Excitation and inhibition of motoneurones in the tortoise

The bacterial instrument as a promising therapy for colon cancer

OBJECTIVE

Colon cancer is a great health concern worldwide, as it is the second leading cause of cancer-related death. Conventional treatment of cancer such as surgery, radiotherapy, and chemotherapy are faced with limitations and side effects. Therefore, strategies for the treatment of cancer need to be modified or new strategies replacing the old one.

AIMS

The aim of this study is to review the role of bacteria or their products (such as peptides, bacteriocins, and toxins) as a therapeutic agent for colon cancer.

RESULTS AND CONCLUSION

Recently, the therapeutic role of bacteria and their products in colon cancer treatment holds promise as emerging novel anti-cancer agents. Unlike the conventional treatments, targeted therapy based on the use of bacteria that are able to directly target tumor cells without affecting normal cells is evolving as an alternative strategy. Moreover, several bacterial species were used in live, attenuated or genetically modified that are able to multiply selectively in tumors and inhibiting their growth.

Electrophysiological and morphological properties of neurons in the ventral horn of the turtle spinal cord

In this report, we present recent findings on the electrophysiological and morphological properties of spinal motoneurons (MNs) and interneurons (INs) of the adult turtle which were studied in slices of the spinal cord. The range of values for the measured electrophysiological parameters in 96 tested cells included: resting potential, -57 to -83 mV; input resistance, 2.5-344 M omega; time constant, 2.5-63 ms; rheobase current, 0.04-5.3 nA; after-hyperpolarization (AHP) duration, 72-426 ms; AHP half-decay time; 11-212 ms; and, slope of the stimulus current-spike frequency relationship, 3.4-235 Hz/nA. For another 20 cells, we made both morphological and electrophysiological measurements (the latter values within the above ranges). Their ranges in morphological properties included: soma diameter, 20-54 microm; soma surface area, 299-2045 microm2; soma volume, 2.3-45 microm3 x 10(4); rostro-caudal dendritic projection distance, 150-1200 microm; and, sum of dendritic lengths, 1.5-16 microm x 10(3). The emphasized findings include: 1) the quality and robustness of the intracellular recordings, which enabled accurate measurement of the action potential's shape parameters (spike, afterhyperpolarization [AHP]); 2) the substantial AHP of the INs' AP; 3) no single action-potential shape parameter (nor combination of parameters) being cardinal for its (or their combined) changes matching the profile of the initial and later phases of spike-frequency adaptation; 4) the utility and flexibility of a cluster analysis (using varying combinations of passive, transitional and active cell properties) for providing a provisional classification of low (like cat S) and high (like cat F) threshold MNs, and groups of INs with non-spontaneous versus spontaneous discharge; 5) the clear-cut morphological confirmation of the provisional classification strategy; 6) the basis for testing the possibility that one of the provisionally classified MN types innervates non-twitch muscle fibers; and 7) the heuristic value of comparing the properties of MNs versus INs across vertebrate species, with an emphasis on the lamprey, turtle, and cat.

Properties of spinal motoneurons and interneurons in the adult turtle: provisional classification by cluster analysis

The purpose of the present study was to compare, in motoneurons (MNs) vs. interneurons (INs), selected passive, transitional, and active (firing) properties, as recorded in slices of lumbosacral spinal cord (SC) taken from the adult turtle. The cells were provisionally classified on the basis of (1) the presence (in selected INs) or absence (MNs and other INs) of spontaneous discharge, (2) a cluster analysis of selected properties of the nonspontaneously firing cells, (3) a comparison to previous data on turtle MNs and INs, and (4) a qualitative comparison of the results with those reported for other vertebrate species (lamprey, cat). The provisional nomenclature accommodated properties appropriate for solely MNs (Main MN group) vs. nonspontaneously firing INs (Main IN-N) vs. spontaneously firing INs (IN-S) and for neurons with two degrees of intermediacy between the Main MN and the Main IN-N groups (Overlap MN, Overlap MN/IN). Morphological reconstructions of additional cells, which had been injected with biocytin during the electrophysiological tests, were shown to provide clear-cut support for the provisional classification procedure. The values for the measured parameters in the 96 tested cells covered the spectrum reported previously across adult vertebrate species and were robust in measurements made on different SC slices up to 5 days after their removal from the host animal. The interspecies comparisons permitted the predictions that (1) our Main MN and Overlap MN cells would be analogous to two MN types that innervate fast-twitch and slow-twitch skeletomotor muscle fibers, respectively, in the cat, and (2) the MNs in our Overlap MN/IN group probably innervate slow (nontwitch, tonic) muscle fibers whose presence has recently been established in the turtle hindlimb. In summary, the results bring out the utility of the SC slice preparation of the turtle for study of spinal motor mechanisms in adult tetrapod vertebrates, particularly as an adjunct to the in vivo cat, because of the ease with which robust measurements can be made of the active properties of both MNs and INs.

A commentary on the segmental motor system of the turtle: implications for the study of its cellular mechanisms and interactions

A commentary is provided on the segmental motor system of the turtle Pseudemys (Trachemys) scripta elegans with an emphasis on neuronal, neuromuscular, and muscular mechanisms that control the development of force under normal, fatiguing, and pathophysiological conditions. For the central neuronal component of the segmental motor system, it has recently been shown that intracellular analysis of the firing properties of motoneurons and interneurons can be undertaken for relatively long periods of time in in vitro slices of the lumbosacral spinal cord of the adult turtle. In other less reduced in vitro preparations, analyses are available on complex motor behaviors generated by the isolated spinal cord. These behaviors of spinal neuronal networks are analogous in key aspects to those generated by the isolated in vivo cord, and by the cord in intact preparations. These results suggest that the neuronal components of the segmental motor system can not be studied from the cellular/molecular level of analysis in in vitro slice preparations to the systems level in conscious, freely moving animals. The in vitro approach can also be used for the analysis of cellular mechanisms in suprasegmental brain structures, which contribute to the control of voluntary movement. For the peripheral neuromuscular component of the segmental motor system, information is now available on muscle fiber types and selected aspects of sensory innervation, and it is feasible to study the mechanical and biochemical properties of motor units. As such, the turtle presents a valuable model for exploring interrelations between the neuronal and mechanical components of the segmental motor system of the generalized tetrapod. A prominent feature of these recent developments is the extent to which they have been driven by findings that have emphasized an evolutionary conservation of motor-control mechanisms extending from ion channels, at the cellular level, to the control of multijointed movements at the systems level of analysis.

A technique to anesthetize turtles with ether

A technique to anesthetize turtles with ether is presented, in which a plastic cannula is passed through the glottis into the trachea. This procedure avoids apnea and allows ether vapours obtained from a chamber to be introduced, by the animal respiratory movements or by means of a pump, into the animal lungs. The anesthesia is rapidly obtained and lasts from 45-90 minutes. The time of recovery from anesthesia ranged from 60-90 minutes. With this technique no deaths were observed and the same animal could be anesthetized repeatedly.

Long-term in vitro turtle preparation for the study of spinal organization

A method by which muscles, nerves, and a section of spinal cord from a turtle can be stably maintained in vitro for many days has been developed. Tests of the viability of central and neuromuscular synapses, and the histochemical properties of muscle fibers have indicated that the preparation is viable and shows little decrement in function over a period of 3-5 days. The system allows continuous access to the muscles, nerves, and the spinal cord, as well as a controlled external environment.

Monosynaptic connexions of low threshold muscle afferents with hindlimb motoneurones in the turtle spinal cord

Excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from hindlimb motoneurones of the anaesthetized fresh water turtle. The EPSPs were evoked from low threshold muscle afferents and the amplitudes saturated for stimuli less than two times the nerve threshold. The segmental latencies of these EPSPs, measured from the initial positive peak of the triphasic cord dorsum potential to the onset of the EPSP, ranged from 1.5 to 3.1 ms. The intraspinal conduction time of afferents was estimated by recording afferent volleys in the grey matter along the vertical course of intraspinal afferent fibres. The synaptic delay was estimated by subtracting the latency of the afferent volley at the deepest region of the dorsal horn from the segmental latency of the EPSP (in the range from 1.6 to 2.1 ms) recorded in the same microelectrode track. The average value was 0.99 ms (range: 0.9-1.1 ms), which was close to the known synaptic delay of cold-blooded animals. Therefore, the EPSPs in this range of segmental latencies were regarded as monosynaptic. Taking account of the intraspinal afferent conduction time (0.8 ms on average) and another synaptic delay, the latency for disynaptic transmission would be 2.8 ms or more. Thus, EPSPs having segmental latencies of 1.5-3.1 ms were suggested to be almost all monosynaptic in nature, at least under the present conditions of deep anaesthesia. On the basis of the above criteria for the monosynaptic nature of EPSPs, the pattern of convergence of monosynaptic excitatory inputs from various muscle afferents was investigated. Monosynaptic EPSPs were induced from the homonymous muscle nerve and the nerve innervating the synergist at the same joint. The heteronymous EPSPs were also found between muscles within each group of the anterodorsal musculature and the posteroventral musculature. No monosynaptic connexions were found between anterodorsal and posteroventral muscles except between the muscles innervated by the peroneal and the tibial nerve.

Dendrite distribution of identified motoneurons in the lumbar spinal cord of the turtle Pseudemys scripta elegans

Motoneurons in the turtle lumbar spinal cord were injected with HRP by electrophoresis after being electrophysiologically identified as innervating a muscle belonging to a functional group. The distribution of dendrites was studied in transverse reconstructions of 45 motoneurons, including 11 motoneurons identified as innervating knee extensor muscles, eight motoneurons innervating hip retractor and knee flexor muscles, 14 motoneurons innervating ankle and/or toe extensors and 12 motoneurons innervating ankle and/or toe flexor muscles. The dorsal dendritic tree of motoneurons innervating distally positioned musculature (ankle and/or toe extensors and flexors) was observed to contain significantly less terminal dendritic branches compared to the dorsal dendritic trees of motoneurons innervating proximally situated (hip and knee) muscles. The distribution of dendrites within the white matter was studied by measuring the total projected length of the dendritic branches within empirically defined sectors in the transverse plane. This kind of analysis also revealed differences between the dorsal dendrites of motoneurons innervating distally and proximally positioned muscles conforming to the counts of terminal dendritic branches. It is suggested that these apparent differences in the size of the dorsal dendrite may be related to the number of synapses made by primary afferents. In the white matter, the highest dendritic density for all four groups of mononeurons was found within the central part of the lateral funiculus. However, only in the ventral funiculus could slight indications be found that the dendritic density of functionally different motoneuron groups may bear some relation to the locations of the terminations of the descending pathways known to establish monosynaptic contacts with lumbar mononeurons.

Terminations of primary afferents on lumbar motoneurons in the turtle Pseudemys scripta elegans

The existence of monosynaptic contacts between primary afferents and motoneurons in the lumbar spinal cord of the turtle Pseudemys scripta elegans was demonstrated by intracellular injections of horseradish peroxidase. Three afferent-motoneuron combinations were satisfactorily labeled and revealed 1, 4 and 6 contacts respectively. All contacts were made on the dorsal dendritic tree of the motoneurons. It is suggested that the contacting primary afferents are from muscle spindles.

Morphology of primary afferents to the spinal cord of the turtle Pseudemys scripta elegans

The morphology of primary afferents to the spinal cord of the turtle Pseudemys scripta elegans was studied by means of intra-axonal injections of horseradish peroxidase. A total of 74 collaterals arising from 34 different afferents in 22 animals was investigated. Within this sample, a division into three morphologically distinct collateral types appeared possible. Collaterals of the same parent axon could always be classified to the same type. Type A collateral arborizations could be found within area I-II and III of the spinal grey matter. The number of presynaptic boutons per collateral varied considerably. However, collaterals of the same parent axon usually possessed a similar general appearance. Type B collaterals terminated within area IV and V-VI. The general shape and number of boutons could differ considerably between collaterals of different parent fibers but also between collaterals of the same axon. Type C collaterals formed terminal arborizations in the lateral parts of areas IV, V, VI and VII-VIII and demonstrated a fair constancy in general appearance and number of presynaptic boutons. Type A collaterals are thought to be derived from fibers innervating various cutaneous receptors. Terminal arborizations of type C collaterals are fully overlapping with the dorsal dendritic trees of turtle lumbar motoneurons. It is suggested that type C collaterals form contacts with these motoneurons and arise from muscle spindle innervating afferents. The origin of type B collaterals is less clear, attractive possibilities may be found in joint and/or tendon organs.

Morphology of lumbar motoneurons innervating hindlimb muscles in the turtle Pseudemys scripta elegans: an intracellular horseradish peroxidase study

Motoneurons in the turtle lumbar spinal cord, electrophysiologically identified as innervating a muscle belonging to a functional group, were injected with horseradish peroxidase by electrophoresis. A total of 45 motoneurons were reconstructed from transverse sections. Eleven motoneurons were identified as innervating knee extensor muscles, eight as innervating hip retractor and knee flexor muscles, 14 as supplying ankle and/or toe extensors, and 12 as innervating ankle and/or toe flexor muscles. The cell bodies were elongated and spindle-shaped in the transverse plane. The mean equivalent soma diameter was calculated to be 33.4 micrometers. The mean axon conduction velocity was 15.7 m/second. Significant, though rather weak, positive correlations were found between soma diameter, axon diameter, and axon conduction velocity. The axons of the reconstructed motoneurons did not reveal a recurrent axon collateral. However, a few unidentified motoneurons did possess such collaterals. The dendritic trees were restricted to the ipsilateral side of the cord, but reached out in lateral, ventral, and ventromedial directions to the subpial surface. Easily recognizable and characteristic dendrites were found both in the dorsal dendritic tree and in the dorsomedial dendritic tree. Correlations were calculated between the soma diameter and (1) the number of first-order dendrites, (2) the mean diameter of the first-order dendrites, and (3) the combined diameter of the first-order dendrites. In each case no correlations or only weak correlations were found. Fair correlations were observed between the diameter of a first-order dendrite and the number of terminal dendritic branches (r = .61) and the combined dendritic length (r = .78). However, correlations between the combined diameter of all first-order dendrites per neuron and the total number of terminal dendritic branches and the total combined dendritic length of a neuron were extremely weak. The overall appearance of turtle spinal motoneurons is comparable to that observed in other "lower" vertebrates such as frog and lizard. However, similarities are also observed between certain morphometric parameters in turtle and cat lumbar motoneurons.

Syntheses of spinal cord field potentials in the terrapin

A compartmental model of a terrapin motoneuron has been set up to compute membrane potential variations associated with synaptic input at different locations or with antidromic invasion. Membrane potential distributions obtained in that way were used to compute field potentials by means of a volume conduction formalism. The model was used to simulate field potentials measured in the spinal cord in response to stimulation of a muscle nerve with the intention to discriminate between different activation hypothesis for the generation of the spinal cord potential. Extracellular potentials calculated with an excitatory input distributed over the whole dorsal dendritic tree were found to give better reconstruction when compared with excitation restricted to the distal part of the dorsal dendrites, or with somatic inhibition.