Characterization and quantitative autoradiographic distribution of [3H]acetylcholine muscarinic receptors in mammalian brain. Apparent labelling of an M2-like receptor sub-type

Cholinergic hyperactivity in the lateral septal area of spontaneously hypertensive rats: depressor effect of hemicholinium-3 and pirenzepine

In the lateral septal area of spontaneously hypertensive rats, but not in Wistar-Kyoto rats, the selective M1 antagonist, pirenzepine, and the depletion of acetylcholine storage, by hemicholinium-3 (HC-3), decreased blood pressure. The selective M1 agonist McNeil-A-343, produced a pressor response only after treatment of the lateral septal area with HC-3 in spontaneously hypertensive rats. Carbachol, at doses that mainly affect M2 muscarinic receptors, caused no cardiovascular changes in either strain, pointing to the main intervention of the M1 subtype of muscarinic receptor in the hypertensive condition. In addition, increases in the density of binding sites for [3H]QNB and in Vmax of sodium-dependent, HC-3-inhibitable, high affinity uptake of choline were demonstrated, without significant changes of the activity of choline acetyltransferase in the lateral septal area of spontaneously hypertensive rats. These results suggest that a hyperactivity of the cholinergic system of this area could play a role in the development and/or maintenance of hypertension in spontaneously hypertensive rats.

Muscarinic receptor subtypes and sexual behavior in female rats

Cholinergic muscarinic systems are involved in the regulation of female sexual behavior in rats and hamsters. This series of experiments was designed to determine whether sexual behavior in female rats is controlled preferentially by one of the traditional muscarinic receptor subtypes. Intraventricular infusion of the muscarinic antagonist scopolamine (10 micrograms bilaterally) which binds with high affinity to both M1 and M2 subtypes inhibited sexual behavior, as indicated by the incidence of lordosis, in ovariectomized rats treated with estrogen and progesterone. In contrast, the M1-selective antagonist pirenzepine failed to reduce the incidence of lordosis following intraventricular infusion (10 to 80 micrograms bilaterally). Biochemical analyses revealed that intraventricular infusion of scopolamine (10 micrograms bilaterally) inhibited both M1 and M2 binding in brain tissues while intraventricular infusion of pirenzepine (10 micrograms bilaterally) completely inhibited M1 binding without affecting M2 binding. Intraventricular infusions of the acetylcholinesterase inhibitor physostigmine (10 micrograms bilaterally), the cholinergic agonist carbachol (1 microgram bilaterally), and the muscarinic agonist oxotremorine-M (0.1 micrograms bilaterally) activated lordosis in ovariectomized females primed with low doses of estrogen. In contrast, the putative M1 agonist McN-A-343 failed to significantly increase lordosis following intraventricular infusions (1, 10, 20 micrograms bilaterally). According to biochemical results, the ability of these agents to activate lordosis in female rats was related to their affinities for M2 binding sites not M1 binding sites. In a final experiment, estrogen treatment of ovariectomized rats did not alter muscarinic subtype binding in several brain areas as measured by the M1-selective ligand [3H] pirenzepine and the M2-selective ligand [3H] oxotremorine-M. The results of these experiments confirm that muscarinic systems contribute to the regulation of lordosis in female rats and indicate that M2 binding sites rather than M1 binding sites may be a critical component of this regulation.

Muscarinic cholinergic receptors in the rat caudate-putamen and olfactory tubercle belong predominantly to the m4 class: in situ hybridization and receptor autoradiography evidence

In order to establish the nature of the muscarinic cholinergic receptors present in the rat caudate-putamen and olfactory tubercle, we have combined in situ hybridization histochemistry with oligonucleotide probes and receptor autoradiography with N-[3H]methyl scopolamine and several subtype-selective antagonists: hexahydro-sila-difenidol, p-fluoro-hexahydro-sila-difenidol, 4-diphenyl-acetoxy-N-methylpiperidine methbromide, AF-DX 116, pirenzepine and methoctramine. In both brain regions, transcripts for the m4 muscarinic receptor subtype were the most abundant, followed by transcripts for the m1 subtype. m2 and m3 transcripts were much less abundant, whereas m5 mRNA was not detected under the present conditions. The binding profiles obtained in these areas were clearly distinct from those obtained in the CA1 layer of the hippocampus and in the pontine nuclei, regions enriched in M1 and M2 sites, respectively. In contrast, they were good agreement with the characteristics of atypical muscarinic receptors present in cell lines such as NG108-15, which contains mRNA for the m4 subtype, and PC12. The profiles displayed by some of the compounds used in the present study for cloned m4 receptors expressed in mammalian cells also agree with our results in rat caudate-putamen and olfactory tubercule. Taken together, these facts support the existence, in rat caudate-putamen and olfactory tubercle, of a major population of muscarinic cholinergic receptors belonging to the M4 type.

Quantitative autoradiography of 11 different transmitter binding sites in the basal forebrain region of the rat--evidence of heterogeneity in distribution patterns

The distribution of 12 different binding sites for acetylcholine, L-glutamate, GABA, 5-hydroxytryptamine, dopamine and noradrenaline was measured with quantitative receptor autoradiography in four regions of the rat basal forebrain (medial septal nucleus including vertical and horizontal limbs of the diagonal band of Broca, magnocellular preoptic nucleus, substantia innominata and basal nucleus of Meynert, ventral pallidum). L-Glutamate binding sites represent the largest portion of the analysed receptors in all regions, followed by muscarinic2, 5-hydroxytryptamine1 and GABAA receptors. Muscarinic1, dopamine1, dopamine2 and 5-hydroxytryptamine2 receptors and alpha 1-, alpha 1A- and alpha 1B-adrenoceptors represent the minor receptor populations. The largest portion of the dopamine receptors is represented by the dopamine1 subtype, and the alpha 1B subtype dominates the alpha 1-adrenoceptor group. A heterogeneity of the distribution patterns of the different receptors throughout the basal forebrain regions is found. A comparison of the patterns shows that alpha 1-adrenoceptors have a similar regional distribution to that of the muscarinic2 receptors, but both receptor types have reciprocal distributions compared with the 5-hydroxytryptamine1 receptors. The results indicate that one transmitter may exert different effects in the basal forebrain regions depending on the densities of the respective receptor subtypes. Moreover, similar or reciprocal distribution patterns of some, but not all, analysed receptors point to a non-random association (co-distribution) of the different transmitter systems in the basal forebrain regions.

Cholinergic receptors in human brain: effects of aging and Alzheimer disease

A general review of cholinergic receptors in human brain is presented. The paper focuses upon changes in normal aging brain and in Alzheimer disease. Studies from five different approaches are reported: 1) molecular biology; 2) receptor binding studies; 3) studies with specific neurotoxins; 4) immunocytochemistry; and 5) PET scan. These studies document profound and characteristic differences between the normal aging and the pathological Alzheimer brain with regard to cholinergic receptor localization, distribution, and function.

Post-training injection of the acetylcholine M2 receptor antagonist AF-DX 116 improves memory

The present study examined the effect of systemic post-training administration of the acetylcholine muscarinic M2 receptor antagonist AF-DX 116 on the acquisition of two 8-arm radial maze tasks. On a win-stay visual discrimination task, a light cue signalled the location of food in 4 randomly selected maze arms, and rats were required to visit each of the 4 lit arms twice within a trial. Rats were given one trial per day and injected immediately post-training on day 5. AF-DX 116 (0.5 and 1.0 mg/kg) significantly improved win-stay acquisition relative to vehicle-injected controls. On a win-shift task, rats were allowed to visit 4 randomly selected maze arms, followed by a delay period. After the delay, rats were returned to the maze for a retention test in which only those 4 arms not visited prior to the delay contained food. On the test (i.e. drug) trial, rats were removed from the maze after the first 4 choices and injected with AF-DX 116 or vehicle. The retention test was given following an 18 h delay. AF-DX 116 (2.0 mg/kg) significantly improved retention relative to vehicle controls. When the injections were given 2 h post-training, no effect on retention was observed in either task. The results demonstrate that post-training injection of the selective M2 receptor antagonist AF-DX 116 improves memory in a time-dependent manner. The findings may have implications for the cholinergic pharmacotherapy of Alzheimer's disease.

Localization of m5 muscarinic receptor mRNA in rat brain examined by in situ hybridization histochemistry

The regional distribution of mRNA coding for the m5 muscarinic acetylcholine receptor subtype was investigated in tissue sections of rat brain by in situ hybridization histochemistry. The highest hybridization signal was observed in the hippocampus, but restricted to the ventral subiculum, pyramidal cells of the CA1 and, with lower intensity, of the CA2 subfields. Significant levels of hybridization were also seen in the substantia nigra pars compacta, ventral tegmental area, lateral habenula, ventromedial hypothalamic nucleus and mammillary bodies. An involvement of the m5 muscarinic receptors in the regulation of the dopaminergic nigrostriatal pathway is suggested.

Choline acetyltransferase-immunoreactive profiles are presynaptic to primary sensory fibers in the rat superficial dorsal horn

The specific aim of this study was to search for morphological counterparts to the known antinociceptive effects of cholinomimetic drugs at the spinal cord level. For this, the light microscopic and ultrastructural distribution of choline acetyltransferase immunoreactivity was studied in laminae I-III of the rat cervical spinal cord. Immunoreactivity was present in cell bodies in lamina III, and in dendrites and axons of all three laminae. Immunoreactive axonal varicosities were often presynaptic to the central varicosities of type II synaptic glomeruli in lamina II and lamina III, less often presynaptic to the central elements of type I glomeruli in lamina II, and often presynaptic to dendrites in both type I and type II glomeruli. In addition, immunoreactive dendrites were often postsynaptic to the central varicosities of glomeruli of all morphological types. These results indicate that 1) primary sensory fibers excite cholinergic interneurons; 2) the acetylcholine released by the axon terminals of these interneurons modulates both nociceptive and non-nociceptive sensory information at the spinal cord level through both pre- and postsynaptic mechanisms. Furthermore, our results reinforce current ideas on reciprocal sensory interaction between thick and fine afferent fibers.

Central neural control of esophageal motility: a review

We review recent studies on the central neural control of esophageal motility, emphasizing the anatomy and chemical coding of esophageal pathways in the spinal cord and medulla. Sympathetic innervation of the proximal esophagus is derived primarily from cervical and upper thoracic paravertebral ganglia, whereas that of the lower esophageal sphincter and proximal stomach is derived from the celiac ganglion. In addition to noradrenaline, many sympathetic fibers in the esophagus contain neuropeptide Y (NPY), and both noradrenaline and NPY appear to decrease blood flow and motility. Preganglionic neurons innervating the cervical and upper thoracic ganglia are located at lower cervical and upper thoracic spinal levels. The preganglionic innervation of the celiac ganglion arises from lower thoracic spinal levels. Both acetylcholine (ACh) and enkephalin (ENK) have been localized in sympathetic preganglionic neurons, and it has been suggested that ENK acts to pre-synaptically inhibit ganglionic transmission. Spinal afferents from the esophagus are few, but have been described in lower cervical and thoracic dorsal root ganglia. A significant percentage contain calcitonin gene-related peptide (CGRP) and substance P (SP). The central distribution of spinal afferents, as well as their subsequent processing within the spinal cord, have not been addressed. Medullary afferents arise from the nodose ganglion and terminate peripherally both in myenteric ganglia, where they have been postulated to act as tension receptors, and, to a lesser extent, in more superficial layers. Centrally, these afferents appear to end in a discrete part of the nucleus of the solitary tract (NTS) termed the central subnucleus. The transmitter specificity of the majority of these afferents remains unknown. The central subnucleus, in turn, sends a dense and topographically discrete projection to esophageal motor neurons in the rostral portion of the nucleus ambiguous (NA). Both somatostatin-(SS) and ENK-related peptides have been localized in this pathway. Finally, motor neurons from the rostral NA innervate striated portions of the esophagus. In addition to ACh, these esophageal motor neurons contain CGRP, galanin (GAL), N-acetylaspartylglutamate (NAAG), and brain natriuretic peptide (BNP). The physiological effect of these peptides on esophageal motility remains unclear. Medullary control of smooth muscle portions of the esophagus have not been thoroughly investigated.

Single cholinergic mesopontine tegmental neurons project to both the pontine reticular formation and the thalamus in the rat

Microinjections of the cholinergic agonist carbachol into a caudal part of the pontine reticular formation of the rat induce a rapid eye movement sleep-like state. This carbachol-sensitive region of the pontine reticular formation is innervated by cholinergic neurons in the pedunculopontine and laterodorsol tegmental nuclei. The same population of cholinergic neurons also project heavily to the thalamus, where there is good evidence that acetylcholine facilitates sensory transmission and blocks rhythmic thalamocortical activity. The present study was undertaken to examine the degree to which single cholinergic neurons in the mesopontine tegmentum project to both the carbachol-sensitive region of the pontine reticular formation and the thalamus, by combining double fluorescent retrograde tracing and immunofluorescence with a monoclonal antibody to choline acetyltransferase in the rat. The results indicated that a subpopulation (5-21% ipsilaterally) of cholinergic neurons in the mesopontine tegmentum projects to both the thalamus and the carbachol-sensitive site of the pontine reticular formation, and these neurons represented the majority (45-88%) of cholinergic neurons projecting to the pontine reticular formation site. The percentage of cholinergic neurons with dual projections was higher in the pedunculopontine tegmental nucleus (6-27%) than in the laterodorsal tegmental nucleus (4-11%). In addition, mixed with cholinergic neurons in the mesopontine tegmentum, there was a small population of dually projecting neurons that did not appear to be cholinergic. Mesopontine cholinergic neurons with dual projections may simultaneously modulate neuronal activity in the pontine reticular formation and the thalamus, and thereby have the potential of concurrently regulating different aspects of rapid eye movement sleep.

Quantitative autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites in rat brain. Comparison with [125I]peptide YY receptor sites

The autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites was quantified in rat brain. The highest level of [125I]Bolton-Hunter neuropeptide Y binding sites was seen in the hippocampus (ventral stratum radiatum, CA3 subfield: 6029 +/- 250 fmol/g tissue). The distribution of these sites was clearly laminated, being particularly concentrated in the oriens layer (dorsal CA3 subfield: 2562 +/- 147 fmol/g tissue) and stratum radiatum (dorsal CA3 subfield: 2577 +/- 95 fmol/g tissue). Lower levels of sites were seen in the pyramidal cell layer (1708 +/- 105 fmol/g tissue) and the molecular layer (1155 +/- 116 fmol/g tissue). The cortical distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites was also laminated, being particularly enriched in superficial laminae (occipital cortex, layers I-II, 4038 +/- 148 fmol/g tissue; layers III-IV, 1392 +/- 97 fmol/g tissue and layers V-VI, 1522 +/- 138 fmol/g tissue). Other areas containing high amounts of sites included the anterior olfactory nuclei (ventral part, 4935 +/- 119 fmol/g tissue; lateral part, 4530 +/- 149 fmol/g tissue; dorsal part, 3378 +/- 140 fmol/g tissue and medial part, 2601 +/- 150 fmol/g tissue); anteromedial (5168 +/- 211 fmol/g tissue), medial (4611 +/- 107 fmol/g tissue) and lateral posterior thalamic nuclei (4465 +/- 189 fmol/g tissue); medial mammillary nucleus (5555 +/- 241 fmol/g tissue); medial geniculate nucleus (4747 +/- 56 fmol/g tissue); claustrum (4123 +/- 235 fmol/g tissue); posteromedial cortical amygdaloid nucleus (3524 +/- 138 fmol/g tissue), tenia tecta (2540 +/- 195 fmol/g tissue); lateral septum (1785 +/- 90 fmol/g tissue); suprachiasmatic hypothalamic nucleus (1604 +/- 115 fmol/g tissue), and substantia nigra, pars compacta (1846 +/- 142 fmol/g tissue) and pars lateralis (1750 +/- 165 fmol/g tissue). Areas moderately enriched with [125I]Bolton-Hunter neuropeptide Y binding sites included the zonal layer of the superior colliculus (1347 +/- 71 fmol/g tissue); anterior pretectal nucleus (1172 +/- 113 fmol/g tissue); ventral tegmental area (1090 +/- 97 fmol/g tissue); periventricular fibre system (1026 +/- 48 fmol/g tissue); core of nucleus accumbens (948 +/- 29 fmol/g tissue) and area postrema (799 +/- 87 fmol/g tissue). These results are discussed with regard to some of the suggested biological effects of neuropeptide Y in the central nervous system such as effects on learning, locomotion and circadian rhythms. Moreover, we also compared the distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites with that of [125I]peptide YY sites in rat brain. The resolution of the autoradiographic image is better with [125I]peptide YY most likely because of higher affinity and percentage of specific labelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of [3H]AF-DX 116 binding sites in the rat brain: evidence for heterogeneity of muscarinic-M2 receptor sites

This study shows that [3H]AF-DX 116 binds specifically, saturably, and with high affinity to putative muscarinic-M2 receptor sites in the rat brain. In homogenates of the hippocampus, cerebral cortex, striatum, thalamus, and cerebellum, [3H]AF-DX 116 appears to bind two subpopulations of muscarinic sites: one class of higher affinity sites (Kd less than 4.0 nM) and one class of lower affinity sites (Kd greater than 50 nM, except in the cerebellum). The apparent maximal capacities (Bmax) of [3H]AF-DX 116 sites in forebrain tissues ranged between 34 and 69 fmol/mg protein for the higher affinity site, and between 197 and 451 fmol/mg protein for the lower affinity site. In cerebellar homogenates, the maximal capacity of [3H]AF-DX 116 binding sites was 10.4 +/- 0.4 (Kd = 1.9 +/- 0.2 nM) and 39.1 +/- 2.6 (Kd = 26 +/- 7 nM) fmol/mg protein for the higher and the lower affinity site, respectively. Determination of the Kd for the higher and lower affinity [3H]AF-DX 116 sites from association and dissociation constants yielded similar values to those obtained from the saturation data. The ligand selectivity pattern reveals that AF-DX 116 is more potent than (-)QNB greater than atropine greater than methoctramine greater than 4-DAMP greater than gallamine greater than NMS greater than carbamylcholine greater than oxotremorine greater than pirenzepine much greater than nicotine in competing for the higher affinity [3H]AF-DX 116 sites. With few exceptions, the pattern was similar for the lower affinity sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative autoradiographic distribution of [3H]AF-DX 116 muscarinic-M2 receptor binding sites in rat brain

The distribution of muscarinic-M2 receptors in rat brain was investigated by in vitro autoradiography using [3H]AF-DX 116, a putative probe for the muscarinic-M2 receptor subtype. Incubation of rat brain coronal sections with 10 nM [3H]AF-DX 116 showed highest binding site densities in discrete areas such as the superior colliculus and certain thalamic and brainstem nuclei, similar to the distribution reported for [2H]acetylcholine/M2 sites. [3H]AF-DX 116 site densities were markedly lower in forebrain areas such as cortex, striatum, and hippocampus, in contrast to the distribution seen for [3H]pirenzepine-M1 binding sites, which were concentrated in these forebrain areas; however, differential patterns of labeling were observed for the two muscarinic-M2 probes, [3H]AF-DX 116 and [3H]acetylcholine, in the hippocampal formation. Although [3H]AF-DX 116 binding was broadly distributed in multiple subfields of the hippocampus, [3H]acetylcholine binding was discretely distributed in a manner resembling that of acetylcholinesterase staining. This suggests the existence of muscarinic-M2 subtypes in the CNS, especially in the hippocampal formation.