrawal response.

Cholinergic effects on spinal dorsal horn neurons in vitro: an intracellular study

The cholinoceptive properties of dorsal horn neurons (lamina III-V) were investigated by means of intracellular recordings from the rat isolated spinal cord slice preparation. In half of the neurons investigated, acetylcholine (ACh) evoked a dose-dependent slow depolarization and increase in excitability; hyperpolarization was observed in 10% of neurons. Acetyl-beta-methylcholine (MCh) similarly depolarized 39% and hyperpolarized 25% of neurons tested; depolarization was also observed following bethanechol. Responses to the muscarinic agonists were abolished by atropine (10(-5) M). Nicotine depolarized 84% of tested neurons; dihydro-beta-erythroidine (5 x 10(-5) M) and (+)-tubocurarine (10(-6) M) antagonized this depolarization. ACh-, MCh- and nicotine-induced depolarizations, associated with changes in input resistance, were maintained in the presence of tetrodotoxin (10(-6) M). Substance P, as well as repetitive electrical stimulation of the dorsal root, also evoked depolarization in ACh-sensitive neurons. Atropine, but not (+)-tubocurarine, diminished responses to both substance P and dorsal root stimulation. These results indicate that dorsal horn neurons are ACh-sensitive and possess both muscarinic and nicotinic receptors. In addition, the parallel sensitivity of neurons to muscarinic agonists, substance P and dorsal root stimulation, as well as the parallel antagonistic effect of atropine, are supportive of a common ionic mechanism underlying the activation of muscarinic and substance P receptors.

Localization of monoamine oxidase B in human brain by autoradiographical use of 11C-labelled L-deprenyl

11C-labelled L-deprenyl in vitro autoradiography was used to study the regional distribution of MAO-B in human brain. 80 microns thick cryosections from two human brains, a 67 years old female and a 58 years old male, were taken on tape/paper and transferred on to a gelatinized glass plate. The sections were then incubated with 34 and 54 nM 11C-L-deprenyl for 15 min and exposed to a film sensitive to high energy radiation for 2 hours. The autoradiograms obtained were analyzed by computerized densiotometry. High 11C-deprenyl binding was found in the caudate nucleus, putamen, thalamus, substantia nigra, medial and lateral geniculate bodies, hippocampus and periaqueductal gray. Moderate to low binding was observed in cerebral cortex. Cerebral cortex and white matter showed the lowest binding. The autoradiographic technique described proved to be a fast and reliable method to investigate the topographic localization of MAO-B in large cryosections of human brain.

Autoradiographic distribution of [3H]acetylcholine binding sites in the cervical spinal cord of man and some other species

The distribution of [3H]acetylcholine ([3H]ACh) and [3H]ACh co-incubated with 1-mM nicotine (muscarinic receptor), and [3H]ACh co-incubated with 1.5 microM atropine (nicotinic receptor) binding sites were studied in man and compared to monkey, cat and rat using quantitative in vitro autoradiography. The highest density of total [3H]ACh binding sites was found in laminae II-III, IX (motor neuron areas) and X close to the central canal. The distribution pattern of the muscarinic cholinergic binding sites was similar to that of the total cholinergic binding. In general the number of nicotinic binding sites in the spinal cord was relatively small. The largest number of such binding sites was found in laminae II-III of the dorsal horn and in laminae X around the central canal. It is evident that the spinal cord has a 2-3 times higher number of muscarinic than of nicotinic cholinergic receptors.

A double-blind trial of the analgesic properties of physostigmine in postoperative patients

A double-blind clinical trial of the analgesic and antisedative effects of physostigmine was carried out on surgical patients (n = 60) during the first hours postoperatively. Pethidine and placebo were included for comparison in the double-blind study. The degree of pain and sedation was estimated when the patient demanded analgesics and immediately before the administration of the test drug. The dosage administered i.v. was: physostigmine salicylate 2 mg, placebo = saline, or pethidine chloride 50 mg. After this, the same parameters were recorded at regular intervals. In addition, ventilatory rate, pulse rate, systolic blood pressure and side effects, if any, were noted. The results showed that physostigmine caused analgesia that was of the same magnitude as pethidine during the first 15 min, after which it decreased to the level of the placebo at 30 min. An antisedative or arousal effect was recorded over a somewhat longer time period; after this, there was no difference between placebo and physostigmine. In contrast to pethidine, physostigmine caused no decrease in the ventilatory rate. The pulse rate and systolic blood pressure did not change in any of the groups. Although the durations of the analgesic and antisedative effects of physostigmine were short, the use of this drug may well be preferable to the use of e.g. naloxone when immediate alertness of the patient is wanted without causing an increase in postoperative pain.

Effects of spinal cord lesions and rhizotomies on cholinergic and opiate receptor binding sites in rat spinal cord

Changes in the distribution of [3H]quinuclidinylbenzilate ([3H]QNB), [3H] alpha-bungaro-toxin ([3H]alpha-Btx) and [3H]etorphine binding sites were studied autoradiographically, and cholinacetyltransferase (ChAT) activity radioenzymatically, in the C6-7 segments of rats 1-20 days after combined dorsal and ventral C3-8 rhizotomies and spinal cord lesions at C3. After dorsal and ventral rhizotomies the number of [3H]QNB, [3H]alpha-Btx and [3H]etorphine binding sites were reduced ipsilaterally in the dorsal horn and those of [3H]QNB and [3H]alpha-Btx in the ventral horn. In the ventral horn ChAT activity was significantly reduced. After a unilateral spinal cord lesion at C3, ChAT activity was reduced in the ipsilateral ventral horn at C6-7 caudal to the lesions, whereas no change in receptor binding sites was observed.

Large-section cryomicrotomy for in vitro receptor autoradiography

A method for processing human postmortem material for application of autoradiography to large cryosections is described. Whole organ or tissue slices 5 mm thick are frozen between copper plates cooled with liquid nitrogen. They are subsequently embedded in carboxymethyl-cellulose, and 40- to 80-microns sections are taken up on adhesive tape and paper and transferred to gelatinized glass plates. Two procedures for incubation of large sections are described. The method is exemplified by autoradiographs of human brain hemisphere ([ 3H]quinuclidinylbenzilate) and whole biceps muscle ([ 3H]alpha-bungarotoxin).

Muscarinic cholinergic receptors in the human spinal cord: differential localization of [3H]pirenzepine and [3H]quinuclidinylbenzilate binding sites

The localization of muscarinic cholinergic receptor subtypes was studied in the human spinal cord using in vitro labelling of cryostat sections with [3H]quinuclidinylbenzilate (QNB) and [3H]pirenzepine (PZ) followed by autoradiography. The highest densities of [3H]QNB binding were localized in laminae II (substantia gelatinosa) and IX (motor neurons); in contrast, the highest density of [3H]PZ binding was localized to lamina II where the binding density was 22-32% higher than in lamina IX. These results suggest that the M1 and M2 muscarinic cholinergic receptor subtypes may be differentially localized in sensory and motor regions of the human spinal cord.

Cholinergic, opioid and glycine receptor binding sites localized in human spinal cord by in vitro autoradiography. Changes in amyotrophic lateral sclerosis

Binding sites for the receptor ligands 3H-quinuclidinylbenzilate, 3H-alpha-bungarotoxin (3H-alpha-Btx), 3H-etorphine and 3H-strychnine were localized autoradiographically at cervical, thoracic and lumbar levels of spinal cords from post-mortem human control subjects and subjects with amyotrophic lateral sclerosis (ALS). The highest densities of muscarinic binding sites were found in the motor neuron areas and in the substantia gelatinosa, while the grey matter binding was very low within Clarke's column. Both 3H-alpha-Btx and opioid receptor binding sites were numerous within the substantia gelatinosa, while glycine receptor binding sites were more uniformly distributed within the spinal grey matter. In ALS cases, muscarinic receptor binding sites were markedly reduced in motor neuron areas and slightly reduced in the dorsal horn, while the other binding sites studied were relatively unchanged.