Takashi Iwayama

Dual adrenergic and cholinergic innervation of the cerebral arteries of the rat. An ultrastructural study.

The innervation of the anterior cerebral artery of the rat was examined by electron microscopy and by the fluorescence method for localizing adrenergic nerves. Two groups of axon bundles were associated with the artery; one at the outer margin of the adventitia (periadventitial bundles) and the other within the adventitia or at the adventitia-media border (adventitial bundles). Periadventitial bundles consisted of nonmyelinated axons (0.1-2μ diam), some of which contained synaptic vesicles; in some bundles, myelinated axons were seen. Adventitial axons often contained many synaptic vesicles and were free of Schwann cell sheath in areas apposed to smooth muscle cells. The closest observed approach of axon to muscle cell was 800 A. No nerve fibers penetrated the medial muscle. After fixation with glutaraldehyde plus osmium, large (1000 A) granular and small (500 A) agranular vesicles were seen within many axon profiles. Small granular vesicles were rare. After permanganate fixation, terminal axons contained (besides large granular vesicles) either predominantly small granular vesicles or exclusively small agranular vesicles. Two days after sympathetic denervation, no axons containing small granular vesicles and no fluorescent fibers were seen. Adrenergic fibers were readily identified after injection of rats with 6-hydroxydopamine; small vesicles of adrenergic axons contained highly opaque granular cores, even in osmium-fixed material. Axons containing small agranular vesicles after 6-hydroxydopamine were considered cholinergic. The density of granulation of the large vesicles of adrenergic, but not cholinergic, axons was considerably enhanced following 6-hydroxydopamine. Both adrenergic and cholinergic axons come into close relationship with smooth muscle cells.

Fine-structural Identification of Autonomic Nerves and their Relation to Smooth Muscle

Publisher Summary Electron microscope and fluorescent histochemical studies of the relationship of individual nerves to single smooth muscle cells have supported and extended the earlier concept of the autonomic ground plexus. Smooth muscle cells, connected by low resistance pathways represented by specialized areas of close apposition or nexus are arranged in efector bundles. Transmitter is released en passage from large numbers of preterminal varicosities, as well as from the terminal varicosity. In most organs, some, but not all, of the smooth muscle cells are directly innervated—that is, have close(less than 500 A) apposition with axon varicosities naked of Schwann cell investment, termed as “directly-innervated cells.” The cells adjoining directly innervated cells are coupled electrotonically to them by low resistance pathways so that passive potential changes, in particular excitatory junction potentials, are observed in these cells, termed as “coupled cells.” When the muscle cells in an area of the effector bundle become depolarized simultaneously, an all-or-none action potential is initiated that propagates through the tissue. In systems, such as the ureter, uterus, arteries, and longitudinal muscle coat of the gut, only a small proportion of muscle cells are directly innervated so a large number of cells are indirectly coupled and are activated via a well developed nexus system for intermuscle fibre spread of activity.

Prolonged hypotension and ultrastructural changes in sympathetic neurones following guanacline treatment

Abstract Changes in systemic blood pressure, catecholamine levels, fluorescent histochemistry and ultrastructure of sympathetic nerves both during and after cessation of chronic treatment of rats with guanacline (5 mg/kg/day) were examined. Comparative studies were also carried out on guanethidine. The systemic blood pressure fell steadily for the first 9–14 weeks in both guanethidine and guanacline-treated animals. Following cessation of drug treatment, the blood pressure of guanethidine-treated animals rose rapidly to normal levels, in contrast to guanacline-treated animals in which the rise was slow. Sections of sympathetic ganglion cells from guanacline-treated rats exhibited strong yellow autofluorescence which was shown by electron microscopy to consist of a massive deposition of lipoprotein granules (comparable to ‘aging pigment’). These granules were still present 12 weeks following cessation of treatment. No comparable changes were observed in guanethidine-treated animals. It is suggested that the cellular effects of guanacline might be related to the postural hypotension which persists in humans some months after withdrawal of therapy.

Terminal axons ensheathed in smooth muscle cells of the vas deferens

SummaryThe ultrastructure of axon profiles which were completely ensheathed in smooth muscle cells has been described in the guinea pig, mouse and rat vas deferens. The axon profiles contained both small (500 Å) and large (1,000 Å) vesicles, neurotubules and mitochondria. Adrenergic axons were clearly identified within smooth muscle cells after treatment of the tissue with 5-or 6-hydroxydopamine, drugs which cause specific ultrastructural changes in adrenergic axons. The ensheathed axons were separated from the surrounding muscle cells by narrow, regular gaps, usually about 100–300 Å wide. Schwann cells seldom accompanied the ensheathed axons. Axons often penetrated the muscle cells in the nuclear region and profiles were sometimes observed among the perinuclear organelles.