Are the semicircular canals of the European mole, Talpa europaea, adapted to a subterranean habitat?

The mechanical sensitivity of vertebrate semicircular canals is directly influenced by the canal dimensions. Three key canal parameters, whose dimensions have been shown to be critical in determining the mechanical sensitivity of semicircular canals, are the streamline length, the cross-sectional area of the canal lumen and the plane area. These parameters were measured in ten specimens of adult T. europaea and compared with the dimensions of the same parameters in R. norvegicus. The major determinant of sensitivity, canal lumen area, is significantly larger in T. europaea.

Present of a toxin in the salivary glands of the marine snail Cymatium intermedius that targets nicotinic acetylcholine receptors.

Presence of a toxin in the salivary glands of the marine snail Cymatium intermedius that targets nicotinic acetylcholine receptors. Toxicon 36, 25-29, 1998.-We present evidence of a neurotoxin from the salivary glands of Cymatium intermedius that displays acetylcholine-like effects on vertebrate (mouse ileum) and invertebrate (molluscan smooth muscle; molluscan heart; leech body wall) tissues. These effects were completely blocked by (+)-tubocurarine (10-100 muM) but not by atropine (up to 200 muM) suggesting that the toxin targets nicotinic-like acetylcholine receptors. This affirms the proposal that this genus may overcome their prey with a paralytic secretion.

Isolation of serotonin from the accessory salivary glands of the marine snail Nucella lapillus.

We report here the presence of a bioactive compound in the secretion of the accessory salivary glands (ASGs) of Nucella lapillus. We have purified the compound using HPLC and identified it as serotonin by mass spectrometry, UV spectroscopy, HPLC and capillary electrophoresis. Serotonin was not found in the secretions of the acinous salivary glands or the hypobranchial gland. The amount of serotonin in the secretion of the ASGs does not show seasonal or regional variation.

A comparison of the performance of two sensory systems in host detection and location in the medicinal leech Hirudo medicinalis.

1. Mechanical and visual stimuli associated with surface waves were separated into their two components. 2. Unfed leeches responded to the mechanical component of artificially generated surface waves by swimming towards their source. 3. Leeches also responded to and orientated towards the source of the waves using visual cues derived from the same surface waves. 4. Visual stimuli elicited fewer and less accurate responses.

Postembryonic Growth of Two Peripheral Sensory Systems in the Medicinal Leech Hirudo medicinalis.

The midbody segments of Hirudo medicinalis have two types of sensory cilia that project from the skin into the surrounding water. These are the proposed mechanosensory S cilia and the putative chemosensory G cilia. The cells bearing these cilia are clustered together into structures known as sensilla. The skin of each midbody segment is externally divided into five annuli. Fourteen large sensilla carrying S and G cilia are found on the central annulus of each segment. Small sensilla carrying only G cilia are found on all five annuli. In this paper we show a positive correlation between the size of a neural sensillum and the number of S and G cilia it contains. Any one leech contains a range of sizes of neural sensilla, but the average area increases with the weight of the leech. In contrast, the annular sensilla show only a modest increase in size with leech weight.

Neuromodulatory effects of acetylcholine and serotonin on the sensitivity of leech mechanoreceptors.

1. Each segmental ganglion of the leech Hirudo medicinalis contains 6 touch (T) cells, 4 pressure (P) cells and 4 nociceptive (N) cells. The receptive terminals of these cells innervate the skin in discrete areas. These cells are known to have extrasynaptic receptors. 2. We tested the effect of transmitter substances present in leech CNS on the sensitivity of T and P cells to mechanical stimuli. Substances tested included octopamine, FMRFamide, proctolin, substance P, glutamate, GABA, acetylcholine and serotonin. 3. Only acetylcholine and serotonin had consistent effects. Serotonin (1 x 10(-3) M) increased the number of action potentials of T cells elicited by a standard stimulus. Serotonin (1 x 10(-4) M) and acetylcholine (1 x 10(-3) M) increased the number and frequency of action potentials in P cells.

The contractile properties and movement dynamics of pigeon eye muscle.

The lateral rectus (LR) muscle of the pigeon was directly stimulated in situ at 41 degrees C. The length tension relationships for active and passive tension were investigated to determine the optimum muscle length (Lo). Isometric responses to single and twin pulses, tetani and sinusoidal stimulation were measured. A linear relationship was found between length and active tension during stimulation. Increase in stimulation frequency produced a corresponding shift in tension with the slope of the curves remaining the same. At Lo (1.21 times resting length) the average contraction time of single twitches was 6.03 ms and the half-relaxation time was 7.77 ms. Stimulation frequencies of 200 Hz and over gave rise to a fused tetanus. Tension increased to a maximum at 200 Hz and rate of tension rise saturated at 600 Hz. The tension response to tetanic stimulation was linear over the range 70-180 Hz. Maximum tetanic tension was around 3.48 N/cm2 and the twitch:tetanus ratio was 0.164. Prolonged activation at fusion frequency showed a high fatigue resistance. Sinusoidal stimulation with pulse trains of 100-180 Hz produced a sinusoidal response over the frequency range 0.6-40 Hz, from which the gain and phase relationships were determined. The muscle response approximates a first order low pass filter, with a characteristic frequency of 11.2 Hz. There is an additional phase lag, equivalent to the response latency, of 2.89 ms. The results are compared to the contractile properties of mammalian eye and avian skeletal muscle. The frequency response of the LR is compared to that of cat soleus and gastrocnemius and to pigeon eye movement dynamics.

Muscle fibre types in the external eye muscles of the pigeon, Columba livia.

Fibre typing with antisera raised against specific myosin types from muscles of known physiological properties were used to characterise the fibre types within the oculorotatory muscles of pigeons. Fibres reacting strongly to antiserum anti-ALD (specific for tonic fibre myosin) were found lying along the global margin of the muscle and also in a layer lying immediately beneath a discrete band of fibres running along the orbital margin. These fibres resembled those of the skeletal muscle ALD in their type properties. Using another antiserum, anti-I, specific for slow twitch and to a lesser extent, slow tonic myosins, it was possible to identify another slow fibre type which formed the orbital layer and also lay scattered randomly through the body of the muscle. No equivalent to this type was found in the skeletal muscles ALD or iliofibularis. The remaining fibres which did not react with either anti-ALD or anti-I formed 58% of the fibre population and reacted with an antiserum specific for fast myosin. However, their response to alkali preincubation suggests that the fast fibres of eye muscles also contain a myosin which is different from those in skeletal muscle.

The mechanics of pigeon eye movements--are they like other vertebrates?

The lateral rectus muscle of the pigeon eye was driven by stimulation of the abducens nucleus. Eye rotation was measured with an opto-electronic movement detector. Eye position was linearly related to stimulation frequency in the range 40-110 Hz and saturated at frequencies above 250 Hz. Maximum eye velocity of 240 degrees/s was obtained with a stimulation frequency of 360 Hz. Stimulation with sinusoidally modulated pulse frequencies (40-110 Hz) over the modulation frequency range 0.01-6.0 Hz were used to determine the gain and phase relationships of the oculomotor system. The response approximates a first order low pass frequency model with a characteristic frequency of 0.45 Hz at high frequencies. There is an additional phase lag equivalent to a time delay of 9.8 ms. The results are compared with similar experiments performed on the dogfish and cat oculomotor systems.

The effects of lowered temperature on spontaneous eye movements in a teleost fish.

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.