Modulation of rat brain alpha- and beta-adrenergic receptor populations by lesion of the dorsal noradrenergic bundle

Bilateral lesion of the ascending noradrenergic fibers in the dorsal bundle of adult Wistar rats with 4 micrograms 6-hydroxydopamine caused extensive depletion of norepinephrine in all forebrain areas, but led to a 54% increase in norepinephrine levels in the cerebellum. beta-Adrenergic receptor binding of [3H]dihydroalprenolol was significantly increased in all forebrain areas depleted of norepinephrine except hypothalamus. The increase in [3H]dihydroalprenolol binding was due to 62% and 34% increases in the number of beta-receptor sites in the frontal cerebral cortex and hippocampus respectively. Binding of [3H]WB-4101 to alpha 1-adrenergic receptors after dorsal bundle lesion was augmented generally to a lesser extent than beta-receptor binding, with significantly increased numbers of sites only in the frontal cortex (74%), thalamus (20%) and septum. Both alpha 1- and beta-receptor binding sites were reduced in number by 25-28% in the cerebellum of dorsal bundle-lesioned rats, whereas intraventricular administration of 6-hydroxydopamine to adult rats, which depletes norepinephrine in the cerebellum by 96%, increased cerebellar alpha 1- and beta-receptor binding by 33-40%. Binding of [3H]clonidine to forebrain alpha 2-adrenergic receptors was significantly elevated in the frontal cortex, but reduced in the amygdala and septum, after dorsal bundle lesion.     

Laminar distribution of NMDA receptors in cat and monkey visual cortex visualized by [3H]-MK-801 binding

Glutamate is the major excitatory neurotransmitter of the mammalian central nervous system. Two major classes of glutamate receptors have been reported. The actions of glutamate on its N-methyl-D-aspartate (NMDA)-type receptor may underlie developmental and adult plasticity as well as neurotoxicity. The NMDA-type of glutamate receptor in cat and monkey visual cortex was visualized by means of in vitro receptor autoradiography with the noncompetitive NMDA-receptor antagonist [³H]-MK-801. The kinetics, performed on tissue sections, revealed an apparently single, saturable site with an approximate dissociation constant (KD) of 18.5 nM in cat and 15.9 nM in monkey visual cortex. Autoradiography, performed on frontal sections of cat and monkey visual cortex, revealed a heterogeneous laminar distribution of NMDA receptors. Cat areas 17,18,19, and the lateral suprasylvian areas exhibited a similar NMDA-receptor distribution. In these areas, NMDA receptors were most prominent in layer II and the upper part of layer III. In monkey striate cortex, NMDA receptors were primarily concentrated in layers II, upper III, IVc, V, and VI. In monkey secondary visual cortex, [³H]-MK-801 labeling was most prominent in layers II, V, and VI; whereas in the temporal visual areas included in this study layer II displayed the heaviest receptor labeling. In neither cat nor monkey could we observe significant differences in NMDA-receptor distribution between different retinotopic subdivisions within a single visual area. Neither did we detect any periodic changes in NMDA-receptor distribution that would correspond to the compartments defined by cytochrome-oxidase in monkey V1 and V2. © 1993 Wiley-Liss, Inc.     

Quantitative autoradiographic mapping of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in the neocortex of the rhesus monkey

The in vitro autoradiographic technique was used to characterize the distribution of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in 11 cortical areas of frontal, parietal, and occipital lobes in the rhesus monkey; 5-HT1 receptors were labeled with [3H]5-HT; 5-HT2 receptors were labeled with [3H]ketanserin; and 5-HT uptake sites were labeled with [3H]citalopram. Five-HT1 and 5-HT2 receptors and 5-HT uptake sites were found in every cortical area examined with the absolute concentration of 5-HT1 receptors higher than that of 5-HT2 receptors in all areas. In eight regions of prefrontal and parietal as well as in prestriate cortex, 5-HT1 and 5-HT2 receptors had complementary distribution profiles: 5-HT1 receptors were concentrated in layers I and II and the upper strata of layer III, while 5-HT2 receptors had their highest concentration throughout layers III and IV. Only the primary motor and visual cortex had receptor distributions different from that described above. Thus, in the primary visual cortex, both 5-HT1 and 5-HT2 receptors were found in high concentration in sublayer IVc beta, though the density of 5-HT1 receptor was also high in other subdivisions of layer IV and in layers III, V, and VI. In the primary motor cortex, both receptor subtypes were concentrated in layers I and II and the upper strata of layer III. The pattern of distribution of serotonin uptake sites did not match the patterns of distribution of either 5-HT1 or 5-HT2 receptors alone; rather it approximated the combined patterns of distribution of both receptor subtypes. The complementary patterns of distribution of 5-HT1 and 5-HT2 receptors in most areas of the monkey cerebral cortex suggest that these two receptor subtypes may make differential contributions to cortical functions.     

Interaction between alpha 2- and beta-adrenergic receptors in rat cerebral cortical membranes: clonidine-induced reduction in agonist and antagonist affinity for beta-adrenergic receptors.

The interaction between alpha 2- and beta-adrenergic receptors was investigated in rat cerebral cortical membranes. Clonidine inhibition of [3H]dihydroalprenolol ([3H]DHA) binding resulted in biphasic competition curves with a mean Hill coefficient of 0.45. The addition of 1 microM yohimbine caused a rightward shift of the first portion of the clonidine inhibition curve. In the presence of 1 microM clonidine, the maximum concentration which did not inhibit [3H]DHA binding, inhibition curves of [3H]DHA binding by isoproterenol shifted to the right. A mean Hill coefficient increased from a control value of 0.63 to 0.76. Computer modeling analysis revealed that 1 microM clonidine decreased a beta-adrenergic high-affinity state from 28% to 13%. However, the addition of 1 microM yohimbine completely prevented the clonidine-induced reduction in the beta-adrenergic high-affinity state. In the presence of 200 microM GTP, the effect of clonidine was not observed. In addition, Kd and Bmax values for [3H]p-aminoclonidine ([3H]PAC) binding were not significantly changed by the addition of 100 nM isoproterenol, the maximum concentration which did not inhibit [3H]PAC binding. Moreover, isoproterenol inhibition of [3H]PAC binding resulted in steep competition curves with a mean Hill coefficient of 0.97. The addition of 1 microM alprenolol did not affect the isoproterenol inhibition curve. These data demonstrated that clonidine caused a decrease in agonist and antagonist affinity for beta-adrenergic receptors, while isoproterenol did not modulate the binding characteristics of alpha 2-adrenergic receptors. Furthermore, these results suggest that regulation between alpha 2- and beta-adrenergic receptors is not bidirectional, but is instead unidirectional from alpha 2-adrenergic receptors to beta-adrenergic receptors.     

Overlap of dopaminergic, adrenergic, and serotoninergic receptors and complementarity of their subtypes in primate prefrontal cortex

Quantitative in vitro autoradiography was used to determine and compare the areal and laminar distribution of the major dopaminergic, adrenergic, and serotonergic neurotransmitter receptors in 4 cytoarchitectonic regions of the prefrontal cortex (Walker's areas 12, 46, 9, and 25) in adult rhesus monkeys. The selective ligands, 3H-SCH-23390, 3H-raclopride, 3H-prazosin, and 3H-clonidine were used to label the D1 and D2 dopamine receptor subtypes and the alpha 1- and alpha 2-adrenergic receptors, respectively, while 125I-iodopindolol was used to detect beta-adrenergic receptors. The radioligands, 3H-5-hydroxytryptamine and 3H-ketanserin labeled, respectively, the 5-HT1 and 5-HT2 receptors. Densitometry was performed on all cortical layers and sublayers for each of the 7 ligands to allow quantitative as well as qualitative comparison among them in each cytoarchitectonic area. Although each monoamine receptor was distributed in a distinctive laminar-specific pattern that was remarkably similar from area to area, there was considerable overlap among the dopaminergic, adrenergic, and serotoninergic receptors, while subtypes of the same receptor class tended to have complementary laminar profiles and different concentrations. Thus, the D1 dopamine, the alpha 1- and alpha 2-adrenergic, and the 5-HT1 receptors were present in highest relative concentration in superficial layers I, II, and IIIa (the "S" group). In contrast, the beta 1- and beta 2-adrenergic subtypes and the 5-HT2 receptor had their highest concentrations in the intermediate layers, IIIb and IV (the "I" group), while the D2 receptor was distinguished by relatively high concentrations in the deep layer V compared to all other layers (the "D" class). Consequently, clear laminar differences were observed in the D1 vs D2 dopaminergic, the alpha- vs beta-adrenergic, and the 5-HT1 vs 5-HT2 serotoninergic receptor subtypes in all 4 areas examined. The anatomical overlap of different monoaminergic receptors in the same cortical strata suggests that there may be families of receptors linked by localization on common targets, while the complementary laminar distribution of the D1 vs D2, the 5-HT1 vs 5-HT2 and the alpha- vs beta-adrenergic receptors raises the possibility that different subtypes within a given class may have distinctive actions in cortex by virtue of their localization on different cells or possibly different portions of the same cell. Understanding the anatomical arrangement of receptors within the cortical layers may aid in the analysis of monoaminergic modulation of higher cortical function.     

Morphology and distribution of neurons and glial cells expressing beta-adrenergic receptors in developing kitten visual cortex.

The morphology and distribution of cells expressing beta-adrenergic receptors has been studied in developing kitten visual cortex using a monoclonal antibody which recognizes both beta-1 and beta-2 adrenergic receptors. We found specific populations of neurons and glial cells which express beta-adrenergic receptor immunoreactivity in the kitten visual cortex. In adult animals, the receptors are most concentrated in the superficial and deep cortical layers (layers I, II, III and VI). About 50% of the stained neural cells in adult cat visual cortex are glial cells. Most of the immunoreactive neurons in layers III and V are pyramidal cells while those in layers II and IV are more likely to be nonpyramidal cells. In neonatal kittens, staining is weaker than that in adult cats and it appears to be concentrated in neurons of the deep cortical layers and in the subcortical plate and white matter. Only a few immunoreactive glial cells were found at this age. Receptor numbers increase after birth and by 24 days of age, the laminar distribution of beta-adrenergic receptors approaches that of adult animals. Immunoreactive glial cells in the white matter show a progressive increase in number throughout postnatal development.     

Pharmacological identification of the alpha-adrenergic receptor type which inhibits the beta-adrenergic activated adenylate cyclase system in cultured astrocytes

The adrenergic agonist norepinephrine can exert its influence on cell function by activating both alpha- and beta-adrenergic receptors. In astrocytes, the alpha-adrenergic receptor activity of norepinephrine is known to inhibit the cyclic AMP response elicited by its action at beta-adrenergic receptors. Pharmacological studies were conducted to identify the subtype of alpha-adrenergic receptor which mediates this inhibitory action. The alpha 2-adrenergic antagonist yohimbine potentiated the cyclic AMP response elicited by norepinephrine, whereas the alpha 1-adrenergic antagonist prazosin did not affect the response. The alpha 2-adrenergic agonist clonidine inhibited the cyclic AMP response elicited by the beta-adrenergic agonist isoproterenol and this inhibition could be blocked by yohimbine but not by prazosin. In contrast, the alpha 1-adrenergic agonist phenylephrine did not inhibit the cyclic AMP response to isoproterenol. These studies indicate that the inhibitory action of norepinephrine is mediated by its action at alpha 2-adrenergic receptors.     

Cyclic AMP-generating systems: regional differences in activation by adrenergic receptors in rat brain

Catecholamine, histamine, and adenosine-mediated accumulations of radioactive cyclic AMP were assessed in adenine-labeled slices from eight rat brain regions. 2-Fluoronorepinephrine, a selective beta-adrenergic agonist, elicited an an accumulation of cyclic AMP in cerebral cortex, cerebellum, hippocampus, striatum, superior colliculi, thalamus, hypothalamus, and medulla-pons. In cerebral cortex and most other brain regions, the beta-adrenergic-mediated response appeared to involve primarily beta 1-adrenergic receptors, while in cerebellum, there was a significant involvement of beta 2-adrenergic receptors. 6-Fluoronorepinephrine, a selective alpha-adrenergic agonist, elicited accumulations of cyclic AMP in all regions except cerebellum. Combinations of the two fluoro derivatives afforded in all brain regions an accumulation of cyclic AMP identical with that elicited by norepinephrine. In hypothalamus, the alpha- and beta-adrenergic responses were significantly greater than additive. In cerebral cortex, the alpha-adrenergic receptor-mediated response appeared to involve alpha 1-adrenergic receptors and to be nearly completely dependent on adenosine, while in other brain regions, the dependence of the alpha-adrenergic response on adenosine was less or absent. Combinations of 6-fluoronorepinephrine and histamine had greater than additive effects in cortex and hippocampus. The results indicate that the interactive control of cyclic AMP-generating systems by alpha-adrenergic, beta-adrenergic, adenosine, and histamine receptors differs significantly among rat brain regions.     

Regulation of subtypes of beta-adrenergic receptors in rat brain following treatment with 6-hydroxydopamine

The technique of quantitative autoradiography has been used to localize changes in the densities of subtypes of beta-adrenergic receptors in rat brain following treatment with 6-hydroxydopamine. Previously reported increases in the density of beta 1-adrenergic receptors in the cerebral cortex were confirmed. The anatomical resolution of autoradiography made it possible to detect changes in the density of beta 2-adrenergic receptors in the cortex and in a number of other brain regions. The density of beta 1-adrenergic receptors increased from 30 to 50% depending on the region of the cortex being examined. The increase in the somatomotor cortex was greater than that in the frontal or occipital cortex. The increase in the density of beta 2-adrenergic receptors in the cortex was not as widespread as that of beta 1-adrenergic receptors and occurred primarily in frontal cortex, where the density of receptors increased by 40%. The densities of both beta 1- and beta 2-adrenergic receptors increased in a number of forebrain, thalamic, and midbrain structures. Selective changes in the density of beta 1-adrenergic receptors were observed in the superficial gray layer of the superior colliculus and in the amygdala. The density of beta 2-adrenergic receptors increased in the caudate-putamen, the substantia nigra, and the lateral and central nuclei of the thalamus, whereas the density of beta 1-adrenergic receptors did not change in these regions. The densities of both subtypes of beta-adrenergic receptors increased in the hippocampus, the cerebellum, the lateral posterior nucleus of the thalamus, and the dorsal lateral geniculate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Autoradiographic study of beta 1-adrenergic receptor development in the mouse forebrain

The development of beta 1-adrenergic receptors has been studied in the mouse forebrain from embryonic day 14 (E14) to adulthood, using autoradiographic visualization of [125I]iodocyanopindolol (ICYP) binding sites. From E14, ICYP binding sites are detected in moderate amounts in the striatum and basal forebrain and in very low concentration in the cortical plate. At E17, binding sites have increased in number in the deep layers of the embryonic cortex and extend over the whole thickness of the cortical ribbon at birth. On postnatal day 4 (P4), ICYP binding sites are more abundant in the superficial than in the inner cortex. By P10 the adult pattern of ICYP binding site distribution is achieved, namely: a high concentration in ventral pallidum, striatum and cortical layers I, II and III, a moderate concentration in layers V and VI and a lower density in septal areas and in cortical layer IV. It is well established that norepinephrine fibers arrive in the embryonic cortex early in development. The present results show that the development of norepinephrine fiber and beta 1 receptor systems are coincident in the mouse.     

Analysis of brain adrenergic receptors in dopamine-beta-hydroxylase knockout mice

The biosynthesis of norepinephrine occurs through a multi-enzymatic pathway that includes the enzyme dopamine-beta-hydroxylase (DBH). Mice with a homozygous deletion of DBH (Dbh-/-) have a selective and complete absence of norepinephrine. The purpose of this study was to assess the expression of alpha-1, alpha-2 and beta adrenergic receptors (alpha1-AR, alpha2-AR and beta-AR) in the postnatal absence of norepinephrine by comparing noradrenergic receptors in Dbh-/- mice with those in Dbh heterozygotes (Dbh+/-), which have normal levels of norepinephrine throughout life. The densities of alpha1-AR, alpha2-AR and beta-AR were assayed with [3H]prazosin, [3H]RX21002 and [125I]-iodo-pindolol autoradiography, respectively. The alpha2-AR agonist high affinity state was examined with [125I]-para-iodoclonidine autoradiography and alpha2-AR functionality by alpha2-AR agonist-stimulated [35S]GTPgammaS autoradiography. The density of alpha1-AR in Dbh-/- mice was similar to Dbh+/- mice in most brain regions, with an up-regulation in the hippocampus. Modest decreases in alpha2-AR were found in septum, hippocampus and amygdala, but these were not reflected in alpha2-AR functionality. The density of beta-AR was up-regulated to varying degrees in many brain regions of Dbh-/- mice compared to the heterozygotes. These findings indicate that regulation of noradrenergic receptors by endogenous norepinephrine depends on receptor type and neuroanatomical region.     

Ontogeny of beta 1- and beta 2-adrenergic receptors in rat cerebellum and cerebral cortex

The development of beta 1- and beta 2-adrenergic receptors was studied in rat cerebral cortex and cerebellum. In the cerebral cortex, which contains mostly beta 1-adrenergic receptors, total beta-adrenergic receptor density increased sharply between postnatal days 10 and 21. The density of receptors remained fairly constant through 6 weeks of age and then subsequently declined. The proportion of beta 1 and beta 2 receptors was relatively constant throughout the development of the cerebral cortex. The development of the two receptor subtypes thus paralleled the development of total beta-adrenergic receptors in the cerebral cortex. The ontogeny of beta-adrenergic receptors in the cerebellum, which contains mainly beta 2 receptors, was strikingly different from that observed in the cortex. Total cerebellar beta receptor density exhibited a slow but steady increase from postnatal day 5 through day 42. The density of receptors then plateaued and remained constant until the animals were approximately 6 months of age. Unlike the results obtained in the cortex, the relative proportions of beta 1 and beta 2 receptors in the cerebellum changed markedly during development. Between postnatal days 8 and 13 approximately 18% of the receptors were of the beta 1 subtype. This proportion steadily decreased with age, and in 3- and 6-month-old animals only approximately 2% of the receptors were of the beta 1 subtype. The results demonstrate that the two subtypes of beta-adrenergic receptors can have different developmental patterns in the same brain area, and that a single receptor subtype can follow different developmental patterns in different brain regions. Possible correlations between the ontogeny of beta 1 and beta 2 receptors and various developmental events are discussed.     

Rapid reduction in [3H]prazosin binding to gerbil forebrain membranes during bilateral common carotid artery occlusion

Transient cerebral ischemia results in selective neuronal cell death. The mechanisms underlying this selective vulnerability to ischemia are only beginning to be elucidated. We studied the effect of ischemia on alpha 1-adrenergic receptor binding by measuring [3H]prazosin binding in gerbil forebrain membranes after 10 min of bilateral carotid occlusion. Binding was reduced from 62 +/- 3 to 33 +/- 4 fmol/mg protein. Binding in the same membranes to beta 2-adrenergic receptors were also decreased, but not to the extent of that to alpha 1-adrenergic receptors. Binding to muscarinic cholinergic [( 3H]quinuclydil benzilate) and beta 1-adrenergic receptors were only slightly depressed. Surprisingly, the protein content was significantly increased in the membrane fraction studied from ischemic forebrain (68 +/- 4 mg/g wet weight) compared with sham operated controls (57 +/- 4). The dramatic decrease in alpha 1-adrenergic receptor binding during ischemia is consistent with receptor binding studies of membranes pretreated with phospholipase A2 in vitro. It is not clear what effect this change in alpha 1-adrenergic receptor binding has on subsequent selective neuronal death. The recent demonstration that catecholamines and locus ceruleus neurons influence the loss of CA1 neurons in the hippocampus suggests that it may play an important modulatory role.     

Autoradiographic localization of β-adrenergic receptors in the rabbit pituitary

The localization and characterization of beta-adrenergic receptors in the rabbit pituitary have been studied using [125I]cyanopindolol as a specific ligand. Slide-mounted frozen sections were used for the autoradiographic localization and characterization of beta-adrenergic receptors. The displacement curves obtained from optical density of radioautograms or counting of scraped off sections demonstrated that beta-adrenergic receptors were mostly of the beta 2-subtype and highly concentrated in the intermediate lobe. Low concentrations of beta 2-adrenergic receptors were also found to be uniformly distributed in the anterior and posterior lobes. These results suggest that epinephrine and/or norepinephrine might play a physiological role in the regulation of the secretion of not only the intermediate lobe but also the anterior and posterior lobes of the rabbit pituitary.     

The distribution of M1 and M2 muscarinic acetylcholine receptor subtypes in the developing cat visual cortex

The binding site characteristics and ontogenesis of [3H]pirenzepine ([3H]PZ) (M1 receptor) and [3H]oxotremorine-M ([3H]OXO-M) (M2 receptor) binding sites were investigated in the cat visual cortex. Scatchard analysis of [3H]PZ binding in adult cat visual cortex revealed a single site with a Kd of 17.3 nm and a Bmax of 352.45 fmol/mg protein. [3H]OXO-M also bound to a single site with a Kd of 7.1 nM and a Bmax of 256.39 fmol/mg protein. Receptor autoradiography revealed that [3H]PZ binding sites were present only in telencephalic structures while [3H]OXO-M sites were distributed heterogeneously throughout the brain. [3H]PZ binding sites in adult visual cortex were present in the superficial and deep cortical layers with the densest labeling in layer I and a distinct band in layer V. [3H]OXO-M sites also avoided the middle cortical layers, but were most prominent in layers V and VI with less pronounced binding in layers I and II. Deafferentation of extrinsic inputs to the visual cortex did not reduce [3H]PZ nor [3H]OZO-M binding, but neuron-specific excitotoxic lesions of visual cortex abolished both populations of binding sites. This indicates that both populations of binding sites are located on cells intrinsic to the cortex. In early postnatal life, both [3H]PZ and [3H]OXO-M binding sites were localized to intermediate cortical layers. Following this, the laminar distribution of both populations redistributed; each with its own idiosyncratic profile. By postnatal day 49, [3H]PZ binding sites redistributed into the superficial and deep layers, the pattern of adult animals, while [3H]OXO-M sites maintained a pattern similar to younger animals, with substantial binding persisting in layer IV. As late as postnatal day 70, well after [3H]PZ binding sites had achieved their mature laminar pattern, [3H]OXO-M binding sites in visual cortex had not achieved their characteristic adult pattern. In addition, the normal laminar redistribution of both [3H]PZ and [3H]OXO-M binding sites during postnatal development of the cat visual cortex was prevented by eliminating cortical afferents in early postnatal life. This indicates that muscarinic receptor rearrangement in development is dependent upon cortical input or output.     

Binding properties, regional ontogeny and localization of adrenergic receptors in chick brain

The pharmacological properties of [3H]-WB4101, [3H]-clonidine and [3H]-dihydroalprenolol binding in chick brain membranes display the characteristics known for alpha 1-, alpha 2- and beta-adrenergic binding sites, respectively. Kinetic studies performed at different embryonic and post-hatching ages have shown one binding component for each one of the above radioactive ligands. The ontogeny of alpha 1, alpha 2 and beta binding sites was studied in cerebral hemispheres, optic lobes, brain stem and cerebellum. In all brain regions studied, the development of alpha 2 binding sites precedes that of alpha 1 and beta, and a very significant decrease of alpha 2 number was observed in the cerebellum, brain stem and optic lobes afterwards. The autoradiographic localization of adrenergic receptors was studied in the optic lobes and cerebellum. In the optic lobes the superficial layers of stratum griseum and fibrosum showed a strong selective labelling of alpha 1, alpha 2 and beta binding sites and the strong selective labelling of alpha 2 binding sites extended to the layer of stratum opticum. Among the nuclei located in the optic lobe only the nucleus mesencephalis lateralis pars dorsalis (MLD) exhibited a strong selective labelling for alpha 1 binding sites while, for beta binding sites, not only the MLD, but also the nucleus isthmic pars parvocellularis (Ipc) and the nucleus isthmic pars magnocellularisa (Imc) exhibited strong labelling. In the cerebellum strong selective labelling for alpha 1 and beta receptors was seen in the molecular layer. Labelling of the granule cell layer was almost equally strong for alpha 1 but significantly less for beta binding sites. No significant labelling could be detected for alpha 2 binding sites.     

Characterization of [125I]HEAT binding to alpha 1-receptors in human brain: assessment in aging and Alzheimer's disease

The binding of [125I]2-(beta-4-hydroxyphenylethylamino-ethyltetralone ([ 125I]HEAT), an alpha 1-adrenergic receptor antagonist, to human brain membranes was characterized and the binding assessed in tissue from subjects with Alzheimer's disease (AD) and aging controls. Under Na+-K+ phosphate buffer conditions, [125I]HEAT bound to a single class of binding sites in prefrontal cortex (Brodmann area 10) with a Kd of about 120 pM. High binding capacities of [125I]HEAT were evident in the hippocampus and neocortex but were low in subcortical areas and cerebral microvessels comparable to the regional distribution of [3H]prazosin binding reported previously. Displacement of [125I]HEAT by various adrenergic drugs was consistent with its binding to alpha 1-adrenergic receptors. The specific binding was not affected by postmortem delay between death and freezing of tissue at autopsy. There was no correlation of [125I]HEAT binding with age of subjects. In AD subjects, the binding was significantly decreased in prefrontal cortex by about 25% but not changed in hippocampus, putamen or cerebellum compared to age-matched controls. The reduced binding of [125I]HEAT in prefrontal cortex may reflect a region-specific change in alpha 1-adrenergic receptors associated with neuronal loss in AD.     

Laminar distribution of receptors in monkey (Macaca fascicularis) geniculostriate system

We have examined the laminar distributions of eight types of receptor in the primary visual cortex (area 17) and the lateral geniculate nucleus (LGN) of the macaque monkey. The receptor populations and subpopulations examined included those selective for gamma-aminobutyric acid (GABA) (using [3H]-muscimol as ligand), L-glutamate-related receptors (using [3H]-L-glutamate and [3H]-AMPA), muscarinic acetylcholine (using [3H]-quinuclidinyl benzilate--QNB and [3H]-N-methyl scopolamine--NMS), cholecystokinin (CCK) (using [3H] pentagastrin), benzodiazepine (using [3H]-flunitrazepam), and adenosine (using [3H]-cyclohexyladenosine--CHA). Each of the receptors examined exhibited characteristic and differing laminar patterns of binding in the striate cortex. Perhaps reflecting the high density of cell bodies and synapses in layer 4C, most receptors, except those labelled by [3H]-L-glutamate or [3H]-AMPA, showed dense concentrations in this layer. Layers 4B and 5, which contain relatively few cell bodies and heavy myelin concentrations, were in general lightly labelled. Layer 6 showed relatively heavy labelling when [3H]-AMPA (quisqualate) or [3H]-pentagastrin (CCK) were used as ligands. The superficial layers of the cortex were zones of relative concentration of GABA, benzodiazepine, acetylcholine, glutamate-related, and adenosine receptors. In general, the binding patterns resembled those previously described for cat visual cortex, but there were also some clear differences. The distributions of all of these receptors likely reflect the differential input substances to different laminae of the visual cortex. Of the receptors examined, only those for GABA, benzodiazepine, and acetylcholine were found in substantial concentration in the LGN. Of these, GABA and benzodiazepine receptors showed especially dense binding in the magnocellular layers of the LGN compared to the parvicellular layers.     

Expression of alpha-adrenoceptors in a human transformed lymphoblastoid cell line

The presence of alpha-adrenergic receptors (absent in normal lymphocytes) has been demonstrated in transformed human lymphocytes of the Raji cell line. Binding properties of beta-adrenergic receptors were similar to those reported for normal lymphocytes. A single population of alpha 2-adrenergic receptors was characterized in intact Raji lymphoblasts by binding and saturation assays with the alpha 2-adrenergic antagonist yohimbine. Competition curves with [3H]yohimbine indicate the presence of typical alpha 2-adrenoceptors. Reaction of Raji with the alpha 2-adrenergic agonist clonidine (10(-6) M) stimulated their growth rate. In contrast, the alpha 1-adrenergic agonist methoxamine (10(-6) M) had no effect. Previous work indicates that Raji can actively produce thromboxanes (TX) and that these decreased atrium contractility. In agreement with these results and with the binding studies, it is now shown that clonidine stimulation enhanced the negative inotropic effects of Raji on isolated rat atria. This reaction was prevented by incubation of Raji with yohimbine (10(-6) M) but not with the alpha 1-adrenergic antagonist prazosin (10(-6) M) or the beta-adrenergic antagonist propranolol (10(-7) M). The biologic effect of Raji on rat atria was probably due to production of cyclooxygenase metabolites of arachidonic acid, because it was blocked by preincubation of the cells with the cyclooxygenase inhibitors indomethacin (10(-6) M) and aspirin (10(-4) M) or the thromboxane synthetase inhibitors nictindol (10(-5) M) and imidazole (10(-4) M).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative distributions of dopamine D-1 and D-2 receptors in the cerebral cortex of rats, cats, and monkeys

The distributions and laminar densities of cerebral cortical dopamine D-1 and D-2 receptors were studied in rats, cats, and monkeys. Distributions were determined by using alternate, adjacent tissue sections processed for D-1 and D-2 receptor subtypes and compared to an adjacent, nearly adjacent, or similar sections stained for Nissl substance. [3H]-SCH 23390 and [3H]-spiroperidol (in the presence of 100 nM mianserin) were used to label the D-1 and D-2 receptors, respectively. The regional distribution and laminar density of dopamine receptors were determined by in vitro quantitative autoradiography and video densitometry of selected isocortical and peri-allocortical regions. Granular (prefrontal, primary somatosensory, and primary visual), agranular (primary motor and anterior cingulate), and limbic (entorhinal and perirhinal) cortices were examined. Where possible, homologous areas among the species were compared. The D-1 receptor was present in all regions and laminae of the cerebral cortex of rats, cats, and monkeys. The regional densities for the D-1 receptor were higher in the cat and monkey than in the rat. The rat D-1 receptor displayed a relatively homogeneous laminar pattern in most regions except that the deeper laminae (V and VI) contained more receptors than the superficial layers. The cats and monkeys, however, had distinctly heterogeneous laminar patterns in all regions of cortex that varied from one region to another and were quite different from that seen in the rat. The cats and monkeys had highest densities of the D-1 receptor in layers I and II and lowest densities in layers III and IV, whereas layers V and VI were intermediate. The density of D-1 receptors was greater than the density of D-2 receptors in all regions and laminae of cerebral cortex of the cat and monkey and greater in most regions and laminae of the rat cerebral cortex. The D-2 receptor was also distributed in all regions of the cerebral cortex of rats, cats, and monkeys. The D-2 receptor was very homogeneous in its regional distribution and laminar pattern compared to the D-1 receptor in all 3 species. The D-2 receptor was denser in the superficial layers (I and II) of the cortex than in the deeper layers in the rats, but more homogeneous in the different laminae of the cat and monkey cerebral cortex. The rat cortical D-2 receptor exceeded the D-1 receptor in restricted laminae of selective regions.(ABSTRACT TRUNCATED AT 400 WORDS)