No abstract

Polyamine levels vary markedly throughout the brain of the rhesus monkey. In general, there is an inverse relationship between spermine and spermidine concentrations; i.e., areas with high spermine levels have low spermidine levels and vice versa. The ratio of spermidine to spermine is as high as 13 in the optic nerve, and as low as 1.2 in the vermis. The variability of this ratio suggests that the functions of the polyamines in the adult brain may be different from those in other tissues. For instance, the ratio of spermidine to spermine in adult rat liver and most other organs is approximately 1, and this ratio increases in growthstimulated systems. The precursor of spermidine, diaminobutane, is present in very low quantities in the brain. Electrical stimulation of the precentral gyrus was found to decrease the content of both spermidine and spermine, and these data provide further evidence for a separate brain function of the polyamines. Depletion of spermidine and spermine in the motor cortex by electrical stimulation suggests that these amines may be involved in transmission phenomena.

Methods were developed for estimation of the area of the microscopic and ultramicroscopic surface of the toad bladder epithelium at various degrees of stretch. Bladder sacs fixed while containing 2.5, 5, 25 or 50 ml of mucosal fluid were studied. For a perfect, hollow elastic sphere, this range of volume corresponds to a sevenfold range of surface area. In the bladder, this increase could be achieved by unfolding of surface irregularities, with no change in surface area, or by stretching the epithelial membrane. The measured microscopic surface area increased threeinstead of sevenfold, but the ultramicroscopic surface remained constant. Thus the bladder stretches (1) by unfolding of the mucosal epithelium, and (2) by flattening of the microvilli. From measurements of the apparent thickness of the mucosal epithelium alone and of the entire bladder, we conclude that the former behaves like a flexible inelastic sheet, whereas the submucosa and serosa stretch elastically. Lateral intercellular spaces do not widen with stretch, but they do become more convoluted because of thinning of the epithelium. Thinning is unlikely to explain the increased sodium transport which follows stretching, because cytoplasmic resistance cannot approach total transepithelial resistance of this preparation.