Cytoarchitectonic analysis of Fos-immunoreactivity in brainstem neurones following visceral stimuli in conscious rats.

Visceral inputs to the brain make their initial synapses within the nucleus of the solitary tract (NTS), where information is relayed to other brain regions. These inputs relate to markedly different physiological functions and provide a tool for investigating the topography of visceral processing in brainstem nuclei. Therefore, Fos immunoreactivity was used to determine whether a gastric stimulus affects neurones within different or similar parts of the NTS, ventrolateral medulla (VLM) and parabrachial nucleus (PBN), compared to a baroreceptive stimulus. The contribution of catecholaminergic neurones in these areas was studied by combining Fos and tyrosine hydroxylase (TH) immunoreactivity. Conscious male rats received either cholecystokinin (CCK) intraperitoneally to activate gastrointestinal afferents, or were made hypertensive by intravenous infusion of phenylephrine (PE) to activate baroreceptors. Tissue sections were processed immunocytochemically for Fos and/or TH. Phenylephrine infusion and CCK injection elicited Fos expression in distinct and in overlapping regions of the NTS and the VLM. Cholecystokinin injections increased the number of Fos-immunoreactive neurones in the area postrema (AP) and throughout the rostral-caudal extent of the NTS, including commissural neurones and the medial subnuclei. Some reactive neurones in NTS were also positive for TH, but most were not, and most of the TH-positive NTS neurones were not Fos-positive. In contrast, PE infusion produced a more restricted distribution of Fos-positive neurones in the NTS, with most neurones confined to a dorsolateral strip containing few TH-positive neurones. The medial NTS at the level of the AP and the AP itself were largely unresponsive, but rostral to the AP the medial NTS was labelled, including some TH-positive neurones. Both treatments produced labelling in the caudal and mid-VLM, but PE infusion had a stronger effect in the rostral VLM. In the PBN, CCK elevated Fos expression in several subregions, whereas PE infusion failed to specifically alter any subdivision. The results suggest that stimulation of baroreceptor and gastric afferents evoke both overlapping and cytoarchitectonically distinct pathways in the brainstem.

Ethylene biosynthesis in isolated vacuoles of Vicia faba L. - requirement for membrane integrity.

The ability of vacuoles prepared from V. faba leaves to convert 1-aminocyclopropane-1-carboxylic acid to C2H4 was destroyed when vacuoles were lysed by passage through a hypodermic needle, freezing and thawing, osmotic shock, treatment with ethanol or with a detergent. Ethylene synthesis in the vacuolar fraction was also inhibited by the uncouplers carbonyl cyanide m-chlorophenyl hydrazone and dinitrophenol and by the ionophores valinomycin, nigericin, and A23187. Ethylene formation increased with increasing pH of the incubation medium over the pH range of 5.0-7.5. These observations support the hypothesis that C2H4 biosynthesis in vacuolar preparations is dependent on membrane integrity, possibly because of the requirement for a transmembrane ion gradient.

Localisation and characterisation of homoserine dehydrogenase isolated from barley and pea leaves.

Two forms of homoserine dehydrogenase exist in the leaves of both barley and pea; one has a large molecular weight and is inhibited by threonine, the other is of smaller molecular weight and insensitive to threonine but inhibited by cysteine. The subcellular localisation of these enzymes has been examined. Both plants have 60-65% of the total homoserine dehydrogenase activity present in the chloroplast and this activity is inhibited by threonine. The low molecular weight, threonine-insensitive form is present in the cytoplasm. Total homoserine dehydrogenase activity from barley leaves showed progressive desensitisation towards threonine with age in a similar manner to that previously described for maize. It was shown that the effect was due to desensitisation of the chloroplast enzyme, and not to an increase in the insensitive cytoplasm enzyme. No corresponding desensitisation to threonine was detected in pea leaves. The different forms of homoserine dehydrogenase could be separated from pea leaves by chromatography on Blue Sepharose; the threonine-sensitive enzyme passed straight through and the threonine insensitive form was bound. A similar separation of the barley leaf isoenzymes was obtained using Matrex Gel Red A affinity columns; in this case however, the threonine-sensitive isoenzyme was bound. In both plants, the threonine insensitive isoenzyme was subject to greater inhibition by cysteine than was the threonine-sensitive isoenzyme.