Tetsuo Inokuchi

Ultrastructural Study of Anterograde Transport of Glial Cell Line-Derived Neurotrophic Factor from Dorsal Root Ganglion Neurons of Rats towards the Nerve Terminal

The glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic substance in the central and peripheral nervous systems. The present immunohistochemical study clarified the ultrastructural localization of GDNF-immunoreactive substance (GDNF-IR) accumulated at transfected sciatic nerve stumps and also at normal spinal dorsal horn, and has demonstrated that GDNF-IR products appear to be located in dense-cored vesicles within the axons. Furthermore, to determine the source of proximally accumulated GDNF in the transected sciatic nerve, we attempted a transection and a double ligation maneuver involving the sciatic nerve. In the early period after the ligation (20 h), GDNF-IR fibers were observed in the proximal and distal segment of the ligations, but no immunoreactivities were detected in the middle segment. On the other hand, at a late period (8 days) after the transection, GDNF-IR fibers had almost disappeared, but weak GDNF-IR was observed in Schwann cells in the proximal and distal stumps of transected nerve. These findings suggest that most of GDNF-IR was transported from the proximal or distal side in the early period, but was locally synthesized by Schwann cells around the ligations in the late period. Spinal rhizotomy caused prominent accumulation of GDNF-IR products at the cut end of the ganglion side of the dorsal root, but not at the ventral root. These results suggested that dorsal root ganglionic (DRG) sensory neurons are one of the origins of GDNF. The fact that small- to medium-sized DRG neurons show enhanced GDNR-IR after the colchicine treatment may support the above suggestion. In conclusion, the present results strongly suggest that a subgroup of DRG sensory neurons synthesized GDNF-containing dense-cored vesicles in the neuronal somata and anterogradely transports the vesicles to peripheral or central axon terminals.

Distribution, chemical coding and origin of nitric oxide synthase-containing nerve fibres in the guinea pig nasal mucosa

The distribution, chemical coding and origin of nitric oxide synthase (NOS)-containing nerve fibres in the respiratory mucosa of the nasal septum of the guinea pig were examined using nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and immunohistochemistry. A rich supply of NADPH-d-positive nerve fibres was observed around blood vessels and in nasal glands where nerve fibres frequently penetrated into the epithelia of acini and intralobular ducts. NADPH-d reactivity was also found in the nerve fibres located under or within the respiratory epithelium. Combined immunofluorescence and histochemical staining of the same preparation demonstrated virtually complete overlapping of NOS immunoreactivity and NADPH-d reactivity in nerve fibres, indicating that NADPH-d can be used as a marker for NOS-containing neurons. Double-labelling using antibodies to vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) revealed that NADPH-d-positive nerve fibres frequently contained VIP or NPY, but not CGRP. Pterygopalatine ganglionectomy significantly reduced the number of NADPH-d-positive nerve fibres innervating the respiratory epithelium as well as blood vessels and nasal glands. Neither superior cervical ganglionectomy nor sensory denervation by capsaicin treatment affected the distribution of NADPH-d-positive fibres. These results indicate that NOS-containing nerve fibres innervating the respiratory epithelium as well as blood vessels and nasal glands in the guinea pig originate mainly from the pterygopalatine ganglion, and suggest that NO may play a significant role as a neurotransmitter and/or neuromodulator in the control of the respiratory epithelium as well as vasculature and nasal glands.

Distribution and Neuropeptide Content of Nitric Oxide Synthase-Containing Nerve Fibers in Arteries and Conduction System of the Rat Heart

The rat heart receives its blood supply not only from the coronary arteries but also from the accessory coronary arteries that supply mainly the atria. The distribution and chemical nature of nitric oxide synthase-containing nerve fibers in the conduction system as well as the coronary and accessory coronary arteries were investigated using immunohistochemistry and NADPH diaphorase (NADPH-d) histochemistry. A few NADPH-d-positive nerve fibers were observed mainly around the main trunk of the coronary arteries, while NADPH-d-positive fibers were found along the entire course of the accessory coronary arteries from their main branches to the arteriolar level. A double-staining method demonstrated that NADPH-d-positive fibers innervating both the coronary and accessory coronary arteries contained vasoactive intestinal polypeptide or neuropeptide Y. NADPH-d-positive fibers were relatively abundant in the sinus node and penetrating bundle but were very sparse in the atrioventricular node and right bundle branch. No NADPH-d-positive fibers were detected in the left bundle branch. Some of the NADPH-d-positive fibers innervating the penetrating bundle exhibited distinct immunoreactivity to calcitonin gene-related peptide. These results suggest that nitric oxide may play a role as a neurotransmitter and/or neuromodulator in the neural control of the cardiac blood flow and impulse conduction.

The ultrastructure of the primate arachnoid granulation, studied with the scanning and transmission electron microscopes

The ultrastructures of the primate arachnoid granulations were observed using the scanning (SEM) and transmission (TEM) electron microscopes. The endothelial cells were slender and overlapped each other. Extracellular spaces which were composed of a network of arachnoid cell processes crisscrossing each other three-dimensionally, were observed under the endothelium. By treating with NaOH (20°C), the collagenous fibers in the specimen were exposed under the SEM. The arachnoid granulations were entirely covered with the fibrous capsule, which was composed of wavy collagenous fibers. Many pores (1–2 μm) were observed on the fibrous capsule. These morphological structures may be closely related to the mechanism for cerebrospinal fluid absorption.