Increased density of fluorescent adrenergic fibers around the middle cerebral arteries of stroke-prone spontaneously hypertensive rats

The effect of steady-state CO2 on regional brain blood flow responses to increases in blood pressure via the cold pressor test

The pressure-passive cerebrovasculature is affected by alterations in cerebral perfusion pressure (CPP) and arterial blood gases (e.g., pressure of arterial [Pa]CO₂), where acute changes in either stimulus can influence cerebral blood flow (CBF). The effect of superimposed increases in CPP at different levels of steady-state PaCO₂ on regional CBF regulation is unclear. In 17 healthy participants, we simultaneously recorded continuous heart rate (electrocardiogram), blood pressure (finometer), pressure of end-tidal CO₂ (P_ETCO₂; gas analyzer), and middle (MCA) and posterior (PCA) cerebral artery blood velocity (CBV; transcranial Doppler ultrasound). Three separate CPTs were administered by passive immersion of both feet into 0-1 °C of ice water for 3-min under three randomized and coached steady-state P_ETCO₂ conditions: normocapnia (room air), hypocapnia (-10 Torr; hyperventilation) and hypercapnia (+9 Torr; 5% inspired CO₂;). CBV responses were calculated as the absolute difference (∆) between baseline and mean MCAv and PCAv during the 3-min CPT. Both the ∆MCAv and ∆PCAv responses to the CPT were larger under hypercapnic conditions. The absolute ∆MCAv response was larger than the ∆PCAv during the CPT across all three CO₂ trials. Cerebrovascular CO₂ reactivity (CVR) was larger in the MCA than PCA in both CPT and baseline conditions, but there were no differences in CVR between CPT and baseline conditions. Our data indicate that (a) increases in CO₂ increases the CBV responses to a CPT, (b) the anterior cerebrovasculature is more responsive to a CPT-induced increases in MAP, and (c) although unchanged during a CPT, CVR is larger in the anterior cerebral circulation.

Age-related changes in the sympathetic innervation of cerebral vessels and in carotid vascular responses to norepinephrine in the rat: in vitro and in vivo studies

We hypothesized that the density of sympathetic noradrenergic innervation of cerebral arteries and vasoconstrictor responses evoked in carotid circulation by norepinephrine (NE) increase with maturation and age. In rats of 4-5, 10-12, and 42-44 wk of age (juvenile, mature, middle aged), glyoxylic acid applied to stretch preparations showed the density of noradrenergic nerves in basilar and middle cerebral arteries was greater in mature than juvenile or middle-aged rats. In anesthetized rats, infusion of NE (2.5 mug/kg iv) increased mean arterial pressure (ABP) to approximately 180 mmHg in mature and middle-aged but to only approximately 150 mmHg in juveniles rats. Concomitantly, carotid blood flow (CBF) decreased in mature and middle-aged rats but remained constant in juveniles because carotid vascular conductance (CVC) decreased more in mature and middle-aged than juvenile rats. We also hypothesized that nitric oxide (NO) blunts cerebral vasoconstrictor responses to NE. Inhibition of NO synthase with l-NAME (10 mg/kg iv) induced similar increases in baseline ABP in each group, but larger decreases in CVC and CBF in mature and middle-aged than juvenile rats. Thereafter, the NE-evoked increase in ABP was similar in juvenile and mature but accentuated in middle-aged rats. Concomitantly, NE decreased CVC in juvenile and mature, but not middle-aged rats; in them, CBF increased. Thus, in juvenile rats, sparse noradrenergic innervation of cerebral arteries is associated with weak NE-evoked pressor responses and weak carotid vasoconstriction that allows autoregulation of CBF. Cerebral artery innervation density increases with maturation but lessens by middle age. Meanwhile, NE-evoked pressor responses and carotid vasoconstriction are stronger in mature and middle-aged rats, such that CBF falls despite the evoked increase in ABP. We propose that in juvenile and mature rats, NO does not modulate NE-evoked pressor responses, cerebral vasoconstriction, or CBF autoregulation, but by middle age, NO limits pressor responses and prevents breakthrough of CBF in the upper part of the autoregulatory range.

Arterial sympathetic innervation and cerebrovascular diseases in original rat models

The role of the arterial sympathetic innervation in cerebrovascular pathology was investigated in new experimental models using Brown Norway (BN) and Long-Evans (LE) rats. The BN rat is susceptible to intracerebral hemorrhage (ICH) within the cerebral cortex when rendered hypertensive whereas the LE rat is prone to cerebral aneurysms (CAs) in arteries of the circle of Willis with hypertension and carotid ligation. Noradrenaline (NA) content, determined by high performance liquid chromatography (HPLC), was lower both in the caudal and cerebral arteries in the BN than in the LE rat. Denervation of cerebral arteries by superior cervical ganglionectomy did not increase ICH lesion incidence in BN hypertensive rats. A possible link between the level of caudal artery NA content and the occurrence of ICH lesions and CAs was studied in rats from two distinct BNXLE crosses: back-cross (BC) rats (F1XBN) and F2 rats (F1XF1) which respectively display, with hypertension and carotid ligation, a high incidence of either ICH lesions or CAs. In BC rats, the level of caudal artery NA content was not related to ICH lesion occurrence. However, in F2 rats a low caudal artery NA content was associated with a high incidence of ruptured CAs. Thus, a low arterial sympathetic innervation may participate in mechanisms leading to rupture of CAs.

Participation of endothelial cells and transformed mesangial cells in remodeling of glomerular capillary loops in Thy-1 nephritis

The relationship between mesangial cells (MC) and endothelial cells (EC) in the remodeling of glomerular capillary loops was investigated in a rat model of anti-Thy-1 antibody (Ab)-induced glomerulonephritis. Immunohistochemical analysis showed that cells positive for alpha-smooth muscle actin (alpha-SMA) appeared in the mesangial stalks at day three, and had increased in number at day seven, after injection of Thy-1 Ab. Double staining for alpha-SMA and proliferating cell nuclear antigen (PCNA) showed that some MC expressing PCNA were negative for alpha-SMA at day three, but by day seven almost all PCNA-positive MC expressed alpha-SMA. Western blotting for alpha-SMA from isolated glomeruli was negative at day one after injection of Thy-1 Ab, but positive at day seven. Type III collagen appeared at day seven, followed by an increase of EC in the capillary loops, as determined by double immunofluorescent staining for rat endothelial cell antigen-1 (RECA-1) and type III collagen. RECA-1-positive cells increased rapidly in number after day seven and eventually showed the same distribution pattern as that in control rats. Both type I and type III collagens were expressed in the mesangial and the ballooning area of the glomerulus at day seven. Electron microscopy revealed that immature MC and EC forming small capillary lumina appeared in the enlarged mesangial area at day seven. In accordance with the increase of capillaries and the enlargement of the lumina, the number of MC and the amount of mesangial matrix decreased gradually, and most of the glomeruli returned to a normal structure by week 4. These data show that type I and type III collagen produced by transformed MC may be of benefit to proliferation of EC and remodeling of the capillary in Thy-1-induced nephritis.

Sympathetic and sensory axons invade the brains of nerve growth factor transgenic mice in the absence of p75NTR expression

Collateral sprouting, a nerve growth factor (NGF)-mediated growth response of undamaged peripheral axons, can be divided into reparative and aberrant axonal growth. We have previously shown that aberrant growth occurs in transgenic mice overexpressing NGF centrally under the control of the glial fibrillary acidic protein promoter. Both sympathetic and sensory fibers, stained immunohistochemically for tyrosine hydroxylase and calcitonin gene-related peptide, respectively, invade the cerebellum of postnatal transgenic mice, whereas no such axons are seen in age-matched wild-type cerebellum. Recent examination of mice possessing a null mutation for p75NTR has suggested that axon growth may be influenced by the functional expression of this receptor. To address the potential role of p75NTR in axon growth, we have generated a new line of hybrid mice overexpressing NGF but lacking functional p75NTR expression. Postnatal (day 14) hybrid cerebellum possessed fewer aberrant sensory and sympathetic fibers compared to their age-matched transgenic counterparts. By adulthood, however, hybrid cerebellum displayed a robust plexus of axons stained immunohistochemically for calcitonin gene-related peptide and tyrosine hydroxylase. No neuronal or nonneuronal localization of p75NTR-immunoreactive elements was observed in postnatal and adult hybrid cerebellum. Interestingly, sympathetic axons within the hybrid cerebellum displayed a markedly reduced axon density and staining intensity for NGF, suggesting a possible alteration in axonal sequestration of NGF. These results show that p75NTR is not vital for new growth of NGF-sensitive sympathetic and sensory axons and that immunohistochemical detection of NGF at sympathetic axons requires the functional expression of p75NTR.

Noradrenergic hyperinnervation may inhibit necrosis of coronary arterial smooth muscle cells in stroke-prone spontaneously hypertensive rats

Noradrenergic (NA) nerve fibre distribution and vascular smooth muscle morphology were investigated in the coronary artery of stroke-prone spontaneously hypertensive rats (SHRSP). Fluorescent NA nerve fibres of SHRSP aged 10, 30, 60, 90 and 180 days were examined by the glyoxylic acid method and compared with those of age-matched normotensive Wistar Kyoto (WKY) rats. The distribution densities of NA nerve fibres were measured by quantitative image analysis using the Interactive Bildanalyse System. The densities of NA nerve fibres of the left coronary artery of SHRSP were significantly higher than those of WKY rats at all ages examined. NA hyperinnervation in the coronary artery of SHRSP may be caused by the hyperfunction of the stellate ganglia which innervate the coronary arteries. Scanning electron microscopy observations showed that the surface of smooth muscle cells of the left coronary artery in SHRSP was smooth and similar to that of WKY rats at 120 days of age, but was slightly modified by more invaginations and projections than that in WKY rats at 180 days of age. No necrotic cells, however, were found in SHRSP. By transmission electron microscopy the smooth muscle cells in SHRSP were shown to be irregular in profile with deep indentations of the plasma membrane and surrounded by many layers of basal laminalike material, but no necrotic cells were found. We suggest that NA hyperinnervation protects the vascular smooth muscle cells from necrosis in the coronary artery of SHRSP by a trophic effect mediated by NA nerve fibres.

Noradrenergic hyperinnervation in the caval vein of stroke-prone spontaneously hypertensive rats

1. The distribution of fluorescent noradrenergic (NA) nerve fibres in the caval vein, which originate from the coeliac ganglion, was examined by glyoxylic acid method in stroke-prone spontaneously hypertensive rats (SHRSP) aged 10, 30, 60, 90 and 180 days. The results were compared with those in age-matched normotensive Wistar Kyoto (WKY) rats. 2. The distribution pattern of NA nerve fibres in the caval vein in both strains changed from a meshwork pattern at 10 days of age to a wavelike line arrangement after 30 days of age. 3. The densities of NA fibres of the caval veins in SHRSP were significantly higher (P < 0.01, Student's t-test, 6 d.f.) than those of WKY at all ages examined. The difference in NA fibre density between SHRSP and WKY showed double peaks at 10 and 90 days of age. 4. The present study suggests that hyperinnervation of the caval vein based on the hyperfunction of the coeliac ganglion is an important factor in the development of hypertension and also may participate in increasing cardiac output because the heart of SHR causes marked hypertrophy from 90 days of age.

Noradrenergic hyperinnervation in the heart of stroke-prone spontaneously hypertensive rats

1. Noradrenergic (NA) nerve fibre distribution was investigated in the epicardium and myocardium of the heart in stroke-prone spontaneously hypertensive rats (SHRSP) and was compared to that in normotensive Wistar-Kyoto (WKY) rats. Fluorescent NA nerve fibres in the left and right epicardium of both strains aged 10, 30, 60, 90 and 180 days, and in the myocardium of left and right ventricles and the ventricular septum of both strains aged 30, 90 and 180 days were examined by the glyoxylic acid method. The distribution densities of NA nerve fibres were measured by quantitative image analysis. 2. The distribution pattern of NA nerve fibres in the epicardium of both strains showed a constant meshwork pattern throughout the entire examination period. 3. In the myocardium, NA nerve fibres were distributed irregularly between myocytes of both strains in all ages examined. 4. The densities of NA nerve fibres in the epicardium of SHRSP were significantly higher (P < 0.01 and 0.05; Student's t-test, 6 d.f.) than those of WKY at all ages examined except left epicardium at 90 days of age. 5. The densities in the right myocardium in 30 and 90 day old SHRSP were significantly higher (P < 0.05; Student's t-test, 6 d.f.) than those of WKY. 6. NA hyperinnervation in the epicardium and the myocardium of SHRSP may be assumed to be caused by the hyperfunction of the stellate ganglia which innervate the heart and may give rise to hypertrophy of the heart in SHRSP by a trophic effect of NA nerve fibre.

Sympathetic hyperinnervation protects vascular smooth muscle cells from necrosis in stroke-prone spontaneously hypertensive rats

Sympathetic nerve fiber distribution and vascular smooth muscle morphology were investigated in the ophthalmic artery of stroke-prone spontaneously hypertensive rats (SHRSP) and were compared with those of normotensive Wistar Kyoto (WKY) rats at the age of 120 days. The distribution of fluorescent noradrenergic (NA) nerve fibers was examined by the glyoxylic acid method. The ophthalmic artery was divided into two portions according to the size of the outer diameter, that is into a proximal portion (above 100 microns) and a distal portion (30-70 microns). The distribution densities of noradrenergic nerve fibers were measured by quantitative image analysis using the Interactive Bild-Analyse System (IBAS). The distribution densities of NA nerve fibers in both portions of the ophthalmic artery were significantly higher (p < 0.01) in SHRSP than that in WKY rats. The difference in the density of NA fibers of the ophthalmic arteries between SHRSP and WKY rats was 1.9 times in the proximal portion and 1.5 times in the distal portion. The vascular smooth muscle cells of the ophthalmic arteries in SHRSP were observed by scanning electron microscope to examine the trophic effect of NA nerve fibers on the vascular smooth muscle cells. The smooth muscle cells of both portions of the ophthalmic arteries in SHRSP showed a smooth surface texture and no necrosis, and were very similar to those of WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)