Mechanosensory afferents innervating the swimmerets of the lobster

Feathered hair sensilla fringe both rami of the lobster (Homarus americanus) swimmeret. The sensory response to hair displacement was characterized by recording afferent impulses extracellularly from the swimmeret sensory nerve while deflecting sensilla with a rigidly-coupled probe or controlled water movements. Two populations of hairs were observed: "distal" hairs localized to the distal 1/3 of each ramus and "proximal" hairs near its base. Distal hairs are not innervated by a mechanosensory neuron but instead act as levers producing strain within adjacent cuticle capable of activating a nearby hypodermal mechanoreceptor. Hair deflections of 25 degrees or more are required to evoke an afferent response and this response is dependent on hair deflection direction. The frequency and duration of the afferent discharge evoked are determined by the velocity of hair displacement. Each proximal hair is innervated by a single mechanosensory neuron responding phasically to hair deflections as small as 0.2 degrees in amplitude. Deflection at frequencies up to 5 Hz elicits a single action potential for each hair movement; at higher frequencies many deflections fail to evoke an afferent response. These sensilla, which are mechanically coupled, may be activated by the turbulent flow of water produced by the swimmerets during their characteristic beating movements.     

Mechanosensory neurons with bend- and osmo-sensitivity in mouthpart setae from the spiny lobster Panulirus argus

The mouthparts of the spiny lobster Panulirus argus hold primarily two types of setae--simple setae and cuspidate setae. Mechanosensory neurons from these setae were examined by electrophysiological recordings. The population of simple setae contained two types of mechanosensory neurons: displacement-sensitive neurons, which responded to deflection at the setal base; and bend-sensitive neurons, which responded to bending of the setal shaft. Displacement-sensitive neurons, in general, responded phasically and only during actual displacement. Typically, their response changed with alteration of the direction, amplitude, and velocity/acceleration of the mechanical stimulus. Bend-sensitive neurons, in general, responded phaso-tonically and carried information on the direction and region of bending. This is the first experimental demonstration of bend sensitivity for arthropod setae. Cuspidate setae contain highly sensitive mechanosensory neurons; however, due to the rigid nature of these setae, whether they were bend sensitive or displacement sensitive could not be determined, and they were thus called "tactile neurons." Bend-sensitive neurons, but not displacement-sensitive neurons or tactile neurons, showed graded responses to changes in osmolarity. The osmosensitivity of these neurons could mediate behavioral responses to changes in the osmolarity of seawater or food.     

Neuronal pathways from low-threshold muscle and cutaneous afferents innervating tail to trunk muscle motoneurons in the cat

We studied neuronal pathways from low-threshold muscle (group I, II) and cutaneous afferents (group A(alpha)beta) innervating the tail to motoneurons innervating trunk muscles (m. iliocostalis lumborum and m. obliquus externus abdominus) in 18 spinalized cats. Stimulation of group I muscle afferents produced excitatory postsynaptic potentials or excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials in all motoneurons innervating the m. iliocostalis lumborum which showed effects (32%), and predominantly inhibitory postsynaptic potentials in motoneurons innervating the m. obliquus externus abdominus (47%). Stimulation of group I+II afferents produced significant increases of the incidence of motoneurons showing postsynaptic potentials (the notoneurons innervating the m. iliocostalis lumborum, 87%; the motoneurons innervating the m. obliquus externus abdominus, 82%). The effects of low threshold cutaneous afferents were bilateral, predominantly producing inhibitory postsynaptic potentials in motoneurons innervating both muscles. These results suggest that neuronal pathways from muscle afferents to back muscle motoneurons mainly increase the stiffness of the trunk to maintain its stability, while those to abdominal muscles help to extend the dorsal column by decreasing their activities. The results also indicate that neuronal pathways from cutaneous afferents to trunk motoneurons functionallY disconnect the tail from the trunk.     

Chemosensory and Mechanosensory Functions of Olfactory Cilia

Biophysics - This review presents the modern understanding of olfactory cilia as organelles that possess both chemosensory and mechanosensory properties. The molecular mechanisms that underlie...     

The Cellular and Synaptic Architecture of the Mechanosensory Dorsal Horn

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Axonal transport of [3H] GABA and [3H] glutamate in excitatory and inhibitory neurons innervating lobster exoskeletal musculature

This paper describes the results of intracellular injections of radiolabelled neurotransmitters and transmitter precursor substances, including glutamate, GABA, aspartate, octopamine, tyramine, tryptophan, and choline, into cell bodies of identified excitatory and inhibitory neurons innervating lobster extensor musculature. The distributions and identities of radioactive substances appearing in axons were examined at various times following injection and in vitro incubation. Injected GABA and glutamate were found in appreciable quantities in both excitatory and inhibitory axons and migrated down axons at an estimated rate of between 16 and 22 mm/day at 12 degrees C, whereas the other substances tested were present in substantially smaller quantities and migrated at an estimated rate of less than 7.5 mm/day at 12 degrees C. Injected GABA, D-glutamate and L-glutamate accumulated proximal to ligatures tied around nerves, whereas neither octopamine nor aspartate accumulated proximal to ligatures. Since GABA is the transmitter substance released by inhibitory neurons and L-glutamate is thought to be released from excitatory nerve terminals, these results are consistent with the suggestion that amino acids serving as neurotransmitters are axonally transported. The specificity of axonal transport does not appear to be restricted to the cognate neurotransmitter, as indicated by the movement of L-glutamate in inhibitory axons and GABA in excitatory axons and of D-glutamate in both excitatory and inhibitory axons, but rather may be relaxed to include substances closely related to the neurotransmitter. Some restrictions, however, are apparently placed on axonal transport of small charged molecules in these neurons in that other substances tested migrated down nerves at a considerably slower rate.     

Direction Selectivity in Drosophila Proprioceptors Requires the Mechanosensory Channel Tmc

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Force-Regulated Refolding of the Mechanosensory Domain in the Platelet Glycoprotein Ib-IX Complex

In platelets, the glycoprotein (GP) Ib-IX receptor complex senses blood shear flow and transmits the mechanical signals into platelets. Recently, we have discovered a juxtamembrane mechanosensory domain (MSD) within the GPIbα subunit of GPIb-IX. Mechanical unfolding of the MSD activates GPIb-IX signaling into platelets, leading to their activation and clearance. Using optical tweezer-based single-molecule force measurement, we herein report a systematic biomechanical characterization of the MSD in its native, full-length receptor complex and a recombinant, unglycosylated MSD in isolation. The native MSD unfolds at a resting rate of 9 × 10^?3 s^?1. Upon exposure to pulling forces, MSD unfolding accelerates exponentially over a force scale of 2.0 pN. Importantly, the unfolded MSD can refold with or without applied forces. The unstressed refolding rate of MSD is ～17 s^?1 and slows exponentially over a force scale of 3.7 pN. Our measurements confirm that the MSD is relatively unstable, with a folding free energy of 7.5 k_BT. Because MSD refolding may turn off GPIb-IX’s mechanosensory signals, our results provide a mechanism for the requirement of a continuous pulling force of >15 pN to fully activate GPIb-IX.     

The Mechanosensory Lateral Line System of the Hypogean form of Astyanax Fasciatus

The mechanosensory lateral line is a distributed, hair-cell based system which detects the water flow regime at the surface of the fish. Superficial neuromasts densely scattered over the surface of some cave fish detect the pattern of flow over the surface of the body and are important in rheotactic behaviors and perhaps in the localization of small vibrating sources. Canal neuromasts are very likely also involved in the detection of small planktonic prey, but seem also to play an essential role in replacing vision as the major sense by which blind cave-fish perceive their surroundings. The flow-field that exists around a gliding fish is perturbed by objects in the immediate vicinity, these perturbations are detected by the lateral line system. In this way the fish can build up a picture of its environment, a process that has been called active hydrodynamic imaging. None of the lateral line behaviors exhibited by blind cave fish are necessarily exclusive to these species, but there is some evidence that their lateral line capabilities are enhanced with respect to their sighted relatives.     

Mechanosensory control of antennal movement by the scapal hair plate in the American cockroach

The voluntary movement of antennae of blinded cockroaches was examined in the tethered-walking condition. An object of metal plate was presented to a tip of a single antenna in order to induce tactile orientation behavior. Horizontal movements of the antenna before and during the object presentation were analyzed both before and after ablation of a mechanosensory organ, the scapal hair plate (S-HP), at the base of antenna. The resting antennal position shifted outwardly by about 20 degrees after the S-HP ablation. Spontaneous antennal movements in ablated animals became stiff and wider ranged. The tactile object was set at two different horizontal positions, 45 degrees and 90 degrees clockwise to the head, for the right side antenna. The number of contacts in a constant test period was significantly decreased in the tests at 45 degrees after ablation. Trajectories of antennal movements before and after contacts were categorized into four patterns. In the case that an antenna made contact with the object during its abduction (outward) movement, it then passed the object outwardly or withdrew inwardly. These were termed "outward-pass (O-P)" and "outward-withdrawal (O-W)" patterns, respectively. Similarly, contacts during the adduction (inward) movement were divided into "inward-pass (I-P)" or "inward-withdrawal (I-W)" pattern. Significant effects of the S-HP ablation appeared in the tests at 90 degrees : the I-P pattern mostly disappeared and was replaced by the I-W pattern. The results strongly suggest that the S-HP has crucial roles for controlling both spontaneous and stimulated movements of the cockroach antenna.     

Cardioacceleratory reflexes triggered by mechanoproprioceptors of the swimmerets in the stomatopod crustacean Squilla oratoria

The heart of Squilla oratoria is innervated by processes arising from the cardiac ganglion, which lies on the outer surface of the heart wall. The ganglion is regulated by one pair of cardioinhibitory nerves and two pairs of cardioacceleratory nerves. Cardiac acceleration accompanied activation of the five pairs of swimmerets in the first to the fifth abdominal segments. The cardioacceleratory nerves were activated when swimmerets beat strongly. Activation of the cardioacceleratory nerves was caused by electrical stimuli to a nerve branch extending to the swimmerets from the first nerve root of the abdominal ganglion. Bursts of afferent impulses were recorded from the nerve branch of the first nerve root corresponding to periods of protractive and retractive swimmeret movements. Afferent impulses were recorded from the nerve branch when the articular membrane was artificially boosted up. Cardiac acceleration during active swimmeret movements in Squilla is attributable to a reflexive response triggered by the movements. Putative mechanoproprioceptors on the articular membrane between the sterna and basipodite in the swimmerets may be responsible for the cardioacceleratory reflex.     

Molecular Modeling of Mechanosensory Ion Channel Structural and Functional Features

The DEG/ENaC (Degenerin/Epithelial Sodium Channel) protein family comprises related ion channel subunits from all metazoans, including humans. Members of this protein family play roles in several important biological processes such as transduction of mechanical stimuli, sodium re-absorption and blood pressure regulation. Several blocks of amino acid sequence are conserved in DEG/ENaC proteins, but structure/function relations in this channel class are poorly understood. Given the considerable experimental limitations associated with the crystallization of integral membrane proteins, knowledge-based modeling is often the only route towards obtaining reliable structural information. To gain insight into the structural characteristics of DEG/ENaC ion channels, we derived three-dimensional models of MEC-4 and UNC-8, based on the available crystal structures of ASIC1 (Acid Sensing Ion Channel 1). MEC-4 and UNC-8 are two DEG/ENaC family members involved in mechanosensation and proprioception respectively, in the nematode Caenorhabditis elegans. We used these models to examine the structural effects of specific mutations that alter channel function in vivo. The trimeric MEC-4 model provides insight into the mechanism by which gain-of-function mutations cause structural alterations that result in increased channel permeability, which trigger cell degeneration. Our analysis provides an introductory framework to further investigate the multimeric organization of the DEG/ENaC ion channel complex.     

The lobster fiefs: Economic and ecological effects of territoriality in the maine lobster industry

Lobstermen from each community along the coast of central Maine claim inshore fishing rights in particular areas. Although their claims are unrecognized by the state, they are well established and backed by surreptitious violence. Two kinds of lobstering territories exist, here termed nucleated and perimeterdefended, which differ essentially in the extent to which exclusive fishing rights are maintained. These differences in territorial organization affect the fishing effort of lobstermen, which in turn has a strong biological and economic impact.On leave 1974–1975 to serve with the National Marine Fisheries Service, Washington, D.C.The research on which this paper is based was financed by the National Marine Fisheries Service (Contract No. N-043-30-72) and a Faculty Research Grant from the University of Maine in 1973.     

Sustaining fibers in the rock lobster

The properties of sustaining fibers (SuF's), whose firing frequency is related to the ambient light intensity, were studied in the rock lobster. Most of the firing patterns shown under various conditions were demonstrated to be physiological, by using chronic implantation techniques. Unusual activity at high light intensities suggests that the lobster visual system is equipped to function only under dim light conditions. Unlike the crayfish, the lobster SuF's do not always indicate light levels but only changes in light intensity. It is suggested that the input from these fibers has a large influence on locomotor activity.     

Cholinergic activation of the lobster cardiac ganglion

The frequency of rhythmic burst activity of the isolated lobster cardiac ganglion is increased by exogenously applied acetylcholine and muscarinic agonists. Responses of individual motor neurons isolated from the ganglion by transection consist of a slow depolarization and repetitive bursting. The pharmacological profile of the receptors mediating this response is similar to that of vertebrate neuronal muscarinic receptors. Isolated ganglia incubated in the presence of [3H]-choline (18-19 h) exhibited radiolabelled acetylcholine accumulation. It is suggested that ganglionic excitation may be accomplished by extrinsic or intrinsic activation of muscarinic receptors on the motor neurons.     

Cellular organization of the embryonic lobster heart

Summary The cellular organization of the embryonic heart of the lobster Homarus americanus was examined in 6-week and 6-month-old animals. The heart wall consists of an outer adventitial layer of fibroblast cells and an inner layer of transversely striated myocardial cells. Present in close association with the myocardium are cardiac neurons, hemocytes and so-called storage cells.Adjacent fibroblasts form fasciae adhaerentes and gap junctions. Adherent junctions also occur between fibroblasts and myocardial cells. Intercalated discs and differentiated membrane regions of close apposition (4 nm) occur between adjacent myocardial cells.The cardiac neurons form a ganglion that contains four small and five large somata. Regions of neuropil are present. Motor axons arising from the cardiac ganglion form neuromuscular synapses with the myocardial cells.The storage cells contain large inclusions and form gap junctions with the myocardial cells. They may supply nutritive material to the developing myocardium.The heart at 6 weeks is about 200 m long and 160 m wide. At 6 months, it is about 300 m long and 250 m wide. The myocardium at 6 weeks is one cell layer thick, and the cells are from 2–6 m in maximum width. At 6 months the myocardium is 2–4 cells thick, and the cells are from 6–12 m in width. Therefore, the myocardium grows by an increase in the number and size of the myocardial cells.     

Monoamine pharmacology of the lobster cardiac ganglion

Monoamine agonists and antagonists were applied to the lobster cardiac ganglion in an attempt to clarify the different actions of 5-hydroxytryptamine (5HT) and dopamine (DA) on this rhythmic pattern generator. Experiments were designed to determine whether the similar responses to 5HT and DA applied to the anterior region of the ganglion could be separated by pharmacological approaches, and whether the different responses to 5HT applied to the anterior and posterior regions of the ganglion could be attributed to mediation by different receptors. A small number of the 5HT agonists which were tested mimic the effects of 5HT, in that they increase the frequency of bursting and decrease burst duration when applied to the whole ganglion, but decrease burst frequency and increase burst duration when applied only to the posterior half. Other 5HT agonists decrease frequency and prolong bursts when applied to the whole ganglion. Of the DA agonists tested, none acts as DA itself does. Rather, they mimic the effects of 5HT applied to the posterior ganglion, by slowing bursting and prolonging bursts. The actions of agonists do not correspond in any clear way to the receptor specificities as defined in vertebrates. Most antagonists tested do not show similar specificities to their effects in vertebrates. In particular, most of the DA antagonists tested are more effective in blocking exogenous 5HT than DA. One monoamine agonist directly alters the properties of endogenous burst-organizing potentials (driver potentials) in the motorneurons of the ganglion.