ABSTRACT
Many distinct ganglion cell types, which are the output elements of the retina, were found to encode for specific features of a visual scene such as contrast, color information or movement. The detailed composition of retinal circuits leading to this tuning of retinal ganglion cells, however, is apart from some prominent examples, largely unknown. Here we aimed to investigate if ganglion cell types in the mouse retina receive selective input from specific bipolar cell types or if they sample their synaptic input non-selectively from all bipolar cell types stratifying within their dendritic tree. To address this question we took an anatomical approach and immunolabeled retinae of two transgenic mouse lines (GFP-O and JAM-B) with markers for ribbon synapses and type 2 bipolar cells. We morphologically identified all green fluorescent protein (GFP)-expressing ganglion cell types, which co-stratified with type 2 bipolar cells and assessed the total number of bipolar input synapses and the proportion of synapses deriving from type 2 bipolar cells. Only JAM-B ganglion cells received synaptic input preferentially from bipolar cell types other than type 2 bipolar cells whereas the other analyzed ganglion cell types sampled their bipolar input most likely from all bipolar cell terminals within their dendritic arbor.
Subject(s)
Retina/cytology , Retinal Bipolar Cells/physiology , Retinal Ganglion Cells/classification , Retinal Ganglion Cells/physiology , Visual Pathways/physiology , Alcohol Oxidoreductases , Animals , Calbindin 2/metabolism , Co-Repressor Proteins , Computer Simulation , DNA-Binding Proteins/metabolism , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Mice , Mice, Transgenic , Microscopy, Confocal , Models, Neurological , Osteopontin/metabolism , Phosphoproteins/metabolism , Retinal Bipolar Cells/metabolism , Retinal Bipolar Cells/ultrastructure , Retinal Ganglion Cells/metabolism , Synaptotagmin II/metabolism , Thy-1 Antigens/geneticsABSTRACT
In male heterozygous transgenic hypertensive rats, TGR(mREN2)27 (TGR), exhibiting an inverse blood pressure profile and in normotensive Sprague-Dawley (SPRD) controls, the density and affinity of angiotensin II receptors were determined at six circadian times in glomeruli of animals 11 weeks old kept under light-dark 12h:12 (LD 12:12) conditions. Angiotensin II receptors were also studied in rats 18-20 weeks old of both strains at 2h after light onset. As a measure of renal excretory functions, diuresis, creatinine, and protein excretion were monitored using metabolic cages. The expression of angiotensin II receptor mRNA was determined in renal arteries 2h-4h after light onset. The following results were obtained: (1) Renal excretory functions showed significant daily variation, with higher excretion rates in the dark span in both TGR and SPRD rats. (2) No circadian phase dependency was found in the glomerular angiotensin II receptors in both rat strains. However, receptor density was significantly lower in TGR than in SPRD rats. In both strains, receptor number increased with aging. (3) In renal arteries, the angiotensin II receptor mRNA of the main receptor subtype AT1A was neither strain nor age dependent, AT1B- and AT2-receptor mRNAs were significantly lower in TGR than SPRD rats. In conclusion, the results demonstrate that the overactive renin-angiotensin system in TGR rats led to a down-regulation of glomerular angiotensin II receptors that was not accompanied by a down-regulation of the mRNA of the dominant AT1A- receptor subtype. Circadian short-term variations in blood pressure in both TGR and SPRD rats are not reflected by daily variation in angiotensin II receptor density of renal glomeruli or by variation in receptor expression in renal vascular tissue.
Subject(s)
Circadian Rhythm , Glomerular Mesangium/metabolism , Hypertension/genetics , Receptors, Angiotensin/genetics , Receptors, Angiotensin/metabolism , Age Factors , Animals , Animals, Genetically Modified , Heterozygote , Hypertension/physiopathology , Kidney/metabolism , Male , RNA, Messenger/metabolism , Rats , Rats, Sprague-Dawley , Time FactorsABSTRACT
It is still a controversial issue whether different classes of antihypertensive drugs are equally effective in the regression of cardiac hypertrophy and associated complications. The present study compared the effects of prolonged treatment with the Ca2+-channel blocker amlodipine and the ACE inhibitor enalapril, respectively, in TGR(mREN2)27 rats (TGR), an animal model of renin-dependent hypertension. TGR were divided into three groups and received either amlodipine, enalapril or drinking water without addition, Sprague-Dawley rats (SPRD) served as normotensive control group. Cardiovascular parameters were monitored by radiotelemetry, and drug doses were titrated until 24-h blood pressure was reduced to approximately 140/90 mmHg in both active treatment groups. After 8 weeks of treatment left ventricular (LV) hypertrophy was completely reversed in both treatment groups despite a tenfold increase in plasma angiotensin II in amlodipine-treated TGR. In untreated TGR LV catecholamines were depleted, and beta1-adrenergic stimulation of adenylyl cyclase was blunted. Treatment of TGR with enalapril prevented both the depletion of tissue catecholamines and the desensitisation of LV beta1-adrenoceptors. Amlodipine had no effect on cardiac adrenergic signal transduction. Basal activity of LV soluble guanylyl cyclase was not different between TGR and SPRD, but its sensitivity to stimulation by nitric oxide was slightly reduced in TGR. Treatment had no effect on basal and stimulated guanylyl cyclase activity. The present study in an animal model of renin-dependent hypertension suggests that blood pressure reduction per se is sufficient for a regression of cardiac hypertrophy. However, beta-adrenergic desensitisation was prevented only in the enalapril-treated group, supporting a blood pressure-independent contribution of the renin-angiotensin system to the regulation of beta-adrenergic signal transduction.
Subject(s)
Amlodipine/pharmacology , Angiotensin-Converting Enzyme Inhibitors/pharmacology , Blood Pressure/drug effects , Calcium Channel Blockers/pharmacology , Enalapril/pharmacology , Hypertension/physiopathology , Adenylyl Cyclases/drug effects , Adenylyl Cyclases/metabolism , Analysis of Variance , Animals , Animals, Genetically Modified , Diastole , Guanylate Cyclase/drug effects , Guanylate Cyclase/metabolism , Heart Rate/drug effects , Heart Ventricles/drug effects , Heart Ventricles/metabolism , Heart Ventricles/pathology , Hypertension/genetics , Hypertrophy , Male , Mice , Rats , Rats, Sprague-Dawley , Receptors, Adrenergic, beta/drug effects , Receptors, Adrenergic, beta/metabolism , Renin/genetics , Signal Transduction/drug effects , Solubility , SystoleABSTRACT
Soluble guanylyl cyclase activity and its stimulation by diethylamineNONOate was measured in aortae from hypertensive TGR(mREN2)27 rats (TGR) and Sprague-Dawley controls. Superoxide dismutase was added in vitro to evaluate the contribution of oxidative breakdown of nitric oxide (NO) by superoxide anions. Expression of soluble guanylyl cyclase was assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). Basal and stimulated soluble guanylyl cyclase activity was significantly reduced in TGR rats, addition of superoxide dismutase had no effect. Expression of soluble guanylyl cyclase subunits was not different between strains. The independent contribution of hypertension and the overactive renin-angiotensin system to soluble guanylyl cyclase subsensitivity was assessed after normalization of TGR's blood pressure by the Ca(2+)-channel blocker amlodipine or the angiotensin converting enzyme-inhibitor enalapril. Soluble guanylyl cyclase activity in TGR was slightly increased by amlodipine and almost completely restored by enalapril. In conclusion, TGR showed desensitized vascular soluble guanylyl cyclase, depending on their overactive renin-angiotensin system.
