Bibliothek

Notizen: Summary 1. Field potentials in the olfactory bulb and intracellular potentials from mitral cells were analyzed in the carp. Electrical shocks were applied to a part of the input (the lateral or medial bundle of the olfactory nerve: l-ON or m-ON respectively) or output pathways (lateral or medial olfactory tract: LOT or MOT respectively) of the olfactory bulb in order to activate the olfactory bulb partially. 2. When shocks were applied to the regions described above, the distributions of the C2-wave component (which reflects the synaptic depolarization of the peripheral dendrites of granule cells) of field potentials were different between the lateral and medial parts of the olfactory bulb. It was suggested that the patterns of excitatory synaptic inputs to peripheral dendrites of the granule-cell population are different between the two parts of the olfactory bulb. 3. The distributions of the C3- and C4-wave components (which reflect the synaptic depolarization of somata and deep dendrites of granule cells by volleys in centrifugal nerve fibers to the olfactory bulb) of field potentials were similar between the two parts of the olfactory bulb. It was suggested that the patterns of excitatory synaptic inputs from the centrifugal fibers to somata and deep dendrites of the granule-cell population are similar between the two parts of the bulb. 4. Mitral cells activated antidromically by LOT shocks or synaptically by l-ON shocks were located mainly in the lateral part of the olfactory bulb. On the other hand, mitral cells activated antidromically by MOT shocks or synaptically by m-ON shocks were located mainly in the medial part of the bulb. 5. Mitral cells, showing IPSPs in response to LOT, MOT and l-ON shocks, but not to m-ON shocks, were located mainly in the lateral part of the olfactory bulb. On the other hand, mitral cells, showing IPSPs to MOT and m-ON shocks, but not to LOT and l-ON shocks, were located mainly in the medial part of the bulb. Such a spatial distribution of mitral cells showing IPSPs was in accordance with that expected from the spatial distribution of the field potentials. 6. These results suggest that the olfactory bulb of the carp can be functionally separated into two subdivisions (the lateral and medial parts); the activities of neurons in the one part exert little influence on neurons in the other part. 7. From these results we suppose that the olfactory system of the carp is composed of two separate systems; in the lateral olfactory system, the lateral part of the olfactory bulb receives inputs mainly from the lateral bundle of the olfactory nerve and sends outputs to the LOT, while in the medial olfactory system, the medial part of the olfactory bulb receives inputs mainly from the medial bundle of the olfactory nerve and sends outputs to the MOT.

Notizen: Summary 1. Anuran tongue is controlled by visual stimuli for releasing the prey-catching behavior (‘snapping’) and also by the intra-oral stimuli for eliciting the lingual reflex. To elucidate the neural mechanisms controlling tongue movements, we analyzed the neuronal pathways from the glossopharyngeal (IX) afferents to the hypoglossal (XII) tongue-muscle motoneurons. 2. Field potentials were recorded from the bulbar dorsal surface over the fasciculus solitarius (fsol) to the electrical stimulation of the ipsilateral IX nerve. They were composed of three successive negative waves: S1, S2 and N wave. The S1 and S2 waves followed successive stimuli applied at short intervals (10 ms or less), whereas the N wave was strongly suppressed at intervals shorter than 500 ms. Furthermore, the S1 wave had lower threshold than the S2 wave. 3. Orthodromic action potentials were intra-axonally recorded from IX afferent fibers in the fsol to the ipsilateral IX nerve stimuli. Two peaks found in the latency distribution histogram of these action potentials well coincided with the negative peaks of the S1 and the S2 waves of the simultaneously recorded field potentials. Therefore, the S1 and S2 waves should represent the compound action potentials of two groups of the IX afferent fibers with different conduction velocities. 4. Ipsilateral IX nerve stimuli elicited excitatory postsynaptic potentials (EPSPs) in the tongue-protractor motoneurons (PMNs) and the tongue-re-tractor motoneurons (RMNs). Inhibitory postsynaptic potentials were not observed. 5. The EPSPs recorded in PMNs had mean onset latencies of 6.4 ms measured from the negative peaks of the S1 wave. The EPSPs were facilitated when paired submaximal stimuli were applied at intervals shorter than 20 ms, but were suppressed at intervals longer than 30 ms. Furthermore, the EPSPs were spatially facilitated when peripherally split two bundles of the IX nerve were simultaneously stimulated. 6. On the other hand, the EPSPs recorded in RMNs had shorter onset latencies, averaging 2.5 ms. In 14 of 43 RMNs, early and late EPSP components could be reliably discriminated. The thresholds for the early EPSP components were as low as those for the S1 waves, whereas for the late EPSP components the thresholds were usually higher than those for the S2 waves. The early EPSP components had mean onset latencies of 2.3 ms and followed each of the successive stimuli applied at short intervals with constant latencies and amplitudes. On the other hand, the late EPSP components appeared at 5.3 ms after the onset of the early EPSP components, and were temporally facilitated by successive stimuli at 10 ms intervals. 7. Double-labeling experiments (horseradish peroxidase and cobaltic-lysine) revealed that some of the IX afferent terminals with beaded bouton-like structures had direct contacts with the dorsal and lateral dendrites and the somata of the XII motoneurons, but not with their medial dendrites. These direct contacts only occurred in the rostral region of the dorsomedial XII nucleus, where RMNs are reported to predominate. 8. Contralateral IX nerve stimuli also elicited EPSPs in both PMNs and RMNs. Latencies measured from the onset of stimuli averaged 10.6 ms and 10.8 ms for PMNs and RMNs, respectively. These EPSPs were smaller than those evoked by the ipsilateral IX nerve stimuli, and were often facilitated by successive stimuli at 10 ms intervals. 9. It appears that the ipsilateral IX nerve afferents connect to PMNs polysynaptically, while they connect to RMNs by two kinds of excitatory pathways: short-latency monosynaptic pathways and longer-latency polysynaptic pathways. Furthermore, it appeared that the contralateral IX nerve afferents connect to both of PMNs and RMNs via polysynaptic excitatory pathways. 10. We also demonstrated a spatial facilitation between the polysynaptic EPSPs evoked by the IX nerve stimuli and those by the stimulations of the ‘snapping’-evoking area in the optic tetum (OT). These results suggest that some common excitatory interneurons, on which the tectal descending volleys and the IX nerve afferent volleys converge, mediate polysynaptic activation of the tonguemuscle motoneurons.

Notizen: Summary 1. To elucidate the neural mechanisms that mediate visual responses of optic tectum (OT) to medullary and spinal motor systems, we analyzed medullary reticular neurons in paralyzed Japanese toads (Bufo japonicus). We examined their responses to electrical stimulation of OT, and stained some neurons intracellularly. Responses to stimulation of the glossopharyngeal nerve (IX) were also analyzed. 2. Extracellular single unit recording revealed excitatory responses of medullary neurons to OT and IX stimulation. Among 92 units encountered, 79 responded to OT stimuli, 10 to IX stimuli, and 3 to both. Some units responded to successive stimuli of short intervals with relatively stable lags. 3. Intracellular recording and staining experiments revealed morphologies of reticular neurons that received excitatory inputs from OT. Thirteen units were identified after complete reconstruction of somata and dendrites. Neurons in the nucleus reticularis medius received excitatory inputs from bilateral OT. They had wide dendrites in ventral, ventrolateral and lateral funiculi, and single axons descending in the ipsilateral ventral funiculus as far caudally as the cervical spinal cord. Some collaterals of these axons projected directly to the hypoglossal and spinal motor nuclei. Some neurons in other medullary nuclei (nuc. reticularis superior, pretrigeminal nucleus, nuc. reticularis inferior, and nuc. tractus spinalis nervi trigemini) also responded to the OT stimulation. 4. Activities in bilateral OT converge onto medullary reticular neurons, which may directly control medullary and spinal motor systems.

Notizen: Abstract. Idiopathic dilated cardiomyopathy (IDC) is characterized by a thin-walled heart with systolic dysfunction of unknown etiology. Because abnormalities in genes for cytoskeletal proteins related to Z-disc function have recently been reported to cause IDC, genomic organization of the gene for nebulette, a novel actin-binding Z-disc protein, was determined and its sequence variations were searched for in Japanese patients with IDC and healthy controls. The nebulette gene consists of 28 exons, and four sequence variations leading to amino acid replacement (Gln187His, Met351Val, Asn654Lys, and Thr728Ala) were identified in the patients. These variations were also found in the healthy controls and hence they were polymorphisms and not disease-specific mutations. Frequencies of Gln187His, Met351Val, and Thr728Ala variants were similar in the patients and controls. However, the frequency of homozygotes for Lys at codon 654, a variant at a relatively conserved residue in an actin-binding motif, was significantly increased in nonfamilial IDC patients (n=106) as compared with healthy control subjects (n=331) (7.54% vs 1.21%, OR=6.25, P=0.002, 95% CI=1.92–20.29), while this association was not found in familial IDC patients (n=24). These observations suggest that the nebulette polymorphism in the actin-binding motif was a novel genetic marker of susceptibility to nonfamilial IDC.

Notizen: Summary 1. As a step to clarifying the neural bases for the visually-guided prey-catching behavior in the toad, special attention was paid to the flipping movement of the tongue. Tongue-musclecontrolling motoneurons were identified antidromically, and their topographical distribution within the hypoglossal nucleus, the morphology, and the neuronal pathways from the optic tectum including the ‘snapping-evoking area’ (see below) to these motoneurons were investigated in paralyzed Japanese toads using intracellular recording techniques. 2. The morphology of motoneurons innervating the tongue-protracting or retracting muscles (PMNs or RMNs respectively) was examined by means of intracellular-staining (using HRP/cobaltic lysine) and retrograde-labeling (using cobaltic lysine) methods. Both PMNs and RMNs showed an extensive spread of the branching trees of dendrites; 4 dendritic fields were distinguished: (1) lateral/ventrolateral, (2) dorsal/dorsolateral, (3) medial, and (4) in some motoneurons, contralateral dendritic fields, although there was a tendency for the dorsal/dorsolateral dendritic field to be less extensive in the PMNs than in the RMNs. The axons of both PMNs and RMNs arose from thick dendrites, ran in a ventral direction without any axon-collaterals branching off, and then entered the hypoglossal nerve. 3. The PMNs and RMNs were distributed topographically within the hypoglossal nucleus; the RMNs were located rostrally within the nucleus, whereas the PMNs were located more caudally within it. 4. In about 3/4 of the RMNs tested, depolarizing potentials [presumably the excitatory postsynaptic potentials (EPSPs)], on which action potentials were often superimposed, were evoked by electrical stimuli applied to the nerve branch innervating the tongue protractor. These EPSPs were temporally facilitated when the electrical stimuli were applied at short intervals (10 ms). 5. Both PMNs and RMNs showed hyperpolarizing potentials (IPSPs) in response to single electrical stimuli of various intensities (10–200 μA) applied to the ‘snapping-evoking area’ (lateral/ventrolateral part of the optic tectum) on either side. These IPSPs were facilitated after repetitive electrical stimulations at short intervals (10 ms) and of weaker intensities (down to 10 μA); i.e., a temporal facilitation of the IPSPs was observed. On the other hand, large and long-lasting EPSPs which prevailed over the underlying IPSPs were evoked after repetitive electrical stimulations (a few pulses or more) at short intervals (10 ms) and of stronger intensities (generally 90 μA or more); thus, a temporal facilitation of the EPSPs was also observed. Basically similar results were obtained when other regions of the optic tectum (e.g., the rostral, medial, and dorsal parts) were stimulated, although the most effective sites for eliciting these postsynaptic potentials (PSPs) were at the ventrolateral part of the optic tectum. In many of the PMNs and RMNs tested, these PSPs were further spatially facilitated; i.e., the PSPs were facilitated when electrical stimuli were applied simultaneously to 2 different sites in the unilateral or bilateral optic tecta. 6. From these results, it was concluded that: (1) there are 2 separate neuronal pathways, i.e., the polysynaptic excitatory and inhibitory pathways from the optic tectum to the tongue-muscle-controlling motoneurons and (2) the threshold for activating the excitatory pathways is higher than that of the inhibitory ones. It was suggested that the descending tectal efferents converge on the interneurons and that the temporal and spatial facilitation of spike discharges occurs within them. 7. These results were discussed with regard to the control of prey-catching behavior; it was suggested that: (1) these polysynaptic pathways (especially the excitatory ones) from the optic tectum to the tongue-muscle-controlling motoneurons are closely related to the generation of the lingual-flip motor-pattern during the prey-catching behavior and that (2) the temporal and spatial integration of synaptic inputs in the premotor interneurons plays a critical role in the initiation of prey-catching.

Notizen: Summary In order to describe precisely the fixed action patterns of salmon sexual behavior, we recorded the electromyographic (EMG) activities of trunk and jaw muscles from freely behaving male and female Himé salmon (landlocked sockeye salmon,Oncorhynchus nerka). A series of action patterns (quivering and spawning act in males, digging, covering, prespawning act and spawning act in females, and the swimming and turning movements in both sexes) were characterized by rhythmic activities of the trunk muscles. Each of these activity patterns is quantitatively distinct from the others in such parameters as frequency, bout duration, duty value, intersegmental phase delay, and spatial distribution of rhythmic activities. However, all of these rhythms share a qualitatively homologous pattern with the forward swimming movement: rhythmic activities alternate on both sides of the body (bilateral coupling) and are posteriorly propagated (intersegmental coupling). In addition, a 3∶1 intersegmental phase coupling occurs in the most anterior trunk muscles during the spawning act in some males. Based on these observations, we discussed the biomechanics for these motor patterns (oviposition, ejaculation, body vibration, and mouth opening), and the neural mechanisms for the pattern generation. A possibility was pointed out that the locomotor pattern generator in the spinal cord may be modulated by descending supraspinal signals and recruited to generate such diverse forms of action patterns in sexual behavior.

Notizen: Summary The terminals of centrifugal fibers to the olfactory bulbs of goldfish were studied by electron microscopy after transection of the medial, lateral or entire olfactory tract. The centrifugal fibers originate in the telencephalic hemisphere, pass through both the medial and the lateral olfactory tract, and form synaptic contacts with dendrites in the granule cell layer.

Notizen: During the breeding season, male anurans display clasping behavior by holding females with their forelimbs. This behavior is peculiar to males, and may require specializations in forelimb musculature. The present study revealed that five kinds of forelimb muscles were heavier in the male Japanese toad than in the female: the flexor carpi radialis (FCR), the flexor antibrachii medialis caput superius (FAMsup), the abductor indicis longus (AIL), the extensor carpi radialis caput superius (ECRsup), and the flexor antibrachii lateralis superficialis caput superius (FALSsup). In addition, one breast muscle, the coracoradialis (CR), was also heavier in males than in females. A quantitative analysis of muscle fibers processed for myosin ATPase activity showed that, in such “sexually dimorphic muscles” of the female, both fast (twitch) and slow (tonic) muscle fibers were of smaller diameter than in other forelimb muscles of both sexes (all male muscles plus “nondimorphic muscles” of the female). Moreover, both types of fibers were less numerous than in the corresponding muscles of the male. These results suggest that the “sexually dimorphic muscles” are used especially for clasping by the male and are degenerative or subnormal in the female. Slow muscle fibers were neither peculiar to, nor abundant in, these clasping muscles, although they may well be necessary for tonic and prolonged contractions of the forelimb muscles during clasping. The mechanism of sexual dimorphism may be a direct action of androgens on clasping muscles or an indirect action on clasping muscles via the innervating motoneurons.