bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of starvation on intestinal cholecystokinin‐like activity and pancreatic growth
Authors: Brand S. J. , Morgan R. G. H. 
Published: December 2014

1. This study examines the influence of starvation on intestinal CCK content and pancreatic growth. Intestinal CCK content was determined by measuring the CCK‐like activity using an in vitro gall‐bladder bio‐assay. Starvation for up to 72 hr causes a parallel fall in intestinal CCK content and pancreatic DNA synthesis. Since there was no significant decrease in liver DNA synthesis, the effect of starvation was probably not simply a consequence of malnutrition. Furthermore there was little effect of starvation on pancreatic protein and DNA content, suggesting that pancreatic cell turnover is particularly sensitive to changes in dietary stimulation.2. With refeeding after starvation CCK‐like activity in intestinal extracts gradually increased, approaching non‐fasting levels 72 hr after refeeding. Pancreatic DNA synthesis also returned to non‐fasting levels after feeding but this rose faster than the intestinal CCK content.3. Pentagastrin treatment prevented the atrophy of both the pancreas and the gastrointestinal tract with starvation without influencing the fall in intestinal CCK‐like activity. This suggests that the control of CCK‐containing cells is different from that of the surrounding intestinal parenchyma.4. The effect of starvation was also studied in antrectomized rats. Antrectomy alone did not reduce pancreatic DNA synthesis although DNA synthesis of the small intestine was significantly reduced. When antrectomized rats were starved pancreatic DNA synthesis fell to the same degree as was found in unoperated animals. The pancreatic atrophy was also accompanied by a drop in intestinal CCK content. Starvation of antrectomized rats, however, did not further depress the already greatly reduced plasma gastrin concentration.
Factors that determine the excitability of parasympathetic reflexes to the cat bladder
Authors: McMahon S. B. , Morrison J. F. B. 
Published: December 2014

1. Spino‐bulbo‐spinal reflex responses could be recorded from the vesical branches of the pelvic nerve following electrical stimulation of afferents in the vesical or colonic branches of the pelvic nerves, the hypogastric or pudendal nerves. The latencies of responses from these different sources were similar.2. Short latency responses could be recorded from the vesical branches of the pelvic nerve on electrical stimulation of descending pathways in the spinal cord and ipsilateral to and just below a hemitransection at the second cervical segment.3. These responses were facilitated by increases in intravesical pressure, maximal facilitation occurring at about 30 mmHg. Conversely, increases in intracolonic pressure inhibited these parasympathetic evoked responses, the maximum effect being seen with intracolonic pressures of 40‐50 mmHg.4. These results suggest that the spino‐bulbo‐spinal responses that are recorded from the vesical parasympathetic efferents can be elicited from nerves innervating viscera other than the bladder, and also somatic structures. The effects of these spino‐bulbo‐spinal pathways on vesical parasympathetic efferents are dependent on antagonistic influences of intravesical and intracolonic pressure.5. The pathways that mediate the changes in excitability in these reflexes appear to act at least in part at the termination of the bulbo‐spinal limb of the reflex, and involve afferents in the pelvic nerves but not the hypogastric or lumbar colonic nerves.6. It is proposed that the neurones that mediate this ‘gating’ action on the excitability of pelvic nerve reflexes are located in the sacral cord, and form a proportion of the population of interneurones described by McMahon & Morrison (1982b). In addition it is proposed that the neurones which mediate the ascending limb of the spino‐bulbo‐spinal reflexes are the long ascending neurones described by McMahon & Morrison (1982a).
Histograms of the unitary evoked potential of the mouse diaphragm show multiple peaks
Authors: Kriebel M. E. , Llados F. , Matteson D. R. 
Published: December 2014

1. Two classes of miniature end‐plate potentials (m.e.p.p.s) were recorded from diaphragm neuromuscular junctions. Amplitude histograms of both classes had multiple peaks that were integral multiples of the smallest peak (s‐m.e.p.p.s). The smaller m.e.p.p.s formed the first three or four peaks of histograms and the number of m.e.p.p.s (skew‐m.e.p.p.s) in each peak decreased, forming an over‐all skewed distribution. The larger m.e.p.p.s (bell‐m.e.p.p.s) formed a more‐or‐less bell‐shaped distribution. The distribution of m.e.p.p.s varied from mainly skew‐ to mainly bell‐m.e.p.p.s. In young adult mice the number of subunits composing the classical m.e.p.p.s varied between ten and fifteen at room temperature; at higher temperatures the range was from three to ten subunits.2. End‐plate potentials (e.p.p.s) were reduced with cobalt ions (ca. 4 m
m) until most nerve impulses failed to release transmitter. The amplitudes of ‘unitary evoked potentials’ were of the bell‐m.e.p.p. class and histograms show integral multiple peaks that correspond to the peaks in histograms of the bell‐m.e.p.p.s.3. The peaks in both m.e.p.p. and unitary e.p.p. histograms remained in the same position throughout the recording period and became more distinct as the sample size increased.4. The variance of the s‐m.e.p.p. was estimated from the noise and measurement error and the variance of all peaks in the histograms. Most variance of the first peak (s‐m.e.p.p.) was due to noise and measurement error.5. The integral peaks in the m.e.p.p. and ‘unitary evoked potential’ histograms are predicted with a probability density model based on the estimated variance of the s‐m.e.p.p. and the assumption that larger potentials are composed of subunits the size of s‐m.e.p.p.s. The data and model support the hypothesis that m.e.p.p.s and unitary potentials are composed of subunits.
Development of post‐tetanic potentiation at identified inhibitory and excitatory synapses in Aplysia
Authors: Ohmori Harunori 
Published: December 2014

1. The development of post‐tetanic potentiation (p.t.p.) was studied at three identified synapses in the abdominal ganglion of Aplysia californica. They are (1) the excitatory synapse made onto R15 by an axon in the right connective (RC1—R15), (2) the inhibitory synapse made by L10 onto one of its follower cells in the rostral quadrant of the left abdominal ganglion (L10—LUQC), and (3) the excitatory synapse made by L10 onto RB cells (L10—RB). Animals examined ranged from stage 11 juveniles weighing 2 mg to stage 13 adults weighing 300 g.2. Despite a marked decrease of the input resistance (34‐fold) and a marked increase in the capacitance of the cells of the LUQC, the amplitude of i.p.s.p. measured at 50 mV more negative than its reversal potential decreases only 4‐fold, between juvenile animals (25‐65 mg) and adult animals (100 g). This suggests a marked increase in the synaptic current. A similar discrepancy in the extent of decrease between the input resistance and e.p.s.p. amplitude was found in the RC1—R15 synapse during development.3. The amount of p.t.p., after tetanization at 5 Hz for 30 sec, increased with development. At the excitatory RC1—R15 synapse, p.t.p. (defined as the percent of the maximal post‐tetanus p.s.p. over the control p.s.p.) increased from 135±11% (mean±
s.d., n = 7) to 334±72% (n = 10). At the inhibitory L10—LUQC synapse, p.t.p. increased from 99±11% (n = 6) to 276±58% (n = 7).4. At both types of synapses, the time course of p.t.p. decay was measured by fitting a single exponential function, showing no systematic developmental change in the time constant of p.t.p. decay from the time p.t.p. was first measured onwards. The time constant was 129±52 sec (n = 39) for RC1—R15, and 45±7 sec (n = 20) for L10—LUQC.5. Divergent connexions made by the same presynaptic neurone L10 on the inhibitory follower cells (L10—LUQC) and on the excitatory cells (L10—RB) showed the same amount of potentiation in the same animal after an L10 tetanus. Convergent connexions onto the RB cells from the axon in the right connective and from L10 produced completely independent potentiation. These results provide an independent support for the well established finding that p.t.p. results exclusively from presynaptic changes.6. At each of these several synapses which show robust p.t.p. in adult animals, p.t.p. appears as a late step in their development. There is thus a discrete and considerable interval of time between the establishment of functional connexions and the emergence of synaptic plasticity in these excitatory and inhibitory synapses in Aplysia.
Desensitization at the frog neuromuscular junction: a biphasic process
Authors: Feltz Anne , Trautmann Alain 
Published: December 2014

1. The desensitization of the cholinergic receptor has been investigated at the frog neuromuscular junction. The agonist was either perfused or applied by ionophoresis.2. In all situations, desensitization develops in two phases: a fast one, experimentally in the second range but likely to be briefer, and a slower one, which extends over tens of seconds.3. When the presence of the agonist is prolonged, desensitization approaches a steady state, estimated through the amplitude of a test response. In steady‐state conditions, this amplitude depends upon the desensitizing agonist concentration. The dose—response curve for desensitization induced by carbachol (CCh) indicates that half of the receptors can be desensitized at room temperature in the presence of 2·3 μ
m‐CCh. The shape of the curve suggests that one desensitized receptor can bind two CCh molecules.4. The recovery from desensitization, estimated with a repetitive test pulse, displays two exponential phases. The time constant of the fast phase is 11‐12 sec, and 4‐5 min for the slow phase, regardless of the concentration or the nature of the agonist (acetylcholine or carbachol).5. The factor which most strikingly affects the relative amplitudes of the fast and slow phases of recovery is the duration of the (desensitizing) agonist application. Desensitizations lasting a few seconds are followed by a ‘fast’ recovery, whereas the slow phase of recovery is prominent when the agonist has been applied for more than 2 min.6. The fast and slow phases of desensitization onset and offset are not due to independent causes but are coupled: in given conditions, the onset can be essentially fast, and the recovery slow.7. All our findings can fit in a cyclic scheme of desensitization, derived from the one of Katz & Thesleff (1957) with two modifications: whether activatable or desensitized, one receptor molecule would have two agonist binding sites; moreover, the desensitized receptor would exist in two distinct and interconverting conformations: D1, giving rise to the fast phases of onset and offset, and D2, responsible for the existence of the slow components of desensitization.
Effects of stimulation of the chorda tympani in bursts on submaxillary responses in the cat
Authors: Andersson P-O. , Bloom S. R. , Edwards A. V. , Jarhult J. 
Published: December 2014

1. The effects of continuous preganglionic stimulation of the chorda tympani at 2 Hz for 10 min were compared with those of stimulation at 20 Hz in 1 sec bursts at 10 sec intervals for the same period in cats treated with atropine (0·5 mg/kg). Both the fall in mean submaxillary vascular resistance (s.v.r.) and the rise in mean vasoactive intestinal peptide (VIP) output from the gland were increased significantly (P < 0·01; P < 0·02) when the same total number of impulses were delivered in the form of bursts at the higher frequency.2. Both responses were also consistently increased by stimulating the post‐ganglionic innervation in bursts in atropinized cats, or by stimulating the preganglionic innervation in bursts in the absence of atropine.3. The effects of stimulation of the chorda tympani in 1 sec bursts at 10 sec intervals for 2‐3 min were investigated over the frequency range 2‐160 Hz. The change in mean s.v.r. under these conditions was significantly reduced by administration of atropine at frequencies between 2 and 20 Hz, but not at higher frequencies. In atropinized cats, the fall in mean s.v.r. was linearly related to stimulus frequency (r = 0·993) over the range 2‐60 Hz and a maximal response was obtained during stimulation at 80 Hz. In the same experiments the fall in mean s.v.r. was linearly related to log mean VIP output over the frequency range 20‐160 Hz (r = 0·998).4. Closely similar changes in mean s.v.r occurred in response to both pre‐ and post‐ganglionic stimulation at all frequencies tested between 2 and 160 Hz in atropinized cats when the stimuli were delivered in bursts. The changes in mean s.v.r. were not significantly affected by varying the duration of individual stimuli over the range 0·1‐25·0 msec.5. The flow of submaxillary saliva was also linearly related to stimulus frequency over the range 2‐40 Hz (r = 0·997) when the stimuli were delivered in bursts in the absence of atropine and secretion of saliva was maximal at 60 Hz.6. It is concluded that release of VIP from the submaxillary gland of the cat is optimal in response to stimulation of the chorda tympani at relatively high frequencies, when the impulses are delivered in bursts. Flow of saliva which is mediated by acetyl choline, may also be potentiated under the same conditions.
Cutaneous mechanoreceptors in macaque monkey: temporal discharge patterns evoked by vibration, and a receptor model
Authors: Freeman Alan W. , Johnson Kenneth O. 
Published: December 2014

1. Vibratory stimuli applied to the hand of a monkey evoke phase locked impulse trains in the three classes of low threshold mechanoreceptive afferents which innervate the area. The responses of each class of afferent (slowly adapting (SA), rapidly adapting (RA), and Pacinian (PC) vary in a systematic but complex way across the range of frequencies and intensities to which they are sensitive. The receptors are not accessible for electrophysiological recording. The aim in this study was to infer the mechanisms underlying their responses from detailed examination of the statistical properties of the impulse trains.2. A very simple receptor model with four degrees of freedom was chosen as a starting point. The independent variables consisted of the resting membrane time constant, τ, a variable membrane conductance, Gr, the fraction of each sinusoidal stimulus cycle producing depolarization, pr, and the noise level, σ, which was assigned to the impulse threshold. The aim was to use the deviations between observed data and predictions from the basic model to construct a more effective model. In fact, the deviations were minor and were mostly explained by periods of increased excitability in the wake of each action potential. Almost all of the differences between the responses of the three mechanoreceptive classes examined in this paper were accounted for by differences in time constants.3. The temporal structure of the responses from each mechanoreceptive class was examined at two levels of resolution, a coarse level where the resolution unit was a full cycle, and a fine level where the unit was 0·1 ms.4. The coarse structure of each response was represented by the presence or absence of an impulse on each stimulus cycle. In each mechanoreceptive class, the impulse sequences were random at low stimulus frequencies and regular at high frequencies. The transition frequencies were roughly 5 Hz for the slowly adapting afferents, 7 Hz for the rapidly adapting afferents, and 110 Hz for the Pacinian afferents. The model matched these data closely when the time constants were set at 80, 60 and 3·4 ms for SAs, RAs and PCs, respectively.5. The fine structure of the responses of each mechanoreceptive class exhibited impulse phase locking, phase advance with increasing intensity, and bimodal phase distributions at higher frequencies. Impulses contributing to the first mode of bimodal distributions always occurred in cycles following cycles in which no impulse occurred. Impulses contributing to the retarded mode always occurred in cycles following filled cycles. The mean phase differences between the two modes was called phase retardation. Phase retardation grew with stimulus frequency for both the receptors and the model; the time constants required to match the model against neural phase retardation curves were 123, 64 and 4·8 ms for SAs, RAs and PCs, respectively.
The formation of appropriate central and peripheral connexions by foreign sensory neurones of the bullfrog
Authors: Frank Eric , Westerfield Monte 
Published: December 2014

1. The ability of foreign sensory neurones to form novel reflex pathways was studied in bullfrogs by removing, during early larval stages of development, the dorsal root ganglion (d.r.g. 2) that normally provides the entire sensory innervation of the front limb.2. After the operation these tadpoles metamorphosed into frogs that responded to sensory stimuli and had nearly normal use of the limb. Sensation in the limb was mediated by sensory neurones located in an adjacent ganglion (d.r.g. 3); these neurones normally never grow into the arm.3. These neurones were shown, by labelling with horseradish peroxidase, to project into the arm and into the region of the brachial spinal cord occupied by motoneurones innervating muscles in the arm. These projections do not occur at any time during normal development.4. Intracellular recordings from identified motoneurones demonstrated that when the operations were done before developmental stage 9 appropriate monosynaptic sensory‐motor pathways were established. The relative strengths of synergistic and antagonistic sensory projections onto motoneurones were normal, although the latencies of the synaptic potentials were somewhat longer.5. When the operation was performed after stage 9 but before metamorphosis, d.r.g. 3 sensory afferents grew into the arm and into the brachial spinal cord but did not make monosynaptic connexions onto motoneurones.6. Removal of d.r.g. 2 from adult bullfrogs failed to produce either central or peripheral changes in the projections of d.r.g. 3 sensory neurones.7. Many d.r.g. 3 neurones still innervated their normal sensory targets in the thorax. These neurones never formed monosynaptic connexions onto brachial motoneurones in either normal or experimental animals. In experimental animals, the polysynaptic projections of these third nerve sensory neurones to brachial motoneurones were stronger than in normal animals independent of when d.r.g. 2 was removed during development.8. Thus foreign sensory cells can form specific, functionally appropriate connexions between peripheral targets and motoneurones if the sensory cells that normally mediate this reflex pathway are removed sufficiently early during development.
The relation between tonicity and impulse‐evoked transmitter release in the frog
Authors: Kita Hiroshi , Narita Kazuhiko , van der Kloot William 
Published: December 2014

1. The increase in miniature end‐plate potential (m.e.p.p.) frequency in response to tetanic stimulation of the motor nerve at frog neuromuscular junctions in Ca2+‐free, Mg2+ EGTA‐containing (0 Ca2+—Mg2+ EGTA) solutions of varying tonicity has been studied. The response to stimulation is markedly increased in hypertonic solutions and is decreased in hypotonic solutions. Under these conditions changes in tonicity have comparable effects on stimulated and spontaneous quantal release.2. The tonicity was raised by adding sucrose, NaCl or glycine to the extracellular solution. The effects of the addition depended primarily on the increase in osmolarity of the solution, not on the chemical species producing it.3. The tonicity was decreased by lowering [NaCl]o. The hypotonic solution decreased the response to tetanic stimulation. When the tonicity of the solution with the low [NaCl]o was restored to normal by adding sucrose, the response was restored to its usual level. These results suggest that in 0 Ca2+—Mg2+ EGTA solutions stimulation does not enhance the probability of quantal release by raising [Na+]i.4. Repeated bouts of tetanic stimulation produced almost identical responses. In some instances the frequency continued to rise after the end of the tetanic stimulation, as reported by Erulkar & Rahamimoff (1978). This suggests that the stimulation of the nerve leads to the elevation within the terminal of a substance that in turn liberates an activator for quantal release.5. The Q10 for the increase in probability of quantal release is as high as 7. High Q10 values have also been reported for spontaneous m.e.p.p. frequencies. Tonicity and temperature appear to affect spontaneous and stimulated quantal release similarly.
Acetylcholine measured at short time intervals during transmission of nerve impulses in the electric organ of Torpedo
Authors: Dunant Y. , Jones G. J. , Loctin Françoise 
Published: December 2014

1. The amounts of total acetylcholine (ACh) and ATP, and of vesicle‐bound ACh were measured at short time intervals in the electrogenic tissue of Torpedo marmorata. The aim of this study is to approach with biochemical analysis the speed of electrophysiological phenomena.2. A stimulator coupled to a rapid freezer device was used to quench a number of tissue samples simultaneously, at different time intervals during transmission of a brief train of impulses at 100 Hz.3. The level of total ACh decreased significantly with the first ten impulses. Then a rapid but transient increase in total ACh occurred, reaching a maximum value by the fifteenth to sixteenth impulse.4. Vesicle‐bound ACh did not exhibit any changes parallel to those of total ACh, and did not decrease beyond the control level during transmission of twenty impulses at 100 Hz.5. The amount of ATP in the tissue varied in close relation to that of total ACh. No significant phase shift was observed between the transmitter and the nucleotide and the ACh/ATP molar ratio was not significantly different from 1.6. The shortest time interval investigated in this work was 10 ms. The rate at which the pieces of tissue are quenched for biochemical measurements when plunged into a liquid at low temperature has been estimated. It has also been evaluated to what extent the freezing rate may distort measurements of the biochemical changes occurring in the tissue.7. It is concluded that fast freezing appears to be a valuable approach for investigating the rapid biochemical changes underlying cholinergic transmission; a better time resolution might be reached at the price, however, of greatly reducing the size of the samples. The second conclusion is that transmission of a brief train of impulses is accompanied by significant changes in the amount of extravesicular ACh.