Different pharmacological anatomy in the paraventricular hypothalamic nucleus, supraoptic nucleus, and suprachiasmatic nucleus of rats: quantitative autoradiography on angiotensin II receptor binding sites.

Angiotensin II (AII) and vasopressin (VP) play important roles in cardiovascular function. Using 125I-[Sar1,Ile8]-angiotensin II (125I-SI-AII), a potent AII antagonist, AII receptor binding sites were autoradiographically localized in three VP-producing areas of the hypothalamus and compared in hypertensive and normotensive rats. Within three major VP-producing areas, AII receptor binding was highest in the paraventricular hypothalamic nucleus and lowest in the supraoptic nucleus, suggesting that a differential AII regulation of separate VP systems exists in the brainstem. No statistical difference in 125I-SI-AII receptor binding was found between WKY and SHR rats in each of the three major VP-producing nuclei studied. These results are consistent with a role of AII receptors in a subtle and complicated regulation of VP in cardiovascular function.

Identification of sodium-dependent, high-affinity choline uptake sites in rat brain with [3H]hemicholinium-3.

[3H]Hemicholinium-3 (HC-3) was used to label sodium-dependent, high-affinity choline uptake sites in regions of rat brain. Autoradiography revealed a high density of [3H]HC-3 binding sites in brain regions with a high density of cholinergic terminals, such as the interpeduncular nucleus, caudate-putamen, and olfactory tubercle. This distribution of [3H]HC-3 binding sites was in close agreement with the amounts of choline acetyltransferase in specific nuclei and subregions of rat brain. Destruction of presynaptic cholinergic projections in the cerebral cortex and the basal ganglia by injection of excitotoxins reduced [3H]HC-3 binding by 40-50%. These data indicate that sodium-dependent [3H]HC-3 binding sites are related to the choline transport system present in cholinergic neurons.

Quantitative autoradiography of 125I-[Sar1, Ile8]-angiotensin II binding in the brain of spontaneously hypertensive rats.

The brain contains its own angiotensin II (AII) system. To better understand the role of central AII in cardiovascular regulation, we used 125I-[Sar1, Ile8]-AII (125I-SI-AII), radioactive AII antagonist, to autoradiographically localize putative AII receptor binding in many parts of the central nervous system of the spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. With 125I-SI-AII binding on brain membrane preparations. Scatchard analysis indicated that Kd values were from 0.10 +/- 0.04 nM to 0.13 +/- 0.05 nM, whereas Bmax values (femtomol/mg protein) were found to be from 6.95 +/- 1.60 to 15.52 +/- 4.99 among brain regions studied. Various SI-AII receptor binding activities among brain regions revealed in this study were therefore most likely due to differences in AII receptor density with high affinity binding of 125I-AII. Using 125I-SI-AII, specific binding for SI-AII was found in the nucleus tractus solitarius (NTS), paraventricular hypothalamic nucleus (PVN), subfornical organ (SFO), suprachiasmatic nucleus (SCN), area postrema, the dorsal motor nucleus of the vagus (DMX), and the nucleus of spinal tract of the trigeminal system (NSV). With quantitative receptor autoradiography in conjunction with radioactive standards, we have observed that the NTS possesses the highest SI-AII binding, followed by the PVN, SFO, NTS, DMX, and NSV. No significant differences were observed between the SHR and WKY rats in the SI-AII binding within the SFO, PVN and NTS. However, SHR at early hypertensive (7 weeks) and established hypertensive (16 weeks) stages contained significantly higher SI-AII bindings in the NSV, as compared to age-matched WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization in rat brain of binding sites for parkinsonian toxin MPTP: similarities with [3H]pargyline binding to monoamine oxidase.

A high-affinity binding site exists in rat brain for the parkinsonian toxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). The pharmacological specificity of this binding site suggests that it may correspond to monoamine oxidase (MAO). We have used quantitative autoradiography to map in detail the anatomical distribution of the [3H]MPTP binding site in rat brain and compared it with the anatomical distribution of MAO as determined by in vitro autoradiography with [3H]pargyline. Under the conditions of the assay, [3H]pargyline labeled the type B form of MAO. There were strong similarities in the anatomical distribution of [3H]MPTP and [3H]pargyline, with high levels of both binding sites occurring in the arcuate nucleus, the locus coeruleus, the dorsal raphe nucleus and all circumventricular organs. Low levels of both binding sites were found in the substantia nigra and the caudate-putamen. These results provide additional evidence that the high-affinity binding site for MPTP is MAO. The parkinsonian actions of MPTP might result from metabolites produced by MAO.

Localization of L-glutamate receptors in rat brain by quantitative autoradiography.

In vitro autoradiography was used to characterize and quantitatively map the sodium-independent binding of [3H]glutamate in rat brain. Measured in the presence of chloride, glutamate binding to frozen brain sections was specific, saturable, and reversible, with a Kd in the low micromolar range. At least two distinct binding sites were detected which had different affinities for quisqualic acid (0.7 microM and 1.2 mM). Autoradiograms revealed very high levels of binding in rostral forebrain areas, especially olfactory structures and frontal cortex. High levels of binding were found in sensory cortex, certain hippocampal subfields, caudate, lateral septum, and other limbic structures. Lowest levels were seen in globus pallidus, preoptic area, brainstem reticular formation, and spinal trigeminal nucleus. All other regions, including midbrain, thalamus, hypothalamus, and cerebellar cortex exhibited moderate levels of [3H]glutamate binding. Within the hippocampus glutamate binding was greatest in the inner two-thirds of the dentate molecular layer, subiculum, and CA1 stratum radiatum. CA3 was much less densely labeled; CA2 and CA4 were intermediate. Unlike cell layers in the cerebellum, hippocampal pyramidal and granule cell layers appeared mostly devoid of binding. The relationship of these binding sites to putative glutamate receptor subclasses and glutamatergic pathways is discussed.

Quantitative autoradiography of binding sites for [3H]AMPA, a structural analogue of glutamic acid.

Binding sites for the potent glutamate agonist [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were localized in rat brain frozen sections by quantitative autoradiography. Highest levels of binding were seen in stratum radiatum and stratum oriens of the CA1 hippocampal subfield and in the dorsal subiculum. Substantially less but still high amounts of [3H]AMPA binding occurred in other hippocampal subfields and in rostral forebrain structures. The heterogeneous nature of [3H]AMPA binding is discussed in relation to [3H]glutamate binding visualized by similar methods. From these data it is suggested that [3H]AMPA may label a particular subclass of the glutamate receptor population which exhibits a high affinity for quisqualic acid.

Localization and characterization by quantitative autoradiography of [125I]LSD binding sites in rat brain.

The binding of [125I]LSD in rat brain was characterized and localized by quantitative autoradiography. Frozen 32 microns thick brain sections were labeled in vitro with [125I]LSD and exposed for 24 h against LKB Ultrofilm to generate autoradiograms. Nonspecific binding was defined as the labelling in the presence of 1 microM D-LSD. Scatchard analysis by densitometry indicated that the binding of [125I]LSD was saturable, with a Kd of 0.2 nM. In agreement with the results of Hartig and co-workers [5,6], [125I]LSD showed a high affinity for 5-HT2 serotonin receptors with some overlap with D-2 dopamine receptors. High concentrations of [125I]LSD sites were observed in layer IV of the cerebral cortex, caudate-putamen, claustrum, olfactory tubercle, nucleus accumbens, ependyma, mammillary nucleus and inferior olive. Co-incubation of sections with sulpiride to block binding to D-2 receptors resulted in a uniform 20-30% reduction in the amount of specific [125I]LSD binding, with no qualitative difference in the pattern of labeling. However, co-incubation with ketanserin to block 5-HT2 receptors resulted in a pattern of binding that was similar to previous descriptions of the location of D-2 receptors, with high levels of residual binding in caudate-putamen, olfactory tubercle, nucleus accumbens and inferior olive. Our results indicate that [125I]LSD is a suitable ligand for quantitative autoradiography of both 5-HT2 and D-2 receptors, and that there is a strong anatomical correspondence between these receptor subtypes, perhaps implying a functional interaction.