Hiro-aki Takeuchi

Behavioral and electrophysiological evidences that the lateral line is involved in the inter-sexual vibrational communication of the himé salmon (landlocked red salmon, Oncorhynchus nerka)

Characteristic vibrational signals are suggested to be exchanged between the sexes during the spawning behavior in the himé salmon (landlocked red salmon, Oncorhynchus nerka). To check whether the lateral line is used to detect and process these vibrational signals, we examined how Co2+, which is known to block the mechano-electrical transduction in the lateral line detector, affects both the spawning behavior and lateral line response of the male himé salmon. The results showed that Co2+ blocked both the spawning behavior towards the vibrating model (Fig. 2) and the lateral line response to the vibrational stimuli (Figs. 5, 6), if the fish were forced to swim in the water containing 1.0 mM Co2+ for 1 to 1.5 h or longer in the presence of 0.25 mM Ca2+. 0.1 mM Co2+ had similar but weaker effects. These results indicate that the vibrational signals from the vibrating model are detected and processed by the lateral line system to elicit the spawning behavior. These are the first experimental evidences that the lateral line sense is involved in the communicational behavior of the fish.

Characterization of vibrational and visual signals which elicit spawning behavior in the male himé salmon (landlocked red salmon, Oncorhynchus nerka)

Himé salmon (landlocked red salmon, Oncorhynchus nerka) have an elaborate communication system, which ensures synchronous spawning by both sexes and successful fertilization. Both the vibrational and visual signals have been suggested to be involved in this communication system. To characterize these signals, vibrating or stationary three-dimensional models of various types were presented to the male, and male behavior elicited was examined. The results showed that the vibrating model mimicking certain aspects of the female behavior (‘prespawning act’) elicits the spawning in the male (Figs. 2, 3, 5). Furthermore, it was found that (1) the presence of both the vibrational and visual cues (Figs. 6, 7), and (2) spatial coincidence of these two cues (Fig. 8) are necessary for eliciting this behavior. Based on these results it was supposed that the vibrational and visual informations converge at the central nervous system where they are integrated to elicit the spawning.

A possible retinal information route to the circadian pacemaker through pretectal areas in the hagfish, Eptatretus burgeri ☆

By recording the locomotor activity rhythm of hagfish, Eptatretus burgeri, in which surgical lesions of the pretectal areas were made, we searched for the route of light information from the eyes to the circadian pacemaker, which is considered to be located in the preoptic nucleus. The entrainment of circadian activity rhythm to the light dark cycle, under 12 h light/12 h dark (12L:12D) was lost in animals whose pretectum was ablated with a pair of scissors and the animals then showed a free-running rhythm. Destruction of the pretectal areas with a high-frequency lesion generator also caused a free-running rhythm under 12L:12D. These findings indicate that retinal information may entrain the circadian rhythm via the pretectal areas, which have retinofugal connections.

Circadian Rhythms in Locomotor Activity of the Hagfish, Eptatretus burgeri VI. The Effects of Cutting the Spinal Cord

Abstract The present study is designed to clarify the mechanism by which the circadian pacemaker controls the locomotor activity of the hagfish and also to estimate the role of brain and spinal cord in the swimming behavior of the animal. We examined the effect of cutting the spinal cord at the 6 different positions on the circadian rhythm and the locomotor behavior of the animal. The most frontal cut was located between the brain and spinal cord, and the other 5 cuts were given to every 1/6 the length of the spinal cord. The relation between the locomotor activity and the cut position of spinal cord was summarized as follows. (1) When the ratio of frontal part before the cut was 0/6–1/6, the animal locomoted under initiative of caudal part, in random direction at the bottom and showed neither nocturnal rhythm in LD nor circadian rhythm in DD. (2) When the ratio of the frontal part before the cut was 4/6–5/6, the animal swam up to the surface under initiative of frontal part, and showed both nocturnal rhythm in LD and circadian rhythm in DD. (3) When the frontal ratio of spinal cord was 2/6 or 3/6, the animal showed both kinds of swimming behavior of (1) and (2). These results suggest that the descending system from the brain enable the hagfish to swim up to the surface and to express the rhythmicity of locomotor activity under control of the circadian pacemaker when at least frontal 2/6 of the spinal cord is connected to the brain by neuronal networks not by humoral factors.

Taste Discrimination in Salamanders

Salamanders are excellent experimental models for studying cellular mechanisms of taste reception because their taste receptor cells are large and form large taste buds of simple structure [1–3]. Intracellular recordings were made from taste receptor cells of the mudpuppy Necturus maculosus [4–7] and the tiger salamander Ambystoma tigrinum [8,9]. The chemosensitivity of the glossopharyngeal nerve (nIX) innervating a large area of the salamander lingual epithelium was studied in the mudpuppy [10,11] and the Mexican salamander Ambystoma mexicanum [12]. The ultrastructure of taste cells and associated synapses was studied in the mudpuppy [2,13,14] and the Mexican salamander [1,3]. Although there has been a wealth of physiological and anatomical studies, behavioral studies of the salamander’s ability to discriminate taste are few [15,16]. Therefore we designed behavioral experiments to examine if salamanders can discriminate the chemicals that are commonly used in physiological experiments as taste stimuli.

Gene expression patterns of chicken neuregulin 3 in association with copy number variation and frameshift deletion

BackgroundNeuregulin 3 (NRG3) plays a key role in central nervous system development and is a strong candidate for human mental disorders. Thus, genetic variation in NRG3 may have some impact on a variety of phenotypes in non-mammalian vertebrates. Recently, genome-wide screening for short insertions and deletions in chicken (Gallus gallus) genomes has provided useful information about structural variation in functionally important genes. NRG3 is one such gene that has a putative frameshift deletion in exon 2, resulting in premature termination of translation. Our aims were to characterize the structure of chicken NRG3 and to compare expression patterns between NRG3 isoforms.ResultsDepending on the presence or absence of the 2-bp deletion in chicken NRG3, 3 breeds (red junglefowl [RJF], Boris Brown [BB], and Hinai-jidori [HJ]) were genotyped using flanking primers. In the commercial breeds (BB and HJ), approximately 45% of individuals had at least one exon 2 allele with the 2-bp deletion, whereas there was no deletion allele in RJF. The lack of a homozygous mutant indicated the existence of duplicated NRG3 segments in the chicken genome. Indeed, highly conserved elements consisting of exon 1, intron 1, exon 2, and part of intron 2 were found in the reference RJF genome, and quantitative PCR detected copy number variation (CNV) between breeds as well as between individuals. The copy number of conserved elements was significantly higher in chicks harboring the 2-bp deletion in exon 2. We identified 7 novel transcript variants using total mRNA isolated from the amygdala. Novel isoforms were found to lack the exon 2 cassette, which probably harbored the premature termination codon. The relative transcription levels of the newly identified isoforms were almost the same between chick groups with and without the 2-bp deletion, while chicks with the deletion showed significant suppression of the expression of previously reported isoforms.ConclusionsA putative frameshift deletion and CNV in chicken NRG3 are structural mutations that occurred before the establishment of commercial chicken lines. Our results further suggest that the putative frameshift deletion in exon 2 may potentially affect the expression level of particular isoforms of chicken NRG3.

Load Changes in Limbs during Orienting in Non-Restrained Cats

We simultaneously investigated eye and head movements and postural adjustment during orienting by measuring load force exerted by four limbs in cats. When light is moved from the fixation point to the target position, the head first begins moving towards the target position, and the eye moves in the opposite direction due to the vestibulo-ocular reflex (VOR). Later, the eye moves quickly in the target direction by saccade, synchronous with the remaining rapid head orientation movement. Head movement is classified as either ‘head rotation’ or ‘head translation’. During head rotation, the load force in ipsilateral limb to the target position decreased, and that in the contralateral limb increased. During head translation, on the contrary, load force in the ipsilateral limb increased and that in the contralateral limb decreased. This phenomenon was observed in fore- and hindlimbs. The latencies of head movement are very similar with those of the load force change in many trials, and in case in which the head movement has short latency, the amount of load force change is larger. In contrast, when head movement has long latency, the amount of load force change is smaller. In a previous study, we recorded two types of neurons from ponto-medullary reticular formation. The firing of these neurons was related with head movement. The cervical reticulospinal neuron (C-RSN) in ponto-medullary reticular formation got off collateral to both neck and forelimb motoneurons. These types were named phasic neuron (PN) and phasic sustained neuron (PSN). We discuss the relation between load changes and the two types of neurons and postural adjustment during orienting.

Zenk expression in the brain of bengalese finch

In songbirds, immediate early genes (IEGs) arc used as tools for analyzing brain mechanisms concerned with song learning and vocalization. In the present study, WC investigated how and where zcnk (homologuc of mammalian egr-1) was expressed in the brain of male Bengalese finches using behavioral and immunohistochcmical techniques. Three different situations were examined; (1) singing only: birds were deafened and sang songs, (2) hearing only: birds were presented conspecific songs and did not sing, (3) control: birds were presented no song and did not sing. Consequently the patterns of the zenk expression were diffcrcnt between singing and hearing situations The zenk expression in song nuclei HVc, RA and X accompanied the motor act of singing, but not hearing. In contrast, zenk expression in NCM: which was suggested the relation to the acquisition of new song-related memories, accompanied the presentation of conspecific song. These results lead to the conclusion that the zcnk expression is involved in song maintenance and song perception.

2210 Location of the circadian pacemaker of the hagfish and the retinal information route to it

Abnormal circadian rhythmicity of locomotor-activity was observed on p53 knockout mice (Hamada T. et al., 18th bunshiseibutsu-gakkai-nenkai). This result suggests that the tumor suppressor gene p53 may be involved in the molecular mechanism of the circadian locomotor-activity. Therefore, we examined the expression of the ~53 gene by using DIG in situ hybridization method and detected the p53 mRNA in the suprachiasmatic nucleus of the rat brain, which is considered to be a major site of the circadian pacemaker in mammals.