Hiroaki Somiya

Neuropeptides as central integrators of autonomic nerve activity: effects of TRH, SRIF, VIP and bombesin on gastric and adrenal nerves.

The nerve activity of the gastric ramus of the splanchnic (sympathetic) nerve, gastric ramus of the vagus, adrenal ramus of the splanchnic nerve and the superior laryngeal nerve (laryngeal ramus of vagus) were assessed before and after i.c.v. injection of neuropeptides in the rat. TRH stimulated the vagal branch but attenuated the sympathetic outflow to the stomach. In contrast, the sympathetic outflow to the adrenal was enhanced by TRH. SRIF suppressed the activity of all the nerves studied. VIP did not affect the sympathetic outflow to the stomach while suppressing the gastric branch of the vagus. The adrenal sympathetic branch as well as the superior laryngeal nerve was stimulated by VIP. Bombesin suppressed both vagal and sympathetic outflow to the stomach but markedly stimulated the laryngeal branch of the vagus. The adrenal sympathetic nerve was either stimulated or attenuated slightly by bombesin. These results indicate that centrally administered neuropeptides produce reactions specific for each nerve.

`Yellow Lens' Eyes of a Stomiatoid Deep-Sea Fish, Malacosteus niger

Bright yellow lenses were found in the eyes of the stomiatoid deep-sea fish, Malacosteus niger Ayres. The optical properties of the yellow lens and the retinal specializations in the eyes were examined. Absorption spectra of the yellow lens revealed two peaks at wavelengths 425 and 460 nm. The photoreceptors were all rods and were arranged in two superimposed layers. An astaxanthin-type retinal tapetum was observed in the pigment epithelium. Some chemical evidence is presented showing that the tapetal material is an astaxanthin ester. The ecological significance of the yellow lens is discussed in connection with that of Malacosteus’ orbital light organ which has a reddish filter.

Functional significance of the yellow lens in the eyes of Argyropelecus affinis

Bright yellow lenses were found in the eyes of the mesopelagic deep-sea fish Argyropelecus affinis Garman. The yellow lenses were studied spectrophotometrically and the eyes were examined histologically. Absorption spectra of the yellow lenses revealed three peaks at wavelengths of 405, 430, and 460 nm. Histological examination revealed the eyes to be typically tubular. The functional significance of the yellow lens in such deep-sea fishes is discussed.

Evidence that endogenous thyrotropin-releasing hormone (TRH) may control vagal efferents to thyroid gland: neural inhibition by central administration of TRH antiserum

The intracerebroventricular (i.c.v.) injection of rabbit antiserum to thyrotropin-releasing hormone (TRH) to the urethane anesthetized rat inhibited the spontaneous electrical discharge of the superior laryngeal nerve (n.sl). On the other hand, the i.c.v. injection of rabbit antiserum to somatostatin (SRIF) failed to influence the nerve activity whereas SRIF itself is capable of inhibiting the n.sl activity. These findings suggest that TRH in the brain takes a role continuously in regulating the neural activity while SRIF is involved in the neuronal circuits as an agent for the down regulation of the autonomic nervous system.

Guanine and its retinal distribution in the tapetum of the bigeye tuna,thunnus obesus

The eye of the bigeye tuna (Thunnus obesus) contains a retinal tapetum composed of guanine. The total amount of the guanine in one eye of the fish (SL=120 cm) was about 88.6 mg. The mean guanine content of the tapetum was approximately 1.25 mg/cm2 of the retinal surface. The highest content of guanine (2.15 mg/cm2) was observed only in the ventro-temporal part of the retina. To distinguish this area from the rest of the eye, we suggested the term ‘locus tapetalis’ for it. The visual accommodation system clearly indicated that the visual axis of the fish is upper-forward and the resulting retinal area for acute vision was suggested to be in the ventro-temporal retina. We discussed that the area centralis of the bigeye tuna may have two functions: to guarantee high visual acuity and to allow for high photo-sensitivity in dim light vision.

Sonic Motor Nucleus and Its Connections with Octaval and Lateral Line Nuclei of the Medulla in a Rockfish, Sebastiscus marmoratus

The sonic motor nucleus and its fiber connections were examined in a rockfish, Sebastiscus marmoratus by means of tracer methods using horseradish peroxidase (HRP), biocytin, and carbocyanine dye (DiI). Sebastiscus has a swimbladder and a pair of extrinsic sonic/drumming muscles. The sonic muscle is ipsilaterally innervated by the occipital nerve which is composed of two ventral roots arising from the sonic motor nucleus. The sonic motor neurons are distributed in the most ventral part of the ventral column from the caudal medulla to the rostral spinal cord, and form a ventrally located columnar nucleus. Each neuron in this nucleus possesses a long thick dendrite and several short dendrites. The long dendrite extends dorsolaterally and branches in the lateral funiculus, whereas the short dendrites branch around their cell bodies. After biocytin injections into the sonic motor nucleus, two groups of premotor neurons were retrogradely labeled bilaterally, one in the dorsomedial portion of the descending octaval nucleus (DO) and the other in the medial zone of the reticular formation (RF) in the medulla. The DO premotor neurons were multipolar with several dendrites branching near the cell bodies, and the RF premotor neurons were bipolar. One of the two dendrites of the RF premotor neurons extends laterally into the ventral portion of the DO, and the other dendrite extends into the ventromedial area in the medulla. In the ventromedial dendritic field of the RF premotor neurons, descending fibers arising from the optic tectum (TO) and torus semicircularis (TS) traverse in the tractus tectobulbaris and terminate bilaterally. After DiI insertion into the ventromedial dendritic field, retrogradely labeled neurons were found bilaterally in the TS and TO. The majority of tectal neurons were located in the stratum griseum centrale. These neurons had two short basal dendrites branching in the cell layer and a long apical dendrite extending to the stratum fibrosum et griseum superficiale and stratum opticum. The toral neurons were bipolar and were distributed throughout the TS. Furthermore, biocytin injections into the medial nucleus of the lateral line system revealed that the nucleus projects bilaterally to the RF premotor neurons. These results show that premotor neurons for the sonic motor nucleus are located in the dorsomedial portion of the DO and the medial zone of the RF in the medulla. It is suggested that the sonic motor nucleus receives auditory input via the DO premotor neurons and input from RF premotor neurons which receive lateral line input via the medial nucleus, vestibular input through the lateral dendrite extending into the ventral portion of the DO, and information from the TO and TS via the tractus tectobulbaris.

Bacterial bioluminescence in chlorophthalmid deep-sea fish: A possible interrelationship between the light organ and the eyes

A small perianal light organ was found on a ventral part of the body of Chlorophthalmus spp. Simple tests, histological preparations and bacterial culture of the luminous contents clearly indicated that the luminous substance consists of symbiotic bacteria. The unique eyes of Chlorophthalmus spp. suggests a possible interrelationship between the eyes and the newly observed light organ.

Somatosensory nucleus in the torus semicircularis of cyprinid teleosts.

Cytoarchitecture and fiber connections of the ventrolateral region of torus semicircularis were studied in goldfish and carp. Cytoarchitectural analyses indicate that two toral nuclei, ventrolateral (TSvl) and external (TSe) nuclei, are present in this toral region. The TSvl mainly receives lateral line inputs from the medial nucleus of the rhombencephalic octavolateral area, while the TSe mainly receives somatosensory fibers from the spinal cord, sensory trigeminal nuclei, and lateral funicular nucleus. The TSe also receives sparse fibers from the retina and the octavolateral area medial nucleus and sends descending fibers to the lateral funicular nucleus. Both toral nuclei receive projections from the ventromedial thalamic nucleus and the central part of dorsal telencephalic area, although the latter descending fibers terminate mainly in the TSvl. Both toral nuclei project to the rostrolateral region of lateral preglomerular nucleus, restricted to the somata layer of the dorsal zone of the region. Ventrolateral and external toral fibers, however, tended to reach lateral and medial zones of the somata layer, respectively. The present study suggests that there are three functional compartments within the cyprinid torus semicircularis (central nucleus: auditory, TSvl: lateral line, and TSe: somatosensory) and that sensory pathways arising from these toral compartments maintain largely separate ascending systems into the forebrain. The present study also extends knowledge of the organization and connections of the lateral valvular nucleus and nucleus praeeminentialis that project to the cerebellar granular layer and cerebellar crest, respectively. J. Comp. Neurol. 518:2475–2502, 2010.

Innervation of Sonic Muscles in Teleosts: Occipital vs. Spinal Nerves

The innervation of sonic muscles in teleosts has been categorized into three types: occipital nerve, spinal nerve, and a combination of occipital and spinal nerves. The innervation patterns of sonic muscles were examined (or re-examined) in seven sonic fish species (rockfish, pinecone fish, sweeper, tigerfish, piranha, dory, and pollack) that use the sonic muscles to vibrate the swimbladder. The peripheral nerves (occipital or spinal) were identified based on skeletal preparations. The sonic muscle innervation was of the occipital type in four species (rockfish, pinecone fish, sweeper, and tigerfish) and of the spinal type in three species (piranha, dory, and pollack); none of the seven species examined showed the combination type. Therefore, we hypothesized that innervation patterns could be divided simply into occipital and spinal types. Moreover, the present results revealed that previously reported innervation patterns are inaccurate for three species (tigerfish, piranha, and dory) re-examined in this study. Therefore, it is important to define the peripheral nerves precisely, by using skeletal preparations, in future investigations of sonic muscle innervation.

Sound characteristics and the sound producing system in silver sweeper, Pempheris schwenkii (Perciformes: Pempheridae)

The sound characteristics and the sound producing system in silver sweeper, Pempheris schwenkii, are described. The main frequency component of the emitted sounds was 100-300 Hz, the mean duration of the sounds being 56 ms. The sounds were produced by paired extrinsic sonic muscles vibrating the swim-bladder. The sonic muscles originated on the pterotic bones and extended to the anterodorsal surface of the swimbladder, and were innervated by two branches of the occipital nerves. Moreover significant sexual dimorphism of the sonic muscles was observed, those in males being three times as large as in females.