Iwao Hidaka

Mechanical sensitivity of the facial nerve fibers innervating the anterior palate of the puffer,Fugu pardalis, and their central projection to the primary taste center

Summary1.Mechanical and chemical sensitivity of the palatine nerve, ramus palatinus facialis, innervating the anterior palate of the puffer,Fugu pardalis, and their central projection to the primary taste center were investigated.2.Application of horseradish peroxidase (HRP) to the central cut end of the palatine nerve resulted in retrogradely labeled neurons in the geniculate ganglion but no such neurons in the trigeminal ganglion, suggesting that the palatine nerve is represented only by the facial component.3.Tracing of the facial sensory root in serial histological sections of the brain stem suggested that the facial sensory nerve fibers project only to the visceral sensory column of the medulla.4.Peripheral recordings from the palatine nerve bundle showed that both mechanical and chemical stimuli caused marked responses. Mechanosensitive fibers were rather uniformly distributed in the nerve bundle.5.Intra-cranial recordings from the trigeminal and facial nerves at their respective roots revealed that tactile information produced in the anterior palate was carried by the facial nerve fibers.6.Elimination of the sea water current over the receptive field also caused a marked response in the palatine nerve bundle or facial nerve root while this did not cause any detectable responses in the trigeminal nerve root.7.Single fiber analyses of the mechanical responsiveness of the palatine nerve were performed by recording unit responses of 106 single fibers to mechanical stimuli (water flow), HCl (0.005M), uridine-5′-monophosphate (UMP, 0.001M), proline (0.01M), CaCl2 (0.5M), and NaSCN (0.5M). All these fibers responded well to one of the above stimuli; however, most taste fibers did not respond well to the inorganic salts. The palatine fibers (n=36), identified as mechanosensitive, never responded to any of the chemical stimuli, whereas chemosensitive fibers (n=70) did not respond to mechanical stimuli at all. The chemosensitive units showed a high specificity to the above stimuli: they tended to respond selectively to hydrochloric acid, UMP, or proline.8.The responses of the mechanosensitive units consisted of phasic and tonic impulse trains and the sensitivity of the units varied considerably.9.The results reveal that the facial nerve fibers innervating the anterior palate of the puffer contain two kinds of afferent fibers, chemosensory and mechanosensory respectively, and suggest that the convergence of the tactile and gustatory information first occurs in the neurons of the primary gustatory center in the medulla.

Self-feeding behavior of yellowtail, Seriola quinqueradiata, in net cages: diel and seasonal patterns and influences of environmental factors

Abstract The self-feeding pattern of yellowtail, Seriola quinqueradiata , maintained in floating net cages was examined throughout a year, and the influence of seasonal changes of the photoperiod and water temperature on the feeding pattern was investigated. Two groups of 50 yellowtail (initial mean body weight about 50 and 80 g, respectively) were kept in two experimental net cages (2×3×4 m deep), with a self-feeding device installed on each. It was possible to maintain yellowtail in net cages using a self-feeder throughout almost a year. The number of daily food demands was greatly affected by the seasonal changes in water temperature. Yellowtail showed high self-feeding activity, above 18 °C; depressing water temperatures did not influence the activity when the water temperature was over 18 °C. However, the activity decreased when the water temperature fell below 18 °C. The feeding pattern in a 24-h period was greatly affected by the temporal changes in light intensity. Annual observations revealed that yellowtail showed generally crepuscular plus nocturnal feeding behavior and had two peaks of feeding activity a day. These peaks appeared at dawn and dusk; moreover, a clear association between the most active time of self-feeding and the period of the greatest change in light intensity was observed. The results suggest that a change in light intensity might stimulate the appetite of yellowtail or that there is a light level at which yellowtail prefer to eat.

Receptor sites for alanine, proline, and betaine in the palatal taste system of the puffer, Fugu pardalis

SummaryTo elucidate the relative independence of the receptor sites for amino acids and betaine in the gustatory system of fish, the neural responses from the ramus palatinus facialis innervating the anterior palate of the puffer, Fugu pardalis, were recorded.There were observed independent amino acidsensitive and betaine-sensitive fibers.Cross-adaptation to pairs of stimulant was studied. The pair stimulants were applied reciprocally, i.e. after adapting with one stimulus the second stimulus was applied and then reversed. There were observed 3 types of cross-effects for the pairs of stimulants tested: (1) a reciprocal profound cross-adaptation; (2) no distinct cross-adaptation; and (3) a reciprocal enhancement of the response between betaine and alanine or glycine. Such an enhancement between betaine and alanine occurred in the amino acid-sensitive fibers, suggesting that betaine has an enhancing effect on the amino acid receptors.The present results suggest at least 3 different groups of receptor sites for the stimulants tested: (1) alanine sites for alanine, glycine and sarcosine; (2) proline sites for proline and dimethylglycine; and (3) betaine sites for betaine and dimethylglycine.

Identification of feeding stimulants from a jack mackerel muscle extract for young yellowtail Seriola quinqueradiata

The feeding-stimulatory components of an aqueous extract of jack mackerel white muscle for young yellowtail were identified. The extract was fractionated using anion-exchange chromatography, and the feeding-stimulatory effectiveness of fractionated components examined by adding them to starch pellets and feeding to yellowtail. The filtrate (FE) of the muscle extract filtered through a membrane having a mol. wt. cut-off of 10,000 Da was found to have a high feeding-stimulatory effectiveness on the yellowtail. FE was fractionated using DEAE-Sephadex A-25 at pH 5.5. The DEAE-Sephadex adsorbate (AA) showed an effectiveness close to but slightly weaker than that of FE. The DEAE-Sephadex non-adsorbate (NA) had no appreciable effect. Subdividing AA components by stepwise elutions with NaCl solutions suggested that inosine-5′-monophosphate and lactic acid were largely responsible for the stimulatory effectiveness of AA. Some components in NA might also be synergistic with AA components to elicit the full effectiveness of FE.

Gustatory and olfactory sensitivity to extracts of jack mackerel muscle in young yellowtail Seriola quinqueradiata.

Abstract The stimulatory effects of extract fractions of jack mackerel muscle, obtained using anion exchange chromatography, and their components on the gustatory and olfactory receptors of young yellowtail were investigated by recording electrical responses from the palatal taste nerve and the olfactory bulb. Ultrafiltrate (mol. wt. cut-off, 10,000 Da) of the muscle extract (FE) stimulated both chemosensory systems. FE was treated with a DEAE-Sephadex A-25 column (pH 5.5). The olfactory receptors showed a high sensitivity to both the adsorbate and non-adsorbate from the DEAE-Sephadex column. Their thresholds in the olfactory bulb response were around 10−5 and 10−8 of the original concentration, respectively. Those in the gustatory nerve response were 10−4 and 10−2. Amino acids were highly effective for the olfactory receptors. The threshold of l -glutamine was around 10−8 M. 5′-Inosinic acid and l -lactic acid were more effective for the gustatory receptors than for the olfactory receptors; their thresholds for the former were 10−4 M and 10−6 M, while those for the latter were 10−3 M and above 10−3 M. These findings suggest that the gustatory receptors are involved in discriminating food items during feeding and that the olfactory receptors may detect foods at some distance.

The anterior cranial gustatory pathway in fish

Mit Hilfe elektrophysiologischer Methodik wurde anFugu pardalis geprüft, ob Geschmackssensationen von den Lippen über Trigeminus- oder Facialisfasern dem Gehirn übermittelt werden. Die Ergebnisse unterstützen die Ansicht, dass ausschliesslich der Facialisnerv bei diesem Vorgang beteiligt ist.

Enhancing Effects of Betaine on the Taste Receptor Responses to Amino Acids in the Puffer Fugu pardalis

It is well known that there exists a synergism between monosodium glutamate and nucleotides in human taste sensation [1,2]. A similar synergism is known for these compounds in the peripheral taste nerve responses in rats [3–5]; the neural response is synergistically enhanced by applying them together.

L-Lactate Sensitivity of Fish Taste Receptors

Organic acids are abundant in the tissue extracts of fish and other aquatic organisms. However, our knowledge of their stimulatory effect on feeding and their stimulatory effect on the taste receptors of fish is still fragmentary. In a previous study [1], the palatal taste receptors of the yellowtail Seriola quinqueradiata were found to be sensitive to some organic acids, especially to L-lactic acid. This suggests the biological importance of these acids associated with the gustatory sense of fish, since the tissues of potential food organisms contain these acids at varying concentrations as cell metabolites. Moreover, it seems interesting to determine whether lactic acid stimulates the receptor sites for amino acids, since its chemical structure has some resemblance to alanine.