Computer-assisted image analysis to quantify regional and specific receptor ligand binding: upregulation of [3H]QNB and [3H]WB4101 binding in denervated hippocampus

Differential regulation of expression of rat hippocampal muscarinic receptor subtypes following fimbria-fornix lesion

Quantitative RNase protection assays were performed to determine the levels of muscarinic receptor subtype (m1-m5) mRNAs in rat hippocampi. Results showed that the m1, m3, and m4 subtype mRNAs were expressed at relatively high levels, but the levels of the m2 and m5 subtype were very low. Three weeks following aspiration lesions of the fimbria-fornix to produce cholinergic denervation of the hippocampus, non-M1 receptors (non-pirenzepine displaceable [3H]quinuclindinyl benzilate binding sites) in the hippocampus were increased significantly, which correlated with increases in the levels of hippocampal m3 and m4 receptor mRNAs (m3: +24% and m4: +41%). These findings indicate that multiple muscarinic receptor subtypes are expressed in the hippocampus with the m3 and m4 subtypes predominantly postsynaptic to the septohippocampal cholinergic terminals.

Effect of vinconate against regional age-related changes in the gerbil brain

We investigated age-related changes in the binding sites of muscarinic acetylcholine, forskolin, adenosine 3',5'-cyclic monophosphate (cAMP), and of a voltage-dependent L-type calcium channel blocker in the gerbil brain using receptor autoradiography. [3H]Quinuclidinyl benzilate (QNB), [3H]forskolin, [3H]cAMP, and [3H]PN200-110 were used to label muscarinic receptors, adenylate cyclase, cAMP-dependent protein kinase, and L-type calcium channels, respectively. In middle-aged animals (16-month-old gerbils), [3H]QNB, [3H]PN200-110, [3H]forskolin, and [3H]cAMP binding sites were elevated in the hippocampal region compared with that of young gerbils (4 weeks old). Further, a significant elevation in [3H]forskolin binding was seen in the nucleus accumbens. In contrast, [3H]QNB, [3H]PN200-110, and [3H]forskolin binding sites were reduced in the cerebellum, neocortex and thalamus, and hypothalamus in middle-aged animals, respectively. [3H]cAMP binding was not altered in other regions except for an elevation in the hippocampus. Thus, the age-related alterations in receptor binding may proceed by different mechanisms in various brain regions. Chronic vinconate treatment partly modulated the age-related alterations in [3H]QNB, [3H]forskolin, and [3H]cAMP binding in the hippocampus, but not that of [3H]PN200-110. Vinconate also regulated the age-related changes in [3H]forskolin binding in the nucleus accumbens. These results indicate that the age-related alterations in the binding sites of muscarinic acetylcholine, forskolin, cAMP, and L-type calcium channel blocker occur in particular in the hippocampus. Further, they suggest that a novel vinca alkaloid derivative, vinconate, can partly modulate age-related changes in these binding sites.

Muscarinic desensitization after septal lesions in rat hippocampus: evidence for the involvement of G-proteins

Three days after bilateral septal lesions, regional and laminar densities of the muscarinic acetylcholine receptors of the dorsal rat hippocampus were studied. The concentration of [3H]N-methylscopolamine binding sites and muscarinic M1 and M2 receptor subtypes, as well as the affinity of muscarinic receptors and their sensitivity to modulation by 5-guanylylimidodiphosphate were analysed by quantitative receptor autoradiography. The measurement of these parameters was performed with a computerized image-processing system allowing a spatial resolution down to the level of single hippocampal layers. No postlesional changes of the density of M1 receptors were detected. M2 receptors showed a remarkable decrease in concentration (less than 21%) in some hippocampal layers after septal lesions. In competition experiments the affinity of muscarinic receptors for the cholinergic agonist carbamylcholine chloride decreased significantly in all hippocampal subregions and layers of the lesioned animals. In contrast to controls, the sensitivity of muscarinic receptors of the lesioned animals could not be modulated by 5-guanylylimidodiphosphate. These findings demonstrate a desensitization of muscarinic receptors in the rat hippocampus three days after septal lesions, which is caused by changes of the coupling of guanine nucleotide-binding proteins to muscarinic receptors. Therefore, the lesion-induced alteration of the muscarinic receptor-effector complex is a major aspect of the hippocampal plasticity after cholinergic denervation.

Functional muscarinic supersensitivity in denervated rat hippocampus

The effects of carbachol (CCh), a cholinergic agonist, were compared in voltage-clamped hippocampal pyramidal neurons in vitro, obtained from normal and fimbria-fornix-lesioned rats. A substantial increase in sensitivity to the effects of CCh was seen in denervated neurons. The supersensitivity was demonstrated on both the inward leak current and the calcium-dependent potassium current, IAHP. These findings provide convincing evidence for cholinergic denervation supersensitivity in the hippocampus.

Quantitative immunocytochemistry using an image analyzer. I. Hardware evaluation, image processing, and data analysis

In this review we describe how video-based image analysis systems are used to measure immunocytochemically labeled tissue. The general principles underlying hardware and software procedures are emphasized. First, the characteristics of image analyzers are described, including the densitometric measure, spatial resolution, gray scale resolution, dynamic range, and acquisition and processing speed. The errors produced by these instruments are described and methods for correcting or reducing the errors are discussed. Methods for evaluating image analyzers are also presented, including spatial resolution, photometric transfer function, short- and long-term temporal variability, and measurement error. The procedures used to measure immunocytochemically labeled cells and fibers are then described. Immunoreactive profiles are imaged and enhanced using an edge sharpening operator and then extracted using segmentation, a procedure which captures all labeled profiles above a threshold gray level. Binary operators, including erosion and dilation, are applied to separate objects and to remove artifacts. The software then automatically measures the geometry and optical density of the extracted profiles. The procedures are rapid and efficient methods for measuring simultaneously the position, geometry, and labeling intensity of immunocytochemically labeled tissue, including cells, fibers, and whole fields. A companion paper describes non-biological standards we have developed to estimate antigen concentration from the optical density produced by antibody labeling (Nabors et al., 1988).

Regional analysis of age-related changes in the cholinergic system of the hippocampal formation and basal forebrain of the rat

In an attempt to clarify conflicting reports of age-related changes in cholinergic systems of the rat hippocampal formation and basal forebrain, we compared aged (40 months) and adult (12 months) male rats using quantitative, regional receptor autoradiography in addition to radiolabelled assays of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE). The activities of ChAT and AChE in Ammon's horn/subiculum are 24% and 38% lower, respectively, in the aged brains. There is also a drop in both ChAT (38%) and AChE (28%) activities in the septum, and a 46% drop in ChAT activity in the nucleus basalis of aged rats. In the septal pole of the hippocampal formation there is no significant change with age in binding of the muscarinic antagonist, tritiated quinuclidinyl benzylate (3H-QNB) in any hippocampal subregion. However, specific binding in the temporal pole is higher in the subiculum (40%), CA (27%), and dentate gyrus (25%) of the aged animals. Because some of the neurons of the diagonal band of Broca project to the temporal areas of the hippocampal formation by way of a ventral pathway, it is possible that with age this septohippocampal pathway is selectively affected. Particularly in Ammon's horn and the subicular regions of the aged rat hippocampus, postsynaptic muscarinic receptors may upregulate to compensate for decreases in presynaptic cholinergic activity.

Intrahippocampal injections of antiserum to nerve growth factor inhibit sympathohippocampal sprouting

Following lesions of the fimbria/fornix system in the rat, noradrenergic sympathetic fibers grow into the hippocampal formation. It has been postulated that these fibers collateralize in response to the presence of a neurotrophic substance similar to Nerve Growth Factor (NGF). We tested this by injecting into the rat hippocampus antibody to NGF, or control serum (contralateral control), immediately prior to a bilateral fimbria/fornix transection. In fluorescent histochemical preparations at four to five weeks following surgery, there are fewer large, brightly fluorescent fibers around the injection site on the experimental side when compared with the contralateral control side. These results support the hypothesis that NGF, or an NGF-like substance, plays an important role in the sprouting of sympathetic fibers into the denervated hippocampal formation.