ISSN:0006-8977    

DOI:10.1159/000113315

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

This essay considers the ontogeny and phylogeny of the cranial neural circuitry producing rhythmic behaviors in vertebrates. These behaviors are characterized by predictable temporal patterns established by a neuronal network variously referred to as either a pacemaker, neural oscillator or central pattern generator. Comparative vertebrate studies have demonstrated that the embryonic hindbrain is divided into segmented compartments called rhombomeres, each of which gives rise to a distinct complement of cranial motoneurons and, as yet, unidentified populations of interneurons. We now propose that novel rhythmic circuits were innovations associated with the adoption of cardiac and respiratory pumps during the protochordate-vertebrate transition. We further suggest that the pattern-generating circuits of more recent innovations, such as the vocal, electromotor and extraocular systems, have originated from the same Hox gene-specified compartments of the embryonic hindbrain (rhombomeres 7–8) that gave rise to rhythmically active cardiac and respiratory circuits. Lastly, we propose that the capability for pattern generation by neurons originating from rhombomeres 7 and 8 is due to their electroresponsive properties producing pacemaker oscillations, as best typified by the inferior olive which also has origins from these same hindbrain compartments and has been suggested to establish rhythmic oscillations coupled to sensorimotor function throughout the neuraxis of vertebrate

ISSN:0006-8977    

DOI:10.1159/000113351

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000113316

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The Insecta encompasses a prodigiously diverse group as measured at the species, family and ordinal levels, but the nervous system bears evidence of conservatism. The early acquisition of flight must have been a major factor in the diversification of body form. Arguments are presented that predator evasion was a primary factor in the origin of flight and that a conserved set of giant interneurons played a key element in the transition.

ISSN:0006-8977    

DOI:10.1159/000113317

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The development of wings has undoubtedly played a major roe in the enormous diversification of insects. New insights into the evolutionary history of insect wings are available from paleontological, physiological and biomechanical studies. A recent hypothesis, derived primarily from paleontological evidence, is that wings arose from leg exites, small flaps associated with proximal leg segments. We present data from studies on physical models that are consistent with this hypothesis. The exites would have been moveable, and measurements on scaled models show that they would have generated aerodynamic lift by unsteady mechanisms associated with vortex shedding. An examination of the sensory structures found on insect wings is also consistent with the interpretation of proto-wings as leg exites. In addition to mechanosensory bristles, such as are found all over the body, the wings of modern insects carry campaniform sensilla sensitive to cuticular deformation and contact chemoreceptors whose stimulation elicits a feeding response. Both classes of receptors are also found on the legs of modern insects but not on the thorax, favoring the leg exite theory.

ISSN:0006-8977    

DOI:10.1159/000113318

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The generation of expectations about sensory input and the subtraction of such expectations from actual input appear to be important features of sensory processing. This paper describes the generation of sensory expectations within cerebellum-like structures of four distinct groups of fishes: Mormyridae; Rajidae; Scorpaenidae; and Apteronotidae. These structures consist of a sheet-like array of principal cells. Apical dendrites of the principal cells extend out into a molecular layer where they are contacted by parallel fibers. The basilar regions of the arrays receive primary afferent input from octavolateral endorgans, i.e., elec-troreceptors, mechanical lateral line neuromasts, or eighth nerve endorgans. The parallel fibers in the molecular layer convey various types of information, including corollary discharge signals associated with motor commands, sensory information from other modalities such as proprioception, and descending input from higher stages of the sensory modality that is processed by the structure. Associations between the signals conveyed by the parallel fibers and particular patterns of sensory input to the basal layers lead to the generation of a negative image of expected sensory input within the principal cell array. Addition of this negative image to actual sensory input results in the subtraction of expected from actual input, allowing the unexpected or novel input to stand out more clearly. Intracellular recording indicates that the negative image is probably generated by means of anti-Hebbian synaptic plasticity at the parallel fiber to principal cell synapse. The results are remarkably similar in the different fishes and may generalize to cerebellum-like structures in other sensory systems and taxa.

ISSN:0006-8977    

DOI:10.1159/000113352

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

An outgroup analysis of multiple ontogenies provides the most robust approach to understanding phylogeny. Such an analysis of the lateral line system among extinct and extant gnathostomes reveals that lateral line placodes constitute the basic ontogenetic unit responsible for the development of this system. Six pairs of lateral line placodes appear to have existed in the earliest gnathostomes, and eight stages (stages A–H) can be recognized in their differentiation. Terminal truncation (heterochronic changes) in the primitive sequence of placodal development has occurred in one or more placodes in each gnathostome radiation, with the most extensive truncations occurring in arthrodire placoderms, lepidosirenid lungfishes and extant amphibians. The most extensive nonterminal changes in the primitive sequence of placodal development involve the failure of electroreceptors to form within the lateral zones of the elongatiang sensory ridges of the placodes. This nonterminal change appears to have occurred independently in ancestral neopterygian bony fishes, in many amphibians and, possibly, in the extinct acanthodians. At least two teleost radiations, osteoglossomorphs and ostariophysines, have re-evolved electroreceptors which may represent additional nonterminal changes in placodal patterning or, possibly, a change in the embryonic source of these receptor

ISSN:0006-8977    

DOI:10.1159/000113319

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Weakly electric fish of the families Gymnotidae and Hypopomidae (Gymnotiformes) are able to locate the electric discharges from conspecifics or from dipole electrodes, and they demonstrate this by making rapid, well-directed approaches toward these electrical sources. A video tracking system was used to follow the movements of electric fish in a large tank and an analytic method was used for computing the direction and magnitude of the electric field anywhere within the cylindrical test tank. Using a static analysis method, we describe the posture of test fish relative to the electric fields during their approaches to stationary or moving electrical stimuli. Using a dynamic analysis, we examine the movements of the fish including the sign and magnitude of velocity and bending in response to electric fields. Electric fish seek to maintain a zero error angle between their body orientation and the local electric field. They do so by bending their body in the direction of the local electric field. The response has a delay of approximately 0.5 s. Swimming in reverse inverts the direction of the bend. These fish also use ''V-turns'' to redirect their swim directions when encountering rapidly-changing electric fields.

ISSN:0006-8977    

DOI:10.1159/000113353

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Using examples from the octavolateral system, evidence is reviewed suggesting a relationship between regressive events, such as loss of one function, or loss of one sensory subsystem, and progressive evolutionary changes in topologically associated systems. While none of the neuronal examples in the evolutionary reorganization of the otic region are as clear-cut as the initial example of non-neuronal reorganization on which the correlation of regressive with progressive changes is based (the functional transformation of the hyomandibular bone into the stapes), the general principle that a chance correlation of two insignificant events may lead to a novel function may be valid for more aspects of the evolution of the ear, in particular the auditory system, than is currently appreciated. It is suggested that regressive events may not only be an evolutionary dead end but that they may provide, through the relaxation of constraints imposed on the respective structure, a source for innovations. However, transformations of functionally uncoupled structures into a novel adaptive function will occur only when topologically adjacent structures require these transformations to improve their own function.

ISSN:0006-8977    

DOI:10.1159/000113320

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Weakly electric fish of the families Gymnotidae and Hypopomidae (Gymnotiformes) are able to locate the electric discharges from conspecifics or from dipole electrodes, and they demonstrate this by making rapid, well-directed approaches toward these electrical sources. A video tracking system was used to follow the movements of electric fish in a large tank and an analytic method was used for computing the direction and magnitude of the electric field anywhere within the cylindrical test tank. Using a static analysis method, we describe the posture of test fish relative to the electric fields during their approaches to stationary or moving electrical stimuli. Using a dynamic analysis, we examine the movements of the fish including the sign and magnitude of velocity and bending in response to electric fields. Electric fish seek to maintain a zero error angle between their body orientation and the local electric field. They do so by bending their body in the direction of the local electric field. The response has a delay of approximately 0.5 s. Swimming in reverse inverts the direction of the bend. These fish also use ''V-turns'' to redirect their swim directions when encountering rapidly-changing electric fields.

ISSN:0006-8977    

DOI:10.1159/000113354

出版商:S. Karger AG    

年代:1997

数据来源: Karger