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C D Drewes

Publications and source records attributed to C D Drewes.

17 recordsLinked to original sources
PubMed2001

Behavioral effects of ivermectin in a freshwater oligochaete, Lumbriculus variegatus.

Ivermectin is a potent antiparasitic drug against nematode and arthropod parasites. In this study, we examined the lethal and sublethal effects of ivermectin in a freshwater oligochaete, Lumbriculus variegatus. The median lethal concentration (LC50) at 72 h after ivermectin exposure was 560 nM. Sublethal endpoints focused on several stimulus-evoked locomotor behaviors: escape reflexes controlled by giant interneuron pathways, swimming and reversal, and crawling. Swimming, reversal, and crawling are controlled by nongiant interneuron pathways. Ivermectin inhibited swimming, reversal, crawling frequency, and crawling speed in a time- and concentration-dependent manner with a mean inhibitory concentration (IC50) at 3 h of 1.1, 16, 91, and 51 nM, respectively. Ivermectin at 0.3 nM also significantly decreased the frequency of helical swimming waves. Picrotoxin, a Cl- channel blocker, antagonized the ivermectin-induced decrease in swimming frequency, crawling frequency, and crawling speed. There were no adverse effects on escape reflex 3 h after exposure to 300 nM ivermectin. Electrophysiological recordings showed that ivermectin had no effects on the conduction velocity of giant fiber systems. The results indicated that locomotor behaviors controlled by nongiant locomotor pathways were more sensitive to ivermectin than pathways controlled by giant interneurons and that Cl- channels may be involved in mediating ivermectin's inhibitory effects.

Animals↗
PubMed1990

Morphallaxis in an aquatic oligochaete, Lumbriculus variegatus: reorganization of escape reflexes in regenerating body fragments.

We describe functional and anatomical correlates of the reorganization of giant nerve fiber-mediated escape reflexes in body fragments of an aquatic oligochaete, Lumbriculus variegatus, a species that reproduces asexually by fragmentation. Since fragments from any axial position always regenerate short heads (seven or eight segments long) and much longer tail sections, segments originating from posterior fragments become transposed along the longitudinal axis and acquire, by morphallaxis, features of escape reflex organization that conform to their new anterior position. Using noninvasive electrophysiological recordings we have quantified, on a day-to-day and a segment-by-segment basis, the reorganization that occurs in sensory field arrangements of the medial (MGF) and lateral (LGF) giant nerve fibers, as well as changes in giant fiber conduction velocity and morphometry. Our results show that (1) posterior fragments, originally subserved by the LGF sensory field gradually become subserved by the MGF sensory field; (2) appropriate increases in the ratio of MGF:LGF cross-sectional area, perimeter, and conduction velocity accompany the reorganization in giant fiber sensory fields; and (3) sensory field reorganization can be repeatedly reversed by additional amputations. These results demonstrate that the functional organization of escape reflexes is highly plastic and that morphallaxis may result from the counterbalance of morphogenic influences localized within the anterior and posterior ends of regenerating body fragments.

Action Potentials↗
PubMed1989

Effects of paraoxon on spike initiation and conduction block in the giant interneurons of the American cockroach, Periplaneta americana.

1. The effects of paraoxon were studied on spike initiation and conduction in the giant interneurons (GIs) of the American cockroach, using electrophysiological techniques. 2. Paraoxon treatment induced high-frequency bursts in GI axons. During these bursts, overshooting spikes recorded in the sixth abdominal ganglion were replaced, in phase, by small, decremental potentials. 3. These small potentials were not EPSPs since current injection could modulate their frequency. 4. An analysis of anteriorly conducted spikes indicates that the site of spike initiation is located near the dendritic region of the GI and is unchanged by paraoxon treatment.

Action Potentials↗
PubMed1988

The lateral giant fibers of the tubificid worm, Branchiura sowerbyi: structural and functional asymmetry in a paired interneuronal system.

Neuroanatomical and ultrastructural studies of the paired lateral giant nerve fibers (LGFs) in posterior segments of the tubificid worm, Branchiura sowerbyi, demonstrate that the fibers are 1) segmental in origin (two cell bodies per segment), 2) joined longitudinally and transversely to form an intersegmental syncytial network, and 3) surrounded by a myelinlike sheath. The LGFs are unique among paired giant fiber systems because of their extreme asymmetry, the diameter of the left fiber being several times greater than that of the right. Electrophysiological studies demonstrate that the small, right fiber has a high input resistance and, during mechanosensory stimulation, functions as the locus for LGF spike initiation. The larger, left fiber contributes by enhancing the speed of LGF spike conduction along the animal. One physiological benefit of this asymmetric arrangement may be optimization of escape reflex sensitivity to mechanosensory inputs.

Action Potentials↗
PubMed1985

Donor-recipient interconnections between giant nerve fibers in transplanted ventral nerve cords of earthworms.

Twelve segments of ventral nerve cord (VNC) from donor earthworms, Eisenia foetida, were transplanted into recipient worms from which a comparable length of VNC had been removed. Within the first few days after transplantation, bud-like formations, containing outgrowths of the giant nerve fibers, were evident at the ends of transplanted and recipient VNC. Morphological and electrophysiological evidence indicated that by 4-10 days after transplantation, medial (MGF) and lateral (LGF) giant fibers within the transplanted VNC formed cell-specific connections with their counterparts in the recipient VNC. Although the diameters of the giant fiber connections in the transplant-recipient junctions were often larger than normal, spike conduction across the junction was initially slow (approximately 1.0 m/s) but gradually increased over the next 2-3 weeks. Within the transplant, giant fibers were initially normal in appearance, but spike conduction was slow (1-2 m/s). During the next few weeks velocities increased by as much as fourfold and then stabilized for the next several months. However, by 4-5 weeks after transplantation, giant fiber morphology within the transplant was altered significantly, as indicated by the formation of numerous branch-like extensions along the length of each giant fiber. By 9-10 months there were further morphological changes in the transplant, as indicated by decreased branching of the giant fibers and altered neuropile. Despite these morphological changes, through-conduction of giant fiber spikes remained reliable.

Animals↗
PubMed1985

Restoration of sensory and motor function in earthworm escape reflex pathways following ventral nerve cord transplantation.

Twelve segments of earthworm ventral nerve cord (VNC) were excised from either segments 10-22 (i.e., within the MGF sensory field) or segments 75-87 (i.e., within the LGF sensory field) in donor worms and heterotopically, or homotopically, transplanted into recipient animals. Morphological evidence indicated that by four days after transplantation, peripheral connections were formed between the transplanted VNC and the body wall of the recipient, many of these connections involving novel pathways projecting ventrally from the transplant. Restoration of giant fiber touch sensitivity in the transplant occurred from 4-14 days after transplantation. Regardless of the site of transplantation, the restored sensitivity (i.e., MGF versus LGF sensory field) always reflected the origin of the donor VNC. Restoration of MGF-mediated motor activity in the transplant occurred approximately 17-22 days after transplantation. In the case of heterotopic transplants (i.e., anterior VNC into posterior segments), the restored MGF-mediated muscle potentials were facilitating, indicating at least some tendency for persistence of this feature after transplantation. Behavioral observations suggested that reconnections involving other reflex pathways (e.g., those controlling setal movements and peristaltic locomotion) were made within the transplant region and that properties of the restored reflexes reflected those of the donor VNC. The rapid restoration of sensory and motor connections, despite heterotopic placement, indicates a significant capacity for peripheral regeneration by the transplanted VNC. On the other hand, the maintenance of various properties of reflex function, despite heterotopic transplantation, suggests a limited capacity for rearrangement of established central connections in the transplanted VNC.

Afferent Pathways↗
PubMed1982

Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. I. Functional development of giant nerve fibers during embryonic and postembryonic periods.

Grids of recording electrodes etched onto printed circuit boards were used for noninvasive recording of medial (MGF) and lateral (LGF) giant nerve fiber spikes in developing earthworms, Eisenia foetida. Stereotyped patterns of through-conducted giant fiber spikes, evoked by light tactile stimulation, were first detectable in the normal crawling embryonic stage and continued to be detectable throughout postembryonic development. Giant fiber spiking activity in normal crawling embryos was accompanied by stereotyped muscle activity and rapid escape withdrawal, suggesting that giant fiber reflex pathways are functionally intact before the worm hatches. For both the MGF and LFG, several age-dependent changes were noted, including the following: increases in spike conduction velocity, increases in giant fiber diameter, and decreases in spike duration. The MGF conduction velocity in normal crawling embryos was 1.1-1.6 m s-1 (6-7 micrometers diameter) and increased to 7.0-8.5 m s-1 (20-25 micrograms diameter) by 60 days after hatching. The LGF conduction velocity in normal crawling embryos was 0.7-1.1 m s-1 (2.5-4.0 micrometers diameter) and increased to 4.0-5.5 m s-1 (8-14 micrometers diameter) by 60 days after hatching. During postembryonic development MGF and LGF conduction velocities were linearly related to fiber diameter.

Aging↗
PubMed1982

Electrophysiological correlates of rapid escape reflexes in intact earthworms, Eisenia foetida. II. Effects of food deprivation on the functional development of giant nerve fibers.

Noninvasive electrophysiological recording methods were used to study the effects of prolonged food deprivation on the postembryonic patterns of giant fiber growth, as indicated by age-dependent changes in giant fiber conduction velocity and diameter, in the earthworm, Eisenia foetida. In addition, giant fiber growth was compared to patterns of somatic growth, as indicated by increases in body weight. Within a wide range of food deprivation levels, normal age-dependent increases in conduction velocity and diameter occurred in spite of marked stunting of somatic growth. Stunting of giant fiber velocity and diameter occurred only during severe food deprivation, but giant fiber spikes and associated rapid escape responses were still readily evoked. The stunting effects of prolonged and severe food deprivation upon giant fiber conduction velocity and diameter were readily reversed by replenishing food. The results demonstrate the persistence of rapid escape reflex functioning, as well as the priority of giant fiber growth relative to somatic growth, during severe and prolonged food deprivation. As a consequence of the priority of giant fiber growth during limited food availability, giant fiber conduction velocity appears to be a more reliable predictor of animal age then body size.

Aging↗
PubMed1978

Specificity of afferent and efferent regeneration in the cockroach: establishment of a reflex pathway between contralaterally homologous target cells.

1. In 132 cockroaches the main leg nerve on one side (right), of the metathoracic segment was crossed to the opposite (left) side and allowed to regenerate. In 3-8 wk, 59% of the animals displayed reflex activity in the left leg (behaviorally demonstrated by leg withdrawal following tarsal stimulation). 2. EMGs from the femoral extensor revealed potentials characteristic of normal activity in the extensor, which is innervated by an identified motor neuron, Ds. 3. Intracellular recordings from processes within the right hemiganglion of the metathoracic ganglion (CNS) demonstrated 1:1 activity between a unit in the CNS recording and the EMG of the left extensor. Subsequent intracellular staining revealed that the unit was on the right side of the CNS and was identified as motor neuron Ds by the location of its soma and dendrites. This finding indicated that specific, contralateral, efferent reinnervation occurs in the cockroach. 4. In normal cockroaches a monosynaptic reflex exists between hair plate afferents and Ds. A temporal analysis (stimulus-interval histogram) indicated that the reflex is also established in the crossed-regenerated animals. These data suggested that specific contralateral afferent reinnervation also occurs in the cockroach and that the monosynaptic nature of the normal reflex was reestablished. 5. Therefore, cell-to-cell specificity in neuron-to-neuron or neuron-to-muscle interactions not only occurs in normally developing or regenerating animals but also occurs between contralaterally homologous target cells, given the proper experimental conditions. It is also suggested that this experimental procedure of redesigning pathways may be a useful tool for further studies of behavior.

Afferent Pathways↗
PubMed1978

Giant nerve fibre activity in intact, freely moving earthworms.

1. An approach is described for recording and characterizing giant nerve fibre activity in intact, freely moving earthworms. 2. Medial giant fibre (MGF) spikes were conducted in an anterior-posterior direction at a mean rate of 32.2 m/s; lateral giant fibre (LGF) spikes were conducted in a posterior-anterior direction at a mean rate of 12.5 m/s. 3. Rates of giant fibre spike conduction and maximal frequencies of firing (up to 500/s) in intact animals were higher than values previously reported in isolated preparations. 4. MGF spikes were followed 1:1 by presumed giant motor axon spikes and facilitating muscle potentials. 5. Single MGF or LGF spikes evoked by applying tactile stimulation were not accompanied by longitudinal contraction, but a series of two or more MGF spikes or three or more LGF spikes were accompanied by such contractions. 6. MGF and LGF spikes occurred infrequently during locomotory movements in the absence of any experimenter-applied stimulation, suggesting that sensory inputs associated with normal locomotion over an irregular substrate are sufficient to excite giant fibres.

Action Potentials↗
PubMed1977

Excitation of the common inhibitory motor neuron: a possible role in the startle reflex of the cockroach, Periplaneta americana.

The responses of the widespread common inhibitory motor neuron (CI) to tactile stimulation of the cercus and the abdomen and electrical stimulation of the cercal nerve and the abdominal connectives are investigated. Tactile stimulation produces high frequency (greater than 500 impulses/s) spike discharge in CI with the onset of CI activity preceding the discharge of the excitatory motor neurons. Electrical stimulation of the connectives demonstrates a monosynaptic connection between at least one intermediate sized fiber (conduction velocity =3.7 m/s) in the abdominal connective and the ipsilateral CIs in the meso-and metathoracic ganglia. Electrical stimulation of the cercal nerve suggests a disynaptic path from cercal nerve to CI. Arguments are presented for a cercal afferent-to-CI reflex and the possible functional role of early excitation of CI is discussed.

Animals↗
PubMed1976

Stretch-sensitive neural units in the body wall of the earthworm, Lumbricus terrestris L.

1. Sensory neural units responding to sinusoidal stretching of the body wall were studied in the earthworm, Lumbricus terrestris L. 2. A phasic stretch-sensitive unit found in segmental nerve I responded optimally to stretching at frequencies of 4-6/min. 3. The number of spikes per stretch and the spike frequency in the unit were directly related to the amplitude of the applied stretch within a range of 0-2-0-7 mm stretch/segment. 4. The ranges of amplitude and frequency sensitivity for the unit in isolated preparations corresponded closely to stretch parameters seen during peristaltic locomotion in intact animals. 5. Stretch-sensitive responses in segmental nerve II-III were more variable; some units responded to longitudinal stretch while others responded to relaxation.

Action Potentials↗