PubMed Health⌕ Search

Biomedical subjects

D H Paul

Publications and source records attributed to D H Paul.

At least 37 records · Page 2Linked to original sources
PubMed1981

The activity of cerebellar neurones of an elasmobranch fish (Scyliorhinus canicula) during a reflex movement of a fin.

1. Response of neurones in the corpus cerebelli of Scyliorhinus canicula (Elasmobranchii) have been recorded in decerebrate unanaesthetized fish during the performance of pectoral fin reflexes (p.f.r.) evoked by electrical stimulation of the fins.2. Of 421 single units recorded in the posterior dorsal quadrant of the corpus, 111 (26%) had their discharges modulated when the reflex was evoked; fifty nine were Purkinje (P) cells discharging single spikes, thirteen were P cells discharging complex responses, thirty-six were stellate (S) cells and three were not positively identified.3. The responses of fifty-one units (thirty-seven P cells and fourteen S cells) were analysed in detail. In thirty-one of the P cells and all the S cells the initial response was excitatory, six P cells gave an inhibitory response only and a further three were inhibited after the initial excitation. Only one S cell had an inhibitory component in its response.4. The discharges of the S cells completely overlapped the inhibitory responses of the P cells.5. Only one cell (a P cell) was evoked at a latency shorter than that of the p.f.r. In one other P cell discharging single spikes spontaneously, the evoked response was a long latency (146 msec) complex response. Four other P cells discharged only complex responses but the pattern of their response to the p.f.r. was similar to that of P cells discharging single spikes only.6. No cerebellar responses were evoked if the fin stimulus was below the threshold necessary to evoke a p.f.r. In curarized fish, unit responses were recorded that were qualitatively similar to those recorded in unparalysed fish.7. These results suggest that (i) because of the long latency of the responses, the cerebellum is unlikely to have a role in the initiation of the p.f.r.; (ii) the responses during the p.f.r. were evoked via a mossy fibre-parallel fibre pathway; (iii) the responses were correlated with motor activity rather than sensory input.

Action Potentials↗
PubMed1980

Combined study of the pattern of spontaneous activity of cerebellar Purkinje cells and phenytoin serum levels in the rat.

The effects of phenytoin (PHT) on the spontaneous activity of cerebellar Purkinje cells and the drug serum levels have been examined following both intravenous and intraperitoneal administration in rats. Purkinje cell activity was assessed by on-line computer analysis of interspike interval distributions. PHT levels were assayed in blood samples taken at the end of the electrophysiological experiments and in successive samples obtained in parallel experiments over periods corresponding to when electrophysiological recordings were made. Single intravenous doses of PHT (10 mg/kg) produced a decrease in the discharge rate in individual Purkinje cells with a time course which was delayed and prolonged compared with the changes in serum levels of PHT. A single intraperitoneal dose of PHt (100 mg/kg) produced a statistically significant (p < 0.02) decrease in Purkinje cell discharge rate. Similar results (p < 0.01) were obtained after pretreatment with PHT (50 mg/kg daily for 14 days, including the day of the experiment). Both injection schedules produced nontoxic serum PHT levels during the recording period. Pretreatment with PHT doses of 10 mg/kg for 14 days (including the experimental day) produced a smaller decrease in Purkinje cell discharge rate (p < 0.05). When pretreatment ceased the day before the electrophysiological experiment, no significant changes in Purkinje cell activity were observed, and serum PHT levels were not detectable at the end of the experiment. None of the pretreatment schedules produced overt signs of cerebellar dysfunction or motor impairment. These findings indicate that PHT may increase the output from the cerebellum by suppressing Purkinje cell activity. Since this effect occurs without producing cerebellar symptoms, it may account for some of the therapeutic action of PHT at nontoxic levels in man.

Animals↗
PubMed1979

An endogenous motor program for sand crab uropods.

A stereotyped pattern of spontaneous, rhythmic bursting in motoneurons of three principal uropod muscles in the sand carb Emerita analoga has been recorded from a deafferented chain of the four most-posterior abdominal ganglia. This endogenous motor program resembles the electromyogram pattern recorded from return-stroke and power-stroke muscles in swimming crabs in that (1) latencies of power-stroke bursts and burst periods are positively correlated with each other and (2) durations of power-stroke bursts are brief and nearly invarient. The endogenous program differs from the electromyogram pattern in having longer periods and return-stroke bursts which are brief and sporadic. The neural oscillator underlying the endogenous motor program, therefore, appears to drive the power stroke. Circumstantial evidence suggests that it may also inhibit return stroke motoneurons concurrently with excitation of the power-stroke excitor.

Animals↗
PubMed1976

Pituitary thyrotropin (TSH) rebound phenomenon and kinetics of secretion in the goitrous rat: differential effects of thyroxine on synthesis and release of TSH.

The protein metabolism and [3H]-uridine uptake of thyroid and adenohypophysis and the kinetics of pituitary TSH rebound (PTR) were studied in goitrous female rats (fed propylthiouracil, PTU: for 7-12 weeks) following single, iv injections of L-thyroxine (T4: 0.8 to 200 mug). Goitrogenesis was associated with reduced protein concentration and enhanced uptake of [3H] uridine in both glands. Plasma levels of TSH were invariably elevated but stores in the adenohypophysis were consistently reduced. Small doses of T4 (4 mug) induced significant TSH repletion in the pituitary within 2-6 h following injection. Accumulations of pituitary TSH to supranormal levels (15-fold increases) were achieved with 20 mug T4 at 6 and 24 h; higher doses (100-200 mug) inhibited the PTR at all time intervals tested (0.5-24 h). Administration of puromycin or actinomycin D did not influence the PTR. Protein content and labeled uridine uptake of the pituitary bore no apparent relationship to T4-induced TSH repletion in the gland. Blood clearance rate of exogenous rat TSH was measured prior to and during PTR. Plasma half-life was determined to be 13.6 and 19.9 min in euthyroid and chronically hypothyroid rats, respectively; it was not significantly altered from the latter during rebound (18.7 min). Calculations of theoretical TSH secretory rates prior to (50.5 +/- 4.4 mU/h) and after rebound with 20 mug T4 (25.4 +/- 4.2 mU/H) revealed that the reaccumulation of TSH in the pituitary induced with T4 cannot be attributed solely to inhibition of release, but may also involve enhancement of synthesis. It is concluded that T4 administration at high dose levels inhibits both synthesis and release of TSH from pituitary thyrotrophs, whereas low critical doses of T4 suppress release, but augment synthesis and/or facilitate conformational change in a pituitary precursor(s) molecule which renders it detectable by bioassay.

Animals↗
PubMed1976

Role of proprioceptive feedback from nonspiking mechanosensory cells in the sand crab, Emerita analoga.

The two programmes underlying uropod beating in Emerita ('swimming' and 'treading water') are distinguished by a difference in timing of the power stroke within the interval between return strokes (cycle). While 'swimming' (cycles approx. 80-400 ms) the phase and while 'treading water' (cycles approx. 100-700 ms) the latency of the power stroke are relatively invariant. Analyses of electromyograms of untrestrained Emerita, before and after bilateral surgical ablation of the four nonspiking mechanoreceptive cells associated with each uropod, established that power strokes in 'treading water' are dependent upon proprioceptive feedback from the nonspiking cells. As cycle duration increases from 80 to 700 ms, the function of the reafference changes from reinforcement of the centrally generated 'swimming' pattern to production of the 'treading water' pattern.

Action Potentials↗
PubMed1975

Responses of fastigial nucleus neurones to stimulation of the caudate nucleus in the cat.

1. Extracellular records were made of single unit activity evoked in the fastigial nucleus (FN) by electrical stimulation of the caudate nucleus (CN) in cats anaesthetized with sodium thiopentone. 2. Single shock stimulation evoked bilaterally complex responses having up to three components. These were, in temporal order, with percent of units exhibiting them, (a) a short burst of evoked spikes with either a latency of smaller than 5-5 msec and no associated field potential (6 percent) or a latency of 7-5-20 msec and associated with a prominent negative-going field potential (36 percent); (b) suppression of spontaneous discharges for a period of 20-150 msec (90 percent); (c) a resumption of spike discharges with a transient increase in frequency lasting for 25-500 msec (66 percent). 3. Changes in component (c) of the response patterns of some units were noted during repetitive stimulation The nature of the change depended on the laterality of the FN with respect to the stimulated CN. 4. Mechanisms which might account for the responses are discussed, but it is emphasized that some of the results cannot yet be satisfactorily explained.

Action Potentials↗