Journal de physiologie最新文献

1. In Aplysia of different ages, three well defined behavioral responses and their substrates were examined. 2. Two of the behaviors and their substrates are age-sensitive, the gill withdrawal reflex, and osmoregulation. They are sensory-dependent for their activation. The third, the gill respiratory pumping movements, GPM, and its substrates is age-invariant. It is initiated by a network in the CNS, and modulated by sensory input. 3. Age-sensitivity of a neuron appears dependent on its pathway: the pathways mediating sensory-initiated behavior are more vulnerable to aging than the pathway mediating CNS-initiated behavior. 4. a) The age-sensitive, GWR, gill withdrawal reflex, in unrestrained animals and in reduced preparations conforms to the age-dependent reduced functioning of L7, the major mediator of the reflex. b) Whereas, the age-invariant GPM conforms to the age-independent functioning of LDG1, a major contributor to GPMs. c) The age-related slowing of osmoregulation is consistent with the lack of response in the putative water balance neuron, R15, to stimulation of osmoreceptors by dilute seawater. 5. Age-sensitivity of L7 is defined by its reduced function, decreased facilitation at its terminals, reduced input resistance, and remodeling of junctions in the muscles it innervates. This is in contrast to the age-invariance of these properties in LDG1 and of the junctions in muscles it innervates. Thus far, the age-sensitivity of R15 is revealed by its reduced responsiveness to synaptic input, reduced input resistance, and little response to osphradial stimulation. 6. Age-sensitivity of the GWR, osmoregulation and of their substrates is not necessarily maladaptive.(ABSTRACT TRUNCATED AT 250 WORDS)

Five subjects performed intermittent exercise on a bicycle ergometer (25 min work, 5 min rest cycles for 2 hours, and 20 min work, 10 min rest cycles for a further hour) in a hot environment (air and wall temperatures = 36 degrees C; dew-point temperature = 10 degrees C; air velocity = 0.6 m.s-1). The relative mechanical work load was of 70 W (30% of the maximal aerobic capacity). Seven experimental tests were carried out in order to induce a plasma hypovolemia associated with either a plasma hypo- or hyperosmolarity. The preexercise level of body hydration was also manipulated by giving a diuretic, or by ingestion of 500 ml of isotonic electrolyte sucrose solution before the start of exercise. Continuous measurements were made of rectal and mean skin temperatures. The sweating responses of the chest and of the thigh (over the active muscles of the leg) were monitored from 4 sweat collection capsules highly ventilated. On each of these body areas, the local skin temperatures under one of the 2 capsules was kept at a constant level (37 degrees C). The effects of the level of body hydration on the sweating response only appear when a high local thermal clamp is imposed beneath the capsule. This local effect is particularly strong over the active muscles of the thigh. The influence of the preexercise hydration appears during dehydration tests. This effect is not significant when fluid is given to the subject during the exercise. The change in the sensitivity of the thermoregulatory system is more strongly associated with plasma osmolarity than hypovolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between speed and the maximal length of time supramaximal runs can be sustained (temps-limite, tlim) has been studied in seven male subjects (physical education students). Within the range of intensity studied, tlim strictly depends on maximal oxygen consumption (VO2max). The relationship between tlim and the relative energy cost of the exercises per unit of time (E), calculated by subtracting the maximal power of aerobic metabolism (Emaxox) from E, removes the interindividual differences of tlim. The function tlim = f(E-Emaxox) is described by an empirical equation of the form: tlim = a.exp[-b(E-Emaxox)] (r = 0.979; P less than 0.001), where the parameters a and b are respectively equal to 330.8 and 0.14 and where tlim, E and Emaxox are respectively expressed in seconds and in watts per kg of body weight.

1.) Core temperature, tail temperature, metabolic heat production, and evaporative heat loss were measured in rats exposed to various ambient temperature conditions. 2.) Control rats increased heat production in the cold and heat loss in a warm environment, thus maintaining a relatively constant core temperature. 3.) Pentobarbital anesthesia reduced the thermoregulatory responses and caused core temperature to vary considerably with ambient temperature. Ketamine anesthesia resulted in minor thermoregulatory deficits. 4.) It is concluded that ketamine can be used in thermal physiological studies that require an anesthetised preparation, although it is not completely devoid of inhibitory effects on thermoregulatory responses.

The responses of the cerebellar Purkinje cell to removal of its climbing fiber input has been studied electrophysiologically in slices of rat cerebella. Using single electrode current clamp methods, membrane potentials were recorded in various conditions from normal and 3-AP deafferented Purkinje cells (PC). The membrane of the deafferented PC showed a rectification for hyperpolarizing currents which varied in degree with length of time after removal of the climbing fiber input. While this rectification was the most pronounced change in membrane properties provoked by the deafferentation, other more subtle effects were observed in experiments with changes in extracellular ionic compositions. Since the rectification began at membrane potentials near -60 mV, it could prevent membrane hyperpolarization by inhibitory synaptic inputs and thus produce an apparent hypersensitivity to excitatory inputs.

1.) Cellular processes that contribute to the acquisition and expression of long-term sensitization have been examined in Aplysia. The tail-siphon withdrawal reflex was studied because the neural circuit for this reflex has been well characterized. Furthermore, the sensory neurons of this neural circuit exhibit cellular changes that accompany short-term sensitization. 2.) Repeated application of noxious stimuli to the animal produces a long-lasting enhancement of reflex withdrawal of the siphon when the animal is tested with a weak stimulus to the tail. These findings confirm the existence of long-term sensitization in Aplysia, first described by Pinkser et al. (1973). 3.) Biophysical correlates of long-term sensitization were examined in the first central relay of the tail-siphon reflex circuit, the sensory neurons that innervate the animal's tail. The net outward membrane currents of these cells reduced after 24 hours as a consequence of long-term sensitization training. 4.) The intracellular signal for the induction of these changes in membrane currents was examined by intracellular injection of cAMP into individual sensory neurons. This procedure mimics at least some of the effects of sensitization training at the single-cell level. cAMP induced a long-term reduction of membrane K+ currents 24 hours after the cells were injected with cAMP. The membrane currents reduced by cAMP were similar to those reduced by long-term sensitization training. 5.) Preliminary experiments indicate that neurotransmitters and agents that induce an evaluation of cAMP in the sensory neurons also alter the incorporation of labeled amino acids into specific proteins in the sensory neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

This paper reports an attempt to measure the dependency of the visual temporal frame on cortical rhythms. As a probe, we used two short flashes of a point light source separated in time by a variable interstimulus interval (ISI). Subjects were asked to judge whether the two short flashes were perceived as simultaneous or as sequential. The onset of the light flashes was triggered at four chosen phases of the occipital alpha rhythm of the viewing subject, and the probabilities of perceived simultaneity at various ISI's were obtained. Data from three experimental subjects show that the triggering phase produced a significant shift along the ISI-axis, thus changing the probability of perceived simultaneity. The magnitude of this shift varied substantially across subjects. These results show that, although cortical rhythms correlate with perceptual framing as previously reported (Varela et al., 1981), the nature of this dependency is different than previously suggested: a visual temporal frame seems to be a local event at the cortex, and not a global coordination uniformly reflected in the alpha rhythm.

1. Recordings of longitudinal displacements of both feet have been performed by linking each foot to a length-voltage transducer by means of threads. The movement transmitted to the transducer was reduced by winding the thread around a sixteen strand pulley block. 2. The aspect of the displacement curves allows a direct analysis of the walk. Some typical curves of normal and pathological gaits are presented. Graphic measurements done on several right and left cycles of a 6 m walk episode in 50 adult subjects provided data to determine the mean and the standard deviation of spatial and temporal parameters of the walk. 3. An advantage of this method is to permit the measurement of the parameters of several successive cycles of both sides and so to detect changes in the length, the duration and the velocity of successive cycles of the same foot and of alternated cycles of both feet. This being important to characterize pathological gaits.

Poorly metabolized hexoses, such as 3-O-methyl-D-glucose, 2-deoxy-D-glucose and D-galactose failed to reproduce the inhibition of 86Rb outflow, the early inhibition and secondary rise in 45Ca efflux and the stimulation of insulin release evoked by D-glucose in perifused rat islets. Insulin release induced by either D-glucose or 2-ketoisocaproate was also unaffected by 3-O-methyl-D-glucose. It is concluded that hexose transport in islet cells does not represent in itself a significant determinant of the cationic and secretory response to D-glucose.