The ultrasonic responses of albino mouse pups to tactile stimuli

Tactile stimuli, like environmental temperature changes, can evoke ultrasonic responses from albino mouse pups. But the changes with age in the intensity of ultrasounds so produced follow a different pattern from those due to temperature changes. The responses begin with very high intensity pulses in the very young pups and then gradually decline with the age of the pups. The present report arises from a systematic study of this phenomenon, the results of which are discussed in relation to those of previous ones.     

Cadmium binding proteins induced in exposed freshwater crayfishProcambarus clarkii

This work describes results on the characterization of cadmium binding proteins (Cd-BPs) obtained from cadmium exposed freshwater crayfishProcambarus clarkii. After acclimation to laboratory conditions, induction of Cd-BPs was achieved by water exposure at a concentration of 100 μg Cd/L during 2, 15, and 30 d: In accordance with the method followed by Engel and Brouwer, in each case two midgut glands were minced and homogenized in Tris-HCl buffer with PMSF to prevent protease activity and DTT to maintain reducing conditions. The homogenate was centrifuged, heat treated, applied to a column of Sephadex G-75, and eluted with the same buffer (pH 8.6). Absorbances of the fractions collected were measure at 245 and 280 nm. Cadmium concentrations were determined by flame photometry. In midgut glands of two-d treated crayfish, significant levels of cadmium occurred in the void volume, and no cadmium-binding protein peak was resolved. On the contrary, a cadmium peak was cleary resolved in samples of 15 and 30 d. Cadmium was accumulated in the low molecular weight fractions (about 20,000). These fractions had high ultraviolet absorption at 254 nm and a higher 254/209 ratio.     

Visual control of steering in locust flight: the effects of head movement on responses to roll stimuli

The contribution of head movement to the control of roll responses in flying locusts (Locusta migratoria) has been examined (i) on a flight balance, recording the angles through which the locust turns when following an artificial horizon; (ii) by recording activity in a pair of flight muscles in restrained conditions; and (iii) by observations on free flying locusts. Responses were compared when the head was free to turn about the thorax, as normal, and when the head was waxed to the thorax, blocking any relative motion between the two (head-fixed). These experiments suggest that the major signal generating corrective roll manoeuvres is the visual error between the angle of the head and the horizon, rather than a signal that includes a measure of the head-thorax angle.

Visual and olfactory responses of haematophagous Diptera to host stimuli

Key biotic and environmental constraints on the host-orientated behaviour of haematophagous Diptera are summarized. For each major group of biting Diptera, responses to host stimuli are reviewed, including activation and ranging behaviour, long-range and short-range olfactory responses and visual responses. Limitations to the comparison of results between groups of species, and the practical problems of experimental method and equipment are discussed.     

Ecdysteroid binding sites in gastrolith forming tissue and stomach during the molting cycle of crayfishProcambarus clarkii

Summary The distribution of ecdysteroid binding sites in the stomach and gastrolith disc tissue of cryafish (Procambarus clarkii) was examined in relation to the molting stage by thaw-mount autoradiography. The radiolabeled hormone analogue ponasterone A (25-deoxy-20-hydroxyecdysone) was used. Ecdysteroid binding sites were demonstrated only in certain molting stages, the small gastrolith period and the aftermolt stage. In gastrolith epithelium, ponasterone A binding sites first appeared in the cytoplasm, and then in the nuclei and cytoplasm. In the stomach epithelium, many nuclear binding sites were detectable during the period of gastrolith secretion. These periodical changes in specific ponasterone A binding when correlated with the molting stages clearly show that ecdysteroids may function as an initiator for gastrolith formation and reabsorption. The findings also suggest that ecdysteroids control calcium transport in the stomach epithelium. The time-related and functional differences of cytoplasmic and nuclear concentration of ecdysteroid receptors indicate the presence of cytoplasmic and nuclear receptors associated with specific actions.     

Synaptic responses evoked by tactile stimuli in Purkinje cells in mouse cerebellar cortex Crus II in vivo

Background

Sensory stimuli evoke responses in cerebellar Purkinje cells (PCs) via the mossy fiber-granule cell pathway. However, the properties of synaptic responses evoked by tactile stimulation in cerebellar PCs are unknown. The present study investigated the synaptic responses of PCs in response to an air-puff stimulation on the ipsilateral whisker pad in urethane-anesthetized mice.

Methods and Main Results

Thirty-three PCs were recorded from 48 urethane-anesthetized adult (6–8-week-old) HA/ICR mice by somatic or dendritic patch-clamp recording and pharmacological methods. Tactile stimulation to the ipsilateral whisker pad was delivered by an air-puff through a 12-gauge stainless steel tube connected with a pressurized injection system. Under current-clamp conditions (I = 0), the air-puff stimulation evoked strong inhibitory postsynaptic potentials (IPSPs) in the somata of PCs. Application of SR95531, a specific GABA_A receptor antagonist, blocked IPSPs and revealed stimulation-evoked simple spike firing. Under voltage-clamp conditions, tactile stimulation evoked a sequence of transient inward currents followed by strong outward currents in the somata and dendrites in PCs. Application of SR95531 blocked outward currents and revealed excitatory postsynaptic currents (EPSCs) in somata and a temporal summation of parallel fiber EPSCs in PC dendrites. We also demonstrated that PCs respond to both the onset and offset of the air-puff stimulation.

Conclusions

These findings indicated that tactile stimulation induced asynchronous parallel fiber excitatory inputs onto the dendrites of PCs, and failed to evoke strong EPSCs and spike firing in PCs, but induced the rapid activation of strong GABA_A receptor-mediated inhibitory postsynaptic currents in the somata and dendrites of PCs in the cerebellar cortex Crus II in urethane-anesthetized mice.     

Coding processes involved in the cortical representation of complex tactile stimuli

To understand how information is coded in the primary somatosensory cortex (S1) we need to decipher the relationship between neural activity and tactile stimuli. Such a relationship can be formally measured by mutual information. The present study was designed to determine how S1 neuronal populations code for the multidimensional kinetic features (i.e. random, time-varying patterns of force) of complex tactile stimuli, applied at different locations of the rat forepaw. More precisely, the stimulus localization and feature extraction were analyzed as two independent processes, using both rate coding and temporal coding strategies. To model the process of stimulus kinetic feature extraction, multidimensional stimuli were projected onto lower dimensional subspace and then clustered according to their similarity. Different combinations of stimuli clustering were applied to differentiate each stimulus identification process. Information analyses show that both processes are synergistic, this synergy is enhanced within the temporal coding framework. The stimulus localization process is faster than the stimulus feature extraction process. The latter provides more information quantity with rate coding strategy, whereas the localization process maximizes the mutual information within the temporal coding framework. Therefore, combining mutual information analysis with robust clustering of complex stimuli provides a framework to study neural coding mechanisms related to complex stimuli discrimination.     

Cadmium,mercury, and lead effects on gill tissue of freshwater crayfishProcambarus clarkii (girard)

Intermolt adult crayfishP. clarkii were used for this work. After acclimatation to laboratory conditions crayfish were exposed to sublethal concentrations of cadmium, mercury, and lead for 96 h. Gills of control and exposed crayfish were removed and ATPase activity and oxygen uptake rate were determined. Structural damage of gill filaments was also observed. Gill tissue respiration rates were measured for individual crayfish using a Gilson differential respirometer. Lead causes a decrease of gill oxygen uptake, but neither cadmium nor mercury seems to affect it at the concentrations employed. Although all metals studied alter gill filament structure, lead damage is the most apparent. In the same way, significant differences in gill ATPase activity owing to metal exposure were only observed in lead treated crayfish.     

Renal responses to stressful environmental stimuli

The effects of stressful environmental stimuli on urinary sodium excretion in conscious dogs, rats, and humans are reviewed. Environmental stress can increase sympathetic neural outflow and decrease sodium excretion. The antinatriuretic response to environmental stress is accompanied by an unchanged renal blood flow and glomerular filtration rate, which indicates mediation via an increased renal tubular sodium reabsorption. The antinatriuresis resulting from environmental stress is associated with increased renal sympathetic nerve activity, and is abolished by surgical renal denervation. In the central nervous system, but not in the kidney, beta adrenoceptors mediate the increased renal sympathetic nerve activity and antinatriuretic responses to environmental stress. The increased renal sympathetic nerve activity and antinatriuretic responses to environmental stress are greater in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto (WKY) rats. In SHR, but not WKY rats, the increased renal sympathetic nerve activity and antinatriuretic responses are enhanced by a high-sodium diet. Similarly, stressful competition in human young adult males results in an antinatriuresis only if a positive family history of hypertension is present. Thus, environmental stress can increase renal tubular sodium reabsorption via a central beta-adrenoceptor mechanism with activation of the renal sympathetic nerves in both conscious dogs and SHR. The antinatriuretic response to environmental stress is greater in rats and humans with a genetic predisposition to develop hypertension.     

Acclimatable cardiac and ventilatory responses to copper in the freshwater crayfish Procambarus clarkii

Mortality and physiological tests following exposure to waterborne copper were performed in the red swamp crayfish Procambarus clarkii from a central Italian population. Mortality tests gave an estimated 96 h LC50 value (with 95% confidence limits) of 162 (132-211) mg L(-1) waterborne copper II. Variations in cardiac and ventilatory rates were simultaneously monitored using a non-invasive plethysmographic technique. In experiments with different sub-lethal copper concentrations (control, 0.5, 1 and 10 mg L(-1)) performed at different times (3, 6, 96 h), copper exposure elicited a reduction in both heart and scaphognatite rates. Following exposure to 10 mg L(-1) copper for 96 h, the heart and scaphognatite rates decreased to about 35% of the initial values. The reduction was fully reversible, since crayfish exposed to 0.5, 1 and 10 mg Cu L(-1) for 96 h resumed control rates after a 3-h residence in clean water. In crayfish pre-exposed (96 h) to sub-lethal copper concentrations (0.1 and 1 mg L(-1)) and then held in control water (3 h), the reduction of heart and scaphognatite rates after exposure to 10 mg Cu L(-1) were significantly lower than in specimens pre-exposed to control water. Therefore, copper induces a concentration and time dependent reduction of both cardiac and ventilatory activity in P. clarkii; these responses can be reduced or fully abolished by pre-exposure to sub-lethal levels of the metal.