Branchial innervation

Inspection of the dorsal end of fish gills reveals an impressive set of nerve trunks, connecting the gills to the brain. These trunks are branches of cranial nerves VII (the facial) and especially IX (the glossopharyngeal) and X (the vagus). The nerve trunks carry a variety of nervous pathways to and from the gills. A substantial fraction of the nerves running in the branchial trunks carry afferent (sensory) information from receptors within the gills. There are also efferent (motor) pathways, which control muscles within the gills, blood flow patterns and possibly secretory functions. Undertaking a more careful survey of the gills, it becomes evident that the arrangement of the microanatomy (particularly the blood vessels) and its innervation are strikingly complex. The complexity not only reflects the many functions of the gills but also illustrates that the control of blood flow patterns in the gills is of crucial importance in modifying the efficiency of its chief functions: gas transfer and salt balance. The "respiratory-osmoregulatory compromise" is maintained by minimizing the blood/water exchange (functional surface area of the gills) to a level where excessive water loss (marine teleosts) or gain (freshwater teleosts) is kept low while ensuring sufficient gas exchange. This review describes the arrangement and mechanisms of known nervous pathways, both afferent and efferent, of fish (notably teleosts) gills. Emphasis is placed primarily on the autonomic nervous system and mechanisms of blood flow control, together with an outline of the afferent (sensory) pathways of the gill arches.     

Branchial musculature of a venerid clam: pharmacology,distribution, and innervation

This study was meant to analyze the neural control of the branchial muscles of the clam Mercenaria mercenaria. Gills isolated from the animal contract in response to 5-hydroxytryptamine (5HT), dopamine (DA), and acetylcholine (ACh); but the ACh contraction occurred only if the gills had been pretreated with the cholinesterase inhibitor eserine. The 5HT antagonists cyproheptadine and mianserin blocked the contractile effects of all of the agonists. However, gills exposed to the 5HT antagonists and eserine relaxed in response to ACh. The DA antagonist SCH-83566 inhibited the effects of DA, but had no effect on contractions induced by 5HT and ACh. The ACh antagonist hexamethonium inhibited both the excitatory and inhibitory effects of ACh, but had no effect on contractions induced by 5HT and DA. 5HT and DA in gill tissue were visualized by using immunohistochemistry. Within each gill filament are dorsoventral neurons running adjacent to the epithelium and containing immunoreactive 5HT and DA. A complex network of 5HT-positive fibers is associated with the septa, blood vessels, and muscles, whereas DA-positive fibers are restricted to the septa. We propose that 5HT is the excitatory transmitter to the gill muscles, and that DA and ACh exert their excitatory effects by stimulating 5HT motor nerves. ACh may also be an inhibitory transmitter of the muscles.     

The sympathetic innervation of the ciliary body and trabecular meshwork of the cat

Summary The ciliary body of the cat was investigated by fluorescence histochemistry and electron microscopy in an attempt to clarify its sympathetic innervation. Subconjunctival doses of 5-hydroxydopamine (5-OHDA) or 6-hydroxydopamine (6-OHDA) were given to establish the precise location of the sympathetic nerve terminals. The distribution of noradrenergic fibers and terminals was shown by fluorescence histochemistry to be sparse in the trabecular meshwork and the anterior portion of the ciliary muscle, but dense in the subepithelial tissue. The small and large dense core vesicles which occur in many nerve endings of the subepithelial tissue adjacent to the pigmented epithelial layer increased in electron density following the administration of 5-OHDA. Many degenerating nerve endings were found in the same region of animals treated with 6-OHDA. In contrast, there were few noradrenergic terminals in the ciliary muscle except for a portion of the smooth muscle which was shown to be dually innervated. The noradrenergic fibers in the subepithelial region and the trabecular meshwork may play an important role in aqueous secretion and outflow.This work was supported in part by a research grant from the Ministry of Education, Japan     

A re-evaluation of morphological characters of the invasive ascidian Corella eumyota reveals two different species at the tip of South America and in the South Shetland Islands, Antarctica

The native solitary ascidian Corella eumyota Traustedt, 1882) is commonly found in the Southern Hemisphere in the cold-temperate waters of the Subantarctic and Antarctic regions. Its recent spread into the Northern Hemisphere throughout the NE Atlantic gave the species the status of invasive. Together with its widespread distribution, reports on its wide variability (several distinct morphological characters, genetic discontinuities and also possible misidentifications) cast doubt on the taxonomic status of different populations of this species. This work, based on the observation, quantification and analysis of specific morphological characters in specimens collected at five different localities of South America and Antarctica, strongly indicates that there are two different species: C. eumyota from South America and Corella antarctica Sluiter, 1905) from Antarctica, which has been till now considered a junior synonym of the former. The species clearly differ in the arrangement of the gonadal ducts, the size of the larvae and the shape of the anus, among other characters. Morphological variation displays a defined, discrete grouping supporting a clear differentiation into two species. This result shows the need for careful inspection of specimens to avoid wrong interpretations in a context of changes of marine biota due to biological invasions.     

A comparative study of the adrenergic innervation of the iris and ciliary structures in 18 species in phylogenesis

A detailed topography of adrenergic innervation in invertebrates (lobster), low vertebrates (fish, amphibians, reptiles, birds), and nine species of mammals is presented. Flack and Hillarp's specific fluorescent histochemical method using freeze-dried material was used. Phylogenetically, adrenergic innervation appeared earlier under the ciliary epithelium and in the muscle than surrounding the vessels, and in all species many fibers were without any connection to the vessel walls. Adrenergic innervation was very rich in the dilator muscle extending toward the epithelium of the posterior chamber; a surprisingly rich network was found in the sphincter muscle and also in ciliary spaces of some species. Numerous fluorescent mast cells were visualized in the pecten of the bird eye and in the ciliary tissue of the sheep and cow.     

Electrophysiological control of ciliary motor responses in the ctenophorePleurobrachia

Prey capture by a tentacle of the ctenophore Pleurobrachia elicits a reversal of beat direction and increase in beat frequency of comb plates in rows adjacent to the catching tentacle (Tamm and Moss 1985). These ciliary motor responses were elicited in intact animals by repetitive electrical stimulation of a tentacle or the midsubtentacular body surface with a suction electrode. An isolated split-comb row preparation allowed stable intracellular recording from comb plate cells during electrically stimulated motor responses of the comb plates, which were imaged by high-speed video microscopy. During normal beating in the absence of electrical stimulation, comb plate cells showed no changes in the resting membrane potential, which was typically about -60 mV. Trains of electrical impulses (5/s, 5 ms duration, at 5-15 V) delivered by an extracellular suction electrode elicited summing facilitating synaptic potentials which gave rise to graded regenerative responses. High K+ artificial seawater caused progressive depolarization of the polster cells which led to volleys of action potentials. Current injection (depolarizing or release from hyperpolarizing current) also elicited regenerative responses; the rate of rise and the peak amplitude were graded with intensity of stimulus current beyond a threshold value of about -40 mV. Increasing levels of subthreshold depolarization were correlated with increasing rates of beating in the normal direction. Action potentials were accompanied by laydown (upward curvature of nonbeating plates), reversed beating at high frequency, and intermediate beat patterns. TEA increased the summed depolarization elicited by pulse train stimulation, as well as the size and duration of the action potentials. TEA-enhanced single action potentials evoked a sudden arrest, laydown and brief bout of reversed beating. Dual electrode impalements showed that cells in the same comb plate ridge experienced similar but not identical electrical activity, even though all of their cilia beat synchronously. The large number of cells making up a comb plate, their highly asymmetric shape, and their complex innervation and electrical characteristics present interesting features of bioelectric control not found in other cilia.     

Membrane control of ciliary movement in ciliates

Ciliary movement is generated in the axoneme by the unidirectional sliding of the outer doublets of microtubules produced by the adenosine triphosphate (ATP)-energized dynein arms. It is composed of an effective stroke phase and a passive recovery stroke phase. Two parameters are modulated to determine swimming characteristics of the cell (speed and direction): beat frequency; direction of the effective stroke. They are linked to the internal Ca++ level and to the membrane potential. The membrane governs the internal Ca++ level by regulating Ca++ influx and efflux. It contains voltage-sensitive Ca++ channels through which a passive Ca++ influx, driven by the electrochemical gradient, occurs during step depolarization. The rise of the Ca++ level, up to 6.10-7M triggers ciliary reversal and enhances beat frequency. Ca+ is extruded from cilia by active transport. Ca++ also activates a multistep enzymatic process, the first component of which is a membrane calmodulin-dependent guanylate cyclase. cGMP interacts with Ca++ to modulate the parameters of the ciliary beat. The phosphorylation-dephosphorylation cycle of axoneme and membrane proteins seems to play a major role in controlling ciliary movement. Hyperpolarization of the membrane enhances beat frequency by an unknown mechanism. It could be a modification of the ratio of axonemal bound Ca++ and Mg++, or activation by cyclic adenosine monophosphate (cAMP) produced by a membrane adenylate cyclase. The ciliary membrane behaves as a receptor able to detect modifications of external parameters, and as a transductor transmitting the detected signal by a second or third messengers toward the interior of the cilia. These messengers. acting at different levels, modulate the parameters of the mechanism that generates ciliary movement.     

Role of innervation in the control of bone remodeling

During the last fifteen years, an increasing number of studies have examined the origin, the ontogeny, and the distribution of nerve fibers in bone. They have also investigated the nature of neuromediators conveyed by these skeletal nerve fibers. Experimental models of sensory and sympathetic denervation and clinical studies have shown that these two neuronal systems are involved in bone development, growth and remodeling. More recently, some new concepts regarding the role of nerve fibers in bone physiology have emerged with the demonstration of a leptin-dependent central control of bone formation via the sympathetic system. This new neural regulating pathway of bone cell functions could have enormous implications for human skeletal biology and treatment of bone pathologies.     

The control of ciliary beat frequency

Ciliary movement is powered by axonemal dynein. This article considers how a signal transduction cascade initiated at the cell membrane may activate outer dynein arms to change the velocity of microtubule sliding and the swimming speed of ciliated cells. For Paramecium, a critical event in the cascade is the cAMP-dependent phosphorylation of a 29 kDa polypeptide that is associated with the outer dynein arm.     

Quantitative control of end products in the melanocyte lineage of the ascidian embryo.

Terminal amounts of tyrosinase (EC 1.10.3.1) activity and melanin pigment in the giant melanocytes of cleavage-arrestedCiona intestinalis (L.) embryos are regulated independently of cell size and number of nuclei in the cells. Embryos were cleavage-arrested in cytochalasin B at a time before the last two divisions of the melanocyte lineage took place. The resulting two giant melanocytes, one from each of the two bilateral melanocyte lineages, developed tyrosinase and melanin. The cells were about three times larger in volume than the normal larval melanocytes and each contained four nuclei instead of just one. Quantitative measurements of melanin synthesized and tyrosinase activity in embryos with the giant melanocytes revealed amounts identical to those found in normal embryos. This specification of exact quantities differs markedly from the situation in mammalian melanocytes where cell volume and gene dosage influence the extent of melanotic differentiation. Quantitative control of differentiation in ascidian melanocytes appears to be mediated by a cytoplasmic determinant segregated through the melanocyte lineage and inherited by one daughter at each division of the lineages.     

Branchial arch muscle innervation by the glossopharyngeal (IX) and vagal (X) nerves in tetraodontiformes, with special reference to muscle homologies

Branchial arch muscle innervation by the glossopharyngeal (IX) and vagal (X) nerves in 10 tetraodontiform families and five outgroup taxa was examined, with special reference to muscle homologies. Basic innervation patterns and their variations were described for all muscle elements (except gill filament muscles). In the tetraodontids Takifugu poecilonotus and Canthigaster rivulata, diodontid Diodon holocanthus, and molid Mola mola, levator externus 4 was innervated by the 3rd vagal branchial trunk (BX3) in addition to BX2, owing to strong posterior expansion of the muscle. Based on nerve innervation, migrations of the muscle attachment sites (i.e., origins and insertions) were recognized in levator internus 2 (in Mola mola), obliquus dorsalis 3 (in Ostracion immaculatus and Canthigaster rivulata), and obliquus ventralis 2 (in Stephanolepis cirrhifer), muscle topologies not necessarily being indicative of homologies. Embryonic origin of the retractor dorsalis and parallel attainment of the swimbladder muscle within the order were also discussed.     

Cupular organs in two species of Corella (Tunicata: Ascidiacea)

Abstract. Simple cupular organs similar to those described in Ciona intestinalis were observed in Corella eumyota. They consist of a macula containing the cell bodies of 20–30 primary sensory neurons whose cilia project into a dome‐ or finger‐shaped structure, the cupula. Rather than being found in the mantle lining as in C. intestinalis, the organs were located on the atrial surface of the branchial sac. The sensory innervation was examined in whole‐mount preparations using anti‐tubulin immunohistochemistry. Sensory neurons in C. eumyota showed no immunoreactivity with antisera raised against gonadotropin‐releasing hormone (GnRH). A novel, elongated sense organ termed the cupular strand was found in Corella inflata. It has the same basic components as the simple type of cupular organ but consists of a single, long structure containing ～1500 sensory cells. Located on the atrial surface of the branchial sac, it extends along the midline of the dorsal fold, from the gonoduct openings almost as far as the brain. Preparations were examined using optical and electron microscopy. Nerves and cilia were visualized by anti‐tubulin immunofluorescence microscopy. It was possible to follow the sensory axons from the macula of the cupular strand to points where they joined branches of the visceral nerve, which enters a nerve root at the back of the brain. In C. inflata the sensory cell bodies and their axons were immunoreactive not only with anti‐tubulin but also with an antiserum raised against Tunicate I GnRH. There was no immunoreactivity, however, with Chicken II and catfish GnRH antisera. All three GnRH antisera labeled the dorsal strand plexus, a structure associated with production of GnRH in its role as a reproductive hormone. We concluded that the GnRH‐like molecule labeled in sensory neurons differs from the form of GnRH found in the dorsal strand plexus, and may have a different function, perhaps in the neural control of ciliary activity. The function of the cupular organs in species of Corella has not yet been investigated physiologically, but by analogy with such structures in other metazoans, cupular organs are probably hydrodynamic sensors registering local disturbances or changes in water flow through the atrial cavity.     

Population survey of the Philippine tarsier (Tarsius syrichta) in Corella, Bohol

In 1986, in response to the rapid habitat destruction throughout the archipelago, the Philippine tarsier was classified as endangered. Since that time, this tarsier has been reclassified as data deficient and more recently as near threatened despite a significant lack of information on the population density of the species. Data were collected at the Philippine Tarsier Foundation Sanctuary from June to October 2010. Population density was estimated using a modified form of the quadrat census method. A total of 55 individuals were located within the sampled area. This is equivalent to approximately 1.55 tarsiers per hectare. Ecologically, there were significantly more tarsiers found in the young secondary forest than in areas characterized as old secondary forest. Extrapolating to the entire protected area, as many as 258 tarsiers may reside in the sanctuary. The vegetation plots where tarsiers were found had substantially more trees per plot, contained trees with larger diameters, and contained slightly taller trees than did the plots where no tarsiers were observed.     

Experimental control of budding and stolon elongation in Perophora orientalis. A compound ascidian

The elongation of stolon and the formation of an endoblastic vesicle leading to the differentiation of a blastozooid in an isolated stolon piece of Perophora orientalis were described. A treatment of isolated stolon pieces with 2 × 10^?2 M thiourea for 5 hr completely inhibited stolon elongation and at the same time accelerated the formation of an endoblastic vesicle. Inversely, 10^?5 M thyroxine and 10^?5 M triiodothyronine markedly stimulated stolon elongation with concomitant suppression of the formation of an endoblastic vesicle. The isolated stolon piece was thus proved to be experimentally directed either to the elongation of stolon or to the formation of an endoblastic vesicle, and to be a potential system for the study of the control mechanisms between the two alternative pathways, growth and differentiation.