Koji Uchizono

Synaptic organization of the Purkinje cells in the cerebellum of the cat

SummaryAn attempt at distinction between excitatory and inhibitory synapses is made in the cat cerebellum. The former are assumed to contain spheroid vesicles (S-type) of average diameter of 500 Å, while the latter flattened vesicles (F-type) of smaller size than the former. The elongation index (the ratio of the length of major versus minor axis of the vesicles) of S-type synaptic vesicles was about 1.2, while that of the F-type was more than 1.7. Parallel fibers of granule cells make S-type synaptic contacts (en-passant type or crossing-over synapse) mostly on the spines of the smaller branchlets of Purkinje cells. Climbing fibers make also S-type synapses on the smaller spines with short necks of the larger dendrites of Purkinje cells, but not frequently on the direct surface of them. It must be emphasized that almost no F-type synapse has been recognized which makes synaptic contacts directly on the spine of any type. It makes synaptic contacts usually on the direct surface of dendrites of Purkinje cells. Basket cell axons embrace directly the somas of the Purkinje cells. Their synaptic contacts were always of F-type and of en-passant character.The hypothesis is proposed that excitatory (E-type) synapses can be identified with synapses of S-type, whereas inhibitory (I-type) synapses would correspond to the F-type terminals.

Mechanism of Inhibition

This chapter focuses on the mechanism of inhibition. The application of microelectrode technique has made the elucidation of inhibitory mechanism within the central nervous system, so far inaccessible to the classical methods, possible. Eccles and his associates showed that if one stimulates the 1A fibers in the spinal dorsal root, which originate at the muscle spindle of quadriceps muscle and run centrally through the dorsal root, contraction of synergist muscles are evoked, while the relaxation of the antagonist muscles are obtained. In this situation, if a microelectrode is impaled into the soma of antagonist motoneuron and 1A fibers are stimulated, the transient hyperpolarizing potentials of the opposite polarity of excitatory postsynaptic potentials (EPSP) is obtained from this motoneuron. This potential change is called inhibitory postsynaptic potentials (IPSPs). The latency of IPSP is somewhat longer than that of EPSP. This delay is explained by imposing a single interneuron in-between. The chapter discusses the mechanism of postsynaptic inhibition. It also explains the morphology of postsynaptic inhibition and the pharmacology of presynaptic inhibition.

Uridine as an active component of sleep-promoting substance: its effects on nocturnal sleep in rats

A 10-h intraventricular infusion of 10 pmol of uridine from 19.00 to 05.00 h resulted in significant increases in sleep in otherwise saline-infused male rats (n = 8) during the environmental dark period (20.00-08.00 h). Increments of slow wave sleep (SWS) and paradoxical sleep (PS) were 21.0% and 68.1%, respectively, of the baseline value. This was due to increases in the frequencies of both SWS and PS episodes but not to their durations. Similar increases occurred the first recovery night under saline infusion, but sleep amounts returned to the baseline levels the second night. Brain temperature was not affected by uridine administration. A small dose of uridine (1 pmol/10 h) exerted no effect (n = 6) while larger doses (100 and 1000 pmol/10 h, each n = 5) resulted in slight but insignificant increases in SWS and PS. The 1000-pmol uridine administration seemed to be non-physiological since it brought about irregularities in locomotor activity and sleep-waking rhythms. Thus, authentic uridine exhibited the same sleep-enhancing effects as a naturally occurring active component of sleep-promoting substance, which was recently identified with uridine.

Little sleep-promoting effect of three sleep substances diurnally infused in unrestrained rats

Delta-sleep-inducing peptide (2.5 nmol), prostaglandin D2 (0.36 nmol) and uridine (10 pmol) were intraventricularly infused for 10 h at daytime in otherwise saline-infused freely moving male rats. In contrast to a nocturnal infusion which may result in marked sleep-promoting effects, such a diurnal infusion brought about almost no change in sleep parameters. It is postulated that the requirement of sleep in rats might be fully achieved at the environmental light period to cancel the effect of the exogenously administered sleep substances. It is proposed that an endogenous sleep substance should be characterized by a property not to cause excessive sleep at the time when sleep is physiologically saturated.

Endogenous sleep-promoting factors

Abstract The classical concept of humoral control of sleep has recently been revived. Sleep-promoting substances, if discovered, would have a great impact on the study of sleep mechanisms and in the treatment of insomnia. A number of endogenous compounds have been reported to be putative sleep-promoting factors. Yet a primary substance which can trigger the state of slow-wave sleep, paradoxical sleep and/or wakefulness is still unknown.

A new method for electron microscopic observation of isolated synaptic vesicles labelled with monoclonal antibody

The immunoreaction of a monoclonal antibody (Mab) and an isolated synaptic vesicle (SV) was processed on a grid mesh and the result could be easily observed with electron microscopy. The SV suspension was obtained and dispersed on the grid mesh where immunoreaction procedures were performed. The resulting immunoreaction was visualized by labelling with ferritin particle (FAD) or horseradish peroxidase (HRP) for the electron microscopic observation. The SV specimen was observed by electron microscopy after faint negative staining with 1% uranyl acetate. With this method, the positive immunoreaction of Mab 171B5 and the isolated SV could be easily identified by the formation of a halo of FAD or a cobweb of HRP surrounding the SV. In the control experiment, the SV specimen was incubated with normal mouse serum instead of the Mab while the other procedures were performed in the same way. The SV was not outlined by FAD in the control experiment. Thus, the positive immunoreaction of the Mab and SV was thought to be an immunologically specific one. It was also determined that the Mab reacted specifically with the SV but not with the small membrane fragments and other unknown material. The present method seems to be useful for observing the immunoreaction of subcellular structures and their antibodies under electron microscopy.

Introduction to Electron Micrographs Indicative of Synaptic Differentiation in Various Parts of the Central Nervous System

This chapter presents electron micrographs indicating synaptic differentiation in various parts of the central nervous system (CNS). It presents a schematic representation of the cerebellar cortex of mammals. Cerebellar cortex contains several kinds of neurons including huge number of granule cells, Purkinje cells, basket cells, mossy fibers, Golgi cells, neuroglial cells, stellate cells, and climbing fibers. These neuronal components have been analyzed anatomically and physiologically. Geometrical regularity of the structure has facilitated electrophysiological studies on the cerebellum. The S–F hypothesis been founded originally on the neuronal organization of this specific area of the central nervous system, being facilitated by the characteristics of the cerebellar cortex. The chapter highlights the characteristics of single synaptic vesicles in S-type and F-type synapses. It illustrates a typical synaptic arrangement of S-type and F-type synapse on the dendrite in the cats cerebellum. A dendrite is tightly surrounded by several synapses, one of which differs from the others in that the vesicle shape is easily differentiated from others by inspection. Synapse that contains spheroid vesicles has been nominated S-type and synapse that contains flattened vesicles F-type.

S-F Hypothesis: Morphological Correlates of Excitation and Inhibition

This chapter presents an overview of the S–F Hypothesis. Uchizono (1965) proposed the hypothesis that insists that when a synapse contains spheroid vesicles, it is functionally excitatory, while when it contains flattened vesicles, it is inhibitory in function. Electron microscopic investigations indicated quite clearly that almost whole surface of cerebellar Purkinje cell was surrounded by the axon terminals of basket cells, which contained unequivocally flattened vesicles. It was also shown that almost all nerve terminals of parallel fibers in the molecular layer of the cats cerebellum contained spheroid vesicles. Likewise, the excitatory nature of the parallel fibers has also been identified. It is permissible to present a hypothesis that the synapse containing spheroid vesicles is excitatory, while the synapse containing flattened vesicles is inhibitory. The same hypothesis was proposed independently by Bodian in which he denotes the S-type and F-type synapse according to the shape of synaptic vesicles. This idea originates from the facts that S-type synapses containing spheroid vesicles invariably occur at the place where the electrophysiological evidence exists that excitatory actions (depolarization) take place, while F-type synapses are always found in the region where inhibitory activity (hyperpolarization) of synapses are always identified.

Transmission in the Sympathetic Ganglion

This chapter highlights transmission in the sympathetic ganglion. Histochemical investigations have suggested the existence of small fluorescent cells in the sympathetic ganglion. Electron microscopic observations also support this suggestion. Small granule containing cells (SG cell) have been identified, which are provided with the characteristics of neuron and chromaffin cells. An electron microscopic evidence was also presented that the small granule containing cell makes synaptic contact with both the preganglionic nerve terminal and the dendrite of the ganglionic neuron. The electron micrographs show also that the small granule containing cell is innervated by S-type synapse indicative of cholinergic link. This type of cell is named connector neuron. It is also reported that nature of granules of this connector neuron in the rabbit inferior mesenteric ganglion is similar to the noradrenergic granules in the adrenal medulla. Observations also show that the small granule containing cell is provided with both afferent and efferent synapses. The latter synapses contain granulated or cored vesicles, which suggest that the catecholaminergic substance is involved in this synaptic transmission.

The Release Mechanism of Transmitters

This chapter focuses on the release mechanism of transmitters. It has been demonstrated that Ach is released upon stimulation of skeletal motor nerves and upon activation of preganglionic sympathetic fibers. The same mechanisms in the central nervous system (CNS), not unequivocally, were also proposed. In one study, while recording from the immediate region of synapse in the skeletal muscle of vertebrates, the random appearance of minute flactuations in the resting potential was observed, the direction of which was always depolarization. Later, it was showed, however, that the direction of the minute fluctuation of potentials in the stretch receptor neuron of crayfish was always hyperpolarization. This is conceivable because it has been well documented that the neuron is exclusively innervated by the inhibitory inputs. Subsequent studies have shown that these small depolarizations are produced not by a molecular overspill but by the random release of quantized packets of transmitter. It was proved that the release is not because of local excitation of terminal axon branches and hence, local excitation should be able to produce a synchronized depolarization in a wider area of nerve terminal.