The innervation of the pyloric region of the crab,Cancer borealis: Homologous muscles in decapod species are differently innervated

Summary The muscles of the pyloric region of the stomach of the crab,Cancer borealis, are innervated by motorneurons found in the stomatogastric ganglion (STG). Electrophysiological recording and stimulating techniques were used to study the detailed pattern of innervation of the pyloric region muscles. Although there are two Pyloric Dilator (PD) motorneurons in lobsters, previous work reported four PD motorneurons in the crab STG (Dando et al. 1974; Hermann 1979a, b). We now find that only two of the crab PD neurons innervate muscles homologous to those innervated by the PD neurons in the lobster,Panulirus interrruptus. The remaining two PD neurons innervate muscles that are innervated by pyloric (PY) neurons inP. interruptus. The innervation patterns of the Lateral Pyloric (LP), Ventricular Dilator (VD), Inferior Cardiac (IC), and PY neurons were also determined and compared with those previously reported in lobsters. Responses of the muscles of the pyloric region to the neurotransmitters, acetylcholine (ACh) and glutamate, were determined by application of exogenous cholinergic agonists and glutamate. The effect of the cholinergic antagonist, curare, on the amplitude of the excitatory junctional potentials (EJPs) evoked by stimulation of the pyloric motor nerves was measured. These experiments suggest that the differences in innervation pattern of the pyloric muscles seen in crab and lobsters are also associated with a change in the neurotransmitter active on these muscles. Possible implications of these findings for phylogenetic relations of decapod crustaceans and for the evolution of neural circuits are discussed.Abbreviations ACh acetylcholine - Carb carbamylcholine - cpv muscles of the cardio-pyloric valve - cpv7n nerve innervating muscle cpv7 - cv muscles of the ventral cardiac ossicles - cv1n nerve innervating muscle cvl - cv2n nerve innervating muscle cv2 - EJP excitatory junctional potential - IC inferior cardiac neuron - IV inferior ventricular neuron - IVN inferior ventricular nerve - LP lateral pyloric neuron - LPG lateral posterior gastric neuron - lvn lateral ventricular nerve - mvn medial ventricular nerve - p muscles of the pylorus - PD pyloric dilator neuron - PD _in intrinsic PD neuron - PD _ex extrinsic PD neuron - pdn pyloric dilator nerve - PY pyloric neuron - pyn pyloric nerve - STG stomatogastric ganglion - VD ventricular dilator neuron     

Neural mechanisms underlying behavior in the locust Schistocerca gregaria I. Physiology of identified motorneurons in the metathoracic ganglion

A preparation of the desert locust, Schistocera gregaria, has been developed, in which it was possible to work with identified neurons while still allowing some behavior. A total of 26 motorneurons to the hind leg were studied singly, and in various pairs, both by direct stimulation, and by recording during spontaneous activity and various reflex actions. Motorneurons were identified by passing current into their somata and correlating the evoked somata spikes with extracellularly or intracellularly recorded events in the muscles. Tension of the muscle was also recorded and motor axons were stimulated to evoke antidromic spikes in the somata. Both epsp's and ipsp's can be seen clearly in recordings from the somata; spikes appear as electrotonically conducted remnants only. Somata exhibited little or no electrogenesis. It is inferred that impulses are initiated in a zone tentatively identified with the region of emergence of the motor axon from the neuropil. Integration occurs in the neuropilar segment, with the soma serving as a parallel RC element. Data was obtained on the central mechanisms of coordination of synergistic and antagonistic motorneurons and on the modes of excitation of slow and fast neurons to the same muscles.     

Independent suboesophageal neuronal innervation of the defense gland and longitudinal muscles in the stick insect (Peruphasma schultei) prothorax

This study investigates the neuroanatomy of the defense gland and a related muscle in the stick insect Peruphasma schultei with axonal tracing and histological sections. The gland is innervated by three neurons through the Nervus anterior of the suboesophageal ganglion (SOG), the ipsilateral neuron (ILN), the contralateral neuron (CLN) and the prothoracic intersegmental neuron (PIN). The ILN has a large soma which is typical for motoneurons that cause fast contraction of large muscles and its dendrites are located in motor-sensory and sensory neuropile areas of the SOG. The CLN might be involved in the coordination of bilateral or unilateral discharge as its neurites are closely associated to the ILN of the contralateral gland. Close to the ejaculatory duct of the gland lies a dorsal longitudinal neck muscle, musculus pronoto-occipitalis (Idlm2), which is likely indirectly involved in gland discharge by controlling neck movements and, therefore, the direction of discharge. This muscle is innervated by three ventral median neurons (VMN). Thus, three neuron types (ILN, CLN, and PIN) innervate the gland muscle directly, and the VMNs could aid secretion indirectly. The cytoanatomy of motorneurons innervating the defense gland and neck muscle are discussed regarding the structure and functions of the neuropile in the SOG. As a basis for the neuroanatomical study on the defense gland we assembled a map of the SOG in Phasmatodea.     

Crustacean cardioactive peptide in the nervous system of the locust,Locusta migratoria: an immunocytochemical study on the ventral nerve cord and peripheral innervation

Summary Crustacean cardioactive peptide-immunoreactive neurons occur in the entire central nervous system of Locusta migratoria. The present paper focuses on mapping studies in the ventral nerve cord and on peripheral projection sites. Two types of contralaterally projecting neurons occur in all neuromers from the subesophageal to the seventh abdominal ganglia. One type forms terminals at the surface of the thoracic nerves 6 and 1, the distal perisympathetic organs, the lateral heart nerves, and on ventral and dorsal diaphragm muscles. Two large neurons in the anterior part and several neurons of a different type in the posterior part of the terminal ganglion project into the last tergal nerves. In the abdominal neuromers 1–7, two types of ipsilaterally projecting neurons occur, one of which gives rise to neurosecretory terminals in the distal perisympathetic organs, in peripheral areas of the transverse, stigmata and lateral heart nerves. Four subesophageal neurons have putative terminals in the neurilemma of the nervus corporis allati II, and in the corpora allata and cardiaca. In addition, several immunoreactive putative interneurons and other neurons were mapped in the ventral nerve cord. A new in situ whole-mount technique was essential for elucidation of the peripheral pathways and targets of the identified neurons, which suggest a role of the peptide in the control of heartbeat, abdominal ventilatory and visceral muscle activity.Abbreviations AG abdominal ganglia - AM alary muscle - AMN alary muscle nerve - CA corpus allatum - CC corpus cardiacum - dPSO distal perisympathetic organ - LHN lateral heart nerve - LT CCAP-immunoreactive lateral tract - NCA nervus corporis allati - NCC nervus corporis cardiaci - NM neuromer - PMN paramedian nerve - PSO perisympathetic organ - SOG subesophageal ganglion - VDM ventral diaphragm muscles - VNC ventral nerve cord     

Anatomy of neurons crossing the tritocerebral commissures of the cockroach Periplaneta americana (Blattaria)

The neuronal connections of the tritocerebral commissures of Periplaneta americana were studied in the brain-suboesophageal ganglion complex and the stomatogastric nervous system by means of heavy metal iontophoresis through cut nerve ends followed by silver intensification. The tritocerebral commissure 1 (Tc1) contains mainly the processes of the subpharyngeal nerve (Spn) whose neurons are located in both tritocerebral lobes and in the frontal ganglion. Some neurons of the frontal ganglion project through the Tc1 to the contralateral tritocerebrum. A few fibers in this commissure were observed projecting to the protocerebrum and the suboesophageal ganglion. There are tritocerebral neurons which pass through the Tc1 or the tritocerebral commissure 2 (Tc2) and extend on into the stomatogastric nervous system. One axon of a descending gaint neuron appears in the Tc2. This neuron lies in the tritocerebrum and connects the brain to the contralateral side of the ventral nerve cord. In addition, sensory fibers of the labral nerve (Ln) traverse both commissures to the opposite tritocerebrum. The anatomical and physiological relevance of the identified neuronal pathways is discussed. © 1995 Wiley-Liss, Inc.     

The central morphology of the giant interneurons and their spatial relationship with the thoracic motorneurons in the cockroach, Periplaneta americana (Insecta)

Three groups of giant fibers are found in the cockroach ventral nerve cord. A latero-dorsal group (dorsal GIs), a latero-ventral group (ventral GIs) and a medio-ventral group. The morphology of all three groups of fibers within the thoracic ganglia is described. The morphology of the dorsal and ventral GI pathways in the abdominal and suboesophageal ganglia is also described. The projection patterns of the neurons in each ganglion are remarkably similar which suggests a common function. When motorneurons 5rl (depressor) and 6Br4 (levator) are stained simultaneously with the dorsal and ventral GI groups, some branches from both motor and giant neurons converge. The branching of the remaining medio-ventral group of fibers and their proximity to areas receiving motorneuronal input suggests that these are the small diameter axons described by Dagan and Parnas (1970).     

Constancies in the neuronal architecture of the suboesophageal ganglion at metamorphosis in the beetleTenebrio molitor L.

Summary Topological organization of identified neurons has been characterized for the larval, pupal and imaginal suboeosphageal neuropil of the meal-worm beetleTenebrio molitor. Neuronal fate mapping allows identification of individually persisting neurons in the metamorphosing suboesophageal ganglion ofTenebrio. Analysis was performed on interneurons characterized by serotonin and CCAP (crustacean cardioactive peptide) immunohistochemistry, on motoneurons that innervate the dorsal and ventral longitudinal muscles, and on suboesophageal descending neurons. All these different populations of neurons show topologically invariant features throughout metamorphosis. Motoneurons, interneurons, and descending suboesophageal neurons of the imaginal suboeosphageal ganglion embody individually persisting larval interneurons. Impacts for a functional interpretation of the neuronal architecture of the suboesophageal ganglion are discussed.     

Neural expression of hikaru genki protein during embryonic and larval development of Drosophila melanogaster

 Hikaru genki (HIG) is a putative secreted protein of Drosophila that belongs to immunoglobulin and complement-binding protein superfamilies. Previous studies reported that, during pupal and adult stages, HIG protein is synthesized in subsets of neurons and appears to be secreted to the synaptic clefts of neuron-neuron synapses in the central nervous system (CNS). Here we report the analyses of distribution patterns of HIG protein at embryonic and larval stages. In embryos, HIG was mainly observed in subsets of neurons of the CNS that include pCC interneurons and RP5 motorneurons. At third instar larval stage, this protein was detected in a limited number of cells in the brain and ventral nerve cord. Among them are the motorneurons that extend their axons to make neuromuscular junctions on body wall muscle 8. Immunoelectron microscopy showed that these axonal processes as well as the neuromuscular terminals contain numerous vesicles with HIG staining, suggesting that HIG is in a pathway of secretion at this stage. Some neurosecretory cells were also found to express this protein. These data suggest that HIG functions in the nervous system through most developmental stages and may serve as a secreted signalling molecule to modulate the property of synapses or the physiology of the postsynaptic cells. Received: 28 May 1998 / Accepted: 4 August 1998     

Neuronal activity recorded extracellularly in chronically decentralized in situ canine middle cervical ganglia

In chronically decentralized in situ middle cervical ganglia of 10 dogs, 279 spontaneously active neurons were identified. One hundred and ten (39%) of these were spontaneously active during specific phases of the cardiac cycle, primarily during systole, and the activity of nearly half of these cardiovascular-related neurons was modified by gentle mechanical distortion of the vena cavae, heart, or thoracic aorta. Another 60 (22%) of the identified neurons had respiratory--related activity, but the activity of only 2 of them was modified by gentle mechanical distortion of pulmonary tissue. Twenty-nine of the other 109 identified neurons were activated by gentle mechanical distortion of localized regions of the neck, ventral thoracic wall, or ventral abdominal wall. Because of the presence of activity in the chronically decentralized middle cervical ganglion, these data infer that some afferent neurons are located in the thoracic autonomic nervous system. Some middle cervical ganglion neurons were activated by single 1-4 ms stimuli delivered to a nerve connected to the ganglion. During repetitive stimuli delivered at 0.5 Hz none were activated after a fixed latency following the stimuli. Many more neurons were activated by 10- to 200-ms trains of 1-4 ms stimuli delivered with interstimulus intervals of 1-10 ms. The majority of these neurons could still be activated electrically after the administration of cholinergic and adrenergic pharmacological blocking agents.(ABSTRACT TRUNCATED AT 250 WORDS)     

even-skipped determines the dorsal growth of motor axons in Drosophila

Axon pathfinding and target choice are governed by cell type-specific responses to external cues. Here, we show that in the Drosophila embryo, motorneurons with targets in the dorsal muscle field express the homeobox gene even-skipped and that this expression is necessary and sufficient to direct motor axons into the dorsal muscle field. Previously, it was shown that motorneurons projecting to ventral targets express the LIM homeobox gene islet, which is sufficient to direct axons to the ventral muscle field. Thus, even-skipped complements the function of islet, and together these two genes constitute a bimodal switch regulating axonal growth and directing motor axons to ventral or to dorsal regions of the muscle field.     

Temporal correlation between neuronal tail ganglion activity and locomotion in the leech,Hirudo medicinalis

Intracellular and extracellular recordings were performed in the posterior ventral nerve cord of restrained crawling preparations of the medicinal leech,Hirudo medicinalis. Short-latency neuronal activities in the tail ganglion nerves correlated with different phases of crawling behavior. Eight neurons with characteristic activation patterns during crawling were identified morphologically and physiologically in the tail ganglia of 23 preparations. The axons of four of these neurons projected through posterior tail brain nerves; four ascending interneurons had projections in the connectives or in Faivre's nerve. These interneurons are suitable candidates for carrying information between the front end and the tail end of the animal to coordinate the behavioral components during a crawling step.     

Somatotopic localization of the eye muscle afferents in the semilunar ganglion.

In the medial dorsolateral portion of the semilunar ganglion of curarized and anaesthetized lambs a cellular pool has been identified which contains the perikarya of the first-order neurons of the eye muscle proprioception. Responses to moderate manual stretch of individual eye muscles were recorded by means of tungsten microelectrodes, from single units of the ganglion. They were of the type induced by muscle spindle excitation. Such responses showed a somatotopic localization. The superior rectus and the superior oblique muscles were represented in the most dorsal layers of the ganglion, while the inferior rectus and the inferior oblique muscles projected on the most ventral portion of the pool. The medial and the lateral recti were represented in the medial and lateral parts and occasionally wedged themselves between the cells innervating the superior and the inferior muscles. Thus a somatotopic arrangement of the eye muscle proprioception has been demonstrated for the first time in the semilunar ganglion.     

The vasopressin-like immunoreactive (VPLI) neurons of the locust,Locusta migratoria. I. Anatomy

Summary Antiserum to arginine-vasopressin has been used to characterise the pair of vasopressin-like immunoreactive (VPLI) neurons in the locust. These neurons have cell bodies in the suboesophageal ganglion, each with a bifurcating dorsal lateral axon which gives rise to predominantly dorsal neuropilar branching in every ganglion of the ventral nerve cord. There are extensive beaded fibre plexuses in most peripheral nerves of thoracic and abdominal ganglia, but in the brain, the peripheral plexuses are reduced while neuropilar branching is more extensive, although it generally remains superficial. An array of fibres runs centripetally through the laminamedulla chiasma in the optic lobes. Lucifer Yellow or cobalt intracellular staining of single VPLI cells in the adult suboesophageal ganglion shows that all immunoreactive processes emanate from these two neurons, but an additional midline arborisation (that was only partially revealed by immunostaining) was also observed. Intracellularly staining VPLI cells in smaller larval instars, which permits dye to reach the thoracic ganglia, confirms that there is no similar region of poorly-immunoreactive midline arborisation in these ganglia. It has been previously suggested that the immunoreactive superficial fibres and peripheral plexuses in ventral cord ganglia serve a neurohaemal function, releasing the locust vasopressin-like diuretic hormone, F₂. We suggest that the other major region of VPLI arborisation, the poorly immunoreactive midline fibres in the suboesophageal ganglion, could be a region where VPLI cells receive synaptic input. The function of the centripetal array of fibres within the optic lobe is still unclear.Abbreviations AVP arginine vasopressin - DIT dorsal intermediate tract - FLRF Phe-Leu-Arg-Phe - FMRF-amide Phe-Met-Arg-Phe-amide - LDT lateral dorsal tract - LVP lysine vasopressin - MDT median dorsal tract - MVT median ventral tract - SEM scanning electron microscopy - SOG suboesophageal ganglion - VIT ventral intermediate tract - VNC ventral nerve cord - VPLI vasopressin-like immunoreactive     

Time-related changes in the labeling pattern of motor and sensory neurons innervating the gastrocnemius muscle,as revealed by the retrograde transport of the cholera toxin B subunit

Summary Morphological changes in the motor and sensory neurons in the lumbar spinal cord and the dorsal root ganglia were investigated at different survival times following the injection of the B subunit of cholera toxin (CTB) into the medial gastrocnemius muscle. Unconjugated CTB, visualized immunohistochemically, was found to be retrogradely transported through ventral and dorsal roots to motor neurons in the anterior horn, each lamina in the posterior horn, and ganglion cells in the dorsal root ganglia at L₃–L₆. The largest numbers of labeled motor neurons and ganglion cells were observed 72 h after the injection of CTB. Thereafter, labeled ganglion cells were significantly decreased in number, whereas the amount of labeled motor neurons showed a slight reduction. Motor neurons had extensive dendritic trees filled with CTB, reaching lamina VII and even the pia mater of the lateral funiculus. Labeling was also seen in the posterior horn, but the central and medial parts of laminae II and III had the most extensively labeled varicose fibers, the origin of which was the dorsal root ganglion cells. The results indicate that CTB is taken up by nerve terminals and can serve as a sensitive retrogradely transported marker for identifying neurons that innervate a specific muscle.     

Transplantation of neurons reveals processing areas and rules for synaptic connectivity in the cricket nervous system

In order to assess the nature of spatial cues in determining the characteristic projection sites of sensory neurons in the CNS, we have transplanted sensory neurons of the cricket Acheta domesticus to ectopic locations. Thoracic campaniform sensilla (CS) function as proprioceptors and project to an intermediate layer of neuropil in thoracic ganglia while cercal CS transduce tactile information and project into a ventral layer in the terminal abdominal ganglion (TAG). When transplanted to ectopic locations, these afferents retain their modality-specific projection in the host ganglion and terminate in the layer of neuropil homologous to that of their ganglion of origin. Thus, thoracic CS neurons project to intermediate neuropil when transplanted to the abdomen and cercal CS neurons project to a ventral layer of neuropil when transplanted to the thorax. We conclude that CS can be separated into two classes based on their characteristic axonal projections within each segmental ganglion. We also found that the sensory neurons innervating tactile hairs project to ventral neuropil in any ganglion they encounter after transplantation. Ectopic sensory neurons can form functional synaptic connections with identified interneurons located within the host ganglia. The new contacts formed by these ectopic sensory neurons can be with normal targets, which arborize within the same layer of neuropil in each segmental ganglion, or with novel targets, which lack dendrites in the normal ganglion and are thus normally unavailable for synaptogenesis. These observations suggest that a limited set of molecular markers are utilized for cell–cell recognition in each segmentally homologous ganglion. Regenerating sensory neurons can recognize novel postsynaptic neurons if they have dendrites in the appropriate layer of neuropil. We suggest that spatial constraints produced by the segmentation and the modality-specific layering of the nervous system have a pivotal role in determining synaptic specificity. © 1993 John Wiley & Sons, Inc.     

Intramural neurons in the urinary bladder of the guinea-pig

Summary The urinary bladder of adult female guinea-pigs was stained histochemically to detect the presence of intramural ganglion neurons. Counts on wholemount preparations of entire bladders revealed the presence of 2000–2500 neurons per bladder, either as individual nerve cells or, more often, as ganglia containing up to 40 neurons. Both ganglia and single neurons lie along nerve trunks and are interconnected to form a plexus. Ganglia occur in every part of the bladder; they are more numerous on the dorsal than on the ventral wall, and they are especially abundant in an area within a radius of 800 m from the point of entry into the bladder wall of ureters and urinary arteries. The ganglia are located inside the muscle coat and close to muscle bundles; they usually lie nearer the mucosa than the serosa. Ultrastructurally, each ganglion is surrounded by a capsule; in addition to neurons and glial cells, the ganglia contain capillaries, collagen fibrils and fibroblasts; ganglion neurons are individually wrapped by glial cells and are separated from one another by connective tissue.     

Brain cells that command sexual behavior in the snail Helix aspersa

Evidence is presented indicating that the mesocerebrum of the terrestrial snail, Helix aspersa, has a major role in the control of sexual behavior. Morphological and physiological results demonstrate a right-sided bias in the mesocerebrum that is consistent with the fact that sexual behavior is executed almost entirely on the animal's right side. Thus, the right lobe has 23% more neurons than the left lobe, and they are 24% larger. Excitatory synaptic inputs derive predominately from neurons on the right side. The axons of right-side mesocerebral neurons go to the right pedal ganglion almost without exception, and even the axons of left-side neurons travel mostly in right-side connective nerves. Direct evidence for a role of the mesocerebrum in commanding sexual behavior comes from experiments with electrical stimulation. Extracellular stimulation of the right mesocerebrum, but not the left mesocerebrum, resulted in movements of the "love dart" sac and the penis. Intracellular stimulation of neurons in the right mesocerebrum evoked measurable movements of either the dart sac or the penis, or both, in 17% of the cells tested. The latencies ranged between 5 and 50 s. In an intact animal, these movements would cause a release of the dart and an eversion of the penis. The motor effects were mediated through the right cerebropedal connective and the pedal nerve NCPD, with the motorneurons probably situated in the right pedal ganglion.     

The oculomotor system of Daphnia magna

Summary The highly mobile cyclopic compound eye of Daphnia magna is rotated by six muscles arranged as three bilateral pairs. The three muscles on each side of the head share a common origin on the carapace and insert dorsally, laterally and ventrally on the eye. The dorsal and ventral muscles are each composed of two muscle fibers and the lateral muscle is composed of from two to five fibers, with three the most common number. Individual muscle fibers are spindle-shaped mononucleated cells with organized bundles of myofilaments. Lateral eye-muscle fibers are thinner than those of the other muscles but are otherwise similar in ultrastructure. Two motor neurons innervate each dorsal and each ventral muscle and one motor neuron innervates each lateral muscle. The cell bodies of the motor neurons are situated dorsally in the supraesophageal ganglion (SEG) and are ipsilateral to the muscles they innervate. The dendritic fields of the dorsal-muscle motor neurons are ipsilateral to their cell bodies; those of the ventral-muscle motor neurons are bilateral though predominantly contralateral. The central projections of the lateral-muscle motor neurons are unknown. In the dorsal and ventral muscles one motor axon synapses principally with one muscle fiber; in each lateral muscle the single motor axon branches to, and forms synapses with, all the fibers. The neuromuscular junctions, characterized by pre- and postsynaptic densities and clear vesicles, are similar in all the eye muscles.     

A lambda-shaped retractor lentis muscle in the yellowfin goby Acanthogobius flavimanus

We identified a morphologically uncommon piscine retractor lentis muscle in the yellowfin goby Acanthogobius flavimanus. This lentis muscle has a shape similar to the Greek small letter lambda (λ). The two legs of the muscle are attached to the retinal periphery at the ventral eyecup, while the tip is connected to the lens surface by a ligament. Scanning electron microscopy showed that the fibers of the lentis muscle run along the length of both the anterior and posterior legs. Immunolabeling with antiacetylated tubulin antibody and neuronal tracing with DiI of the whole lentis muscle revealed that the anterior leg is innervated by one or more nerves. The topographic distribution of ganglion cells in the retina was investigated to identify the visual axis. Three high cell density areas were observed in the dorso-temporal, ventro-nasals and ventro-temporal retina. These findings suggest that the λ-shaped lentis muscle may enable accommodatory movement of the lens toward the temporal as well as the nasal and/or ventral retina.