Immunocytochemical characterization of quisqualic acid- and N-methyl-D-aspartate-induced excitotoxicity in the retina of chicks.

A single, large dose of N-methyl-D-aspartate (NMDA) or quisqualic acid (QA) injected into the chick eye has been shown previously to destroy many retinal amacrine cells and to induce excessive ocular growth accompanied by myopia. The purpose of this study was to identify distinct populations of retinal cells, particularly those believed to be involved in regulating ocular growth, that are sensitive to NMDA or QA. Two pmol of NMDA or 0.2 micromol of QA were injected unilaterally into eyes of 7-day-old chicks, and retinas were prepared for observation 1, 3, or 7 days later. Retinal neurons were identified by using immunocytochemistry, and cells containing fragmented DNA were identified by 3'-nick-end labelling in frozen sections. NMDA and QA destroyed many amacrine cells, including those immunoreactive for vasoactive intestinal polypeptide, Met-enkephalin, and choline acetyltransferase, but they had little effect upon tyrosine hydroxylase-immunoreactive cells. Other cells affected by both QA and NMDA included those immunoreactive for glutamic acid decarboxylase, gamma-aminobutyric acid, parvalbumin, serotonin, and aminohydroxy methylisoxazole propionic acid (AMPA) receptor subunits GluR1 and GluR2/3. Cells largely unaffected by QA or NMDA included bipolar cells immunoreactive for protein kinase C (alpha and beta isoforms) and amacrine cells immunoreactive for glucagon. DNA fragmentation was detected maximally in many amacrine cells and in some bipolar cells 1 day after exposure to QA or NMDA. We propose that excitotoxicity caused by QA and NMDA induces apoptosis in specific populations of amacrine cells and that these actions are responsible for the ocular growth-specific effects of QA and NMDA reported elsewhere.

Receptor subtypes mediating renal actions of calcitonin gene-related peptide.

We previously reported that the renal arterial infusions of non-hypotensive doses of calcitonin gene-related peptide (CGRP) caused renal vasodilatation and increases in glomerular filtration rate at a low dose, but renal vasoconstriction, natriuresis and kaliuresis at a high dose. In the present study, we examined the effects of the specific CGRP1 receptor antagonist (CGRP-(8-37) (1 and 10 nmol/kg) and the putative CGRP receptor antagonist, [Tyr(0)]CGRP-(28-37)(3 and 30 nmol/kg), on the renal vascular and tubular effects of CGRP in inactin-anaesthetized Sprague-Dawley rats. Renal arterial infusion of single doses of CGRP (0.3-300 pmol/kg per min) did not significantly alter mean arterial pressure or heart rate. However, during the continuous renal arterial infusion of either CGRP-(8-37) or [Tyr(0)CGRP-(28-37) incompletely inhibited the vasoconstriction but did not inhibit diuresis, natriuresis and kaliuresis elicited by a high but non-hypotensive dose of CGRP. On the basis that CGRP-(8-37) is a competitive CGRP1 receptor antagonist, our results suggest: (1) the renal vascular effect of CGRP is completely mediated via the activation of CGRP1 receptors, (2) the renal tubular effects of CGRP are not mediated via CGRP1 receptors, and (3) [Tyr(0)]CGRP-(28-37) is a CGRP1 receptor antagonist with potency and efficacy less than those of CGRP-(8-37).

Effects of calcitonin gene-related peptide receptor antagonists on renal actions of adrenomedullin.

1. Adrenomedullin is a novel vasoactive peptide which is produced in the lungs, ventricle, kidneys, heart and adrenal medulla. Adrenomedullin shows homology to calcitonin gene-related peptide (CGRP) and has similar pharmacological actions to CGRP. 2. This study examined the dose-response effects of adrenomedullin (rat, 11-50) on mean arterial pressure (MAP), heart rate (HR), renal blood flow (RBF), glomerular filtration rate (GFR) and renal tubular electrolyte excretion in Inactin-anaesthetized Sprague Dawley rats. The possible involvement of CGRP receptors in actions of adrenomedullin was also examined via renal arterial injection of a CGRP receptor antagonist, CGRP (8-37) (1 or 10 nmol kg-1) or [Tyr0]CGRP(28-37) (3 or 30 nmol kg-1), starting 15 min prior to the administration of adrenomedullin. 3. Renal arterial infusion (0.001 to 1 nmol kg-1) of adrenomedullin did not alter MAP, HR and renal K+ excretion but dose-dependently increased RBF and arterial conductance, GFR, urine flow and Na+ excretion. 4. The renal actions of adrenomedullin were not blocked by either the low or the high dose of CGRP(8-37) or [Tyr0]CGRP(28-37). 5. The results show that adrenomedullin causes renal vasodilatation, increments in GFR, diuresis and natriuresis. The renal actions of adrenomedullin are not mediated via the activation of CGRP1 receptors.