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PubMed1975

Comparative strategies in the investigation of neural networks.

Comparative studies on nervous systems, though infrequently undertaken for the purpose of comparison, have yielded some important generalities about the formats of nervous networks, and about the cell biology of certain neural types. In the first category, it is clear that convergent evolutionary processes arrived at very similar networks to accomplish reciprocal and lateral inhibition, and load-compensation in "resistance reflexes." A newer general network format is described, command-derived inhibition, in which the central nervous elements controlling a rapid movement deliver presynaptic inhibition to the terminals of sensory neurons that carry reafferent excitation from the movement. It is argued that such circuits occur in several groups of animals, and that they include as a special class the efferent inhibitory neurons innervating acoustico-lateralis receptors in vertebrates. The properties of circuit elements that now seem to constitute useful generalizations include size principle (the inverse relationship between size and excitability in a variety of neurons), and the late differentiation of sensory neurons, failure to decussate, and their inability to mediate inhibition. Many other generalities have emerged, only to fall; one conclusion from such searches is that many supposedly "basic" properties of cell types or neural circuits are in fact not phylogenetically conservative, however much the physiologist may expect them to be.

Action Potentials↗
PubMed1975

Extensive and intensive factors determining the performance of striated muscle.

Striated muscle is obviously a versatile tissue, one which has been malleable to selective pressure and has become modified for many specific tasks. The variations which adapt striated muscle to particular functions involve both changes in its structural organization and changes in the chemical nature of its components. Although a number of factors have been identified which contribute to the diversity of muscle performance, it is not yet possible to account adequately for the wide range in muscle performance throughout the animal kingdom. While not a new direction in comparative physiology, developing quantitative explanations for the diversity of muscle performance is still an obvious, remaining task.

Action Potentials↗
PubMed1976

Neurohemal organ extracts effect the ventilation oscillator in crustaceans.

Extracts of the pericardial organs of crabs injected into intact animals cause an increase in the frequency of scaphognathite beating. The active factor is not dopamine of 5-hydroxytryptamine, which are present in pericardial organs; it is probably a peptide. The factor may represent a hormonal mechanism of coordinating heart rate and ventilation.

Animals↗
PubMed1982

Central organization of crustacean abdominal posture motoneurons: connectivity and command fiber inputs.

Intracellular recordings and Lucifer dye injections were used to locate five of the six tonic abdominal flexor motoneurons, as well as several of the extensor motoneurons in the fourth abdominal ganglion of the crayfish, Procambarus clarkii. Each motoneuron was identified by its morphology and root records, and each was characterized by its inputs from identified flexion- and extension-evoking interneurons (command fibers). Finally its connections to other motoneurons were examined by current injection experiments. As indicated by others, the somata of most of the tonic flexor motoneurons are electrically silent; recordings were, therefore, made from neuropilar branches, but at unknown locations. The majority of motoneurons were found to be polysynaptically connected to the command neurons, although several apparent monosynaptic excitatory and inhibitory connections were also seen. Coupling between motoneurons was confirmed, but the major functional input to the motoneurons was from premotor interneurons. Coupling between motoneurons and interneurons is also indicated by the data, and may be responsible for the inhibition of some motoneurons seen during depolarizing current injections into other motoneurons. Again, such coupling is shown to be a minor influence in the overall organization of the behavior. The data suggest that flexion and extension behavior is predominantly organized via interneurons including the command fibers rather than by connections among the motoneurons themselves.

Animals↗
PubMed1983

The organization of flexion-evoking interneurons in the abdominal nerve cord of the crayfish, Procambarus clarkii.

Intracellular recording and dye injection was used to investigate the flexion-evoking interneurons in the isolated abdominal nerve cord of the crayfish, Procambarus clarkii. The interneurons described in this study have all of the characteristics of cells called flexion command fibers in earlier works. These interneurons show cell bodies in all of the abdominal ganglia, all are interganglionic, and those with posteriorly directed axons enter the terminal caudal ganglion. Some cells were found in as many as eight different preparations, supporting the idea that these interneurons are identified cells. In addition to presenting evidence for identities, evidence was obtained for serial homology in this premotor system. A summary of the general organization of the flexion premotor apparatus is offered. It consists primarily of parallel elements (command interneurons) that are either bipolar or monopolar whose axonal projections course to the terminal caudal ganglion or rostrally into the thoracic region, perhaps into the cerebral ganglion. When activated singly, these parallel elements do not recruit additional interneurons but there are data to suggest that several of these elements could act in concert and interact in a low-gain fashion to produce coordinated positioning behavior.

Action Potentials↗
PubMed1984

Abdominal positioning interneurons in crayfish: projections to and synaptic activation by higher CNS centers.

Intracellular recording, stimulation, and Lucifer dye injections were used to characterize abdominal positioning interneurons from the neuropile of the second through sixth abdominal ganglia of the crayfish, Procambarus clarkii. Motor outputs of these cells were recorded with extracellular electrodes placed on various flexion and extension roots along the nerve cord. In an effort to assess the functional relationships between the postural interneurons in the abdomen and those known to exist in the circumesophageal connectives ( CECs ), a stimulus pulse train was delivered to each of the CECs while monitoring the intracellular responses of the impaled interneurons. Abdominal positioning interneurons were grouped into four general categories based on their responses to CEC stimulation: 1) those that projected their axons directly through the CECs ; 2) those that were remotely activated to spiking; 3) those locally activated to produce EPSPs or IPSPs; and 4) those that were not affected by CEC stimulation. The majority of abdominal positioning interneurons encountered in this study evoked flexion (N = 82), with relatively fewer evoking extension (N = 29). A major difference appeared between the two classes. Whereas 39% of the flexion interneurons had axons coursing to the brain, only 7% of the axons of extension interneurons coursed rostrally beyond the thoracic level. Finally, the large majority of those flexion and extension interneurons that lacked processes in the CEC received synaptic inputs at various levels along the lower CNS from other CEC neurons. Thus, control of abdominal positioning involves neurons at all levels in the CNS - some sequentially organized, others forming "through" pathways, but all with multiple input sites.

Action Potentials↗
PubMed1988

A quantitative study of command elements for abdominal positioning behavior in the crayfish Procambarus clarkii.

We develop a statistical method to estimate the total number of command elements devoted to abdominal positioning behavior in crayfish. We assumed that all command elements can be identified, that each identified cell is equivalent to a tagged individual in a population, and that the cells were sampled randomly. Samples of 29, 30, 20, and 35 cells from abdominal ganglia A3, A4, A5, and A6, respectively, were taken from our catalog. We characterized each cell using several morphological and physiological criteria, determined how many times each identified cell was present in the sample, and estimated the total number of command elements using both a maximum likelihood method and a modification of the Lincoln index. The larger the proportion of identified cells seen only once in the sample, the more identified cells there were that were unrepresented in the sample. We estimate there are approximately 34, 60, 86, and 98 command elements in ganglia A3, A4, A5, and A6, respectively. Using a slightly different data set we show that the motor output of unipolar cells is more often stronger in the direction of the cell's axonal projection. In bipolar command elements, the output strength was uncorrelated with the relative sizes of the two projecting axons. No two cells in our sample were completely identical, and this morphological variability sometimes made it difficult to determine whether or not two cells obtained from different individuals were the same identified cell. We discuss why caution should be exercised in studies requiring precision in cell identification.

Animals↗
PubMed1990

Unexpected divergence among identified interneurons in different abdominal segments of the crayfish Procambarus clarkii.

The command elements that initiate and coordinate the abdominal movements in crayfish show little similarity between the various abdominal segments. Our criteria for similarity among interneurons were based on both cell morphology and electrophysiology. By contrast, previously published evidence shows much greater intersegmental similarity in the skeletal, muscular, motoneuronal, and sensory components of the abdominal system in crayfish, structures that are controlled by or send information to the command elements. Therefore, unlike the command elements, these structures have retained nearly identical form and function in the various segments. We also found in different ganglia examples of interneurons involved with abdominal positioning behavior that have similar morphology but different function and vice versa. Such interneurons could represent divergent pairs of serial homologues. It is unknown why so many of the abdominal positioning interneurons have become different. The various ganglia may perform subtly different functions, requiring differences in the positioning interneurons but not in the motor neurons or muscles. Alternatively, some of the abdominal positioning interneurons underlie more than one behavior; consequently, selection acting on these multiple functions may have changed these interneurons through evolution.

Abdomen↗
PubMed1993

On the existence of epithelial chloride channels in intact frogs and crayfish.

Chloride channels in isolated amphibian skins have been shown to be open (high PCl) when the transepithelial potential (TEP) across the skin is > 30 mV, inside positive, and [Cl-] in the external medium is high. In the absence of either of these signals PCl is much lower. Using Cl- efflux as a criterion, it is shown here that when the same cues are presented to intact frogs, channels open as in the in vitro preparation. The augmented efflux is partially inhibited by high I- in both preparations. However, salt-depleted frogs do not show channel opening, differing in this regard from isolated skins. Elevating external [Cl-] resulted in an even larger efflux stimulation in crayfish than in frogs. The TEP in these animals is usually small and sometimes blood negative; it does not appear to play a role in augmenting the efflux. Gluconate and NO3- also caused Cl efflux to increase markedly. Salt-depletion reduced the stimulation by high [Cl-] but did not abolish it as in frogs. Iodide had no effect on chloride efflux in crayfish. The results may indicate that gated channels exist in these animals, but interpretation is complicated by the possibility that the augmented efflux is due to exchange diffusion.

Animals↗
PubMed1993

Cyclic postural behavior in the crayfish, Procambarus clarkii: properties of the pattern-initiating network.

Crayfish exhibit complex cyclical adjustments in abdominal posture during certain forms of backward walking. An isolated nerve cord preparation was used to investigate the properties of the interneurons which direct this alternation of abdominal flexion and extension. The command function for this cyclic postural behavior appears to be the domain of a distributed network of multiple pattern-initiating interneurons: each interneuron may be viewed as a command element within a command system. The cyclic pattern may be elicited by stimulation of small axon bundles pulled from the ventrolateral margins of any of the abdominal connectives. As few as one stimulus pulse to the axon bundle can elicit a single cycle of patterned output, although more pulses are generally necessary. This suggests some convergence or amplification step in the pattern-initiating interneurons. The amplification may be accomplished by several pattern-initiating interneurons that are coupled to one another and converge on pattern generating circuits in each ganglion. Evidence supporting this interpretation is presented. Experiments involving resection of the cord reveal that the pattern-initiating signals transfer laterally across all of the abdominal ganglia, but the network contains a bias for descending signal conduction once a lateral transfer is made. This finding agrees with other results. For example, recordings from pattern-initiating axon bundles at rostral and caudal locations in the abdominal nerve cord show several descending but only one ascending unit activated during cyclic pattern generation. We also show that an isolated ganglion is capable of producing the cyclic motor program, although the outputs are much weaker than those elicited in the intact abdominal cord. Therefore, the pattern-initiating system is both central and distributed.

Abdomen↗
PubMed1995

Interneurons involved in the control of multiple motor centers in crayfish.

A number of studies have suggested that abdominal positioning interneurons (APIs) in the crayfish Procambarus clarkii can influence activity in multiple motor centers. Previous work on this population of neurons has demonstrated that they control the activity of tonic abdominal motor neurons (MNs) which generate postural movements of the abdomen and, to some extent, the activity of swimmeret MNs. This investigation demonstrates that many identified APIs also affect the activity of two populations of MNs which open and close the uropods and, in some cases, that of the swimmeret MNs as well. The majority (64%) of APIs examined in this study have an excitatory effect on both populations of uropod MNs. A smaller number (23%) increase the level of activity in one population of uropod MNs, and suppress, or have no effect on, the activity of the other population of uropod MNs. Approximately 25% of the APIs which were examined influence the output of swimmeret MNs, in addition to affecting the activity of uropod MNs. There are also indications that previous estimates of the number of APIs may have been too low. This is based on the observation that many APIs possess what appear to be similar morphologies but generate different patterns of motor output. Taken together, these findings support the idea that APIs influence the output of multiple motor centers which play a role in the control of general body posture and balance in crayfish.

Abdominal Muscles↗
PubMed2003

Dopaminergic regulation of crustacean hyperglycemic hormone and glucose levels in the hemolymph of the crayfish Procambarus clarkii.

The effects of dopamine on crustacean hyperglycemic hormone (CHH) release and hemolymph glucose levels in the crayfish Procambarus clarkii were investigated. A quantitative sandwich enzyme-linked immunosorbent assay (ELISA) using antibodies specific for Prc CHH was developed and characterized. The sensitivity of the ELISA was about 1 fmol/well. Specific measurement of CHH in hemolymph samples by the ELISA was demonstrated by the parallelism between CHH standard curve and sample (hemolymph) titration curve. Moreover, thermally stressed P. clarkii exhibited a characteristic change of hemolymph CHH levels as revealed by the ELISA. CHH and glucose levels increased significantly within 30 min of dopamine injection, peaked at 1 h, and returned to the basal levels at 4 h. Dose-dependent effects of dopamine on CHH and glucose levels were observed between 10(-8) to 10(-6) mol/animal. Dopamine-induced increases in CHH and glucose levels were absent in eyestalk-ablated animals. Finally, dopamine significantly stimulated the release of CHH from in vitro incubated eyestalk ganglia. These results suggest that dopamine enhances release of CHH into hemolymph that in turn evokes hyperglycemic responses and that the predominant site of dopamine-induced CHH release is the X-organ-sinus gland complex located within the eyestalk.

Animals↗