Perifused rat pancreatic islets, prelabelled with 45Ca, were exposed for 90 min to a medium containing 30 mM K+, 0.25 mM diazoxide and 0.5 mM EGTA, but deprived of CaCl2. Either verapamil (0.05 mM) or Cd2+ (0.05 mM) were also present in the perifusate. Under these conditions a rise in D-glucose concentrations from either 2.8 to 16.7 mM or zero to 8.3 mM increased both 45Ca outflow and insulin release, after an initial and transient decrease in effluent radioactivity. These findings suggest that, in islets depolarised by exposure to a high extracellular concentration of K+, D-glucose provokes an intracellular redistribution of Ca2+ ions and subsequent stimulation of insulin release. The functional response to D-glucose is apparently not attributable to either the closing of ATP-sensitive K+ channels, which were actually activated by diazoxide, or stimulation of Ca2+ influx, which was prevented by the absence of extracellular Ca2+. The present experimental design thus reveals a novel component of the glucose-induced remodelling of Ca2+ fluxes in islet cells. Such an effect might also be operative under physiological conditions, when the hexose leads to depolarisation of the islet B-cells.
Radioimmunoassay of progesterone in systemic and placental blood of pregnant rabbits and guinea pigs. 1. The level of progesterone in pregnant rabbits and guinea pigs serum was measured directly (without extraction) using a RadioImmunoAssay (RIA). 2. Hormonal concentrations in systemic blood were shown to increase with gestational age, being at their highest half-way through pregnancy (16.03 +/- 2.63 ng/ml for rabbits; 319.01 +/- 42.10 ng/ml for guinea pigs) and decreasing at the end of the pregnancy. 3. Progesterone was not detectable in rabbit placental blood, whereas a high level of this hormone was found in guinea pig placental blood, which increased with gestational age. From the 28th to the 56th post-coital day, the level increased from 143.22 +/- 13.15 to 283.30 +/- 36.84 ng/ml. 4. The method used enables to measure correctly progesterone concentrations in rabbit and guinea pig serum without extraction.
The effects of presynaptic impulse activity on the transmitter secretion at developing neuromuscular junctions were examined in Xenopus nerve-muscle cultures. Repetitive suprathreshold stimulation of the presynaptic neuron results in marked potentiation of spontaneous synaptic activity, as shown by whole-cell voltage-clamp recording of synaptic currents in the postsynaptic muscle cell. Our results are consistent with the notion that synaptic efficacy of the developing synapse is potentiated by the presence of electrical activity. Such activity-dependent synaptic modulation enables the early neuronal activity to play a regulatory role during the maturation of synaptic connections.
Experiments were performed using chronically implanted electrodes on the dog smooth muscle wall of the stomach and of the small and large intestines. Electrical activity of the muscle wall was recorded before and after feeding. When reaching the terminal ileum the active part of the migrating myoelectrical complex (MMC) continuously induced bursts of spike potentials superimposed on the slow waves. This electrical activity spread to the ascending colon. We also showed the existence of a spike activity on the terminal ileum independent of the MMC (appearing during the phase 1) and propagating to the colon. A relationship between the spike activities of the small and large intestines was also present after feeding. Beside the well-known gastro-colic reflex, we observed an increase in the spike activity of the terminal ileum and ascending colon between the 4th-5th hours after feeding. This probably corresponds to the arrival of the first portions of contents, evacuated from the arrival of the first portions of contents, evacuated from the stomach, and of the last portions of small intestinal contents. In conclusion, there is a relationship between the spike activities of the small and large intestines in starving animals and after feeding, and the terminal ileum plays a substantial role in this relationship.
It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.
It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.
1. Plasma renin activity was measured in non pregnant rabbits and guinea pigs under Ketamine-induced general anesthesia after pretreatment either with Propranolol or with a Placebo. Study was performed using a radio-immunoassay for angiotensin I. 2. Twenty minutes after the beginning of the observation period, renin activity in rabbits who had received Placebo alone (11.47 +/- 2.35 ng/ml/h) or associated with Ketamine (11.36 +/- 2.54 ng/ml/h) was similar. However, enzyme activity was significantly lower (P less than 0.001) when Propranolol was associated with Ketamine (3.97 +/- 0.58 ng/ml/h) or with Placebo (4.10 +/- 0.55 ng/ml/h). 3. In the same way, renin activity was significantly higher (P less than 0.001) in guinea pigs without Propranolol than in those who had received this drug. 4. These findings indicate that stress induced by general anesthesia with Ketamine or by simple manipulation of animals (Placebo) was accompanied by an excessive increase in plasma renin activity. Propranolol maintained the level of this enzyme activity within normal limits.
In co-cultures prepared from the septum and the hippocampus, cholinergic fibers originating in the septal slices grew into the neighboring hippocampal tissue and established functional cholinergic connections with pyramidal cells. To get further insight into the mechanisms governing cholinergic fiber growth, we have added TTX to the growth medium (2 x 10(-7) M) to block propagated electrical activity. Under these conditions, considerably fewer cholinergic cells appeared to survive. A few cholinergic fibers still invaded hippocampal target tissue, but their number was markedly reduced compared with control cultures. Simultaneous application of NGF together with TTX, however, not only increased enzyme levels and enhanced survival of cholinergic neurons, but also led to hippocampal ingrowth in virtually all septo-hippocampal co-cultures. These data, therefore, suggest, that in the absence of spiking activity, cholinergic fibers are capable of growing into a co-cultured target tissue. To test the specificity of growth of septal cholinergic fibers, we have co-cultured septal slices with slices of various brain areas which in situ lack a major cholinergic innervation, in particular the cerebellum. In the vast majority of such co-cultures, cholinergic fibers remained restricted within the septal slices, without innervating cerebellar tissue. This failure might in part be related to the lack of trophic factors released by the target tissue. We have, therefore, grown septo-cerebellar cultures in the presence and absence of NGF. Following application of 100 ng/ml NGF during the entire growth of the cultures, numerous AChE-positive fibers originating in the septal slices invaded the co-cultured cerebellar slices.(ABSTRACT TRUNCATED AT 250 WORDS)
1.) Total renin, active renin, prorenin, angiotensin II, estradiol and progesterone were measured in maternal, placental and fetal blood and in trophoblastic and uterine tissues of the guinea pig. Furthermore, membrane angiotensin II receptors were measured in trophoblastic tissues. 2.) Blood and tissue concentrations of total renin, active renin, angiotensin II and steroids are shown to increase with gestational age. At the full term of pregnancy (70th post-coital day), tissue concentrations of total renin in chorion (23,900 +/- 2,752 ng/g of tissue/h), maternal placenta (14,210 +/- 1,131), fetal placenta (12,475 +/- 927) and uterus (7,677 +/- 798) are 100 time higher than those observed in placental, fetal and maternal blood. Distribution of blood and tissue prorenin (inactive renin) is similar to that found for total renin. Active renin/Total renin ratio reaches 1% in uterine, placental and chorion tissues and 9.3 +/- 1.0% in maternal, placental and fetal blood. 3.) Angiotensin II levels in systemic maternal blood (690 +/- 99 pg/ml) and in uterine blood (467 +/- 84) are higher than those found in placental blood (266 +/- 39) and in different trophoblastic tissues (between 200 and 400 pg/g). Angiotensin II receptor concentrations are highest in chorion. 4.) Regarding the steroid hormones, it is noted that placental and maternal blood contain more progesterone than trophoblastic tissues. The highest concentrations of estradiol are found in chorion tissue and uterine blood. 5.) A positive correlation is observed between angiotensin II and estradiol in uterine blood (r = 0.69, P less than 0.01) and in chorion (r = 0.71, P less than 0.01). These findings indicate that angiotensin II and estradiol could, by their interactions, play an important role in the physiology of pregnancy.
1-degrees) Total renin, active renin, prorenin, angiotensin II, estradiol and progesterone were measured in maternal, placental and fetal blood and in trophoblastic and uterine tissues of the guinea pig. Furthermore, membrane angiotensin II receptors were measured in trophoblastic tissues.2-degrees) Blood and tissue concentrations of total renin, active renin, angiotensin II and steroids are shown to increase with gestational age. At the full term of pregnancy (70th post-coital day), tissue concentrations of total renin in chorion (23 900 +/- 2 752 ng/g of tissue/h), maternal placenta (14 210 +/- 1 131), fetal placenta (12 475 +/- 927) and uterus (7 677 +/- 798) are 100 time higher than those observed in placental, fetal and maternal blood. Distribution of blood and tissue prorenin (inactive renin) is similar to that found for total renin. Active renin/Total renin ratio reaches 1% in uterine, placental and chorion tissues and 9,3 +/- 1,0% in maternal, placental and fetal blood.3-degrees) Angiotensin II levels in systemic maternal blood (690 +/- 99 pg/ml) and in uterine blood (467 +/- 84) are higher than those found in placental blood (266 +/- 39) and in different trophoblastic tissues (between 200 and 400 pg/g). Angiotensin II receptor concentrations are highest in chorion.4-degrees) Regarding the steroid hormones, it is noted that placental and maternal blood contain more progesterone than trophoblastic tissues. The highest concentrations of estradiol are found in chorion tissue and uterine blood.5-degrees) A positive correlation is observed between angiotensin II and estradiol in uterine blood (r = 0.69, P < 0.01) and in chorion (r = 0.71, P < 0.01). These findings indicate that angiotensin II and estradiol could, by their interactions, play an important role in the physiology of pregnancy.
Radioimmunoassay of progesterone in systemic and placental blood of pregnant rabbits and guinea pigs. 1. The level of progesterone in pregnant rabbits and guinea pigs serum was measured directly (without extraction) using a RadioImmunoAssay (RIA). 2. Hormonal concentrations in systemic blood were shown to increase with gestational age, being at their highest half-way through pregnancy (16.03 +/- 2.63 ng/ml for rabbits; 319.01 +/- 42.10 ng/ml for guinea pigs) and decreasing at the end of the pregnancy. 3. Progesterone was not detectable in rabbit placental blood, whereas a high level of this hormone was found in guinea pig placental blood, which increased with gestational age. From the 28th to the 56th post-coital day, the level increased from 143.22 +/- 13.15 to 283.30 +/- 36.84 ng/ml. 4. The method used enables to measure correctly progesterone concentrations in rabbit and guinea pig serum without extraction.
In human, it has been shown that interactions between locomotor and respiratory patterns may lead to locomotor-respiratory couplings termed entrainment. In order to prove that this coupling is really an entrainment, we tried to show that it obeys one of the expected rules, i.e. that it evolves and is not present for all imposed locomotor frequencies. For that purpose, seventeen healthy volunteers were asked to run on a treadmill at 14 different locomotor rates (instead of 2 or 3 in previous works) for 40 s. All the subjects did not exhibit the same coupling and different relationships could be obtained: the most commonly observed was 2:1 (2 locomotor activities for a respiratory one) but other forms could appear (4:1 and even 5:2 or 3:2). When the coupling evolution was followed in the same subject, it did not appear for all locomotor frequencies but only for locomotor periods close to harmonics of respiratory ones (absolute coordination). On both sides of these values, it progressively evolved to relative coordination and to the lack of coordination. When two forms of absolute coordination were observed in a same subject, the phase relationships followed the rules of the entrainment. Compared to data obtained in quadrupeds, these results suggest that the entrainment of breathing frequency by the locomotor activity is due to central interactions between the respiratory and locomotor pattern generators and does not depend on a chemical regulation avoided here by short locomotor sequences.
The events by which [Ca]O modifies diastolic depolarization (DD) were analyzed in sheep cardiac Purkinje fibers perfused in vitro. Cs (2 mM) reduced diastolic depolarization (DD) at different [Ca]O and in 10.8 mM [Ca]O revealed an oscillatory potential (VOS) and the decay of a prolonged depolarization (Vex). In the presence of Cs, procedures that reduce Cai (a slower driving rate, lower [Ca]O or tetrodotoxin) abolished VOS and Vex and partially restored DD. In 10.8 mM [Ca]O and at all driving rates, Cs reduced DD slope, DD amplitude and VOS amplitude but had little effect on the VOS time to peak. In 10.8 mM [Ca]O, decreasing calcium overload by different means (2.6 microM TTX, 0.2 mM Cd) abolished VOS and decreased DD slope and amplitude. Substituting Na with Li induced marked aftercontractions but small VOS. In 10.8 mM [Ca]O, Li increased the amplitude of the aftercontractions and decreased that of VOS. Li also depolarized slightly the resting membrane and abolished the voltage undershoot (Emax) at the end of the action potential. In low [K]O, Li repolarized the resting membrane but the repolarization was maintained only in the presence of Ca. It is concluded that Ca overload causes both VOS and Vex which can either be masked by or can mask DD depending on the magnitude of DD and of Ca overload. VOS is apparently caused by an electrogenic Na-Ca exchange since Li-induced Ca overload increases the aftercontraction but decreases VOS.
The purpose of this study was to investigate secondary muscle spindle afferents from the triceps-plantaris (GS) and posterior biceps and semitendinosus (PBSt) muscles with respect to their fusimotor reflex control from different types of peripheral nerves and receptors. The activity of single secondary muscle spindle afferents was recorded from dissected and cut dorsal root filaments in alpha-chloralose anaesthetized cats. Both single spindle afferents and sets of simultaneously recorded units (2-3) were investigated. The modulation and mean rate of firing of the afferent response to sinusoidal stretching of the GS and PBSts muscle were determined. Control measurements were performed in the absence of any reflex stimulation, while test measurements were made during reflex stimulation. The reflex stimuli consisted of manually performed movements of the contralateral hind limb, muscle stretches, ligament tractions and electrical stimulations of cutaneous afferents. Altogether 21 secondary spindle afferents were investigated and 20 different reflex stimuli were employed. The general responsiveness (i.e. number of significant reflex effects/number of control-test series) was 52.4%, but a considerable variation between different stimuli was found, with the highest (89.9%) for contralateral whole limb extension and the lowest (25.0%) for stretch of the contralateral GS muscle. The size of the response to a given stimulus varied considerably between different afferents, and, in the same afferent, different reflex stimuli produced effects of varying size. Most responses were characterized by an increase in mean rate of discharge combined with a decrease in modulation, indicative of static fusimotor drive (Cussons et al., 1977). Since the secondary muscle spindle afferents are part of a positive feedback loop, projecting back to both static and dynamic fusimotor neurones (Appelberg Et al., 1892 a, 1983 b; Appelberg et al., 1986), it is suggested that the activity in the loop may work like an amplified which, during some circumstances, enhance the effect of other reflex inputs to the system (Johansson et al., 1991 b).
The experiments were performed on 21 cats anaesthetized with alpha-chloralose. The aim of the study was to investigate sets of simultaneously recorded spindle afferents (2-4 in each set) from the triceps surae muscle (GS) with respect to the pattern of fusimotor reflex effects evoked by different types of ipsi- and contralateral reflex stimulation. The afferents' responses to sinusoidal stretching of the GS muscle were determined and the fusimotor reflex effects were assessed by comparing the afferent responses (i.e. the mean rate of firing and the depth of modulation) elicited during reflex stimulation with those evoked in absence of any reflex stimulus. Natural of electrical activations of ipsi- and contralateral muscle, skin and joint receptor afferents were used as reflex stimuli. The spindle afferents were influenced by several modalities and from wide areas, with a majority responding to both ipsi- and contralateral stimuli. A particular reflex stimulus often caused different effects on different afferents, and the various reflex stimuli seldom gave similar effects on a particular afferent. Multivariate analysis revealed that the variation in response profiles among simultaneously recorded afferents were as great as between afferents recorded on different occasions. This suggests that the individualized response prifiles, observed in earlier investigations, represent a very diversified reflex control of the spindle primary afferents, and are not a reflection of changes in the setting of the spinal interneuronal network, occurring during the time interval between the recordings of different units. Also, there was no relation between the conduction velocity of the afferents and the reflex profiles of the afferents, but non-linear relations were found between effects elicited by different types of stimuli. Indications were also found that it may be possible to separate the population of GS muscle spindles into subgroups, according to the fusimotor effects exhibited by activation of various categories of ipsi- and contralateral receptor afferents. It is concluded that one possible way of making the very complex reflex system controlling the muscle spindles intelligible may be a combination of multiple simultaneous recordings of spindle afferents and multivariate analysis.
To determine if there was a role for the submucosal nerves in cholera toxin (CT)-induced secretion, we studied the effects of serosal addition of two neurotoxins, the nerve conduction blocking agent, tetrodotoxin (TTX), and the nicotinic ganglionic blocking agent, hexamethonium (HXM), on electrolyte secretion in control isolated rabbit ileum and in that stimulated by CT. 1). In the absence of CT, the short circuit current (Isc) decreased after TTX (10(-7) M) (P less than 0.01) and was unaltered by HXM (10(-5) M). In the presence of CT, Isc increased but was not modified by 10(-7) M TTX or 10(-5) M HXM. 2) In control tissues the mean isotopic Na+ and Cl- fluxes were not significantly altered by TTX addition. Cl- absorption alone was significantly reduced by HXM (delta JCl- = 1.95 +/- 0.81 microEq.hr-1.cm-2; P less than 0.02). After stimulation with CT, TTX significantly inhibited Na+ and Cl- secretion (delta JNa+ = 2.15 +/- 0.61 and delta JCl- = 2.15 +/- 0.76 microEq.hr-1.cm-2; P less than 0.01). Similarly, HXM significantly inhibited CT-stimulated Na+ and Cl- secretion (delta JNa+ = 1.73 +/- 0.70 and delta JCl- = 1.46 +/- 0.62 microEq.hr-1.cm-2; P less than 0.02). 3) In TTX and HXM treated tissues there was no difference in the increase in Isc caused by cAMP (2 x 10(-3) M), calcium ionophore A 23187 (4 x 10(-6) M) and glucose (10(-3) M) compared to the untreated tissues in the presence or absence of CT.(ABSTRACT TRUNCATED AT 250 WORDS)
1.) Total renin, active renin, prorenin, angiotensin II, estradiol and progesterone were measured in maternal, placental and fetal blood and in trophoblastic and uterine tissues of the guinea pig. Furthermore, membrane angiotensin II receptors were measured in trophoblastic tissues. 2.) Blood and tissue concentrations of total renin, active renin, angiotensin II and steroids are shown to increase with gestational age. At the full term of pregnancy (70th post-coital day), tissue concentrations of total renin in chorion (23,900 +/- 2,752 ng/g of tissue/h), maternal placenta (14,210 +/- 1,131), fetal placenta (12,475 +/- 927) and uterus (7,677 +/- 798) are 100 time higher than those observed in placental, fetal and maternal blood. Distribution of blood and tissue prorenin (inactive renin) is similar to that found for total renin. Active renin/Total renin ratio reaches 1% in uterine, placental and chorion tissues and 9.3 +/- 1.0% in maternal, placental and fetal blood. 3.) Angiotensin II levels in systemic maternal blood (690 +/- 99 pg/ml) and in uterine blood (467 +/- 84) are higher than those found in placental blood (266 +/- 39) and in different trophoblastic tissues (between 200 and 400 pg/g). Angiotensin II receptor concentrations are highest in chorion. 4.) Regarding the steroid hormones, it is noted that placental and maternal blood contain more progesterone than trophoblastic tissues. The highest concentrations of estradiol are found in chorion tissue and uterine blood. 5.) A positive correlation is observed between angiotensin II and estradiol in uterine blood (r = 0.69, P less than 0.01) and in chorion (r = 0.71, P less than 0.01). These findings indicate that angiotensin II and estradiol could, by their interactions, play an important role in the physiology of pregnancy.
This paper shows a medial prefrontal cortex (CxAP9) facilitating influence upon the unit activity of the centralis lateralis (Cl) nucleus of the thalamus, in rats anesthetized with urethane. Cortical influences were studied using both cortical cooling and cortical spreading depression (CSD) procedures. Both spontaneous and noxious thermally evoked activities were considered. When CSD was propagated and affected the CxAP9, as well as during the cooling of this area, both spontaneous activity and the responses evoked in Cl cells by noxious stimulation were blocked. This effect was interpreted as a cortical disfacilitation upon Cl cells. During the cortical silent period we tested the excitability of a few Cl cells, provoking their activation by passing electrical current across the same Cl recording electrode. No changes were observed in their excitable response threshold during CSD or cortical cooling. Our results are in agreement with the proposition of a tonic cortical facilitatory action upon the spontaneous and noxious-evoked responses recorded in the Cl cells.
The experiments reported here attempted to examine in two groups of rats the effects on the taste preferences, food and fluid intake, energy balance and body weight gain of corticocerebellar lesions involving, primarily, the Lobulus VI (LVI) or the Lobulus Paramedianus (LP). The results showed that the lesions of LVI or LP did not affect the daily intake of total fluid and salty solution. The intake of sweet solution increased in both groups of lesioned rats, while the intake of deionized water and acid and bitter solutions decreased only in the LVI lesioned rats. Food intake decreased in the LVI-lesioned rats but not in the LP-lesioned animals. Body weight gain, efficiency of food utilization, caloric intake and body surface gain decreased in both groups. It seems therefore that the cerebellar cortex, which probably receives taste fibers, somehow influences taste preferences and water intake, and that it may be involved in the mechanisms of food intake, its utilization and body energy balance.
