Statocyst Hair Cells Research Articles

Histamine Immunoreactive Elements in the Central and Peripheral Nervous Systems of the Snail, Biomphalaria spp., Intermediate Host for Schistosoma mansoni.

Histamine appears to be an important transmitter throughout the Animal Kingdom. Gastropods, in particular, have been used in numerous studies establishing potential roles for this biogenic amine in the nervous system and showing its involvement in the generation of diverse behaviours. And yet, the distribution of histamine has only previously been described in a small number of molluscan species. The present study examined the localization of histamine-like immunoreactivity in the central and peripheral nervous systems of pulmonate snails of the genus Biomphalaria. This investigation demonstrates immunoreactive cells throughout the buccal, cerebral, pedal, left parietal and visceral ganglia, indicative of diverse regulatory functions in Biomphalaria. Immunoreactivity was also present in statocyst hair cells, supporting a role for histamine in graviception. In the periphery, dense innervation by immunoreactive fibers was observed in the anterior foot, perioral zone, and other regions of the body wall. This study thus shows that histamine is an abundant transmitter in these snails and its distribution suggest involvement in numerous neural circuits. In addition to providing novel subjects for comparative studies of histaminegic neurons in gastropods, Biomphalaria is also the major intermediate host for the digenetic trematode parasite, which causes human schistosomiasis. The study therefore provides a foundation for understanding potential roles for histamine in interactions between the snail hosts and their trematode parasites.

Aminoglycoside-Induced Damage in the Statocyst of the Longfin Inshore Squid, Doryteuthis pealeii

Squid are a significant component of the marine biomass and are a long-established model organism in experimental neurophysiology. The squid statocyst senses linear and angular acceleration and is the best candidate for mediating squid auditory responses, but its physiology and morphology are rarely studied. The statocyst contains mechano-sensitive hair cells that resemble hair cells in the vestibular and auditory systems of other animals. We examined whether squid statocyst hair cells are sensitive to aminoglycosides, a group of antibiotics that are ototoxic in fish, birds, and mammals. To assess aminoglycoside-induced damage, we used immunofluorescent methods to image the major cell types in the statocyst of longfin squid (Doryteuthis pealeii). Statocysts of live, anesthetized squid were injected with either a buffered saline solution or neomycin at concentrations ranging from 0.05 to 3.0 mmol l(-1). The statocyst hair cells of the macula statica princeps were examined 5 h post-treatment. Anti-acetylated tubulin staining showed no morphological differences between the hair cells of saline-injected and non-injected statocysts. The hair cell bundles of the macula statica princeps in aminoglycoside-injected statocysts were either missing or damaged, with the amount of damage being dose-dependent. The proportion of missing hair cells did not increase at the same rate as damaged cells, suggesting that neomycin treatment affects hair cells in a nonlethal manner. These experiments provide a reliable method for imaging squid hair cells. Further, aminoglycosides can be used to induce hair cell damage in a primary sensory area of the statocyst of squid. Such results support further studies on loss of hearing and balance in squid.

The neuroanatomical and ultrastructural organization of statocyst hair cells in the pond snail,Lymnaea stagnalis

The ultrastructure, neuroanatomy and central projection patterns, including the intercellular connections of the statocyst hair cells of the pond snail, Lymnaea stagnalis, were studied, applying different intra- and extracellular cellular staining techniques combined with correlative light- and electron microscopy. Based on the ultrastructure different hair cells could be distinguished according to their vesicle and granule content, meanwhile the general organization of the sensory neurons was rather uniform, showing clearly separated perinuclear and "vesicular" cytoplasmic regions. Following intra- and extracellular labeling with fluorescence dyes or HRP a typical, local arborization of the hair cells was demonstrated in the cerebral ganglion neuropil, indicating a limited input-output system connected to the process of gravireception. Correlative light- and electron microscopy of HRP-labeled hair cells revealed both axo-somatic and axo-axonic output contacts of hair cell varicosities, and input on sensory axons located far from the terminal arborizations. Our findings suggest (i) a versatile ultrastructural background of hair cells corresponding possibly to processing different gravireceptive information, and (ii) the synaptic (or non-synaptic) influence of gravireception at different anatomical (terminal, axonal and cell body) levels when processed centrally. The results may also serve as a functional morphological background for previously obtained physiological and behavioral observations.

5-HT and GABA Modulate Intrinsic Excitability of Type I Interneurons in Hermissenda

The sensory neurons (photoreceptors) in the visual system of Hermissenda are one site of plasticity produced by Pavlovian conditioning. A second site of plasticity produced by conditioning is the type I interneurons in the cerebropleural ganglia. Both photoreceptors and statocyst hair cells of the graviceptive system form monosynaptic connections with identified type I interneurons. Two proposed neurotransmitters in the graviceptive system, serotonin (5-HT) and gamma-aminobutyric acid (GABA), have been shown to modify synaptic strength and intrinsic neuronal excitability in identified photoreceptors. However, the potential role of 5-HT and GABA in plasticity of type I interneurons has not been investigated. Here we show that 5-HT increased the peak amplitude of light-evoked complex excitatory postsynaptic potentials (EPSPs), enhanced intrinsic excitability, and increased spike activity of identified type I(e(A)) interneurons. In contrast, 5-HT decreased spike activity and intrinsic excitability of type I(e(B)) interneurons. The classification of two categories of type I(e) interneurons was also supported by the observation that 5-HT produced opposite effects on whole cell steady-state outward currents in type I(e) interneurons. Serotonin produced a reduction in the amplitude of light-evoked complex inhibitory PSPs (IPSPs), increased spontaneous spike activity, decreased intrinsic excitability, and depolarized the resting membrane potential of identified type I(i) interneurons. In contrast to the effects of 5-HT, GABA produced inhibition in both types of I(e) interneurons and type I(i) interneurons. These results show that 5-HT and GABA can modulate the intrinsic excitability of type I interneurons independent of the presynaptic effects of the same transmitters on excitability and synaptic efficacy of photoreceptors.

The relationship between body size and evoked potentials from the statocysts of the prawnPalaemon serratus

The organisation of the statocyst hair cells and auditory evoked potentials (AEPs) generated by the afferents in three body size classes of prawn (Palaemon serratus) have been studied using a combination of anatomical, electron microscopic and electrophysiological approaches. The statistical examination of the relationship between the sensory setae and body size showed an increase in both the length and number of statocyst hair cells as the animal grows. In view of this finding, the response of the statocyst organ to a 500 Hz tone burst was recorded from four specimens from each size class using two subcutaneous electrodes, positioned in the carapace close to the supraoesophageal ganglion and statocyst. Neither body size nor the number of afferents in the statocyst has any significant impact on the amplitude of AEPs in response to the 500 Hz tone burst. The findings of this study show that P. serratus is capable of hearing a 500 Hz tone regardless of body size, a finding that is of ecological importance when considering the effect of anthropogenic sound on crustaceans.

Subcellular, cellular, and circuit mechanisms underlying classical conditioning in Hermissenda crassicornis

A breakthrough for studying the neuronal basis of learning emerged when invertebrates with simple nervous systems, such as the sea slug Hermissenda crassicornis, were shown to exhibit classical conditioning. Hermissenda learns to associate light with turbulence: prior to learning, naive animals move toward light (phototaxis) and contract their foot in response to turbulence; after learning, conditioned animals delay phototaxis in response to light. The photoreceptors of the eye, which receive monosynaptic inputs from statocyst hair cells, are both sensory neurons and the first site of sensory convergence. The memory of light associated with turbulence is stored as changes in intrinsic and synaptic currents in these photoreceptors. The subcellular mechanisms producing these changes include activation of protein kinase C and MAP kinase, which act as coincidence detectors because they are activated by convergent signaling pathways. Pathways of interneurons and motorneurons, where additional changes in excitability and synaptic connections are found, contribute to delayed phototaxis. Bursting activity recorded at several points suggest the existence of small networks that produce complex spatiotemporal firing patterns. Thus, the change in behavior may be produced by a nonlinear transformation of spatiotemporal firing patterns caused by plasticity of synaptic and intrinsic channels. The change in currents and the activation of PKC and MAPK produced by associative learning are similar to those observed in hippocampal and cerebellar neurons after rabbit classical conditioning, suggesting that these represent general mechanisms of memory storage. Thus, the knowledge gained from further study of Hermissenda will continue to illuminate mechanisms of mammalian learning.

2P367 Photoresponse in statocyst hair cells of Lymnaea stagnalis(44. Neuro-biophysics,Poster Session,Abstract,Meeting Program of EABS & BSJ 2006)

2P367 Photoresponse in statocyst hair cells of Lymnaea stagnalis(44. Neuro-biophysics,Poster Session,Abstract,Meeting Program of EABS & BSJ 2006)

Statocyst hair cell activation of identified interneurons and foot contraction motor neurons in Hermissenda.

Pavlovian conditioning of Hermissenda produces both light-elicited inhibition of normal positive phototactic behavior and conditioned stimulus (CS)-elicited foot-shortening. Rotation, the unconditioned stimulus (US) elicits foot-shortening and reduced forward ciliary locomotion. The neural circuit supporting ciliary locomotion and its modulation by light is known in some detail. However, the neural circuits responsible for rotation-elicited foot-shortening and reduced forward ciliary locomotion are not known. Here we describe components of the neural circuit in Hermissenda that produce anterior foot contraction and ciliary activation mediated by statocyst hair cells. We have characterized in semi-intact preparations newly identified pedal ventral contraction motor neurons (VCMNs) and interneurons (I(b)). Type I(b) interneurons receive polysynaptic input from statocyst hair cells and project directly to VCMNs and cilia-activating motor neurons. Depolarization of VCMNs with extrinsic current in normal artificial seawater (ASW) and high-divalent cation ASW, and under conditions where central synaptic transmission was suppressed with 5 mM Ni(2+) ASW, elicited a contraction of the ipsilateral anterior foot measured from videotape recordings. Mechanical displacement of the statocyst or depolarization of identified statocyst hair cells with extrinsic current elicited spikes and complex excitatory postsynaptic potentials (EPSPs) in type I(b) interneurons and complex EPSPs and spikes recorded in VCMNs. Type I(b) interneurons are electrically coupled and project to VCMNs and VP1 cilia-activating motor neurons located in the contralateral pedal ganglia. The results indicate that statocyst hair-cell-mediated anterior foot contraction and graviceptive ciliary locomotion involve different interneuronal circuit components from the circuit previously identified as supporting light modulated ciliary locomotion.

Neural correlates of Pavlovian conditioning in components of the neural network supporting ciliary locomotion in Hermissenda.

Pavlovian conditioning in Hermissenda consists of pairing light, the conditioned stimulus (CS) with activation of statocyst hair cells, the unconditioned stimulus (US). Conditioning produces CS-elicited foot shortening and inhibition of light-elicited locomotion, the two conditioned responses (CRs). Conditioning correlates have been identified in the primary sensory neurons (photoreceptors) of the CS pathway, interneurons that receive monosynaptic input from identified photoreceptors, and putative pedal motor neurons. While cellular mechanisms of acquisition produced by the synaptic interaction between the CS and US pathways are well-documented, little is known about the mechanisms responsible for the generation or expression of the CR. Here we show that in conditioned animals light reduced tonic firing of ciliary activating pedal neurons (VP1) below their pre-CS baseline levels. In contrast, pseudorandom controls expressed a significant increase in CS-elicited tonic firing of VP1 as compared to pre-CS baseline activity. Identified interneurons in the visual pathway that have established polysynaptic connections with VP1 were examined in conditioned animals and pseudorandom controls. Depolarization of identified type Ie interneurons with extrinsic current elicited a significant increase in IPSPs recorded in VP1 pedal neurons of conditioned animals as compared with pseudorandom controls. Conditioning also enhanced intrinsic excitability of type Ie interneurons of conditioned animals as compared to pseudorandom controls. Light evoked a modest increase in IPSP frequency in VP1 of conditioned preparations and a significant decrease in IPSP frequency in VP1 of pseudorandom controls. Our results show that a combination of synaptic facilitation and intrinsic enhanced excitability in identified components of the CS pathway may explain light-elicited inhibition of locomotion in conditioned animals.

Photoresponse from the statocyst hair cell in Lymnaea stagnalis

Sensory cells for associative learning of light and turbulence were studied in Lymnaea. Intracellular recordings with Lucifer Yellow filled electrodes were made from photoreceptors and statocyst hair cells. Photoreceptors had a long latency, graded depolarizing response to a flash of light; they extended their axon to the cerebral ganglion. The caudal hair cell, one of 12 cells in the statocyst, responded to brief light with a depolarization and superimposed impulse activity. It formed its terminal arborization close to the photoreceptor endings in the cerebral ganglion. Ca 2+-free saline reversibly abolished the photoresponse in the hair cell, suggesting the information was conveyed via a chemical synapse. These findings demonstrated that sensory information for associative learning was convergent at the statocyst hair cell.

Immunocytochemical study of the statocyst hair cells in the gastropod mollusc Pleurobranchaea japonica

Immunocytochemical study of the statocyst hair cells in the gastropod mollusc Pleurobranchaea japonica

Directional sensitivity of hair cell afferents in the Octopus statocyst

Changes in threshold sensitivity of hair cell afferents of the macula and crista of the Octopus statocyst were analyzed when the hair cells were stimulated with sinusoidal water movements from different directions. The experiments indicate that cephalopod statocyst hair cells are directionally sensitive in a way that is similar to the responses of the hair cells of the vertebrate vestibular and lateral line systems, with the amplitude of the response changing according to the cosine of the angle by which the direction of the stimulus (the deflection of the ciliary bundle) deviates from the direction of the hair cell's morphological polarization.

Spontaneous activity of hair cells of the snail statocyst and its changes during intracellular stimulation

The following conclusions were drawn from an electrophysiological study of statocyst hair cell activity inHelix lucorum using intracellular recording. The maximal input resistance of the receptors is observed with hyperpolarizing currents of not more than 0.1 nA, close in magnitude to that arising during inhibitory synaptic transmission. Background noise, a special type of activity of statocyst hair cells, is neither synaptic nor pacemaker in nature, but depends entirely on the degree of contact between the cilia and statoconia. The hair cells possess pacemaker properties which are manifested on depolarization. The zone of action potential generation of the receptors lies in the axon. Inhibitory interactions take place between hair cells, leading to the generation of IPSPs in their spontaneous activity, which do not disappear after division of the vestibular nerve.

Voltage noise power spectra reflect ciliary movement frequencies in statocyst hair cells

Voltage noise from statocyst hair cells of Hermissenda crassicornis was analyzed. In 40% of the cells the power spectrum was non-regular with a hump (broad peak) near 7 Hz, which is the mean frequency of the inherent movement of the hairs. When the cells were cooled or heated with chloral hydrate, treatments known to slow or stop hair movement, the hump either was shifted towards lower frequencies and greatly reduced, or it disappeared entirely. Removal of extracellular sodium, an ion that carried much of the current which produced voltage noise, also eliminated the hump, but did not affect hair movement. The results indicate that most of the voltage noise is due not to hair movement itself, but to collision of statoconia with the motile hairs. Thus, the power spectra reflect the frequency of these events.

An infraciliary network in statocyst hair cells.

Ultrastructural analysis of the statocyst, a primitive vestibular organ, of the nudibranch mollusc Hermissenda crassicornis, indicates that in addition to the basal foot, there is an infraciliary rootlet system between basal bodies of adjacent sensory cilia. These rootlets project perpendicularly from the basal bodies and parallel to the cell surface in an astral array. A polarity within the network also appears to exist; the array is longest and most extensive on the side of the basal body directed away from the cell centre, but the overall arrangement of the basal bodies indicates a multidirectional sensitivity for each of the 13 sensory cells. This rootlet system, in conjunction with the attachment system of the basal bodies to the cell membrane (button anchors), may serve an integrative function for the mechanical stimuli experienced by sensory cells and/or be involved with their transductive processes by maximizing the stress to, and membrane distortion of, the transductive site caused by weighting of the cilia. Evidence was also obtained for the intracellular synthesis of statoconia by the nonsensory supporting cells.

A common origin of voltage noise and generator potentials in statocyst hair cells.

Voltage noise, generator potentials, and hair movements in the Hermissenda statocyst were analyzed. Motile hairs on the cyst's luminal surface moved as rods through +/- 10 degrees Hz when free and at 7 Hz when loaded with the weight of the statoconia (at 120 degrees C). For hair cells oriented opposite to a centrifugal force vector, rotation caused depolarization and increase of voltage noise variance. The depolarizing generator potential and the increase in voltage noise variance were similarly reduced by perfusion with zero external sodium or chloral hydrate. Cooling, perfusion with zero external sodium or chloral hydrate reduced the movement frequencies of the hairs but increased their range of motion. The same treatments reduced voltage noise variance and increased input resistance of the hair cell membrane. The results indicate that voltage noise and hair cell generator potential have a common origin: exertion of force on statocyst hairs by the weight of statoconia. The collision of statoconia with the motile hairs, not the hairs' bending, produces most of the voltage noise.

Interaction of chemosensory, visual, and statocyst pathways in Hermissenda crassicornis.

Neurons in the cerebropleural ganglia (CPG), photoreceptors in the eye, optic ganglion cells, and statocyst hair cells of the nudibranch mollusk Hermissenda crassicornis responded in specific ways, as recorded intracellularly, to stimulation of the chemosensory pathway originating at the tentacular chemoreceptors as well as to stimulation of the visual pathway originating at the photoreceptors. Synaptic inhibition of photoreceptors occurs via the chemosensory pathway. The possible significance of such intersensory interaction is discussed with reference to preliminary investigation of the animal's gustatory behavior and possible neural mechanisms of behavioral choice.

Afferent response patterns of the crayfish statocyst with ferrite grain statolith to magnetic field stimulation

1. Magnetic field stimulation to simulate the rotation of the crayfish statocyst has been performed to determine the response characteristics of the statocyst hair cells. Ferrite grains were introduced about one month before the experiment as a replacement for the natural statoliths to effect magnetic pulling. 2. Several types of response discharge could be recognized. Excitatory response types included tonicon, tonic-on-off, phasic-on, and phasic-on-off types. Inhibitory types can be divided into tonic-inhibition with off-excitation and phasic-inhibition with offinhibition. 3. Statocyst afferent neurons could be classified into several groups depending on the direction of the preferred sensitivity within the simulated rotation plane tested. Among 21 units examined, 9 units showed a single preferred direction with excitatory response and were thus unidirectional units; 3 units were bidirectional, and 5 units were multidirectional. There were 2 bidirectional inhibitory units and 2 multidirectional inhibitory units. 4. Analysis of the response pattern suggests that the central nervous system in the crayfish should be capable of averaging responses of more than one unit among the statocyst afferent neurons to detect the coincidence of discharge frequency change in order to obtain the positional information.