ABSTRACT
Origin and ultrastructural characteristics of serotonergic fibers of the spinal dorsal horn in the rat have been confirmed by means of a combined method of HRP and immunocytochemistry and immunoelectron microscopic observation. The results showed that serotonergic axonal terminals in the spinal dorsal horn come mainly from nucleus raphe magnus and the ventral part of the reticular formation of medulla oblongata. Serotonin immunoreactive positive structures of the spinal dorsal horn have been found in lamina Ⅰ (marginal zone) and lamina Ⅱ (substantia gelatinosa) as fine myelinated and unmylinated fibers. There were mainly axo-axonic synapses between the labeled and nonlabeled terminals. The labeled terminals were presynaptic or postsynaptic element. Axo-dendritic synapses were rarely found. The non-synaptic releasing figures have not been found. Based on the ultrastructural characteristics the authors suggest that in performing analgesia role the serotonergic system in the spinal dorsal horn might influence directly or indirectly the excitability of interneurons and inhibit directly the nerve impulses of primary afferents by means of synaptic connections instead of non-synaptic releasing manner.
ABSTRACT
The distributions of neurotensin(NT) and substance P(SP) in the arcuate nucleus of rat hypothalamus have been studied by means of double labeled pre-embedding immunoelectron microscopic technique. It was observed that there were SP- and NT-containing dendrites, perikarya and axons in the arcuate nucleus. SP- and NT-containing dendrites and axons received asymmetric afferent synapses from immunonegative axons. SP-positive axonal terminals established symmetric axo-somatic and axo-dendritic synapses with immunonegative perikarya and dendrites as well as symmetric axo-somatic synapses with NT-positive perikarya. The results of this study directly indicate for the first time that the NT-ergic neurons in rat arcuate nucleus receive innervation from SP-ergic neurons, and provided an ultrastructural evidence for the synaptic regulation of the neuroendocrine of the hypothalamus.
ABSTRACT
Ultrastructures of the neurohypophysis in the rats have been studied by means of electron microscopy. Besides identifying the fact that the neurosecretory substances store in the nerve terminals and release into the blood, there are also axo-axonic synaptoid structures existed between neurosecretory terminals and neuro-glial synaptoid contacts between neurosecretory terminals and pituicytes. The characteristics of these contacts mentioned above are as follows: (1) the pre-and postsynaptic membranes are insignificantly thickened; (2) clustered microvesicles are close to and attach to the presynaptic membrane; (3) the synaptic cleft is about 20 nm wide and contains various amount of electron dense materials. The authors suggest that the two kinds of synaptoid structures and pituicytes are all involved in the regulation for the releasing of the neurosecretory substances.
ABSTRACT
The distribution of somatostatin (SRIF) in substantia gelatinosa of the rat spinal cord was studied by means of immuno-electron microscopy. The ultrastructural features showed that nerve terminals containing SRIF take part in forming presynap- tie elements of axe-somatic, axe-dendritic and axo-axonic synapses. The immune- reactive products locatl at the external membrane of mitochondria, around the small clear synaptie vesicles and in the large granular vesicles. Most of synaptic vesicles are round or ovoid in shape. Only a few of them are flattened. Based on the ultrastructural characteristics mentioned above and related experimental results the authors believe that SRIF in substantia gelatinosa of the rat spinal cord is probably involved as a neurotransmitter instead of neuromodulator.
ABSTRACT
Using the immunohistochemical and immunoelectron microscopic methods, the localization and pattern of vasoactive intestinal polypeptidergic nerves in the wall of cerebral vessels were investigated. The results revealed that the VIP-like immunoreactive (VIPLI) fibres were located in the adventitia or at the adventitia-media border. No synaptic contacts were identified among the nerve terminals or between nerve terminal and smooth muscle cell. VIPLI terminals directly apposed to the smooth muscle cells with a distance of 100 nm.The observations mentioned above indicate that there is peptidergic innervation in the wall of the cerebral vessels besides traditional adrenergic and cholinergic innervations. The regulatory function of VIP-containing nerves to the cerebral vessels may be performed by affecting the smooth muscle directly through the nonsynaptic release. In addition, present study identified and discussed the distribution and function of substance P(SP) in the cerebral vessels.
ABSTRACT
The ultrastructural characteristics of the arcuate and median eminence in the rat have been studied by means of folmaldehyde-osmic acid fixation method. The observations showed that there are two kinds of neurons (dark and light) in the arcuate nucleus which might be responsible for producing both dopamine and releasing hormones. The tanycytes of the ependyma of the third ventricle run longitudinally through various zones of the median eminence and reach the perivascular space of the portal capillaries. The neurosecretory substance-containing nerve terminals may travel between ependymal cells or end around the basal membrane of the capillaries of the median eminence, even keep close to the endothelial fenestrae of "open-type capillary". The axo-somatie and axo-dendritic synapses are formed at the soma and dendrites of neurons of the arcuate nucleus. Both agranular type and granular type axo-axonic synapses are encountered in the fibrous zone of the median eminence. There are also synaptic connections between the basic processes and the large granular vesicles containing nerve terminals in the palisade zone of the median eminence. The ultrastructural characteristics mentioned above suggest that (1) the releasing (or inhibiting) hormones of the hypothalamus might be released into the portal capillaries from nerve terminals directly or into the cerebro-spinal fluid of the third ventricle and then uptaken by the tanycytes, and transported to the portal capillaries by their processes. (2) each step of synthesis, storage, transport and release of the releasing (or inhibiting) hormones could be regulated by nervous mechanism