Inositol Phospholipid Hydrolysis in Rat Cerebral Cortical Slices: I. Receptor Characterisation

Characterisation of receptor-mediated breakdown of inositol phospholipids in rat cortical slices has been performed using a direct assay which involves prelabelling with [3H]inositol. When slices were preincubated with [3H]inositol, lithium was found to greatly amplify the capacity of receptor agonists such as carbachol, noradrenaline, and 5-hydroxytryptamine to increase the amount of radioactivity appearing in the inositol phosphates. Using a large variety of agonists and antagonists it could be shown that cholinergic muscarinic, alpha 1-adrenoceptor, and histamine H1 receptors appear to be linked to inositol phospholipid breakdown in cortex. The large responses produced by receptor agonists allowed a clear discrimination between full and partial agonists as well as quantitative analysis of competitive antagonists for each receptor. Whereas carbachol and acetylcholine (in the presence of a cholinesterase inhibitor) were full agonists, oxotremorine and arecoline were only partial agonists. Very low concentrations of atropine shifted the carbachol dose-response curve to the right and allowed inhibition constants for the antagonist to be easily calculated. The nicotinic antagonist, mecamylamine, was ineffective. Noradrenaline adrenaline were full agonists at alpha 1-adrenoceptors, but phenylephrine and probably methoxamine were partial agonists. Prazosin, but not yohimbine, potently and competitively antagonised the noradrenaline inositol phospholipid response. Mepyramine but not cimetidine competitively antagonised the histamine response. These data provide strong confirmation for the potentiating effect of lithium on neurotransmitter inositol phospholipid breakdown and emphasise the ease with which functional responses at a number of cortical receptors can be characterised.     

Experimental toxocariasis and hyperactivity in mice

An observational study using videorecordings and computer-assisted data analysis was undertaken in order to investigate the behaviour of mice infected with larvae of Toxocara canis. The findings indicated that the infection had a marked effect on five readily and reliably differentiable categories of murine behaviour. A marked increase in the number of shorter bouts of each of the five behaviours was also associated with the infection. These results support previous findings and further suggest that T. canis infection affects the way in which mice respond to their environment. In particular the infection appears to be associated with hyperactivity in mice. Possible causes of such behavioural abnormalities as well as implications of these findings for clinical studies concerned with relationships between T. canis infection and hyperactivity in children are discussed.     

The fine structure of the salivary glands of the desert locust Schistocerca gregaria Forskål

Summary This paper describes the structure of the salivary glands of Schistocerca gregaria as seen under the electron microscope and the light microscope. The salivary glands consist of a number of acini located on both sides of the pro-, meso-, and metathoracic segments of the locust. Each acinus is drained by a duct which unites with others from the same side to form a lateral collecting duct. The ducts from the two sides join in the head capsule and open into a salivary cup on the labium. Each acinus consists of parietal cells, zymogenic cells, duct cells, tracheoblasts, sheath cells and pigment cells. The parietal and zymogenic cells are the main sites for the production of the salivary gland secretions, which pass through microvilli from the zymogenic cells to the lumen of the ducts within the acinus. Outside the acinus each duct is composed of highly specialized cells with infolded basement membranes extending about a third of the way across the cell. The cytoplasm between the membranes contains elongated mitochondria and glycogen granules. The apical border of the cell is thrown into microvilli which are closely aggregated under the cuticle lining the duct. These cells have all the features of cells previously described in vertebrates and invertebrates which are known to absorb water and/or ions. Absorption of water from the gut could allow the excretion of hypertonic saliva by the locust.     

Inositol Phospholipid Hydrolysis and Potentiation of Cyclic AMP Formation by Noradrenaline in Rat Cerebral Cortex Slices Are Not Mediated by the Same α-Adrenoceptor Subtypes

A pharmacological study was undertaken to determine whether the noradrenaline-stimulated breakdown of inositol phospholipids and the potentiation of isoprenaline-stimulated cyclic AMP by noradrenaline in rat cerebral cortex slices are mediated by the same alpha-receptor subtype. The rank order of potency of a range of alpha 1 and alpha 2 antagonists suggests that both responses may involve an alpha 1 receptor, but there were several differences between the pharmacological profiles for the two systems. Although in both cases, all selective alpha 1 antagonists were more potent than alpha 2 antagonists, the rank orders and the absolute potencies differed for the two responses. The inhibition of the inositol phosphate response was characterised by a high alpha 1/alpha 2 antagonist ratio, and in most cases, Hill slopes of inhibition were consistent with the involvement of a single receptor site. Inhibition of the cyclic AMP response had a much lower alpha 1/alpha 2 antagonist ratio and generally exhibited Hill slopes less than one. Evidence has been provided suggesting that adenosine is involved in the potentiation of cyclic AMP and that other, as yet unidentified, factors may also be involved. Even in the absence of an adenosine component, the results presented support the suggestion that the potentiation due to noradrenaline is mediated by a receptor whose identity does not easily fit with the currently accepted classification of alpha adrenoceptors.     

The effects of hydrocortisone on lung structure in fetal lambs

The effect of cortisol infusion on fetal lung development was studied in lambs. Changes were compared with those of control groups of saline-infused fetuses of the same age (day 132) and normal late gestation fetuses (142 +/- 4.6 days). Cortisol was infused into five fetal lambs at 129 days of gestation at a rate of 17.0 mg/day. Four fetuses were delivered by hysterotomy at the onset of labour-like uterine activity (58 +/- 3 h). In cortisol-infused fetuses the concentration of cortisol in fetal plasma and tracheal fluid rose to levels similar to those in normal fetuses during the last week of gestation. Progesterone concentration in maternal plasma declined at about 48 h after the start of treatment. Cortisol-infused lambs showed increases in fixed lung volume, specific lung volume, absolute volume of both parenchyma and non-parenchyma and the proportion of the parenchyma which was potential airspace and a decrease in the proportion of parenchyma. For cortisol-infused lambs Type II cell size and the abundance of lamellar bodies, and the volume fraction of cell occupied by the nucleus were similar to the 142 day group, whereas Golgi apparatus and RER were closer to age matched saline-infused (day 132) controls. Glycogen content was midway between the two control groups. We conclude that infusion of cortisol for about 60 h at physiological levels, beginning at 0.85 of gestation, accelerates many, but not all aspects of pulmonary parenchymal maturation, expressed in terms either of morphogenesis of the gas exchange area or differentiation of Type II alveolar cells.     

Exercise and blood lymphocyte subset responses: intensity, duration, and subject fitness effects

This study examined the effect of exercise intensity and duration on the percent blood lymphocytes in men of low [LF; maximal O2 uptake (VO2max) less than 50 ml.kg-1.min-1 and sedentary], moderate (MF; VO2max = 50-60 ml.kg-1.min-1 and recreationally active), and high (HF; VO2max greater than 60 ml.kg-1.min-1 and recent training history) fitness. Thirty healthy adult men (aged 20-31 yr) participated in four randomly ordered cycle ergometer rides: ride 1 (65% VO2max, 30 min), ride 2 (30% VO2max, 60 min), ride 3 (75% VO2max, 60 min), and ride 4 (65% VO2max, 120 min). Blood samples were drawn at various times before and after the exercise sessions. Lymphocyte subsets were determined by flow cytometry using monoclonal antibodies for total T (CD3+), T-helper (CD4+), and T-suppressor (CD8+) lymphocytes and for a subset of cells expressing a natural killer (NK) cell antigen (Leu7+). Plasma catecholamines were assayed to determine exercise stress. There were sharp reductions (P less than 0.01) in the percentage of pan-T and T-helper lymphocytes immediately after exercise across all fitness levels; the magnitude of this reduction was greatest after the highest intensity (ride 3) or longest duration (ride 4) work. In contrast, the absolute number of T and T-helper cells tended to increase after exercise and significantly so in the HF subjects (P less than 0.005). There was no significant effect of exercise or subject fitness category on the percentage of T-suppressor lymphocytes, although the absolute numbers of this subset increased significantly after exercise in LF subjects. Marked increases (P less than 0.01) in the percentage of NK cells occurred immediately after exercise at all intensities and durations tested; numerical increases in total NK cells were significant in all fitness groups after the highest intensity work (ride 3; P less than 0.005). Irrespective of whether the changes were expressed as percentage or total numbers, recovery to base line occurred at 30 min after exercise. The results suggest that the exercise effect on blood lymphocyte subset percentages in men is transient and occurs across all fitness levels. Concomitant changes in plasma catecholamine concentrations are only weakly associated with these lymphocyte subset percentage responses to exercise. Furthermore, this study shows that the exercise-induced changes in lymphocyte percentages do not consistently reflect changes in the absolute numbers of cells.     

Competition between functional signal peptides demonstrates variation in affinity for the secretion pathway.

We have developed a system for examining the relative affinity of two different signal peptides for the protein secretion pathway in Escherichia coli. This system involves the expression of a modified alkaline phosphatase which possesses two signal peptides arranged in tandem. When both signal peptides have the wild-type sequence, cleavage after the first and cleavage after the second occur with nearly equal frequency. In both cases the remainder of the protein is transported to the periplasm. Thus both signal peptides effectively compete with each other for entrance to the secretion pathway. When the hydrophobicity of the second signal peptide is altered by small increments, we find that the more hydrophobic signal peptide is preferentially utilized. Thus, a more hydrophobic signal peptide can outcompete even an efficient wild-type signal sequence. The crossover point, for utilization of the second to the first signal peptide, is marked and occurs over a very small change in hydrophobicity. Our results suggest that the small differences in the hydrophobicity of wild-type signal peptides may have critical consequences: preproteins with the more hydrophobic signals could dominate one pathway, leaving those with only slightly less hydrophobic signals to require additional factors such as chaperonins, SecB, and other binding proteins.     

Serotonin 5-HT1A Receptor Activation Increases Cyclic AMP Formation in the Rat Hippocampus In Vivo

Abstract: In vivo microdialysis was used to examine the efflux of cyclic AMP (cAMP) into the extracellular fluid of the ventral hippocampus in the freely moving rat. The changes in extracellular cAMP concentration were monitored in response to forskolin and the serotonin 5-HT_1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). The basal level of hippocampal extracellular cAMP was 2.3 ± 0.2 pmol/ml (n = 6), after a 3-h postsur- gery stabilisation period. Perfusion of forskolin (100 μM) through the probe for 30 min significantly increased the efflux of cAMP, which returned to baseline levels within 90 min. 8-OH-DPAT (0.3 mg/kg s.c.) also significantly increased cAMP efflux, whereas a similar volume of saline had no effect. Desensitisation of the 8-OH-DPAT-induced increase in cAMP efflux was observed following a second administration of 8-OH-DPAT after a 4-h interval. Administration of 8-OH-DPAT did not alter the efflux of cAMP when forskolin was perfused through the probe. Pretreatment with WAY 100135 [N-tert-butyl 3–4-(2-methoxyphenyl)piperazine-1 -yl-2-phenylpropanamide dihydrochloride] (5 mg/kg s.c.), a specific 5-HT_1A receptor antagonist, prevented the 8-OH-DPAT-induced increase in cAMP efflux. The data indicate that the 8-OH-DPAT-induced increase in cAMP efflux in vivo is mediated by a 5-HT_1A receptor.