No abstract

Extensive information has now accumulated on the neuronal organization of the brain's nitroxidergic systems. Increased interest from researchers in nitric oxide (NO) is largely due to its role in supporting a multitude of neuronal functions [2,5,6,8,12,17,21]. Knowledge of the distribution of NO-ergic neurons in the brain thus acquires particular importance. However, there is still no unified view as to the topography or the numbers of neurons expressing the enzyme NO synthase, especially the neuronal form of NO synthase (nNOS), which in physiological conditions has a role in NO synthesis in nerve cells [8,9,12].The locations of nNOS in the structural formations of the brain are often assessed in terms of the fact that they containing NADPH-diaphorase, as this is colocalized with nNOS in some neurons [11,[14][15][16]. Although results obtained by histochemical detection of NADPH-diaphorase and immunohistochemical detection of nNOS quite frequently do not agree [13,19,21], studies of the brain's NO-ergic systems have thus far made wide use of the histochemical reaction for NADPHdiaphorase.The aim of the present work was to undertake a comparative study of the topography and numbers of NADPHdiaphorase-and nNOS-positive neurons in several medulla oblongata nuclei in rats. MATERIALS AND METHODSExperiments were performed on Wistar rats (n = 8) weighing 240-280 g, kept in laboratory animal-house conditions on a standard diet. Experimental manipulations were performed in compliance with the requires of the "Regulations for Studies Using Experimental Animals" (USSR Ministry of Health Decree No. 755 of August 12, 1977). Animals were sacrificed by overdosage with 3% thiopental sodium. Brains were extracted from skull cavities, the medulla oblongata was separated and fixed for 1 h in 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.4) at 4°C, followed by preparation of sections of thickness 30 μm on a cryostat.NADPH-diaphorase was detected in neurons using the histochemical (HC) method of Hope and Vincent [16]. Reaction specificity was verified by incubating several secThe distribution of nitroxidergic neurons in the medulla oblongata nuclei in Wistar rats (n = 8) was studied using histochemical (NADPH-diaphorase) and immunohistochemical methods with antisera to the neuronal form of nitric oxide synthase (nNOS). NADPH-diaphorase was found in large and small neurons in the sensory, autonomic, and motor nuclei. The latter were found to contain particularly large numbers of neurons expression this enzyme activity. In contrast to NADPH-diaphorase, nNOS in the corresponding nuclei was always present in smaller quantities of mainly smaller neurons. The sensory nuclei (solitary tract nucleus, reticular parvocellular and lateral nuclei, spinal nucleus of the trigeminal nerve) showed 1.5-3 times more nNOS neurons than the motor nuclei. In some nuclei (the nucleus ambiguus, the nucleus of the hypoglossal nerve) containing large numbers of NADPH-diaphorase-positive neurons, immunoreactive cells were particularly rare.

The distribution of two enzymes involved in H(2)S synthesis, cystationine β-synthase (CBS) and cystationine γ-liase (CSE), was studied in the walls of the internal carotid artery, order I-V branches of the middle cerebral artery basin, and intracerebral vessels of adult Wistar rats. Immunohistochemical staining showed the presence of CBS in the endothelium of small pial arteries (order IV-V branches) and intracerebral arterioles and in the capillary walls, neurons, and vascular nerves. As for CSE, in the internal carotid artery and large (order I-II) pial branches it was found mainly in the tunica media myocytes, in order III-IV vessels in myocytes and endothelium, and in smaller pial and intracerebral vessels in the endothelium. Along with enzyme-positive vessels, many pial and intracerebral arteries contained no these enzymes in the walls.

The endothelium-dependent and myogenic reactions of pia mater arteries of the 1st-5th branching orders were studied in 1-, 3-, and 24-month-old rats by biomicroscopy method. The endothelium-independent (myogenic) reaction predominated in the 1st-3rd order branches and the endothelium-dependent vascular reaction in the 5th order branches of 3-month-old rats. Both regulatory mechanisms were equally developed in the 4th order branches. In 1-month-old rats, the endothelium-dependent reaction was more active in the majority of branches. In 24-month-old rats, this reaction was significantly higher than the endothelium-independent one only in the 4th and 5th order branches. In contrast to 3-month-old rats, the myogenic reaction of 24-month-old animals predominated in the 1st and 2nd order branches and the endothelium-dependent one in the 4th and 5th order branches. Vascular reactivity of 24-month-old rats was lower than in younger rats in all cases.

Pial arteries of different diameter were studied in intact rats and after 6-month modeling of chronic tobacco smoking in rats. Expression of tachykinin NK1 receptors in pial arteries was studied by biomicroscopy and immunohistochemical methods. Chronic tobacco smoking induced considerable reorganizations of the arterial bed. The intensity of changes depended on the diameter of vessels. In small pial vessels that directly participate in the blood supply to the brain, pronounced vasodilatation and enhanced expression of NK receptors in the endothelium mediating the effects of substance P were observed; the number of these vessels also increased. The intensity of the response to tobacco smoke components decreased with increasing vessel diameter.