PubMed Health⌕ Search

Biomedical subjects

T Crow

Publications and source records attributed to T Crow.

52 records · Page 3Linked to original sources
PubMed1985

Serotonin immunoreactivity in the circumesophageal nervous system of Hermissenda crassicornis.

Immunohistochemical techniques were used to examine the distribution of serotonin-immunoreactive (5-HT-IR) neurons and processes in the circumesophageal nervous system of Hermissenda. Both the pedal and the cerebropleural ganglia contained immunoreactive neuronal somata, with the majority occurring in the pedal ganglia. Immunoreactive fibers and varicosities were identified in portions of the central neuropil, where we noted a consistent and specific relationship between 5-HT-IR axons, the optic nerve and the synaptic region in the neuropil near the photoreceptor terminals.

Animals↗
PubMed1985

Serotonin modulates photoresponses in Hermissenda type-B photoreceptors.

Light responses of Hermissenda type-B photoreceptors evoked by flashes of light were enhanced and prolonged by bath application of serotonin (5-HT). 5-HT appears to act directly on the B photoreceptors and not indirectly through 5-HT-sensitive interneurons since similar effects were observed in the presence of tetrodotoxin and in axotomized preparations which eliminated synaptic input to the B photoreceptors. We also examined the effect of 5-HT on light-evoked membrane currents with voltage-clamp techniques. The increase in the duration of the light response in 5-HT can be explained by the prolonged decay of the light-activated current evoked by constant-intensity test flashes. 5-HT appears to prolong the light response by slowing a late process in the decay of light-activated membrane current. In contrast to the effects of 5-HT an alpha 2-agonist, clonidine, enhanced the peak photoresponse but did not prolong the light response. Serotoninergic modulation of light-dependent processes in the B photoreceptors may contribute to the development of long-term changes produced by conditioning.

Animals↗
PubMed1985

Conditioned modification of phototactic behavior in Hermissenda. I. Analysis of light intensity.

Psychophysical experiments examined the control of phototactic behavior by light intensity in the nudibranch mollusk Hermissenda by measuring the time that Hermissenda remained in an illuminated area. This measure of phototactic behavior exhibits a closer correspondence to changes in test light intensity than other previously examined measures of phototaxis. Changing the intensity of a test light in a series of increasing steps resulted in a graded increase in positive phototactic behavior. Behavioral responses to different light intensities were examined in conditioned and control animals. Conditioning resulted in a significant suppression of phototactic behavior at all light intensities examined. Random control procedures did not produce suppression of phototactic responding. These behavioral results provide a data base to examine how well neural correlates produced during conditioning fit the behavior.

Animals↗
PubMed1985

Conditioned modification of phototactic behavior in Hermissenda. II. Differential adaptation of B-photoreceptors.

Changes in the response of B-type photoreceptors to illumination were examined in the isolated nervous systems of Hermissenda following the conditioning procedures described in the preceding paper. Analysis of the transient peak amplitude of the depolarizing generator potential at the onset of two of the three light intensities used in the behavioral studies did not reveal an enhanced photoresponse to the light. However, when the activity of the same B-photoreceptors was examined after 5 min of continuous light, there was a significant decrease in the light-adapted discharge rate and a decreased generator potential amplitude in conditioned animals as compared to the random controls. An examination of the light adapted photoresponse in preparations where spike generation and synaptic interactions were eliminated showed that the decreased photoresponse of conditioned animals was due to factors that are intrinsic to the B-photoreceptors. These results are consistent with previous work suggesting that conditioning produces substantial adaptation effects in B-photoreceptors (Crow, T. (1982) Soc. Neurosci. Abstr. 8: 824). Since the cellular changes qualitatively follow the behavioral changes and are observed at times and light intensities that are similar to those where the suppression of phototactic behavior is expressed, phototactic suppression may be directly related to the changes in the B-photoreceptors and may not require the previously proposed complex network interactions within the eyes of Hermissenda.

Action Potentials↗
PubMed1984

Conditions of illumination during rearing affect specific components of phototactic behavior of laboratory-reared Hermissenda.

We have investigated the effect of 3 different conditions of illumination during rearing on phototactic behavior of the marine mollusk Hermissenda. Rearing Hermissenda in the dark results in a significant increase in the variability of positive phototactic behavior of adults and decreases responsiveness to illumination. The decrease in the positive phototactic response, as measured by the significant increase in the time taken by dark-reared Hermissenda to enter an illuminated area, was due to a decreased velocity of locomotion in the light gradient. These changes in phototactic behavior were not observed for Hermissenda reared on 12 h light-12 h dark cycles or under constant illumination. The affects of dark rearing on phototactic behavior cannot be the result of abnormal photoresponses since the photoreceptors of dark-reared Hermissenda exhibited normal generator potentials in response to light. A cellular analysis of the behavior of laboratory-reared Hermissenda will be useful in studying phototaxis since learning and experiences during rearing have two quite different behavioral consequences.

Animals↗
PubMed1984

Campylobacter enteritis on Hopi and Navajo Indian reservations. Clinical and epidemiologic features.

From June 22 through September 30, 1981, stool specimens from 522 Hopi and Navajo outpatients were cultured because of diarrheal illnesses at the Keams Canyon Indian Health Service Hospital, Arizona. Campylobacter jejuni was isolated from the specimens of 26 (5%) of the patients. This pathogen was found as frequently as Shigella in patients younger than 2 years or older than 20 years, but was significantly less common in the 2 to 20-year age group (P<.000001). Campylobacter enteritis was indistinguishable clinically from shigellosis in adult patients, but in children younger than 5 years, a rectal temperature higher than 38 degrees C (100.5 degrees F) was significantly more common with Shigella than with Campylobacter infection (P=.003). In a field study of 20 families, we found that households with a case of Campylobacter enteritis were more likely than age- and community-matched controls to own farm animals (P=.05), but were not more likely to own household pets. C jejuni is less common than Shigella as a cause of summer seasonal diarrhea and dysentery among the Hopi and Navajos; the striking differences in the age-specific rates of these two infections suggest different routes of transmission.

Adolescent↗
PubMed1983

Modification of the initiation of locomotion in Hermissenda: behavioral analysis.

We have examined the effect of a conditioning procedure on various components of visually guided locomotion in Hermissenda. Temporally specific stimulation of the visual system and gravity detecting system (statocysts) with light and rotation produced long-term changes in locomotor behavior. We found that the latency to initiate locomotion in the presence of light was significantly increased for the conditioned group as compared to baseline pre-test latencies and groups that received random presentations of the conditioning stimuli. The variability in the time taken by animals to enter a central illuminated area as reported in earlier studies can be accounted for by the increase in the latency to initiate locomotion. The modifications of visually influenced locomotion exhibits stimulus (CS) specificity since locomotor behavior is not changed following conditioning in the absence of light. In addition, conditioned animals remained in the brightest part of the light gradient significantly less than pre-test measurements. Since this response (initiation of locomotion) can be studied in a semi-intact preparation, it should be possible to investigate how this example of learning generates changes in behavior.

Animals↗
PubMed1983

Conditioned modification of locomotion in Hermissenda crassicornis: analysis of time-dependent associative and nonassociative components.

The contribution of associative and nonassociative factors to the conditioned modification of phototactic behavior in Hermissenda was examined after varying the number of conditioning trials and the time between training and testing. Five or 10 conditioning trials did not produce significant changes in phototactic behavior when tested immediately after training. Both 5 and 10 conditioning trials resulted in significant short-term nonassociative changes in behavior (resembling sensitization) when the time between training and testing was 15 min or longer. Following 50 conditioning trials (single session training), nonassociative effects made the major contribution to the change in behavior when the post-training test interval was 30 min. These nonassociative changes decremented during a 1-hr period following training. Significant associative effects were observed 45 min after 50 conditioning trials; however, significant associative effects were not observed when the same animals were tested 24 hr after training. With 3 days of training (multiple session training-150 trials), associative effects were found 30 min after training and nonassociative effects again showed a rapid decrement during the 1-hr period following the end of training. The associative effects observed soon after training were persistent during the retention period and showed significant effects 24 hr after training. These data indicate that (1) the behavioral effects found after single session training (5 and 10 trials) are nonassociative, and (2) these nonassociative effects do not increase significantly over the course of multiple session training.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Optical sectioning of HRP-stained molluscan neurons.

The use of high-resolution differential interference contrast(DIC) microscopy on cleared whole-mounts of the circumesophageal nervous system from Hermissenda crassicornis permits visualization of neuronal morphology in detail without the need for physical sectioning. Such optical sectioning, when preceded by intracellular iontophoresis of horseradish peroxidase (HRP) permits rapid and accurate examination of the arborization of electrically characterized neurons. Details such as varicosities and terminal swellings can readily be resolved. This method has revealed new morphological features of neurons implicated in training-specific behavioral modification in Hermissenda, and promises to be of further general use for the quantitative morphometry of electrically identified neurons.

Animals↗
PubMed1979

Ultrastructure of photoreceptors in the eye of Hermissenda labelled with intracellular injections of horseradish peroxidase.

The terminal processes of single and of pairs of identified photoreceptors in the eyes of the nudibranch mollusc Hermissenda crassicornis were studied by light and transmission electron microscopy after their somata were labelled by intracellular iontophoresis of horseradish peroxidase (HRP). The HRP spread from the somata into the axons and fine terminal processes within the neuropil of the cerebropleural ganglia. The photoreceptors ended in extensive secondary branches in the neuropil where previous electrophysiological studies had indicated the probable site of synaptic interactions between photoreceptors. Clear round vesicles (54-126 nm diameter) within labelled processes were similar to the vesicles found in the somata and axon hillocks. The terminal processes of pairs of type B photoreceptors contained different intensities of the HRP label. Uniform intensities of the HRP label were found in the terminal processes of single type B photoreceptors. These differences in intensity suggested that the terminal processes were from different type B photoreceptors. This finding suggests that the connections between type B photoreceptors are probably monosynaptic.

Animals↗