Control of resting bronchial hemodynamics in the awake dog.

In the resting awake dog a continuous-wave Doppler flow transducer on the right bronchoesophageal artery inscribes a sharp early systolic spike and low flow in late systole and throughout diastole, indicating a highly resistive bed. An analysis of autonomic factors using intravenous, cumulative, and randomly applied cholinoceptor, beta 1- and beta 2-adrenoceptor, and alpha 1- and alpha 2-adrenoceptor antagonists indicates that the low vascular conductance is due to cholinoceptor and alpha 1- and alpha 2-adrenoceptor effects in a ratio 3.6:1. No beta-adrenoceptor tone is present. Sighing behavior invokes a transient (< 2 s) fall in intrapleural pressure (and thus rise in bronchovascular transmural pressure) of 10-30 mmHg, which is followed by a two- to threefold increase over 30 s in bronchial flow and conductance, an effect simulated in 50% of dogs when bronchovascular transmural pressure is acutely raised and maintained over 40-60 s by inflating an intra-aortic balloon distal to the origin of the bronchial artery. Autonomic blockade has no effect on bronchovascular dilatation evoked either by sighing or by balloon inflation. It is concluded that, in the resting bronchial circulation, there exists strong cholinoceptor and alpha-adrenoceptor-based vasoconstrictor activity which can be overpowered by strong nonadrenergic noncholinergic local vasodilator reflexes evoked by sudden changes in intrathoracic transmural pressure possibly acting on stretch-sensitive sensory nerve endings containing substance P, calcitonin gene-related peptide, and neurokinins. The tonic vasoconstrictor but not the sigh-evoked vasodilator effects are sensitive to pentobarbital sodium anesthesia.

Structural maturation of synapses in the rat superior cervical ganglion continues beyond four weeks of age.

We have examined the morphology of preganglionic synapses in the rat superior cervical ganglion (SCG) at 10 days, 4 weeks and 1 year. Between 10 days and 4 weeks the mean thickness of the postsynaptic density (PSD) increased from 45.9 +/- 0.1 nm to 52.1 +/- 1.7 nm (P = 0.017), the mean length of the PSD (0.41 +/- 0.02 microns) did not change, and the distribution of synapses on the neuronal surface changed with a decrease in the proportion of somatic and an increase in the proportion of dendritic spine synapses. Since both synapse elimination and synapse formation are occurring during this period several mechanisms may contribute to these changes. However, between 4 weeks and 1 year, when there is no net change in the number of synapses, the mean length of the PSD increased to 0.53 +/- 0.02 microns (P = 0.001), there was no change in either the mean thickness of the PSD or the distribution of the synapses but the proportion of concave ('smile') synapses increased. A comparison with previous developmental studies of synapses in cerebral cortex of rat and chicken indicate that both the nature and the rate of synapse maturation can vary between different populations of synapses.

A rapid Percoll gradient procedure for isolation of synaptosomes directly from an S1 fraction: homogeneity and morphology of subcellular fractions.

A method for preparation of synaptosomes from rat cerebral cortex, on a discontinuous Percoll gradient, was previously developed for use with a P2 pellet (Brain Research, 372 (1986) 115-129). Here the Percoll method has been adapted for use with an S1-supernatant which eliminates a potentially damaging resuspension step and saves over 30 min, representing a third of the total preparation time. The homogeneity of the synaptosomes in each of the 5 subcellular fractions obtained with the S1-Percoll method was determined biochemically by analysis of the distribution of total protein, myelin basic protein, synapsin I and pyruvate dehydrogenase across the gradient. Electron microscopy was also used to determine the homogeneity of the synaptosomes, as well as to determine their morphological characteristics. Fraction 4 was the most enriched in synaptosomes and contained the lowest level of contamination by myelin, extrasynaptosomal mitochondria and plasma membranes. The yield of synaptosomes in fraction 4 with the S1-Percoll method was 1.4-fold greater than with the P2-Percoll method. While all other fractions contained some synaptosomes the major additional content in fractions 1-3 and 5 was, respectively, unidentified small membranes, myelin, synaptic plasma membranes and extrasynaptosomal mitochondria. Fraction 1 was enriched for very small synaptosomes (0.34 micron mean diameter) only 8% of which contained mitochondria, while fractions 2-4 progressively included larger synaptosomes containing more mitochondria. Fraction 5 synaptosomes were approximately the same size as those in fraction 4 (0.63 micron mean diameter), but 83% contained mitochondria, significantly more than in fraction 4. The synaptosomes in fraction 5 were found to be relatively resistant to hypotonic lysis, explaining a previously observed lack of phosphorylation of synapsin I in this fraction. The differences in homogeneity and morphological characteristics of the synaptosomes in fractions 1-5 suggest that the basis for their fractionation on Percoll gradients is different from that achieved with the more traditional procedures for isolating synaptosomes and that unique synaptosomal fractions are obtained with the S1-Percoll procedure.