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Biomedical subjects

D J Prior

Publications and source records attributed to D J Prior.

At least 19 recordsLinked to original sources
PubMed1994

Morphological correlate of regional partitioning of integumental water absorption in terrestrial slugs.

An ultrastructural study of the foot surface of the terrestrial mollusc, Limax maximus, has revealed a correlation of epithelial cell type with the functional partitioning of the surface. The lateral absorptive bands of the foot are comprised exclusively of microvillar epithelial cells, while those of the medial locomotor band are all ciliated. Thus, there is a clear partitioning of epithelial cell types between areas of the foot surface with distinct functional roles. Consistent with the proposed role for paracellular absorption, varying states of hydration are shown to affect the extent of the intercellular spaces, but not the intracellular architecture.

Absorption↗
PubMed1991

Modulation of heart activity in the terrestrial slug Limax maximus by the feeding motor program, small cardioactive peptides and stimulation of buccal neuron B1.

Activation of the feeding motor program (FMP) increases the force of ventricular contractions in heart/central nervous system (CNS) preparations of the terrestrial slug Limax maximus (Linnaeus). The FMP-induced increase in ventricular activity requires innervation of the heart by abdominal ganglion nerves N9 and N11. Application of the small cardioactive peptides SCPA and SCPB to isolated preparations of the heart causes dose-dependent increases in the force of ventricular contractions. In addition, the SCPs induce rhythmic contractions in quiescent heart preparations. The effects of the SCPs appear to be specific in that the neuropeptide FMRFamide has an inhibitory effect on ventricular activity. SCP-like and FMRFamide-like immunoreactive material is found in the heart, kidney and pericardium and in the nerves that innervate these organs. Unilateral intracellular stimulation of buccal neuron B1, which contains SCP-like and FMRFamide-like immunoreactive material, mimics the FMP- and SCP-induced increases in ventricular activity. The effect of B1 on ventricular activity is frequency dependent and requires innervation of the heart by N11. These results are consistent with the hypothesis that the SCPs are involved in feeding-related alterations in heart activity in Limax and that the control of this effect involves neuron B1.

Analysis of Variance↗
PubMed1988

The molluscan neuropeptide, SCPB, increases the responsiveness of the feeding motor program of Limax maximus.

Small cardioactive peptide B (SCPB) has an excitatory effect on both buccal neurons and musculature in numerous molluscan species. The present study reports the effects of SCPB on the activity of specified buccal neurons and the expression of the feeding motor program of the terrestrial slug, Limax maximus. Superfusion of an isolated CNS preparation with 10(-6)M SCPB results in a 3-4-fold increase in the burst frequency of the fast salivary burster neuron (FSB), while having no effect on the activity of another endogenous burster, the bilateral salivary neuron (BSN). The response of the FSB to SCPB is dose dependent, with a threshold concentration of 2 X 10(-8)M. The response of the FSB to SCPB showed no indication of desensitization, even after long-term exposure (20 min). The feeding motor program (FMP) in Limax is a discrete pattern of cyclical motor activity that can be initiated by lip nerve stimulation. In the presence of SCPB a previously subthreshold stimulus can initiate the full FMP. The pattern of the FMP, once initiated, appears unaffected by SCPB. Thus it is the responsiveness of the initiation process that is enhanced by SCPB. Histochemical studies revealed a number of buccal neuron somata and fibers that stain for SCPB-like immunoreactive material (SLIM).

Action Potentials↗
PubMed1988

The pneumostome rhythm in slugs: a response to dehydration controlled by hemolymph osmolality and peptide hormones.

1. One response of the terrestrial slug, Limax maximus to dehydration is the initiation and modulation of the pneumostome rhythm. When a slug has lost 15-20% of its initial body weight by evaporation, the frequency of pheumostome closures, which is less than 0.5 closures/min in fully hydrated slugs, begins to increase. 2. The frequency increases with further dehydration, but the average duration of each closure remains constant. Thus, the proportion of time during which the pneumostome is closed increases. Simultaneously, the area of the pneumostome opening decreases. 3. This behavior appears to be controlled in part by both the osmolality of the slug's hemolymph and by a peptide closely related to arginine vasotocin (AVT) and arginine vasopressin (AVP). Injecting intact slugs with mannitol, which increases the osmolality of the hemolymph, or with AVT or AVP, can initiate the pneumostome rhythm. 4. Mannitol injections, however, do not provoke the decrease in the area of the pneumostome opening which is induced by natural dehydration or by AVT or AVP injection. This suggests that at least two systems may be involved in the overall control of the pneumostome.

Animals↗
PubMed1986

Modification of cardiac activity in response to dehydration in the terrestrial slug, Limax maximus.

The level of body hydration in the terrestrial slug Limax maximus modifies several aspects of behavior such as pneumostome activity, feeding responsiveness, huddling, and contact-rehydration. The relationship between water balance and pneumostome activity and respiratory function suggested that cardiac activity might also be affected. To pursue this possibility, intact slugs and isolated heart-central nervous system (CNS) preparations were used to investigate cardiac responses to the increase in hemolymph osmolality which occurs during dehydration. In intact animals, heart rate increased in response to progressive air-dehydration and to increases in hemolymph osmolality resulting from injections of hyperosmotic solutions of mannitol or NaCl. In isolated preparations, the heart or CNS were separately exposed to hyperosmotic saline. Exposure of the heart alone to hyperosmotic saline resulted in decreased heart rate while exposure of only the CNS resulted in an increase in heart rate. These observations suggest that the increase in heart rate that is observed in intact air-dehydrated slugs is primarily mediated by the CNS.

Animals↗
PubMed1985

Paracellular water uptake and molecular sieving by the foot epithelium of terrestrial slugs.

A paracellular pathway in the foot epithelium of Lehmannia valentiana can be opened by dehydrating the slug. Movement of water from a wet pad through the opened pathway into the haemolymph of this terrestrial slug is rapid. The sieving properties of this paracellular pathway have been determined using the reference isotope 3HOH and various 14C-labelled solutes. Paracellular uptake of 14C-insulin (Fig. 1) and 3HOH (Fig. 2) is initial rate for at least 3 min. If the wet pad contains 1,000 cpm of 14C per ml of 3HOH, slugs absorb only about 400 cpm of 14C with each ml of 3HOH absorbed representing a sieving ratio of 0.4 for insulin. The sieving ratio of 14C-inulin does not change when the concentration is increased from 0.1 to 2.5 mmol/l. Moreover, the sieving ratio of 14C-inulin was not affected significantly by the nature of the labelling, i.e., 14C-carboxyl vs 14C-methoxy. Sieving ratios for 14C-mannitol (182 Da), 14C-polyethylene glycol (4,000 Da), and 14C-inulin (5,250 Da) were 0.92, 0.63, and 0.39, respectively (Table 1), indicating that sieving is dependent on molecular size. 14C-Dextran (70,000 Da) and blue dextran (200,000 Da) were excluded from the paracellular pathway (Fig. 4). The effective pore size of the paracellular pathway was estimated using the relationships between sieving ratio and molecular weight of 3HOH and the various solutes that can pass through the pathway. The extrapolated pore size is equivalent to that of a sieve having a molecular weight cutoff of about 10,000 Da (Fig 3).

Animals↗
PubMed1985

Locomotor activity of the terrestrial slug, Limax maximus: response to progressive dehydration.

The circadian locomotor rhythm of the terrestrial slug, Limax maximus, was measured with activity wheels during exposure to both humid and drying conditions. Slugs kept in wet wheels (100% RH) remained fully hydrated while those in dry wheels (less than 30% RH) experienced progressive dehydration. Transfer of slugs from a wet wheel to a dry wheel resulted in an increase in the intensity and duration of their patterned locomotor activity that persisted for 3 days. Once the slugs were returned to wet wheels, their locomotor activity returned to normal.

Animals↗
PubMed1985

Body hydration and haemolymph osmolality affect feeding and its neural correlate in the terrestrial gastropod, Limax maximus.

When terrestrial slugs (Limax maximus) are dehydrated to 65-70% of their initial body weight (IBW) their feeding responsiveness is greatly decreased. There is a 90% decrease in feeding responsiveness when slugs are injected with hyperosmotic mannitol solution that raises the haemolymph osmolality to that of slugs dehydrated to 65-70% IBW (i.e. 200 mosmol kg-1 H2O). The duration of the Feeding Motor Programme (FMP) that can be recorded from an isolated CNS-lip preparation is reduced by increasing the osmolality of the saline bathing the preparation. The osmolality of the saline that can modify the FMP corresponds to that of the haemolymph of a slug dehydrated to 65-70% IBW. The pattern of the motor programme is not affected. A gradual increase in saline osmolality which temporally mimics the progressive increase in haemolymph osmolality of a dehydrating slug also causes a decrease in the duration of the FMP. The neural network underlying the FMP appears to adapt to hyperosmotic saline since the duration of FMP bouts gradually returns to normal levels after long-term exposure (6-8 h).

Animals↗
PubMed1984

Analysis of contact-rehydration in terrestrial gastropods: osmotic control of drinking behaviour.

Contact-rehydration in slugs is mediated by a specific behavioural pattern in which dehydrated slugs move onto a moist surface, assume a flattened posture while water is absorbed through the surface of the foot and move off once they are rehydrated. 'Drinking behaviour' is initiated when slugs have been dehydrated to the threshold level of 60-70% of initial body weight (IBW). Drinking behaviour is terminated once slugs have rehydrated to their individual rehydration set-points. The mean 'rehydration set-point' for Limax is 93.6 +/- 12.2% IBW (+/- S.D.). Slugs can achieve their individual set-point regardless of the extent of initial dehydration. Drinking behaviour can be initiated by injections of hyperosmotic mannitol solution and terminated by injections of dilute saline. This indicates that variation in the osmolality of the haemolymph is involved in the control of the behavioural sequence.

Animals↗
PubMed1984

Analysis of contact-rehydration in terrestrial gastropods: absorption of 14C-inulin through the epithelium of the foot.

Contact-rehydration in terrestrial slugs involves a specific drinking behaviour during which water is rapidly absorbed through the integument of the foot. When dehydrated slugs were placed on wet filter paper containing 14C-inulin, they displayed the characteristic drinking posture and absorbed both water and 14C-inulin. Samples of haemolymph from dehydrated slugs after 12 min of contact-rehydration contained about 6 micrograms of 14C-inulin 100 mg-1 of haemolymph (0.24 mmol l-1 14C-inulin in the substrate). The haemolymph of hydrated slugs however contained no detectable radioactivity after 12 min on the filter paper. Electron microscopy revealed that the intercellular spaces between the epithelial cells of the foot were reduced in dehydrated slugs, but were rapidly enlarged during contact-rehydration. It is concluded that contact-rehydration in terrestrial slugs is mediated by bulk flow of water through an epithelial paracellular pathway in the integument of the foot.

Animals↗
PubMed1982

Effects of temperature on the endogenous activity and synaptic interactions of the salivary burster neurones in the terrestrial slug Limax maximus.

(1) The activity of the endogenously active salivary burster neurones (SBs) shows temperature acclimation and has characteristic cold and warm blockade temperatures. (2) Temperature acclimation affects the upper and lower limits of the temperature range over which SBs are active. The absolute range, in centigrade degrees, during warming, is unaffected by acclimation. (3) Acclimatization of burster activity is a slow response to the mean ambient temperature. (4) There is increased synchrony of activity between the right and left salivary bursters at low temperature which is correlated with an increased electrical coupling between the SBs and protractor motoneurones (B7s). There is a corresponding increase in the input resistance of B7 at low temperatures.

Action Potentials↗
PubMed1979

Behavioural and physiological aspects of swimming in cercariae of the digenetic trematode, Proterometra macrostoma.

1. Cyclical swimming behaviour of the cercariae of the digenetic trematode, Proterometra macrostoma, involves a highly regular alternating swim-sink sequence. During periods of swimming the cercariae are propelled upward through the water by alternating lateral contractions of the tail. Following each burst of swimming the cercariae passively drift downward. 2. Suction electrode recordings from the tail during swimming reveal that a single biphasic potential precedes each contraction in a burst. 3. The site of initiation of the rhythmic activity is the transverse band at the junction of the furcae and body of the tail. Sensory feedback does not play a major role in maintenance of the rhythm. 4. A burst of swimming can be initiated by tactile stimulation of the tail. At no time is a cercaria refractory to tactile stimulation. 5. The tail of P. macrostoma cercariae is an autonomous locomotor organ specialized for the brief free-living period between emergence from the snail host and infestation of the primary host.

Action Potentials↗
PubMed1977

An ultrastructural study of peripheral neurons and associated non-neural structures in the bivalve mollusc, Spisula solidissima.

The ultrastructural morphology of peripheral neurons and associated structures in the bivalve mollusc. Spisula solidissima have been studied in an effort to describe the synaptic topography and to provide anatomical correlates of previous physiological observations. The somata of the peripheral neurons are located within the perineurium at branch points of the siphonal nerves. There are many fiber-fiber synaptic contacts which are characterized by isolated sites of contact with membrane specialization and unilateral accumulation of synaptic vesicles. There are also synaptic contacts involving the somata, both axo-somatic and somato-axonic, the two being distinguishable on the basis of the polarity of vesicle accumulation. All of the observed synaptic profiles were similar in appearance regardless of the neuron loci involved. Much of the non-synaptic soma surface is covered with processes of glial cells. Likewise, in many cases, individual fibers and groups of fibers are encases with glial processes. Unique clusters of membrane bound, pigment containing glial like cells occur throughout the nervous system of Spisula. The heterogenous appearance of the inclusions and the presence of lysosome-like bodies in the cytoplasm of these cells suggest a possible phagocytic role.

Axons↗
PubMed1977

A circadian rhythm in the locomotive behaviour of the giant garden slug Limax maximus.

The locomotor activity of the garden slug Limax maximus was examined for components of circadian rhythmicity. Behavioural (running wheel) studies clearly demonstrated that the activity satisfies the principal criteria of circadian rhythmicity. In constant darkness at a constant temperature, the locomotor activity freeran with a period of about 24 h (range 23-6-24-6 h). The rhythm was also expressed in constant light with a period for individual slugs that tended to be shorter in LL than in DD. The period of the rhythm was temperature compensated (11-5-21-5 degrees C) with a Q10 approximately equal to 1-00. The locomotor rhythm could be entrained to 24 h LD cycles such that the circadian activity peak occurred during the dark. The phase angle between the onset of activity and lights-off was not fixed, but was a function of the photoperiod of the entraining light cycle.

Animals↗