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D W Parsons

Publications and source records attributed to D W Parsons.

16 recordsLinked to original sources
PubMed1990

The effect of gas emboli on rabbit cerebral blood flow.

Many bubbles that enter the brain circulation pass through the arterioles and capillary beds and do not obstruct blood flow. Nevertheless, such bubbles could still disrupt brain function. An open-brain model in five anesthetized rabbits used the minimum dose of air (25 microliters) necessary to cause embolism of the exposed vessels, and these bubbles passed through the vessels without any trapping. Despite their rapid transit, the bubbles provoked a marked dilatation of the affected pial arterioles (mean increase after 15 minutes of 27%) that persisted for 90 minutes after the bubbles had disappeared. The changes in vessel diameter were associated with a delayed, but significant and progressive, reduction in both cerebral blood flow measured by hydrogen clearance and neural function measured by cortical somatosensory evoked response. The decrease in blood flow correlated well with the depression of neural function (r = 0.67). Because both cerebral blood flow and neural function temporarily returned to normal after air embolism, the subsequent changes seen in this model cannot be explained simply by the mechanical obstruction of blood flow by bubbles.

Air↗
PubMed1990

The effect of carbon monoxide on the function of a crustacean sensory receptor is no different to the effect of hypoxia.

The crayfish Cherax was used as a model to determine whether there are behavioural and neural effects that can be attributed to a direct carbon monoxide toxicity rather than to the hypoxia it produces. A comparison was made by replacing the oxygen in the ambient liquid with carbon monoxide or with nitrogen. We found that Cherax is resistant to extreme hypoxia produced by either gas, and that there is therefore no meaningful behavioural carbon monoxide toxicity. We describe hypoxia-induced changes in the tonic and phasic activity recorded from in-vitro preparations of the muscle receptor organs that are the same for nitrogen and carbon monoxide substituted saline solutions. We conclude that in the single cells of the muscle receptor organs of Cherax, carbon monoxide has no toxic effects additional to those attributable to hypoxia.

Action Potentials↗
PubMed1989

Egg laying in Aplysia. I. Behavioral patterns and muscle activity of freely behaving animals after selectively elicited bag cell discharges.

Aplysia egg laying is a complex sequence of head and neck movements initiated by the release of ovulatory and neuroactive hormones from the neurosecretory bag cells. This behavioral pattern is difficult to study in reduced preparations, because they do not show ovulation or egg laying behaviors. This paper describes the use of chronically implanted electrodes to elicit normal neurosecretory activity and provides an analysis of egg laying behaviors and the underlying muscle activity in intact, freely behaving A. californica and A. brasiliana. 1. Bag cell discharges elicited with a fine wire electrode implanted in the connective tissue sheath above the cell bodies were typically without noxious behavioral side effects. 2. Following selectively elicited bag cell discharges, egg laying consisted of four rhythmic head and neck movements that were separated functionally into appetitive behaviors ('waves' and 'undulations') used to explore and prepare the substrate and consummatory behaviors ('weaves' and 'tamps') used to distribute and attach the egg string. The amount of time an animal performed consummatory behaviors was positively related to the amount of eggs deposited. By contrast, the appetitive phase of egg laying was independent of the size of the egg mass. 3. The individual behaviors and their temporal sequence were similar following selectively elicited bag cell discharges, spontaneous discharges of animals with implanted electrodes and during normal egg laying of unoperated animals. 4. Three longitudinal muscle systems occurred within the head and neck. Following a selectively elicited bag cell discharge, spatially and temporally coordinated patterns of EJP bursts of different durations were recorded chronically from each muscle group. These EJP patterns were characteristic for specific head and neck movements used in appetitive and consummatory egg laying behaviors.

Animals↗
PubMed1989

Swimming in Aplysia brasiliana: behavioral and cellular effects of serotonin.

1. Aplysia brasiliana is a marine mollusk that swims by repeated metachronal flapping movements of its bilateral fleshy parapodia. Animals with bilateral cerebropedal connective (CPC) lesions do not swim when suspended above the substrate, although tonic CPC stimulation can elicit normal parapodial flapping. Although the parapodial opener-phase (POP) cells, a previously identified group of neurons, fire synchronous bursts of efferent spikes in-phase with parapodial opening movements in both intact animals and dissected preparations, they are not likely to be primary parapodial motoneurons. These cells receive one or more large, apparently monosynaptic excitatory postsynaptic potentials (EPSPs) during CPC stimulation that are effective in producing the swimming motor program (SMP). 2. In suspended CPC-lesioned animals, injections of serotonin (5-HT) that produce an average hemolymph concentration of 10(-5) M induced full-amplitude parapodial flapping. Selected episodes of flapping were similar in frequency to normal suspended swimming. 3. In suspended CPC-lesioned animals, 5-HT injections elicited an apparently normal swimming motor program that was associated with synchronous bursts of large-amplitude efferent spikes in the parapodial nerves. In many semi-intact preparations, exposing the circumoesophageal ganglia to 5-HT elicited a similar rhythmic motor program, but usually at a lower frequency than during normal swimming or during tonic CPC stimulation. 4. In isolated-ganglion preparations, bath application of 5-HT produced immediate depolarization and tonic firing of individual POP neurons, followed by smooth and regular bursting in the apparent absence of synaptic input. In such preparations, the motor program elicited by bath-applied 5-HT differed from the one elicited by tonic CPC stimulation in that the 5-HT-elicited rhythmic bursting usually was not synchronous in different POP neurons. Tonic CPC stimulation during bath applications of 5-HT produced immediate synchronization of bursts among the POP neurons. 5. Hyperpolarization (or depolarization) of a POP neuron during bath application of 5-HT increased (or decreased) the burst period, but membrane polarization did not change the burst period elicited during tonic CPC stimulation.

Animals↗
PubMed1988

Swimming in Aplysia brasiliana: identification of parapodial opener-phase and closer-phase neurons.

1. In freely behaving Aplysia brasiliana, spontaneous swimming in the laboratory occurred primarily in the dark hours of the day-night cycle. Suspending an intact animal above the substrate elicited continuous parapodial flapping with the same frequency and amplitude as spontaneous swimming. Parapodial flapping with decreased frequency and amplitude could still be elicited by suspending minimally dissected, but not more radically dissected, preparations. 2. In otherwise intact animals, severing the cerebropedal connective (CPC) bilaterally abolished suspended parapodial flapping, but normal flapping was elicited by tonic stimulation of the distal CPC. In minimally dissected preparations, tonic CPC stimulation elicited parapodial flapping, but with reduced frequency and amplitude. 3. During normal parapodial flapping, chronically implanted electrodes on parapodial nerves recorded the swimming motor program (SMP). The whole-nerve SMP consisted of rhythmic bursts of large-amplitude efferent units in phase with parapodial opening, with no observable activity during parapodial closing. By contrast, simultaneous electromyogram (EMG) recordings from antagonistic parapodial muscles showed antiphasic bursts of activity during opening and closing. The SMP was inhibited by touching food to the animals' lips. 4. Parapodial nerve backfills, using nickel chloride, labeled several cell clusters in the ipsilateral pedal ganglion. Two of these clusters were located caudally: one tightly clustered medial group had large cell bodies, and another, more distributed, lateral group had small cell bodies. The two clusters were identified in semi-intact preparations and isolated brains, using tonic CPC stimulation to elicit a fictive SMP recorded in parapodial nerves, and intracellular electrodes to characterize and stain individual cells. 5. The large parapodial opener-phase (POP) neurons were normally silent. At the onset of CPC stimulation, POP neurons depolarized and fired tonically, and then burst rhythmically in phase with each other, and one for one with large-amplitude axon spikes observed extracellularly in parapodial nerves during the fictive SMP. Intracellular firing of POP cells, singly or in pairs, never produced observable papapodial movements or one-for-one responses in parapodial muscles. Lucifer yellow-filled POP neurons showed a process (with a pronounced rostral loop) that gave off many short, fine neurites in the pedal neuropile before branching into two or three axons projecting into different parapodial nerves. 6. The smaller parapodial closer-phase (PCP) neurons normally discharged tonically at low frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Spontaneous and elicited bag cell discharges in gonadectomized Aplysia.

The neuroendocrine bag cells of the hermaphroditic marine gastropod, Aplysia, secrete peptide hormones that induce release of ripe eggs from the ovotestis. The egg string is subsequently deposited on the substrate by means of a complex sequence of rhythmic head and neck movements. Gonadectomy (removal of the ovotestis) was performed in two closely related species of Aplysia to prevent completely the synthesis, build-up and release of eggs. Chronically implanted electrodes were used either to monitor spontaneous bag cell discharges (A. brasiliana) or to selectively elicit bag cell discharges (A. californica) in gonadectomized and mock-operated animals. Gonadectomized animals showed the normal occurrence of spontaneous bag cell discharges in the complete absence of eggs, indicating that feedback from ripe eggs in the ovotestis is not necessary for normal activation of the bag cells. However, gonadectomized animals showed a significant decrease in specific head and neck movements following elicited bag cell discharges. This finding indicates that, once the bag cells fire and the eggs are released, input from the eggs is necessary for normal expression of the behaviour associated with egg deposition.

Animals↗
PubMed1985

Temperature dependence of egg laying in Aplysia brasiliana and A. californica.

The temperature dependence of egg laying was examined in winter-caught Aplysia. Cold-water Aplysia californica and warm-water A. brasiliana were individually housed in the same large aquarium for 16 days at 15 degrees C, and then for 16 days at 20 degrees C. Initially, the majority of the A. californica were not reproductively mature (as determined by injections of atrial gland extracts) whereas all of the A. brasiliana were reproductively mature. When the temperature was increased from 15 to 20 degrees C, both species showed a marked increase in the frequency of egg laying. At both temperatures, A. brasiliana laid eggs more frequently but produced smaller egg masses than A. californica. We conclude that increased egg laying in A. californica was attributable both to facilitation of oogenesis in previously reproductively immature animals and to increased activity of the bag cells which release an egg-laying hormone. Increased egg laying in A. brasiliana was attributable primarily to increased bag cell activity.

Animals↗
PubMed1985

Flight-initiating interneurons in the locust.

We have used intracellular recording and staining techniques to investigate the cellular mechanisms for the initiation and maintenance of flight in the locust, Locusta migratoria. In particular, we examined the properties of a small group of interneurons in the mesothoracic ganglion. We refer to these interneurons as 404 neurons. Their structure has been described, in a closely related species, by Watson and Burrows (21). Using a preparation in which intracellular recordings could be made from the main neurite of a 404 neuron during the generation of flight activity, we observed that the 404 neurons discharged tonically throughout flight episodes elicited by a constant wind stimulus on the head and by a sudden dimming of the lights. Their discharge rate was linearly related to the frequency of the flight activity. Depolarization of individual 404 neurons often initiated flight activity in quiescent preparations, and the application of hyperpolarizing currents during a flight episode either slowed or stopped flight activity. Hyperpolarizing currents also prevented the initiation of flight activity in some preparations. Individual 404 neurons were not always necessary for the generation of flight activity, since flight activity sometimes persisted when all spiking in a 404 neuron was prevented by the application of a hyperpolarizing current. We conclude that the 404 neurons function to initiate and maintain flight activity in response to wind stimulation of the head, but we have not yet established that they are the only thoracic neurons with this function. The 404 neurons discharged with a high-frequency burst at the time of triggering of a kick. Since the motor program for a jump is similar to that for a kick, the 404 neurons may also be involved in linking the initiation of flight activity to the jump. None of our data indicate that the 404 neurons receive input from the central rhythm generator. Thus the neuronal circuitry for flight appears to be hierarchically organized with at least one distinct neuronal system providing a tonic drive to initiate and maintain activity in the system that patterns activity in flight motoneurons.

Animals↗
PubMed1983

Selective recording and stimulation of individual identified neurons in freely behaving Aplysia.

A neuroethological technique is described for selective recording and stimulation of an individual neuron in freely behaving Aplysia by means of a fine wire glued into the connective tissue sheath above the identified cell body. A whole-nerve cuff electrode simultaneously monitored functionally related multiunit axon activity. For biophysical analysis the soma was impaled with a microelectrode when the ganglion was subsequently exposed. The technique is illustrated for several identified neurons involved in different behaviors.

Animals↗