Serially Homologous Research Articles

EVOLUTION OF THE TELSON NEUROMUSCULATURE IN DECAPOD CRUSTACEA

The neuromusculature in the telsons of three macrurans (Pandalus platycerus, Procambarus clarkii, Upogebia pugettensis) and three anomurans (Munida quadrispina, Blepharipoda occidentalis, Emerita analoga) are compared to provide a framework for neurophysiological comparisons of their roles in the swimming behaviors of these decapods. The stereotypical arrangement in macruran telsons comprises a group of massive axial muscles and a trio of small appendage muscles (Fig. 1). The various arrangements of telson neuromusculature in the anomurans (Fig. 3) are interpreted in terms of specific modifications of particular macruran features. Homologies among muscles and nerve roots in the telsons of the six decapods are identified (Figs. 1, 3, 4, Table II) and homologies among particular axial and appendage motoneurons in the sixth abdominal ganglia are suggested (Fig. 5, Table III). The appendage neuromusculature in decapod telsons is inferred to be ontophyletically part of the seventh abdominal segment that was present in the ancestors of decapods. These muscles and their motoneurons, like most of the axial neuromusculature in the telson (Dumont and Wine, 1983, in prep.), may be serial homologs of muscles and motoneurons in abdominal segments.

Visual interneurons in the leech brain

1. The medicinal leech has five pairs of simple eyes (Fig. 1A). The photoreceptors of some eyes are known to excite one of the bilateral pair of lateral visual (LVa) cells in the first segmentai ganglion (G1). A new pair of neurons, the LVb cells, has been found in subganglion 4 (SubEG4) of the subesophageal ganglion. Since G1 and SubEG4 develop from adjacent ganglionic primordia, the LVa and LVb cells may be serial homologues. 2. The somata and dendrites of the LVa and LVb cells lie in corresponding positions (Fig. 3), and their axons run side-by-side and terminate together in the supraesophageal ganglion. 3. Both neurons have bulbous contralateral branches (Figs. 2, 3), and fibrous ipsilateral dendrites that match the two zones where photoreceptors of the ipsilateral eyes 3–5 have synaptic terminals (Fig. 1C). Moreover, both neurons are Lucifer Yellow dye-coupled to the photoreceptors of those same eyes (Fig. 2B). 4. When the ipsilateral eyes 3–5 are illuminated, the LVa and LVb cells both show a characteristic complex response that includes a compound EPSP produced by electrical coupling potentials from the photoreceptors (Figs. 5, 6), small spike-like events, and conventional-looking action potentials (Fig. 4). 5. The compound EPSP is thought to elicit local spikes in ipsilateral dendritic branches, which then spread electrotonically into the main neurite and soma as small spikes. In turn, the summation of these small spikes in the neurite evidently elicits propagating action potentials. 6. LV cells produce extended plateau-like depolarizations (Fig. 7) in weak or continuously varying light, or in response to current injection. These slow potentials appear to be generated by a noninactivating Na conductance and a TEA-sensitive K conductance (Fig. 8). Since slow potentials are accentuated when extracellular Ca is replaced by Ba (Fig. 9), Ca appears to participate in the response, presumably via a Ca-dependent K channel. 7. Although the LVa and LVb cells may be homologous, they are not identical (Fig. 5). For example, unlike the LVa cells, the LVb cells are not inhibited by input from the contralateral eyes 3–5. Moreover, eyes 1 and 2 weakly inhibit the LVa cells, but weakly excite the LVb cells.

Functional ontogenetic changes in Branchinecta ferox (Milne-Edwards) (Crustacea: Anostraca)

Functional ontogenetic changes in <i>Branchinecta ferox</i> (Milne-Edwards) (Crustacea: Anostraca)

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.

Genetically displaced sensory neurons in the head of Drosophila project via different pathways into the same specific brain regions

The sensory projection pattern of homoeotic antennal or leg tissue in the proboscis of the mutant proboscipedia in Drosophila melanogaster was studied using orthograde diffusion of cobalt chloride. Both kinds of ectopic nerve fibers terminate in the normal center of the proboscis and in the antennal glomerulus of the brain. These centers are attained by axons which may pass via four different peripheral nerves. In contrast, wild-type proboscis fibers use only one pathway. Depending on the site of entrance into the brain, homoeotic axons may project into the proboscis center first, and then into the antennal glomerulus, or vice versa. Consequently, the tract between these two brain regions may be followed in opposite directions. Ectopic leg axons extending into normal leg centers in the thoracic ganglion have not been found. Projection patterns in proboscipedia are discussed together with those of the leg-like antenna in spineless-aristapedia ( R. F. Stocker and P. A. Lawrene, 1981, Dev. Biol. 82, 224–237). The fact that displaced antennal and leg neurons project specifically into normal proboscis and antennal centers may reflect the serial homology of antennal, leg, and proboscis neurons, and similar homology of the corresponding centers.

The nervous system of the Glossiphoniid leechHaementeria ghilianii

Synaptic pathways linking sensory neurons, interneurons and motoneurons participating in local bending and whole-body shortening reflexes inHaementeria ghilianii were found to be generally similar in both connectivity pattern and physiology to those ofHirudo medicinalis, although some difference in detail was observed. In both species the local bending reflex is accounted for in part by direct connections from the mechanosensory neurons to the segmental body wall shortening motoneuron cell L: rectifying electrical synapses from cells T, P and N and excitatory chemical synapses from cells P and N. Moreover, in both species the whole-body shortening reflex involves the giant intersegmental nerve fiber formed by longitudinal articulation of the axon of serial homologs of interneuron S; it is excited by T, P and N mechanosensory neurons and in turn excites cell L along the whole body. However, impulses evoked in cell S by intracellular stimulation reliably elicit whole-body shortening only inHaementeria, and not inHirudo. Thus theHaementeria cell S, but not theHirudo cell S, may be considered a putative command neuron, although both may play a similar role in the control of whole-body shortening. This neural difference in the cell S circuitry may account for the difference in behavioral response ofHirudo andHaementeria to sensory stimuli that excite cell S. And, in contrast to its homolog inHirudo, the Retzius cell ofHaementeria was found to elicit inhibitory junctional potentials in longitudinal muscle fibers. The pathway of Retzius cell-mediated inhibition appears to be indirect, passing via inhibitory motoneurons.

A model for the genetic control of differential adhesion in insect epidermis

Adhesive relations among cells are believed to play a major role in determining patterns of serial homology, of intercalary regeneration, and of neuronal connectivity. Models for the genetic control of adhesion during development can provide a framework for further analysis of these phenomena. Investigators studying development of Drosophila have proposed that differentiation of segments and of imaginal discs is controlled by a set of bistable “selector genes”. In each region the settings of the selector genes form a binary “word” which determines the properties of cells in the region, including their adhesiveness. I have made an explicit proposal for the relation between binary words and adhesiveness, by assuming that active selector genes repress synthesis of “adhesor” macromolecules, which promote adhesion. This hypothesis correctly predicts the relative cohesiveness of cells in four pupal tissues of the moth Manduca. Works of cohesion and adhesion among the four cell types are deduced from published results of grafting experiments by modelling insect epidermis as a viscoelastic fluid. Further comparisons between deductions from the genetic and fluid models suggest that selector genes, or the adhesor molecules they regulate, interact within single cells in determining adhesiveness between cells. From a specific version of the genetic model I deduce that pairwise interactions between selector genes or adhesor molecules can determine many, though not all, of the relative works of adhesion between unlike cells in Manduca. The genetic and fluid models thus provide a set of working hypotheses for predicting patterns of intercellular adhesion in insect epidermis and for analyzing results of experiments designed to test such predictions.

Lack of specific neurons in the ventral nerve cord for the control of prothoracic glands

There is a distinct serial homology in the distribution of afferent neurons in different ventral ganglia of wax moth larvae. No neurons specific to the thoracic ganglia which innervate the prothoracic glands were found. 2 peptidergic cells in the suboesophageal and 4 such cells in the prothoracic ganglion probably send axons to the glands, but seem to release their secretion also at other sites. Specific control of prothoracic glands is possible providing that liberation of neurohormones is regulated at the axonal level.

The structure and function of serially homologous leg motor neurons in the locust. I. Anatomy.

Twenty-one prothoracic and 17 mesothoracic motor neurons innervating leg muscles have been identified physiologically and subsequently injected with dye from a microelectrode. A tract containing the primary neurites of motor neurons innervating the retractor unquis, levator and depressor tarsus, flexor tibiae, and reductor femora is described. All motor neurons studied have regions in which their dendritic branches overlap with those of other leg motor neurons. Identified, serially homologous motor neurons in the three thoracic ganglia were found to have: (1) cell bodies at similar locations and morphologically similar primary neurites (e.g., flexor tibiae motor neurons), (2) cell bodies at different locations in each ganglion and morphologically different primary neurites in each ganglion (e.g., fast retractor unguis motor neurons), or (3) cell bodies at similar locations and morphologically similar primary neurites but with a functional switch in one ganglion relative to the function of the neurons in the other two ganglia. As an example of the latter, the morphology of the metathoracic slow extensor tibiae (SETi) motor neurons was similar to that of pro- and mesothoracic fast extensor tibiae (FETi) motor neurons. Similarly the metathoracic FETi bears a striking resemblance to the pro- and the mesothoracic SETi. It is proposed that in the metathoracic ganglion the two extensor tibiae motor neurons have switched functions while retaining similar morphologies relative to the structure and function of their pro- and mesothoracic serial homologues.

Fish and amphibian auditory neuroanatomy

Morphological variation in the primary projections of the inner ear and acousticolateralis variation in agnathans, chondrichthians, bony fishes, and amphibians is reviewed and used to examine several hypotheses concerning auditory evolution in anamniotes. The acousticolateralis hypothesis regarding the origin of the inner ear is rejected on the basis that all vertebrates, including the earliest fossil agnathans, possess both lateralis and labyrinth systems. Embryonic evidence regarding development of the labyrinth, lateralis, and other special sense organs suggests they are serial homologues sharing a common neural crest-placodal origin, and that all special senses are equally old phylogenetically. The labyrinth hypothesis of the origin of audition can not be rejected or accepted, as there is insufficient evidence regarding the phylogenetic distribution of audition in anamniotes. The hypothesis that audition arose by the invasion and replacement of lateralis fibers by acoustic afferents in the acousticolateralis medullar centers is rejected, based on new experimental evidence that these systems in fishes maintain primarily separate central pathways. Finally, the acousticolateralis area of Latimeria is discussed and compared with that of amphibians.

The morphology of the mammalian cervical pleurapophysis

Current osteological literature manifests an unacceptable lack of uniformity in the topographical definition of the mammalian cervical pleurapophysis. Definitions advanced are inadequate or erroneous or even mutually contradictory. A new and corrective definition of the cervical pleurapophysis is therefore propounded satisfactory to the phylogenetic and morphological requirement of vertebral serial homology.

The structure of tonic flexor motoneurons in crayfish abdominal ganglia

1. The tonic flexor motoneurons were filled with cobalt dye via the cut ends of their axons. All six physiologically defined cells were identified anatomically (Figs. 2–4). 2. The cell somata are widely scattered in the ventral rind of the ganglia; three cells have ipsilateral and three cells have contralateral somata in reference to their axons; cells with contralateral somata tend to be more rostral in the ganglion (Figs. 2, 11). 3. All cells have bilateral dendritic domains (Figs. 5, 6, 8, 10). Each soma is connected to a long, thin neurite which travels dorsally and enlarges into a thick process (neuropilar segment) that crosses the midline in the posterior outer commissure (Figs. 8, 9) except for fl, which crosses anteriorly (Fig. 10). Many branches emerge from the neuropilar segment; the proximal portions of these branches and the neuropilar segment contribute to the coarse dorsal neuropile. Distal branches are found in the fine ventral neuropile (Figs. 9, 10). No recurrent collaterals were observed. 4. Most of the neuropilar segments converge into a narrow arc that sweeps across the dorsal neuropile (Figs. 8, 9). The close correspondence of the processes, especially of contralateral homologues (Figs. 10, 12) provides an anatomical basis for functional interactions among the tonic flexors. The main masses of finer processes that run along the longitudinal axis are located laterally. 5. Bilateral, serial and interanimal homologies of soma position all showed similar degrees of variation. Positions were relatively constant but might vary by up to 100 μ relative to external landmarks (Fig. 11). 6. Dendritic geometries were sufficiently similar to permit unambiguous identification of homologues, but variability in the number and shape of branches is common.

On the rami intermedii of the spinal nerves and their equivalent offshoots. A contribution to classification of the trunk muscles.

Distribution patterns of the nerves of supply to the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum were carefully studied in nine body-halves of male human cadavers. Any of these muscles lie wegded in between the commencements of the dorsal and ventral primary rami of the spinal nerves. In the great majority of the cases the levatores costarum breves derived their nerve supply in the upper segments from both primary rami of the corresponding spinal nerves and in the lowest segments as the rami intermedii from the bifurcation of each spinal nerve into its primary rami. Both patterns of the nerve supply to the levatores costarum breves were turned into one another in the intervening segments. The intertransversarii posteriores cervicis of similar location to the levatores costarum breves in the thoracic region were regarded as the upper serial homologues of these muscles, because they were supplied by both primary rami of the spinal nerves, similarly the intertransversarii laterales lumborum, principally supplied by the rami intermedii of the spinal nerves, as the lower serial homologues of the same muscles.

Electrophysiology and anatomy of the large neuron pairs in the subesophageal ganglion of the leech

1. 1. The functional and structural characteristics of the large neuron pairs located within each of the four subganglia which comprise the subesophageal ganglion of the horse leech, Haemopis marmorata (Say), were investigated by intracellular recording and iontophoretic injection of the fluorescent dye, Procion Yellow. 2. 2. The large paired neurons of the three posterior subganglia are very similar to Retzius cell pairs in segmental ganglia: they are coupled by a bidirectional electrotonic junction and send their axons into their ipsilateral roots. 3. 3. The pair of large neurons in the anterior subganglion have decussating axons which enter their contralateral neuropiles, but lack both electrotonic interconnections and peripheral axons. 4. 4. The four large neuron pairs are probably serial homologues to Retzius cells and the anterior pair appears to have lost the peripheral function of Retzius cells—the control of mucus release by the skin.

Specific re-innervation of limbs transplanted between segments in the cockroach, Periplaneta americana.

ABSTRACT The connexions of single, identified motor neurons have been studied in the thoracic ganglia of the cockroach, Periplaneta americana. Selected cell bodies were identified on purely morphological criteria from one animal to another. Similarly, serially homologous cell bodies were identified from one ganglion to another. Their connexions to particular limb muscles were demonstrated by intracellular stimulation through the cell body and subsequent marking with procion yellow dye. Serially homologous cell bodies in the mesothoracic and metathoracic ganglia innervate serially homologous muscles in the mesothoracic and metathoracic limbs. Metathoracic limbs transplanted to the mesothoracic segment retain their metathoracic characteristics. They become functionally incorporated in the mesothoracic segment and are used normally during walking movements. These transplanted metathoracic limbs become re-innervated from the mesothoracic ganglion. Identified mesothoracic cell bodies make specific connexions with those metathoracic muscles which are the serial homologues of their own muscles.

Innervation Patterns of Fast and Slow Muscle in the Uropods of Crayfish

ABSTRACT The innervation of 18 uropod and telson muscles in the crayfish has been studied in varying detail. Some muscles display purely phasic properties (short sarcomeres, electrically excitable membrane responses); others are strictly tonic (long sarcomeres, junctional potentials only, spontaneously active motor neurones); a few are mixed, but with anatomical segregation of fibre types. At least 55 efferent neurones are employed to operate these muscles. The tonic muscles all receive peripheral inhibition, and a given inhibitory axon serves only a single tonic muscle. Inhibitory and excitatory axons serving a given muscle discharge reciprocally and often respond to different reflex inputs. The average number of excitatory axons innervating tonic muscles is 2-3. The phasic muscles differ in the richness of excitatory innervation. Some receive as many as five axons per muscle, and as many as four per fibre; others are innervated by only a single motor axon. Many lack inhibitory innervation; where present, peripheral inhibitors may be shared between different phasic muscles. In no case were excitatory axons found to innervate anatomically separate muscles. In ‘mixed’ muscles there is predominantly separate innervation of phasic and tonic fibres; but in at least one case axons were found to serve fibres of both types. The shared axon was phasic in character. Some of the uropod and telson muscles are clearly homologous with axial muscles in more anterior abdominal segments. In a few of the former it was possible to make direct comparisons with the efferent neurones innervating their serial homologues. Differences were found in the size ratios of homologous axons, in their central location, and in their presence or absence.

THE STRUCTURE OF THE FUNCTIONAL PRONEPHROS IN LARVAE OF AMBYSTOMA OPACUM AS STUDIED BY LIGHT AND ELECTRON MICROSCOPY.

AbstractThe functional pronephros in early larvae of Ambystoma opacum, studied in serial sections, consists of an anterior and posterior nephrostome, respective proximal tubules which fuse into a common proximal tubule, a ciliated intermediate segment, and a distal tubule, which leaves the pronephros posteriorly as the nephric duct. In the coelom medial to each pronephros is a glomus, arising from the dorsal aorta.In electron micrographs of osmium‐fixed, methacrylate‐embedded pronephros and glomus, the fine structure generally resembles that seen in adult kidneys. Proximal tubule cells show a brush border of irregular microvilli, tubular invaginations, resorption granules, and very few basal infoldings. Cells of the distal tubule have numerous radially‐oriented mitochondria, and the basal infoldings are generally well developed. The fine structure of the nephric duct seems to resemble that of the distal tubule. Cells of the nephrostomes and intermediate segment bear cilia of usual fine structure, and contain melanin granules, lipid droplets and slender mitochondria. The glomus resembles a glomerulus in having an endothelium with sparse pores, a basement membrane, and epithelial cells with numerous interdigitating foot processes.The similarity at the fine structure level between the pronephros and the more posterior mesonephros and metanephros of adult vertebrates suggests the serial homology of vertebrate nephrons, and thus constitutes further evidence for the archinephros or holonephros theory of the origin of vertebrate kidneys.

Pupae of the Genus Culiseta Felt. I. The Homology of Larval and Pupal Setae (Diptera: Culicidae)

Nerves connecting larval and pupal setae of prepupal mosquitoes were used to establish the homologies of the abdominal setae. Both larval and pupal setal patterns were then utilized to deduce serial (segment to segment) homologies. The chaetotactic system proposed is based on previous ones but contains several modifications suggested by the present work. The studies described were clone with prepupae of Culiseta inornata (Williston), Culex pipiens quinquefasciatus Say and Psorophora confinnis (Lynch Arribalzaga).

THE EVOLUTION OF ARTHROPODAN LOCOMOTORY MECHANISMS. PART 71. FUNCTIONAL REQUIREMENTS AND BODY DESIGN IN COLOBOGNATHA (DIPLOPODA), TOGETHER WITH A COMPARATIVE ACCOUNT OF DIPLOPOD BURROWING TECHNIQUES, TRUNK MUSCULATURE AND SEGMENTATION

THE EVOLUTION OF ARTHROPODAN LOCOMOTORY MECHANISMS. PART 71. FUNCTIONAL REQUIREMENTS AND BODY DESIGN IN COLOBOGNATHA (DIPLOPODA), TOGETHER WITH A COMPARATIVE ACCOUNT OF DIPLOPOD BURROWING TECHNIQUES, TRUNK MUSCULATURE AND SEGMENTATION

Serial homologies among three pairs of abdominal appendages of certain male crayfishes (Decapoda, Astacidae)

Serial homologies among three pairs of abdominal appendages of certain male crayfishes (Decapoda, Astacidae)