Search PubMed⌕ Search

Biomedical subjects

R L Cooper

Publications and source records attributed to R L Cooper.

At least 19 recordsLinked to original sources
PubMed2001

Altered responsiveness to 5-HT at the crayfish neuromuscular junction due to chronic p-CPA and m-CPP treatment.

Serotonin (5-HT) levels in the hemolymph of crustaceans has been implied to alter aggressiveness which influences social interactions. The activation of IP3 as a second messenger cascade within crayfish motor neurons in response to application of 5-HT, suggests that the 5-HT receptor subtypes on the motor neurons are analogous to the vertebrate 5-HT2A receptors. Based on evidence in other systems, it would be expected that chronically sustained 5-HT levels in aggressive individuals would result in a compensatory negative feed-back regulation and/or that target tissues would diminish their sensitivity to high levels of circulating, free 5-HT. We addressed the issue of up- and down-regulation in the sensitivity of the responsiveness to exogenously applied 5-HT at the NMJs of crayfish in which the animals have altered endogenous 5-HT levels. Injections of the 5-HT1 and 5-HT2 vertebrate receptor agonist, 1-(3-Chlorophenyl) piperazine dihydrochloride (m-CPP), for 1 week resulted in a decreased responsiveness to application of 5-HT. The compound p-chlorophenylalanine (p-CPA) blocks the enzymatic synthesis of 5-HT and following 7 days of p-CPA injections, a super-sensitivity to exogenous application of 5-HT for both tonic and phasic neuromuscular junctions (NMJs) was observed. However, acute applications of p-CPA and m-CPP, followed by extensive saline washing, did not reveal any altered receptivity to 5-HT application.

Aggression↗
PubMed2001

Alterations in habituation of the tail flip response in epigean and troglobitic crayfish.

We demonstrate that the probability of the crayfish, P. clarkii, to tail flip in response to a touch on the dorsal tail fan is dependent on both the size and the behavioral state of the animal. Alterations in the animal's internal physical state, such as when the animal autotomizes its chelipeds, will cause larger-sized animals to tail flip; if they were not autotomized, then no tail flip response would occur. Altering the external environment by removal of water causes small crayfish, which normally habituate slowly, to rapidly habituate. Observation of large adult crayfish in a species, O. australis packardi, one that evolved to live in total cave darkness, revealed that they are more likely to tail flip than are the sighted, adult P. clarkii. Results indicate that the behavioral state of the crayfish can result in rapid and long-term alterations in the tail flip response and in habituation rates to repetitive stimuli. This ability to show plasticity in gain setting may be regulated by neuromodulators and can occur in large adults of the sighted crayfish. Differences between the two species indicate that size may not be the sole contributing factor to account for tail flip behaviors. J. Exp. Zool. 290:163-176, 2001.

Animals↗
PubMed2001

Muscle phenotype remains unaltered after limb autotomy and unloading.

Loss of chelipeds in crustaceans results in severe atrophy of the major muscle responsible for lifting the limb, the anterior levator. We decided to test if this loss of mechanical load altered muscle phenotype as measured by SDS-PAGE analysis of levator total protein and actomyosin fractions. Levator muscles of adult crayfish, Procambarus clarkii, with either functional regenerate limbs or lack of limb buds (papilla stage) were compared with those from normal contralateral limbs and those from pristine animals. We find that there is no difference in protein profiles among the three conditions. However, the total protein profile for the dually excited levator muscle is unique compared to those of fast or slow muscles of the abdomen (L and SEL, respectively), which receive only phasic or tonic excitatory innervation. The levator myosin heavy chain profile is similar to that of slow phenotype muscles such as the SEL and opener. We conclude that load does not influence levator phenotype. This is likely due either to the intact innervation and continued activation of the levator during atrophy or to the maintenance of passive tension on the muscle. J. Exp. Zool. 289:10-22, 2001.

Animals↗
PubMed2001

Effects of the ecdysoneless mutant on synaptic efficacy and structure at the neuromuscular junction in Drosophila larvae during normal and prolonged development.

Hormonal regulation in development and maintenance of synaptic transmission involves examination of both the presynaptic and postsynaptic components and a system in which the hormones can be controlled. We used the ecdysoneless heat-sensitive mutation (l(3)ecd(1)/l(3)ecd(1)) of Drosophila to provide the ability to regulate endogenous ecdysone production at various larval stages. In conjunction, we used the neuromuscular junctions of Drosophila since they offer the advantage of assessable preparations for both morphological and physiological measures. The growth in the Ib and Is motor nerve terminals and the corresponding muscle 6 in segment 4 of the larval Drosophila throughout the third instar stage in the presence of normal and a much reduced endogenous ecdysone level was investigated. Muscle 6 and the motor nerve terminals parallel in growth throughout the third instar. The nerve terminals increase in length and varicosity number, thus providing an increase in the number of synaptic release sites. The ecdysoneless larvae also show an increase in muscle size, however the Is and Ib motor nerve terminals do not mature to the extent of the wild-type ecdysone producing flies. The motor nerve terminal length is shorter with fewer numbers of varicosities per terminal. In spite of a shorter nerve terminal and fewer varicosities, with an increasing muscle fiber, the compound excitatory junctional potentials of Ib and Is in the ecdysoneless flies are larger, which is suggestive of synaptic structural modification. This study demonstrates ecdysone's role in modifying nerve terminal development and neuromuscular junction function.

Animals↗
PubMed2001

Alteration of catecholamines in pheochromocytoma (PC12) cells in vitro by the metabolites of chlorotriazine herbicide.

The effects of four major chlorotriazine metabolites on the constitutive synthesis of the catecholamines dopamine (DA) and norepinephrine (NE) were examined, using undifferentiated PC12 cells. NE release and intracellular DA and NE concentrations were quantified, for up to 24 h after initiation of treatment with different concentrations, ranging from 0 to 400 microM, of the metabolites hydroxyatrazine (HA), 2-amino-4-chloro-6-isopropylamino-s-triazine (deethylchlorotriazine), 2-amino-4-chloro-6-ethylamino-s-triazine (deisopropylchlorotriazine), and diaminochlorotriazine (DACT). Hydroxyatrazine significantly decreased intracellular DA and NE concentrations in a dose- and time-dependent manner. This metabolite also caused a significant inhibition of NE release from the cells. In contrast, deethylchlorotriazine and deisopropylchlorotriazine significantly increased intracellular DA concentration following exposure to 50-200 microM from 12 to 24 h. Intracellular NE was significantly reduced at these same concentrations of deethylchlorotriazine at 24 h while the concentration of NE in PC12 cells exposed to deisopropylchlorotriazine was not altered at any dosage or time point measured. NE release was decreased at 18 (200 microM) and 24 h (100 and 200 microM) following exposure to deethylchlorotriazine and at 24 h (100 and 200 microM) following deisopropylchlorotriazine. DACT, at the highest concentration (160 microM), significantly increased intracellular DA and NE concentrations at 18 and 24 h. NE release was also increased at 40-160 microM at 24 h. The viability of the PC12 cells was tested using the trypan blue exclusion method. Following 18 to 24 h of treatments with HA, cell viability was reduced 10-12% at the two higher concentrations (200 and 400 microM), but, with other metabolites, the viability was reduced by only 2 to 5% at the highest concentrations. These data indicate that HA affects catecholamine synthesis and release in PC12 cells in a manner that is similar to synthesis of atrazine and simazine. On the other hand, deethylchlorotriazine and deisopropylchlorotriazine altered catecholamine synthesis in a manner similar to that observed in the rat brain following in vivo exposure (i.e., increased DA and decreased NE concentration), whereas DACT appeared to produce an increase in NE release as well as in the intracellular DA and NE concentrations. Overall, these findings suggest that the catecholamine neurons may be a target for the chlorotriazines and/or their metabolites, that the metabolites produce a unique pattern of catecholamine response, and that all of the changes were seen within the same range of doses.

Animals↗
PubMed2001

Alterations in development, behavior, and physiology in Drosophila larva that have reduced ecdysone production.

We investigated behavior, physiology, sensitivity to exogenous application of ecdysone, and nerve terminal structure for differences between the reduced ecdysone genotype, ecd(1)/ecd(1), and wild-type control ecd(1)/TM6B animals during the early and late third instars when raised at 25 degrees C. The ecd(1) mutants were able to survive through larval development and form pupae. However, the results demonstrate that the time to pupation is lengthened by about 50 h for the ecd(1)/ecd(1) as compared with the wild-type control siblings. In addition to the lengthened larval cycle in the mutant, ecd(1)/ecd(1) animals, they also display behavioral differences as compared with controls. The rate of body wall contraction and mouth hook movements are reduced in the early third instar of ecd(1)/ecd(1) as compared with controls. The physiological measure of excitatory junction potential amplitude for the combined Is and Ib terminals did not reveal any differences among the two genotypes during the early third instar but the synaptic strength is reduced in the late third instars for controls. Application of exogenous ecdysone is still effective during the late third instar for the ecd(1)/ecd(1) but not the controls. This suggests that endogenous production of ecdysone have already taken place in the wild-type but not the ecd(1)/ecd(1) larvae, thus the rapid nongenomic responses could still be observed in the late third ecd(1)/ecd(1) larvae. Structurally the number of varicosities and the terminal length showed significant differences between ecd(1)/ecd(1) and the wild-type ecd(1)/TM6B genotype in the late third instars.

Animals↗
PubMed2001

Comparative evaluation of vessel elements in S alix spp. (Salicaceae) endemic to the Athabasca sand dunes of northern Saskatchewan, Canada.

Vessel element (VE) characters, including density, lumen diameter, length, and clustering, were evaluated using light and scanning electron microscopy in four endemic Salix taxa from the Lake Athabasca sand dunes in northern Saskatchewan, Canada. These data were compared with the widespread putative sister species for each endemic. Endemic taxa exhibited similar VE densities as compared to their associated sister species. Salix brachycarpa var. brachycarpa and its derived endemic, var. psammophila, had the highest VE density values of all endemic-progenitor pairs in this study. Values for VE lumen diameter and VE length were significantly different in some of the species pairs. Lumen diameter of the endemic S. planifolia ssp. tyrrelli was significantly less than that of its widespread sister species, ssp. planifolia. Salix turnorii had significantly greater values for both VE lumen diameter and length than its progenitor, S. lutea. Vessel element clustering did not differ significantly between endemic and progenitor taxa with the exception of S. silicicola and its arctic progenitor, S. alaxensis. Structural differences for these endemic willows appear related to their open sand habitat, and taxonomic implications for endemic-progenitor pairs are discussed.

Journal Article↗
PubMed2000

Statistical methods for assessing the dimensions of synaptic vesicles in nerve terminals.

Chemical transmission between neurons occurs by the release of neurotransmitter packaged within vesicles of the presynaptic neuron onto a postsynaptic target. The amount of transmitter contained within a vesicle is in part regulated by the size of the vesicle. Thus, it is of general interest to quantify the dimension of vesicles in understanding the basic principles of chemical synaptic transmission. These vesicles can only be measured by electron microscopic techniques. Obtaining the true dimensions of synaptic structures is therefore complicated by stereological considerations. In this study, we suggest improved methods for determining the distributions (and mean sizes) for populations of vesicle diameters by mathematical processes involving (1) an implicit inversion of the empirical data distribution, (2) an explicit inversion approach, and (3) an approach based on substituting the empirical distribution into the inversion formula and then isotonizing using an iterated convex minorant algorithm. These procedures provide distributions that better represent the true population distributions (and means) for comparisons with other data sets of vesicle diameter measures.

Animals↗
PubMed2000

Characterization of muscles associated with the articular membrane in the dorsal surface of the crayfish abdomen.

The anatomy, physiology, and biochemistry of the dorsal membrane muscle (DMA) and the superficial extensor muscle accessory head (SEAcc) in the abdomen of the crayfish, Procambarus clarkii and lobster, Homarus americanus, are reported. These muscles have not been previously characterized physiologically or biochemically. The anatomy was originally described by Pilgrim and Wiersma (1963. J Morph 113:453-587). The arrangement of these muscles varies depending on the abdominal segment. The function of the dorsal membrane muscle is to retract the thin articulating membrane joining the cuticular segments so that the dorsal membrane does not evert during extension of the abdomen. Consequently, the articular membrane does not protrude, and thus potential damage to the membrane is minimized. Examination of nerve terminal morphology revealed strings of varicosities, usually only associated with tonic terminals. The electrophysiological data indicate that there are at least four tonic excitatory and one inhibitory motor neuron innervating these muscles. Facilitation indices and fatigue-resistance indicate physiologically the tonic nature of innervation. Anti-GABA antibodies demonstrate the anatomical presence of an inhibitor motor neuron. The SDS electrophoretic analysis of myofibrillar proteins and Western blots of key protein isoforms for these muscles in crayfish and lobsters also indicate that the DMA and SEAcc muscles are tonic phenotype. J. Exp. Zool. 287:353-377, 2000.

Abdomen↗
PubMed2000

Assessing accurate sizes of synaptic vesicles in nerve terminals.

Chemical synaptic transmission occurs when vesicles within a presynaptic neuron fuse to the membrane and release their neurotransmitter content into the synaptic cleft, eliciting a response in the postsynaptic cell. If concentration of neurotransmitter is the same in all synaptic vesicles, the volume of the vesicle determines how much transmitter is released. Thus, variation in vesicular volume may contribute to observed variance of synaptic quantal unit size. The present study provides an approach to more fully and accurately characterize the dimensions of synaptic vesicles within a population containing varied sizes of vesicles. The methodology can be applied in a wide range of stereological problems. The approach characterizes the distribution of vesicle sizes within a population and provides a means to assess effects of experimental manipulations on vesicle dimensions. The mathematical treatments to obtain the true distribution of vesicle sizes involve extraction of the observed distribution from an enlarged population containing smaller vesicle diameters produced by sectioning of the specimens. A FORTRAN program is provided.

Algorithms↗
PubMed2000

Influence of serotonin on the kinetics of vesicular release.

The mechanisms by which synaptic vesicles are transported and primed to fuse with the presynaptic membrane are important to all chemical synapses. Processes of signal transduction that affect vesicular dynamics, such as the second-messenger cascades induced by neuromodulators, are more readily addressed in assessable synaptic preparations of neuromuscular junctions in the crayfish. We assessed the effects of serotonin (5-HT) through the analysis of the latency jitter and the quantal parameters: n and p in the opener muscle of the walking leg in crayfish. There is an increase in the size of the postsynaptic currents due to more vesicles being released. Quantal analysis reveals a presynaptic mechanism by an increase in the number of vesicles being released. Latency measures show more events occur with a short latency in the presence of 5-HT. No effect on the frequency or size of spontaneous release was detected. Thus, the influence of 5-HT is presynaptic, leading to a release of more vesicles at a faster rate.

Animals↗
PubMed2000

Muscle type-specific myosin isoforms in crustacean muscles.

Differential expression of multiple myosin heavy chain (MyHC) genes largely determines the diversity of critical physiological, histochemical, and enzymatic properties characteristic of skeletal muscle. Hypotheses to explain myofiber diversity range from intrinsic control of expression based on myoblast lineage to extrinsic control by innervation, hormones, and usage. The unique innervation and specialized function of crayfish (Procambarus clarkii) appendicular and abdominal musculature provide a model to test these hypotheses. The leg opener and superficial abdominal extensor muscles are innervated by tonic excitatory motoneurons. High resolution SDS-PAGE revealed that these two muscles express the same MyHC profile. In contrast, the deep abdominal extensor muscles, innervated by phasic motoneurons, express MyHC profiles different from the tonic profiles. The claw closer muscles are dually innervated by tonic and phasic motoneurons and a mixed phenotype was observed, albeit biased toward the phasic profile seen in the closer muscle. These results indicate that multiple MyHC isoforms are present in the crayfish and that differential expression is associated with diversity of muscle type and function.

Animals↗
PubMed2000

The effects of 5-HT on sensory, central and motor neurons driving the abdominal superficial flexor muscles in the crayfish.

Serotonin (5-HT) induces a variety of physiological and behavioral effects in crustaceans. However, the mechanisms employed by 5-HT to effect behavioral changes are not fully understood. Among the mechanisms by which these changes might occur are alterations in synaptic drive and efficacy of sensory, interneurons and motor neurons, as well as direct effects on muscles. We investigated these aspects with the use of a defined sensory-motor system, which is entirely contained within a single abdominal segment and consists of a 'cuticular sensory neurons segmental ganglia abdominal superficial flexor motor neurons-muscles' circuit. Our studies address the role of 5-HT in altering (1) the activity of motor neurons induced by sensory stimulation; (2) the inherent excitability of superficial flexor motor neurons; (3) transmitter release properties of the motor nerve terminal and (4) input resistance of the muscle. Using en passant recordings from the motor nerve, with and without sensory stimulation, and intracellular recordings from the muscle, we show that 5-HT enhances sensory drive and output from the ventral nerve cord resulting in an increase in the firing frequency of the motor neurons. Also, 5-HT increases transmitter release at the neuromuscular junction, and alters input resistance of the muscle fibers.

Abdominal Muscles↗
PubMed2000

Heart rate measures in blind cave crayfish during environmental disturbances and social interactions.

Most animals continually assess the environment in which they live and alter their behavior according to various stimuli. As an observer, one looks for changes in a behavior indicating that an animal responded to a particular event. When the animal does not make significant behavioral changes as measured by bodily movements, the animal may be characterized as unresponsive to a given stimulus. This study demonstrates that when behavioral body movements can not be observed an internal physiological measure of heart rate (HR) shows dramatic changes following presentation of defined stimuli. This study used the blind cave crayfish and examined their responsiveness to the following stimuli: light (infrared, dim red, and white), water-borne vibrations, removal of water, olfactory cues, and social interaction with partners. This study demonstrates that there is substantial individual variation of HR at basal levels and with the intensity of an social interaction. We find HR is a reasonable measure of the responsiveness of blind cave crayfish to given stimuli even in the absence of observable behavioral changes. This enables the observer to determine if an individual is responsive to and making an assessment of particular cues.

Animals↗
PubMed2000

Sensitivity of transformed (phasic to tonic) motor neurons to the neuromodulator 5-HT.

Long-term adaptation resulting in a 'tonic-like' state can be induced in phasic motor neurons of the crayfish, Procambarus clarkii, by daily low-frequency stimulation [Lnenicka, G.A., Atwood, H.L., 1985b. Long-term facilitation and long-term adaptation at synapses of a crayfish phasic motoneuron. J. Neurobiol. 16, 97-110]. To test the hypothesis that motor neurons undergoing adaptation show increased responses to the neuromodulator serotonin (5-HT), phasic motor neurons innervating the deep abdominal extensor muscles of crayfish were stimulated at 2.5 Hz, 2 h/day, for 7 days. One day after cessation of conditioning, contralateral control and conditioned motor neurons of the same segment were stimulated at 1 Hz and the induced excitatory post-synaptic potentials (EPSPs) were recorded from DEL(1) muscle fibers innervated by each motor neuron type. Recordings were made in saline without and with 100 nM 5-HT. EPSP amplitudes were increased by 5-HT exposure in all cases. Conditioned muscles exposed to 5-HT showed a 2-fold higher percentage of increase in EPSP amplitude than did control muscles. Thus, the conditioned motor neurons behaved like intrinsically tonic motoneurons in their response to 5-HT. While these results show that long-term adaptation (LTA) extends to 5-HT neuromodulation, no phenotype switch could be detected in the postsynaptic muscle. Protein isoform profiles, including the myosin heavy chains, do not change after 1 week of conditioning their innervating motor neurons.

Animals↗
PubMed2000

Heart rate within male crayfish: social interactions and effects of 5-HT.

Behaviors, such as those that establish dominant and subordinate social status, are thought to be driven by various neuromodulators and hormones. In crustaceans, the level of serotonin (5-HT) in the hemolymph is correlated with degree of aggressiveness. The crustacean heart is neurogenic and is modulated by neural secretion of 5-HT in the hemolymph, which bathes the cardiac tissue. We discuss and present the results of measuring heart rate (HR) of crayfish during interactions, as an indication of their state of excitability. HR is the result of multiple influences: a cocktail of hormones and modulators. HR was monitored during the periods in which crayfish established aggressive and submissive social status, during sham injections, and following injections of various doses of 5-HT. Crayfish, during an interaction to establish social status, can increase HR. Both the aggressive and submissive crayfish can dampen their HR within seconds during a pause in the interaction, while still posturing in an aggressive or submissive state. Injections of 5-HT to obtain systemic levels of approximately 100 nM-10 microM increase HR substantially for hours. This suggests that aggressive interactions and the establishment of a dominant posture may not be related to large increases in the free concentrations of 5-HT within the circulating hemolymph, since a sustained HR is not observed in aggressive animals. Instead, the results may demonstrate that inhibitory cardiac regulation is present in the aggressors during interactions and that a regulator is possibly 5-HT.

Animals↗
PubMed2000

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid activity in the female rat. A focus on the EDSTAC recommendations.

In 1996, the US Environmental Protection Agency was given a mandate by Congress to develop a screening program that would evaluate whether variously identified compounds could affect human health by mimicking or interfering with normal endocrine regulatory functions. Toward this end, the Agency chartered the Endocrine Disruptor Screening and Testing Advisory Committee in October of that year that would serve to recommend a series of in vitro and in vivo protocols designed to provide a comprehensive assessment of a chemical's potential endocrine-disrupting activity. A number of these protocols have undergone subsequent modification by EPA, and this review focuses specifically on the revised in vivo screening procedure recommended under the title Research Protocol for Assessment of Pubertal Development and Thyroid Function in Juvenile Female Rats. Background literature has been provided that summarizes what is currently known about pubertal development in the female rat and the influence of various forms of pharmaceutical and toxicological insult on this process and on thyroid activity. Finally, a section is included that discusses technical issues that should be considered if the specified pubertal endpoints are to be measured and successfully evaluated.

Animals↗