Divergent Regulation of Muscarinic Binding Sites and Acetylcholinesterase in Discrete Regions of the Developing Human Fetal Brain

Summary The expression of muscarinic acetylcholine binding sites and of cholinesterases was studied in extracts prepared from discrete regions of the human fetal brain, between the gestational ages of 14 and 24 weeks. The specific binding of [³H]N-methyl-4-piperidyl benzilate ([⁴H]-4NMPB) to muscarinic binding sites ranged between 0.05 and 1.30 pmol/mg protein in the different brain regions, withK _d values of 1.2 ± 0.2 nM. Binding of the cholinergic agonist oxotremorine fitted, in most of the brain regions examined, with a two-site model for the muscarinic binding sites. The density of muscarinic binding sites increased with development in most regions, with different rates and onset times. It was higher by about sixfold in some areas destined to become cholinergic, such as the cortex and midbrain, than in noncholinergic areas such as the cerebellum. In other areas destined to become cholinergic, such as the hippocampus and the caudate putamen, the receptor density remained low. Average density values increased from 0.1 ± 0.1 at 14 weeks up to 0.7 ± 0.4 pmol/mg protein at 24 weeks.The variability in the specific activities of cholinesterase was relatively low, and extracts from different brain regions hydrolyzed from 5 to 30 nmol of [³H]acetylcholine/min/mg protein. These were mostly true acetylcholinesterase (EC 3.1.1.7) activities, inhibited by 10^–5 M BW284C51, with minor pseudocholinesterase (EC 3.1.1.8) activities, inhibited by 10^–5 M iso-OMPA. The enzyme from different brain regions and developmental stages displayed similarK _m values toward [³H]acetylcholine (ca. 4 × 10^–4 M ^–1). The ontogenetic changes in cholinesterase specific activities had no unifying pattern and/or relationship to the cholinergic nature of the various brain areas. In most of the brain regions, the arbitrary ratio between the specific activity of cholinesterase and the density of muscarinic binding sites decreased with development, with average values and variability ranges of 83 ± 50 and 19 ± 19 at 14 and 24 weeks, respectively. Our findings suggest divergent regulation for cholinergic binding sites and cholinesterase in the fetal human brain and imply that the expression of muscarinic receptors is related to the development of cholinergic transmission, while acetylcholinesterase is also involved in other functions in the fetal human brain.I.B. took part in this work as partial fulfillment of the requirements of the Sackler Faculty of Medicine for an M.D. degree.     

Characterisation, Density, and Distribution of Kainate Receptors in Normal and Alzheimer''s Diseased Human Brain

The specific binding of [3H]kainic acid was investigated in membrane preparations from human parietal cortex obtained postmortem. Saturation studies revealed that binding occurred to a single population of sites with a KD of 15 nM and a Bmax of 110 fmol/mg of protein. The kinetically determined dissociation constant for these sites agreed well with that obtained from saturation analyses. Pharmacological characterisation of these sites gave a profile consistent with those reported for kainate receptor sites in animal brain. The integrity of kainate receptors was studied in several brain regions from six patients who had died of Alzheimer's disease and from six closely matched control subjects. No change in either the affinity or the number of kainate receptors was seen in any of the regions studied, despite the loss of neocortical and hippocampal glutamatergic terminals in the Alzheimer's diseased brains, as previously reported.     

Characterisation of Na+-Independent L-[3H]Glutamate Binding Sites in Human Temporal Cortex

The binding of L-[3H]glutamate to membranes from human temporal cortex was studied in the absence of Na+, Ca2+, and Cl- ions. Pharmacological characterisation revealed that approximately 35% of specific binding at 50 nM L-[3H]glutamate was sensitive to a combination of kainate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. The remaining approximately 65% of specific binding was to a single population of sites with a KD of 844 nM and a Bmax of 0.92 pmol/mg protein. The pharmacological characteristics were consistent with an interaction at the N-methyl-D-aspartate subclass of excitatory amino acid receptor. The inclusion of Cl- ions revealed additional glutamate binding; this was sensitive to quisqualate and DL-2-amino-4-phosphonobutyrate, but not to kainate, DL-2-amino-7-phosphonoheptanoate, or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid.     

Evidence that Tobacco Smoking Increases the Density of (−)-[3H]Nicotine Binding Sites in Human Brain

In a postmortem study of nicotinic receptors in human brain, cigarette smoking was found to be associated with increased (-)-[3H]nicotine binding to membranes prepared from gyrus rectus (Brodmann area 11) (p less than 0.001), hippocampal neocortex (Brodmann area 27), cerebellar cortex (p less than 0.01), hippocampal formation (Ammon's horn + subiculum), and the median raphe nuclei of the midbrain (p less than 0.05) but not the medulla oblongata. Analysis of the binding data suggested that the increased binding reflected an increase in the density of the receptors rather than a change in their affinity for (-)-nicotine. The effects of smoking were not influenced significantly by either the sex or age of the subject. It is concluded that smoking evokes an increase in high-affinity nicotine binding similar to that observed previously in animals treated chronically with nicotine and that the effect of smoking on these sites is probably caused by the nicotine present in the tobacco smoke.     

Solubilization and Characterization of Opioid Binding Sites from Frog (Rana esculenta) Brain

Active opioid receptors were solubilized from frog (Rana esculenta) brain membrane fractions by the use of 1% digitonin. It was found by kinetic as well as by equilibrium measurements that both the membrane and the solubilized fractions contain two binding sites. For the membrane preparations, KD values were 0.9 and 3.6 nM, and Bmax values were 293 and 734 fmol/mg protein. For the solubilized preparations, KD values were 0.4 and 2.6 nM, an Bmax values were 35 and 266 fmol/mg protein. The stereospecificity of the binding did not change during solubilization. Both the membrane-bound and the solubilized receptors showed weak binding of enkephalin and mu-specific drugs, suggesting that they are predominantly of the kappa-type. The membrane-bound and the soluble receptors showed the same distribution of subtypes, i.e., 70% kappa, 13% mu, and 17% delta for the membrane-bound and 71% kappa, 17% mu, and 12% delta for the soluble receptors.     

Somatostatin Binding Sites in Human and Monkey Brain: Localization and Characterization

A radioiodinated analogue of somatostatin 28, 125I [Leu8,D-Trp22,Tyr25] SS-28, was used to localize and characterize somatostatin binding sites in both human and monkey brain. High-affinity binding sites (approximately 1 nM) were found in cerebral cortex. The highest binding was in cerebral cortex with intermediate binding found in hippocampus, striatum, and amygdala and low binding in hypothalamus and brainstem. There was a rough correlation between somatostatin receptor binding and concentrations of somatostatin-like immunoreactivity (SLI) in human brain. Somatostatin receptors were stable for up to 24 h in an animal model simulating human autopsy conditions and there was no correlation between postmortem interval and receptor binding in human brain. Pharmacologic characterization in human cortex showed that there was a correlation between the inhibition of receptor binding by somatostatin analogues and their known abilities to inhibit growth hormone secretion. These findings demonstrate that a highly specific membrane-associated receptor for somatostatin is present in both monkey and human brain. Examination of somatostatin receptor binding in Alzheimer's disease and Huntington's disease may improve understanding of the role of somatostatin in both these illnesses.     

Effect of Pertussis Toxin on Radioligand Binding to Rat Brain Adenosine A1 Receptors

In a previous study we showed that in vivo treatment with pertussis toxin could inhibit some, but not all, effects of adenosine in the rat hippocampus. In this study we investigated the effect of pertussis toxin on the binding of adenosine analogues to A1 receptors in rat brain. Intraventricular injection of pertussis toxin (10 micrograms into the lateral ventricle) did not affect A1 receptor binding in any brain region studied, as evaluated by autoradiography. In vitro treatment of brain sections (10 microns) with pertussis toxin for 5 h, under conditions when greater than 80% of the G proteins were ADP ribosylated, did not alter radioligand binding to adenosine A1 receptors. GTP (10 microM) virtually abolished the high-affinity agonist binding to the A1 receptor. On the other hand, in solubilized cortical membrane preparations, pertussis toxin pretreatment induced a complete shift of the A1 receptors to the low-affinity state. This suggests that the ability of pertussis toxin to affect G proteins coupled to A1 receptors in brain depends not only on the distribution of the toxin but also on the configuration of receptors and G proteins.     

Pharmacological and Physicochemical Properties of Pre-Versus Postsynaptic 5-Hydroxytryptamine1A Receptor Binding Sites in the Rat Brain: A Quantitative Autoradiographic Study

Numerous data suggested that the pharmacological and biochemical properties of 5-hydroxytryptamine1A (5-HT1A) receptors exhibit some regional differences in the CNS, notably within the raphe nuclei compared with various forebrain areas (such as the hippocampus). This possibility has been further investigated in the dorsal raphe nucleus and two areas within the hippocampus, the dentate gyrus and the CA1 area, using the quantitative autoradiographic technique. The potencies of 5'-guanylylimidodiphosphate to inhibit the specific binding of 125I-Bolton-Hunter-8-methoxy-2-(N-propyl-N-propylamino)tetralin (125I-BH-8-MeO-N-PAT) to 5-HT1A sites and of N-ethylmaleimide to block these sites irreversibly were identical in the dorsal raphe nucleus and the hippocampal areas in rat brain sections. In contrast, slight but significant differences were noted in the pH dependence and pharmacological properties of 5-HT1A sites labeled by 125I-BH-8-MeO-N-PAT in these three regions. Similarly, heat denaturation experiments and tissue exposure to either phospholipase A2 or the alkylating agent 8-methoxy-2-(N-2'-chloropropyl,N-propyl)aminotetraline revealed regional differences in the properties of 5-HT1A sites. However, in most cases, the observed variations were of greater amplitude between the CA1 area and the dentate gyrus, where 5-HT1A sites are located postsynaptically, than between any one of these areas and the dorsal raphe nucleus where they act as (presynaptic) somatodendritic autoreceptors. These data further support that subtypes of 5-HT1A receptors probably exist in the rat brain, but this heterogeneity seems unrelated to the pre- or post-synaptic location of these receptors.     

Cyclic AMP-Dependent Protein Kinase Activity in Human Brain Across Age

Abstract: Cyclic AMP-dependent protein kinase activity was measured in the cerebral cortex of humans 2 days to 83 years of age and in the cortex of F344 rats 3, 22, or 30 months of age. Protein kinase activity was detected in the human brain, but no age-related differences in activity were observed in the presence or absence of cyclic AMP. Age differences were also not seen in protein kinase in the rat cerebral cortex. Enzyme activities in rat and human brain were similar.     

In Human Brain Two Subtypes of D1 Dopamine Receptors Can Be Distinguished on the Basis of Differences in Guanine Nucleotide Effect on Agonist Binding

D1 dopamine receptors were identified in membranes of human nucleus caudatus, nucleus accumbens, amygdala, and globus pallidus, by the specific binding of [3H](+)-R-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7 -ol [( 3H]SCH 23390). In these four brain regions, dopamine/[3H]SCH 23390 competition binding curves were computer-analyzed to a two-site model, distinguishing a high- (RH) and low- (RL) affinity site for dopamine. The ability of guanine nucleotides (0.4 mM GTP or 0.1 mM 5'-guanylylimidodiphosphate) to provoke a conversion of RH into RL was different between these brain regions. In amygdala, a complete conversion was seen, whereas there was no guanine nucleotide-effect on RH in globus pallidus. In nucleus caudatus and nucleus accumbens, guanine nucleotides provoked only a partial conversion of RH into RL, suggesting that these brain regions may contain guanine nucleotide-sensitive and -insensitive receptors. Heating of the membranes at 60 degrees C for 5 min had the same effect as guanine nucleotides. The pharmacological profiles of the guanine nucleotide-sensitive and -insensitive D1 receptors were similar, suggesting that D1 receptors in human brain are heterogeneous only with respect to their effector-coupling mechanism: guanine nucleotide-sensitive receptors, which are capable of undergoing functional coupling with Gs, and guanine nucleotide-insensitive receptors, which are not.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sulfhydryl Modification of Two Nicotinic Binding Sites in Mouse Brain

Two distinct binding sites with properties corresponding to those expected for nicotinic cholinergic receptors can be identified in brain by the specific binding of nicotine (or acetylcholine) and alpha-bungarotoxin. The effects of modification of these binding sites by treatment with the disulfide-reducing agent dithiothreitol were examined in tissue prepared from DBA mouse brains. Treatment with dithiothreitol reduced the binding measured with either ligand, and reoxidization of the disulfides fully restored binding. The effects of dithiothreitol treatment appeared to be due to a reduction in the maximal binding of nicotine and to a decrease in the binding affinity for alpha-bungarotoxin. Agonist affinity for the alpha-bungarotoxin binding site was reduced by treatment with low concentrations of dithiothreitol. The nicotine binding sites remaining after disulfide treatment displayed rates of ligand association and dissociation similar to those of unmodified tissue, but treatment of previously unmodified tissue with dithiothreitol accelerated the rate of nicotine dissociation. After reduction, both binding sites could be selectively alkylated with bromoacetylcholine. The results suggest that both putative nicotinic receptors in brain respond similarly to disulfide reduction and that their responses resemble those known for the nicotinic receptor of electric tissue.     

Subcellular Localization of Rat Brain Insulin Binding Sites

Fractions and subcellular structures were prepared from rat brain homogenate and their purity was assessed using enzyme markers, gamma-aminobutyric acid binding, DNA content, and electron microscopy. Insulin binding was highest on the plasma membrane preparations and approximately 50% less so on brain homogenate crude mitochondrial (P2), myelinated axon, and synaptosome preparations. Very low levels of binding were found on mitochondria and nuclei. Differences in binding between fractions were due to numbers of binding sites, and not variable binding affinity. There was a close relationship between insulin binding and the activity of Na/K ATPase (E.C. 3.6.1.4) in all fractions (r = 0.98). Insulin binding to the P2 was compared with plasma membrane fractions in seven brain regions, and the results demonstrated the same close relationship between insulin binding and plasma membrane content in all regions except hypothalamus. Plasma membrane insulin binding was well represented by the binding on P2 membranes in all regions except hypothalamus and brainstem. It was concluded that insulin binding is distributed evenly over the surface of brain cells and is not increased on nerve endings.     

Daily Modifications of 3h-Naloxone Binding Sites in the Rat Brain: A Quantitative Autoradiographic Study

The endogenous opioid peptides, the opiate receptors and several related behaviours, like opioid-mediated analgesia, show daily variations in different animal species including rats. The attempt to correlate the daily rhythm of opiate receptors in the central nervous system (CNS) to opiate related rhythmic phenomena requires an experimental approach with a high anatomical resolution, as the opioid distribution is very heterogeneous. In this paper we present the study of daily variations of 3H-naloxone binding sites in the different regions of the adult male rat brain, performed by means of quantitative autoradiography. Five rats are sacrificed at each investigated time of the day (0200, 0600,1000,1400,1800 and 2200). The ligand is 3H-naloxone(4nM), the quantification is performed by means of densitometric procedures (image analyzer Tesak VDC 501, computer Digital PDP11,3H-microscale). The statistical analysis is performed according to the single Cosinor method and the one-way analysis of variance followed by the multiple range test of Duncan. We analysed 33 different regions of the rat CNS, and the daily variations of opiate receptors are regionally selective. A circadian rhythm is found in the anterior cingulate cortex, hippocampal cortex, periventricular, medial, ventral, reticular and posterior nuclei of the thalamus, rhomboid, gelatinosus and rheuniens nuclei, lateral hypothalamus, locus coeruleus, grey substance of the pons, reticular formation of medulla oblongata, inferior olivary complex, medial part of the nucleus of the solitary tract and nucleus of the spinal tract of the trigeminal nerve. An ultradian rhythm is found in the medial and lateral preoptic areas, in the medial hypothalamus, in the medial and in the lateral nuclei of habenula. No significant variations during 24 hr according to the Cosinor analysis are found in the dorsal and lateral cerebral cortex, striatum, globus pallidus, bed nucleus of the stria terminalis, septal nuclei, lateral nucleus of the thalamus, cochlear nuclei, nucleus of the solitary tract, lateral and caudal parts, dorsal motor nucleus of the vagal nerve, XII and IX nerve nuclei. The amplitude of the daily variations observed ranges from 10 to 40%. Our results demonstrate the high anatomical selectivity of the daily modifications of 3H-naloxone binding sites in the rat CNS. They also indicate that quantitative autoradiography is a suitable and sensitive technique for these studies.     

Detection of a Novel Serotonin Receptor Subtype (5-HT1E) in Human Brain: Interaction with a GTP-Binding Protein

[3H]Serotonin (5-hydroxytryptamine, [3H]5-HT) was used as a radioligand probe of brain 5-HT receptors in homogenates of human cortical tissue. Two binding sites were detected in the presence of 1 microM pindolol (to block 5-HT1A and 5-HT1B receptors), and 100 nM mesulergine (to block 5-HT1C and 5-HT2 receptors). One of these sites demonstrated high affinity for 5-carboxyamidotryptamine (5-CT) and ergotamine, consistent with the known pharmacology of the 5-HT1D receptor; the second site demonstrated low affinity for 5-CT and ergotamine. Computer-assisted analyses indicated that both drugs displayed high affinities (Ki values of 1.1 nM and 0.3 nM for 5-CT and ergotamine, respectively) for 55% of the sites and low affinities (Ki values of 910 nM and 155 nM for 5-CT and ergotamine, respectively) for 45% of the sites. To investigate the non-5-HT1D component of the binding, 100 nM 5-CT (to block 5-HT1A, 5-HT1B, and 5-HT1D receptors) was coincubated with [3H]5-HT, membranes, and mesulergine. The remaining [3H]5-HT binding (hereafter referred to as "5-HT1E") displayed high affinity and saturability (KD, 5.3 nM; Bmax, 83 fmol/mg) in human cortical tissue. Competition studies with nonradioactive drugs indicated that, of the drugs tested, 5-CT and ergotamine displayed the highest selectivity for the 5-HT1D site versus the 5-HT1E site.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adenylyl Cyclase Activity in Postmortem Human Brain: Evidence of Altered G Protein Mediation in Alzheimer''s Disease

The effects of agonal status, postmortem delay, and age on human brain adenylyl cyclase activity were determined in membrane preparations of frontal cortex from a series of 18 nondemented subjects who had died with no history of neurological or psychiatric disease. Basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were not significantly reduced over an interval from death to postmortem of between 3 and 37 h and were also not significantly different between individuals dying with a long terminal phase of an illness and those dying suddenly. Basal and aluminum fluoride-stimulated enzyme activities showed a negative correlation with increasing age of the individual. In subsequent experiments, basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were compared in five brain regions from a series of eight Alzheimer's disease and seven matched nondemented control subjects. No significant differences were observed between the groups for either basal activity or activities in response to forskolin stimulation of the catalytic subunit of the enzyme. In contrast, enzyme activities in response to stimulation with guanosine 5'-O-(3-thiotriphosphate) and aluminum fluoride were significantly reduced in preparations of neocortex and cerebellum from the Alzheimer's disease cases compared with the nondemented controls. Lower guanosine 5'-O-(3-thiotriphosphate)-, but not aluminum fluoride-, stimulated activity was also observed in preparations of frontal cortex from a group of four disease controls compared with nondemented control values. The disease control group, which contained Parkinson's disease and progressive supranuclear palsy patients, showed increased forskolin-stimulated activity compared with both the nondemented control and the Alzheimer's disease groups. These findings indicate a widespread impairment of G protein-stimulated adenylyl cyclase activity in Alzheimer's disease brain, which occurs in the absence of altered enzyme catalytic activity and which is unlikely to be the result of non-disease-related factors associated with the nature of terminal illness of individuals.     

[3H]Ketanserin Binding in Human Brain Postmortem

This study aimed at comparing the binding characteristics of [³H]ketanserin, a high-affinity serotonin 2A (5-HT_2A) receptor antagonist, in the prefrontal cortex, hippocampus and striatum of human brain post-mortem. The results indicated the presence of a single population of binding sites in all the regions investigated, with no statistical difference in maximum binding capacity (B_max) or dissociation constant (K_d) values. The pharmacological profile of [³H]ketanserin binding was consistent with the labeling of the 5-HT_2A receptor, since it revealed a competing drug potency ranking of ketanserin = spiperone > clozapine = haloperidol > methysergide > mesulergine > 5-HT. In conclusion, the 5-HT_2A receptor, as labeled by [³H]ketanserin, would seem to consist of a homogenous population of binding sites and to be equally distributed in human prefronto-cortical, limbic and extrapyramidal structures.     

Solubilized Rat Brain Adenosine Receptors Have Two High-Affinity Binding Sites for l, 3-Dipropyl-8-Cyclopentylxanthine

The specific binding of L-N6-[3H]phenylisopropyladenosine (L-[3H]PIA) to solubilized receptors from rat brain membranes was studied. The interaction of these receptors with relatively low concentrations of L-[3H]PIA (0.5-12.0 nM) in the presence of Mg2+ showed the existence of two binding sites for this agonist, with respective dissociation constant (KD) values of 0.24 and 3.56 nM and respective receptor number (Bmax) values of 0.28 +/- 0.03 and 0.66 +/- 0.05 pmol/mg of protein. In the presence of GTP, the binding of L-[3H]PIA also showed two sites with KD values of 24.7 and 811.5 nM and Bmax values of 0.27 +/- 0.09 and 0.93 +/- 0.28 pmol/mg of protein for the first and the second binding site, respectively. Inhibition of specific L-[3H]PIA binding by 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (0.1-300 nM) performed with the same preparations revealed two DPCPX binding sites with Ki values of 0.29 and 13.5 nM, respectively. [3H]DPCPX saturation binding experiments also showed two binding sites with respective KD values of 0.81 and 10.7 nM and respective Bmax values of 0.19 +/- 0.02 and 0.74 +/- 0.06 pmol/mg of protein. The results suggest that solubilized membranes from rat brain possess two adenosine receptor subtypes: one of high affinity with characteristics of the A1 subtype and another with lower affinity with characteristics of the A3 subtype of adenosine receptor.     

Effects of Postmortem Delay and Temperature on Neurotransmitter Receptor Binding in a Rat Model of the Human Autopsy Process

Abstract: Studies of neurotransmitter and drug receptor alterations in neurodegenerative disorders have contributed to our understanding of the pathophysiology of these conditions. The effect of postmortem delay in freezing tissue after death and prolonged storage of tissue prior to analysis on receptor binding assays are potential artifacts that may limit interpretation of the effects of disease on receptor populations. We used a rat model of the human autopsy process to study the effects of increasing postmortem delay and storage time on N -methylscopolamine (NMS), p -aminoclonidine (PAC), flunitrazepam (FLU), and spiperone binding in a variety of rat brain regions. The rat brains were cooled using a temperature-controlled environment and thermistor probe to follow cooling curves obtained in human brain. Brains were cooled to either room temperature (22°C) or refrigerator temperature (4°C). For three of the four receptors, receptor binding decreased as postmortem delay before freezing increased, particularly in tissue cooled to room temperature. Unlike binding at other receptor sites, FLU binding increased with increasing postmortem delay to freezing. Different effects on K _D and B _max were noted for each ligand studied. No effects of the freezing process itself or storage at -80°C were detectable.     

Distribution of [3H]GR65630 Binding in Human Brain Postmortem

We investigated the distribution of serotonin (5-HT) receptors of type 3 (5-HT₃) in human brain areas, by means of the the specific binding of [³H]GR65630. The brains were obtained during autoptic sessions from 6 subjects. Human brain membranes and the binding of [³H]GR65630 were carried out according to standardized methods. The highest density (Bmax ± 6 SD, fmol/mg protein) of [³H]GR65630 binding sites was found in area postrema (13.1 ± 9.7), followed at a statistically lower level, by nucleus tractus solitarius (6.7 ± 3.4), nervus vagus (5.5 ± 2.1), striatum (4.8 ± 2.4) with a progressive decrease in amygdala, olivar nuclei, hippocampus, olfactory bulbus and prefrontal cortex, and then by the other cortical areas and the cerebellum, where no binding was detected. These observations extend previous findings on the distribution of 5-HT₃ receptors and confirm interspecies variations that might explain the heterogeneous properties of 5-HT₃ receptors in different animals.     

Autoradiographic Visualization of the Receptor Subclasses for Vasoactive Intestinal Polypeptide (VIP) in Rat Brain

Vertongen, P., S. N. Schiffmann, P. Gourlet and P. Robberecht. Autoradiographic visualization of the receptor subclasses for Vasoactive Intestinal Polypeptide (VIP) in rat brain. Peptides 18(10) 1547–1554, 1997.—Vasoactive Intestinal Polypeptide (VIP) exerts its biological effects through interaction with two high affinity receptors named the VIP₁- and the VIP₂ receptors. Their messenger RNAs have been mapped in rat brain by in situ hybridization. A cyclic peptide (RO 25-1553) and a secretin analogue ([R¹⁶]chicken secretin) were identified as selective agonist peptides for the VIP₂- and VIP₁ receptors, respectively. The iodinated peptides retained the high affinity and selectivity of the unlabelled peptides and were used for the mapping of each receptor subclass in rat brain. VIP₁ receptors were present in the cerebral cortex, the piriform cortex, the claustrum, the caudate-putamen, the dentate gyrus, the lateral amygdaloïd nucleus, the anteroventral thalamic nucleus, the rhomboïd nucleus, the supraoptic nucleus and the choroïd plexus. VIP₂ receptors were present in the cerebral cortex, the claustrum, the caudate-putamen, the nucleus accumbens, the lateral septal nuclei, the bed nucleus of the stria terminalis, the basolateral amygdaloïd nucleus, the Ammon’s horn, the thalamic nuclei except some centromedial nuclei, the medial habenula, the suprachiasmatic nucleus, the periventricular nucleus, the mammilary nucleus, the superior colliculus and the choroïd plexus.