Pairs Of Nerves Research Articles

Spatial Distribution of Vestibulospinal Neurons in Frog Vestibular Nuclear Complexes

The vestibular nuclear complex (VNC) is a region with direct inputs from the VIII cranial nerve conducting impulses from the labyrinthine sensory organs. Through this pathway, the body muscular tone and equilibrium are, as well as its orientation in the threedimensional space maintained [1]. In amphibians, this region is extended along the entire rostrocaudal medulla oblongata from the cerebellum to obex [2]. Phylogenetically, amphibian vestibular nuclei are assigned to the supraspinal cell groups that are spatially separated not only from the auditory sensory system, but also from the reticular formation. Their tract fibers descending into the spinal cord constitute one of the ancient systems for suprasegmentary control [3, 4]. The spatial organization of the mammalian vestibular system has been studied in detail. Different VNC areas proved to contain vestibulospinal neurons sending their axons into different segments of the spinal cord, which suggests a distinct somatotopic arrangement of the region [1, 5]. The distribution of vestibulospinal neurons in the amphibian VNC was described in only a few reports [6, 7]; therefore, it is still an open question. We carried out electrophysiological analysis of the spatial distribution of frog vestibulospinal neurons, The neurons were identified by means of recording intracellular potentials, and the sites of their location were stained. Ninety-eight male and female adult Rana ridibunda were used. The animals were anesthetized with ether or an MS-222 solution (3-aminobenzoic acid ethyl ester, Sigma) at a dose of 2 mg/kg body weight and covered with chipped ice to cool. For immobilization, 1% solution of succinylcholine was injected intramuscularly at a dose of 2 mg/kg of body weight. The preparations of frog perfused brain [8] were stimulated with single rectangular current pulses (0.1 to 0.2 ms; 0.04 to 0.05 mA) applied through bipolar tungsten electrodes insulated to the 50 μ m tips. The electrodes were placed on the anterior branch of the ipsilateral vestibular nerve and on the cervical and lumbar enlargements of the ventral branch of the spinal cord (the II and VIII‐X pairs of the spinal nerves, respectively) to cause antidromic activation of the vestibulospinal neurons. Glass microelectrodes filled with 3 M KCl with the resistance of 10‐30 M Ω were used for intracellular recordings. The sites of recorded activity were stained with Fast Green dye introduced through the recording microelectrode [9]. After each experiment, histological sections were prepared. The results were processed on a com

Partial spectral analysis of cardiac-related sympathetic nerve discharge.

We have studied the relationship between pulse synchronous baroreceptor input (represented by the arterial pulse, AP) and the cardiac-related rhythm in sympathetic nerve discharge (SND) of urethan-anesthetized cats by using partial autospectral and partial coherence analysis. Partial autospectral analysis was used to mathematically remove the portion of SND that can be directly attributed to the AP, while partial coherence analysis was used to removed the portion of the relationship between the discharges of sympathetic nerve pairs that can be attributed to linear AP-SND relationships that are common to the nerves. The ordinary autospectrum of SND (AS(SND)) and coherence functions relating the discharges of nerve pairs (Coh(SND-SND)) contained a peak at the frequency of the heart beat. When the predominant mode of coordination between AP and SND was a phase walk, partialization of the autospectra of SND with AP (AS(SND/AP)) left considerable power in the cardiac-related band. In contrast, when the predominant mode of coordination between AP and SND was phase-locking, there was virtually no cardiac-related activity remaining in AS(SND/AP). Partialization of Coh(SND-SND) with AP reduced the peak coherence within the cardiac-related band in both modes of coordination but to a much greater extent during phase-locking. After baroreceptor denervation, Coh(SND-SND) at the cardiac frequency remained significant, although a clear peak above background coherence was no longer apparent. These results are consistent with a model in which the central circuits controlling different sympathetic nerves share baroreceptor inputs and in addition are physically interconnected. The baroreceptor-sympathetic relationship contains both linear and nonlinear components, the former reflected by phase-locking and the latter by phase walk. The residual power in AS(SND/AP) during phase walk can be attributed to the nonlinear relationship, and the residual peak in partialized nerve-to-nerve coherence (Coh(SND-SND/AP)) arises largely from nonlinearities that are common to the two nerves. During both phase walk and phase-locking, in addition to common nonlinear AP-SND relationships, coupling of the central circuits generating the nerve activities may contribute to Coh(SND-SND/AP) because significant Coh(SND-SND) was still observed following baroreceptor denervation.

Distribution and innervation of lateral line organs in the channel catfish

The lateral line system of the channel catfish is formed by mechanoreceptive neuromasts located within five pairs of cephalic and one pair of trunk canals, as well as superficial lines of neuromasts, termed accessory and/or pit lines. Five pairs of pit lines occur on the head, and three pairs of superficial lines occur on the trunk. In addition to these mechanoreceptors, which are found in most teleost fishes, catfish also possess a total of over 4000 electroreceptive ampullary organs scattered over the entire body. The lateral line receptors are innervated by five pairs of lateral line nerves whose rami are secondarily associated with facial and trigeminal fibers that innervate taste buds and the dermis of the skin, respectively. The neuromasts of the trunk canal and the ramules of the posterior lateral line nerve that innervate them seem to be organized in a segmental pattern. The same is true for the intervertebral ramules of the recurrent facial ramus, which innervate the external taste buds on the trunk. The fibers of the gustatory and lateral line systems may use the neural crest, the developing spinal nerves, or both, to establish this segmental pattern. In this context, it may not be surprising that there is an intimate relationship among each of the sensory systems in the trunk.

Coherent rhythmic discharges in sympathetic nerves supplying thermoregulatory circulations in the rat.

1. In anaesthetised rats, activity recorded from sympathetic postganglionic neurones innervating the tail circulation has characteristic rhythmicity (0.4-1.2 Hz). At the population level this rhythmicity can be seen as a peak (T-peak) in autospectra of sympathetic activity recorded from ventral collector nerves (VCNs). 2. Here we investigated whether nerves supplying thermoregulatory circulations share common rhythmic discharges at T-peak frequency. Activity was recorded from nerve pairs consisting of left ventral collector nerve (LVCN) and one of the following: right ventral collector nerve (RVCN), left dorsal collector nerve (DCN), left saphenous nerve (SN) or left renal nerve (RN). 3. During central apnoea, T-peak frequencies in RVCN autospectra were similar to those of simultaneously recorded LVCN and these activities were coherent. Similar observations were made for nerve pairs involving LVCN-DCN and LVCN-SN. In contrast, autospectra of RN activity did not contain T-peaks. 4. In comparison to the peaks in autospectra of RN activity, when the frequency of rhythmic phrenic nerve activity was manipulated T-peaks in VCN, DCN and SN autospectra did not show obligatory 1:1 locking. 5. We conclude that T-peaks are a robust feature of autospectra of sympathetic discharges supplying thermoregulatory circulation but not those influencing the kidney. The high coherence demonstrated between the T-peak discharges is consistent with the view that common/coupled oscillators located within the CNS influence cutaneous vasoconstrictor sympathetic activity.

Topographic organization of efferent neurons with different neurochemical characters in the cerebral ganglia of the snail Helix pomatia.

This study provides a description of the organization of neurons efferent to different head areas in the cerebral ganglia of Helix pomatia, revealed by simultaneous Ni-lysine and Co-lysine back-filling of different pairs of cerebral nerves. The backfills show that labeled cerebral neurons that innervate the head areas are concentrated in seven representation foci distributed in different parts of the cerebral ganglia. Almost each head area is represented in each focus. At a gross level, the representation of the different head areas in the representation foci shows a topographic arrangement. Each focus is constituted by neurochemically different groups of neurons. All head areas are innervated by serotonin-containing fibers from a single focus (Focus 2) and by dopamine-containing fibers from Foci 1, 2, and 4. However, they are innervated by CARP and FMRFamide-containing fibers from all of the foci. The combination of retrograde labeling with 5, 6-dihydroxytriptamine induced pigment labeling of serotonin-containing neurons or with fluorescence tyrosinehydroxylase immunocytochemistry to detect dopamine-containing neurons showed that the different head areas are topographycally represented in the clusters of both the serotonin- and dopamine-containing cells. The combination of Ni-lysine backfillings from different cerebral nerves with fluorescence CARP and FMRFamide immunocytochemistry revealed that the head areas are represented also in both the CARP and FMRFamide immunoreactive groups of neurons in the different foci.

Cardioacceleratory reflexes triggered by mechanoproprioceptors of the swimmerets in the stomatopod crustacean Squillaoratoria

The heart of Squilla oratoria is innervated by processes arising from the cardiac ganglion, which lies on the outer surface of the heart wall. The ganglion is regulated by one pair of cardioinhibitory nerves and two pairs of cardioacceleratory nerves. Cardiac acceleration accompanied activation of the five pairs of swimmerets in the first to the fifth abdominal segments. The cardioacceleratory nerves were activated when swimmerets beat strongly. Activation of the cardioacceleratory nerves was caused by electrical stimuli to a nerve branch extending to the swimmerets from the first nerve root of the abdominal ganglion. Bursts of afferent impulses were recorded from the nerve branch of the first nerve root corresponding to periods of protractive and retractive swimmeret movements. Afferent impulses were recorded from the nerve branch when the articular membrane was artificially boosted up. Cardiac acceleration during active swimmeret movements in Squilla is attributable to a reflexive response triggered by the movements. Putative mechanoproprioceptors on the articular membrane between the sterna and basipodite in the swimmerets may be responsible for the cardioacceleratory reflex.

Cold stress alters characteristics of sympathetic nerve discharge bursts.

Frequency-domain analyses were used to determine the effect of cold stress on the relationships between the discharge bursts of sympathetic nerve pairs, sympathetic and aortic depressor nerve pairs, and sympathetic and phrenic nerve pairs in chloralose-anesthetized, baroreceptor-innervated rats. Sympathetic nerve discharge (SND) was recorded from the renal, lumbar, splanchnic, and adrenal nerves during decreases in core body temperature from 38 to 30 degrees C. The following observations were made. 1) Hypothermia produced nonuniform changes in the level of activity in regionally selective sympathetic nerves. Specifically, cold stress increased lumbar and decreased renal SND but did not significantly change the level of activity in splanchnic and adrenal nerves. 2) The cardiac-related pattern of renal, lumbar, and splanchnic SND bursts was transformed to a low-frequency (0-2 Hz) pattern during cooling, despite the presence of pulse-synchronous activity in arterial baroreceptor afferents. 3) Peak coherence values relating the discharges between sympathetic nerve pairs decreased at the cardiac frequency but were unchanged at low frequencies (0-2 Hz), indicating that the sources of low-frequency SND bursts remain prominently coupled during progressive reductions in core body temperature. 4) Coherence of discharge bursts in phrenic and renal sympathetic nerve pairs in the 0- to 2-Hz frequency band increased during mild hypothermia (36 degrees C) but decreased during deep hypothermia (30 degrees C). We conclude that hypothermia profoundly alters the organization of neural circuits involved in regulation of sympathetic nerve outflow to selected regional circulations.

Regulation of the sympathetic nerve discharge bursting pattern during heat stress.

Frequency-domain analyses were used to determine the effect of heat stress on the relationships between the discharge bursts of sympathetic nerve pairs and sympathetic and phrenic nerve pairs in chloralose-anesthetized rats. Sympathetic nerve discharge (SND) was recorded from the renal, splanchnic, splenic, and lumbar nerves during increases in core body temperature (Tc) from 38 to 41.4 +/- 0. 3 degreesC. The following observations were made: 1) hyperthermia transformed the cardiac-related bursting pattern of SND to a pattern that contained low-frequency, non-cardiac-related bursts, 2) the pattern transformation was uniform in regionally selective sympathetic nerves, 3) hyperthermia enhanced the frequency-domain coupling between SND and phrenic nerve bursts, and 4) low-frequency SND bursts recorded during hyperthermia contained significantly more activity than cardiac-related bursts. We conclude that acute heat stress profoundly affects the organization of neural circuits responsible for the frequency components in sympathetic nerve activity and that SND pattern transformation provides an important strategy for increasing the level of activity in sympathetic nerves during increased Tc.

Early development of the peripheral nervous system in a lancelet species

The developmental pattern of the lancelet (amphioxus) peripheral nervous system from embryos to larvae has been studied by using wholemount immunostaining and transmission electron microscopy. The peripheral nerves first appeared on the anterior dorsal surface of the medulla at the middle neurula stage, when the anterior nerve cord was just closing. A single axon with a large growth cone was the progenitor of each nerve. The nerve roots adopted an asymmetric arrangement soon after. The first nerve, likely a pair of pure sensory nerves, sprouted from the anterior tip of the nerve cord. This nerve may be comparable topographically to the preoptic nerve (the posterior branch of the terminal nerve) in lungfishes. However, the neuron that first extends its axon was located in the medulla, as in the other posterior nerves. One of the extramedullary primary sensory neurons, the corpuscles of de Quatrefages, appeared in larvae with the mouth and two anterior gill pores. Their axons were seemingly fasciculated with the efferent axon of the first nerve. The second nerve, the most complex one to appear during embryonic and early larval development, innervated the preoral pit and the buccal region. The third and fourth nerves on the left side also innervated the buccal region. The larval innervation patterns in the anterior region differed from the adult organization, suggesting a segmental rearrangement of the nerve supply during development. There was no evidence to dichotomize the peripheral nerves into cranial and spinal nerves, as exist in vertebrates. These characteristics of the peripheral nervous system in the lancelet indicate that this animal has a rather derived or primitive developmental system of peripheral nerves, making the analysis of homology with vertebrates difficult. J. Comp. Neurol. 393:415–425, 1998. © 1998 Wiley-Liss, Inc.

Early development of the peripheral nervous system in a lancelet species

The developmental pattern of the lancelet (amphioxus) peripheral nervous system from embryos to larvae has been studied by using wholemount immunostaining and transmission electron microscopy. The peripheral nerves first appeared on the anterior dorsal surface of the medulla at the middle neurula stage, when the anterior nerve cord was just closing. A single axon with a large growth cone was the progenitor of each nerve. The nerve roots adopted an asymmetric arrangement soon after. The first nerve, likely a pair of pure sensory nerves, sprouted from the anterior tip of the nerve cord. This nerve may be comparable topographically to the preoptic nerve (the posterior branch of the terminal nerve) in lungfishes. However, the neuron that first extends its axon was located in the medulla, as in the other posterior nerves. One of the extramedullary primary sensory neurons, the corpuscles of de Quatrefages, appeared in larvae with the mouth and two anterior gill pores. Their axons were seemingly fasciculated with the efferent axon of the first nerve. The second nerve, the most complex one to appear during embryonic and early larval development, innervated the preoral pit and the buccal region. The third and fourth nerves on the left side also innervated the buccal region. The larval innervation patterns in the anterior region differed from the adult organization, suggesting a segmental rearrangement of the nerve supply during development. There was no evidence to dichotomize the peripheral nerves into cranial and spinal nerves, as exist in vertebrates. These characteristics of the peripheral nervous system in the lancelet indicate that this animal has a rather derived or primitive developmental system of peripheral nerves, making the analysis of homology with vertebrates difficult.

Altered frequency characteristics of sympathetic nerve activity after sustained elevation in arterial pressure.

We tested the hypothesis that sustained elevation in mean arterial pressure (MAP) alters the frequency-domain characteristics of efferent sympathetic nerve discharge (SND) after the return of MAP to control levels. Renal, lumbar, and splanchnic SND were recorded before, during, and after a 30-min increase in MAP produced by phenylephrine (PE) infusion in alpha-chloralose-anesthetized, spontaneously hypertensive (SH) rats. The following observations were made. 1) The basic cardiac-locked pattern of renal, lumbar, and splanchnic SND bursts was altered after sustained elevation in MAP, demonstrating prolonged effects on the neural circuits involved in entraining efferent SND to the cardiac cycle. Importantly, discharge bursts in afferent baroreceptor nerve activity remained pulse-synchronous after sustained increases in arterial pressure. 2) The frequency-domain relationships between the activity in sympathetic nerve pairs were altered after sustained elevation in MAP, suggesting a transformation from a system of tightly coupled neural circuits to one of multiple generators exerting selective control over SND. 3) The most prominent reduction in SND power after sustained elevation in MAP occurred in the frequency band containing the cardiac cycle, indicating that the prolonged suppression of SND after sustained increases in arterial pressure is due primarily to the selective inhibition of cardiac-related SND bursts. We conclude that sustained elevation in MAP profoundly affects the neural circuits responsible for the frequency components of basal SND in SH rats.

A novel procedure for mediastinal vagotomy inhibits neurogenic inflammation in rat bronchial tree

Tachykinin-containing sensory axons originating from the cervical vagal nerves and the first several pairs of thoracic spinal nerves are involved in neurogenic inflammation evoked by capsaicin in the bronchial tree. Unilateral degeneration of the cervical vagal trunk by surgical lesion inhibits neurogenic inflammation in the ipsilateral bronchial airways. The vagal trunk has two main branches, the thoracic vagus nerve and recurrent laryngeal nerve in the thorax. The main purpose of this study was to determine whether the thoracic vagus nerve or recurrent laryngeal nerve was significantly involved in the neural control of bronchial inflammation in the rat. A novel and safe surgical procedure was used for selectively cutting the right thoracic vagal trunk, thoracic vagus nerve, or recurrent laryngeal nerve by introducing the surgical instrument through an aperture between the first and second ribs in the ventral wall of the rostral mediastinum. This surgical operation could be completed without causing a pneumothorax. After 2 postoperative weeks, the effects of denervation on capsaicin-induced plasma extravasation in the respiratory tract were tested. Either right thoracic vagal trunk transection or thoracic vagus section significantly decreased plasma extravasation in the right bronchial tree. Thoracic vagus section was obviously more effective. Evans blue extravasation in the right lobar bronchi was reduced by 44–78% after thoracic vagal trunk transection, while that in the right mainstem and lobar bronchi was reduced by 58–81% after thoracic vagus section. Area densities of India ink-labeled leaky blood vessels in the right lobar bronchi were reduced by 40–65% after thoracic vagal trunk transection, and those in the right mainstem and lobar bronchi were reduced by 83–88% after thoracic vagus neurectomy. Recurrent laryngeal neurectomy did not change the plasma extravasation induced by capsaicin in the trachea and bronchi. These results suggest that capsaicin-sensitive fibers running in the vagal trunk, which largely mediated neurogenic inflammation in the bronchial tree, were projected into the thoracic vagus nerve which, in turn, sent these nerve fibers to the ipsilateral bronchial tree. For the trachea, the remaining sensory fibers surviving denervation might provide sufficient tachykinins to trigger neurogenic inflammation.

Evidence from motoneurone synchronization for disynaptic pathways in the control of inspiratory motoneurones in the cat.

1. Motoneurone synchronization was measured by cross-correlation between paired inspiratory discharges in external and internal intercostal nerves or their intramuscular branches (T3 to T8) or in the phrenic nerve (C5 root or both C5 and C6 roots independently) in anaesthetized, paralysed cats. 2. All cross-correlation histograms showed central peaks, for which the durations at half-amplitude (half-widths) from internal nerve pairs in adjacent segments were all less than for external nerve pairs in adjacent segments or within a segment (means, 1.6 ms vs. 3.4 ms for adjacent segments). Values for external-internal pairs covered the ranges for both these two. Lowest values came from two phrenic pairs (1.2 and 1.4 ms). 3. The peaks from ipsisegmental external-internal pairs were usually asymmetric and the maximum of the peak was often displaced to a lag of about -1 ms (external nerve providing the reference spikes), whereas peaks from external-external pairs were always symmetrical and centred on zero. Phrenic-internal peaks gave maxima with lags about 1 ms less than for phrenic-external peaks from the same segments. 4. Two explanations were considered possible for the differences in duration and timing: an extra synapse on the pathway to the external nerve motoneurones, or a correlation kernel for a monosynaptic connection to the external nerve motoneurones that had a slower time course than that for the internal or phrenic nerve motoneurones. Computer simulations, assuming the extra synapse, gave a good fit to the observed time courses of the correlation peaks for all categories of nerve pairs using single values of parameters (e.g. EPSP rise time) consistent with those in the literature. This could not be achieved with the different correlation kernel model. The timing of high-frequency oscillation (HFO), which was sometimes present in the correlations, was also better predicted with the extra synapse model. 5. It is concluded that most of the synchronization between external nerve motoneurones is derived from disynaptic common inputs and that any motoneurone synchronization peak with a half-width greater than about 2.2 ms should be assumed to be likely to contain di- or oligosynaptically derived components.

Evidence for cholinergic inhibitory and serotonergic excitatory neuromuscular transmission in the heart of the bivalve Mercenaria mercenaria

The heart of Mercenaria mercenaria is innervated bilaterally at the atria. A pair of cardiac nerves arise as a branch of the cerebro-visceral connective and run to the posterior end of the junction between each atrium and its efferent branchial vessel. Innervation evidently spreads over the heart, since both inhibitory and excitatory junctional potentials (IJPs and EJPs) can be recorded from the atria, the atrio-ventricular (AV) valve or the ventricle. The cardiac nerves contain inhibitory and excitatory axons. Neural stimulation can cause increases in the frequency or amplitude of beating, depending on the strength and frequency of stimulation. Electrical stimulation of the nerves to the incurrent and excurrent siphons causes bradycardia or tachycardia even after cutting the cerebro-visceral connective at a site anterior to the origin of the cardiac nerves. This may indicate a reflex pathway involving neurons whose cell bodies are located in the visceral ganglion. Neural depression of myocardial action potentials is mediated by discrete IJPs, which follow nerve stimuli one-to-one. IJPs can be recorded from the atria, the AV valve or the ventricle. A long-lasting hyperpolarization follows cessation of excitatory stimulation of the cardiac nerve. IJPs may be produced by cholinergic nerves and are mediated primarily by Cl-. They are blocked by Mytolon and by d-tubocurarine (dTC), but not by methylxylocholine. In low-[Cl-] solution, IJPs are inverted into depolarizing junctional potentials, which are blocked by Mytolon and dTC. Neurally induced tachycardia is mediated by discrete EJPs, which also follow stimuli applied to the cardiac nerve in a one-to-one manner. EJPs can be recorded from the atria, the AV valve and the ventricle. The myocardium and the AV valve were excited by application of serotonin. EJPs recorded from these sites were reduced in amplitude by methysergide (1-methyl-d-lysergic acid butanolamide), suggesting that the EJPs may be serotonergic. Just after entering the heart, at the posterior end of the junction with the efferent branchial vessel, the cardiac nerves contain thick processes which show serotonin-like immunoreactivity. These processes spread along the ramifications of the nerves, which extend to the atrium, the AV valve, the ventricle and even into the wall of the aorta. This study provides direct electrophysiological evidence for serotonergic EJPs and cholinergic IJPs, plus immunocytochemical evidence for neural processes containing serotonin, in the myocardium.

Nervous System of the Larva of the Ascidian Molgula citrina(Alder and Hancock, 1848)

AbstractFeatures of the nervous system, especially those of the peripheral nervous system, are described in the larva of Molgula citrina. In the peripheral nervous system, antibodies raised against acetylated α–tubulins mark a pair of rostral nerves arising from 8 to 10 sensory cells in the trunk epithelium, and a pair of tail nerves. In the sensory vesicle of the trunk, a pair of antennal cells is associated with the statocyte, and a tuft of ca. 150 cilia is labelled inside the hypophysial duct. A dorsal bundle of fibres forms a plexus over the surface of the sensory vesicle which extends caudally over the visceral ganglion. The latter contains somala that were back‐filled by Co2+–lysine through the cut tip of the tail. Antibodies directed against the transmitter candidates: peptides substance P, FMRFamide, somatostatin, neuropeptide Y, CGRP, VIP, and the amines: 5‐HT, dopamine, noradrenaline and GABA, all failed to demonstrate immunoreactivity anywhere in the nervous system. The trunk epithelium is ciliated uniformly but lacks papillae; this is remarkable given the presence of rostral nerves. The latter are presumed to be sensory, and can be compared with those in larvaceans and the larva of amphioxus. Sensory cells in the tail nerve, if present, lack cilia. The tail nerves are lateral in this species and presumed to be motor. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd

The Lateral Line System of Hagfishes (Craniata: Myxinoidea)

AbstractThe morphology of the peripheral lateral line system in Eptatretus stoutiiis described using a combination of electron microscopical, histological and immunocytochemical techniques. The epidermis and cranial nerves of Myxine glutinosawere also examined for evidence of a lateral line system. Together with results previously published by other researchers, we conclude that most or all eptatretid hagfish possess a lateral line system composed of shallow trenches, or grooves, lined with a single class of flask‐shaped receptive cells. No species of myxinid hagfish has been shown to possess any component of this system. Three groups of lateral line grooves are present in eptatretids: preoptic, dorsal postoptic, and ventral postoptic groups. The preoptic grooves are innervated by a single pair of ganglionated cranial nerves and the two postoptic series of grooves are innervated by a pair of cranial nerves which each possess two ganglia, possibly as a result of fusion of two pairs of ganglionated nerves. Morphometric analysis indicates that these grooves continue to grow throughout life and that the variability in the distribution of grooves between animals may result from developmental instability in lateral line ontogeny. The morphology of the receptive organs is compared to neuromasts of the vertebrate lateral line system and ciliated receptor cells of other chordates. The morphology of hagfish lateral line receptors may represent the primitive condition for craniate lateral line organs, or more likely, they are highly derived as a result of regressive evolution. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.

Coupled oscillators account for the slow rhythms in sympathetic nerve discharge and phrenic nerve activity.

Phase-locked slow rhythms in sympathetic nerve discharge (SND) and phrenic nerve activity (PNA) are generally thought to arise from a common brain stem "cardiorespiratory" oscillator. The results obtained in vagotomized and baroreceptor-denervated cats anesthetized with pentobarbital sodium do not support this view. First, partial coherence analysis revealed that the discharges of pairs of sympathetic nerves remained correlated at the frequency of the central respiratory cycle after mathematical removal of the portion of these signals common to PNA. The residual coherence suggests that the slow rhythm in SND is dependent on central mechanisms in addition to those responsible for rhythmic PNA. Second, the rhythms in SND and PNA became coupled in a 2:1 relationship during either moderate systemic hypocapnia or hypercapnia. Third, the slow rhythm in SND was maintained when rhythmic PNA was eliminated during extreme hypocapnia. Fourth, during extreme hypercapnia, coherence of the rhythms in SND and PNA was drastically reduced. These results suggest that the slow rhythms in SND and PNA arise from separate oscillators that are normally coupled.

The chordoid larva of Symbion pandora (Cycliophora) is a modified trochophore.

Developmental and free-living stages of the chordoid larva of the cycliophoran species, Symbion pandora Funch and Kristensen 1995, were studied using light and electron microscopy. In the free-living stage of the larva, about 200 μm long, four ciliated areas are found: two anterior bands, a ventral ciliated field, and a posterior unit on the ventral side of the foot. The nervous system consists of a dorsal brain and a pair of ventral longitudinal nerves. A gut is absent. A pair of protonephridia, each with a single multiciliated terminal cell and at least one duct cell, is present. Nephridiopores are not localized. A pair of corsal ciliated organs is posterior to the brain. The homology between these and the apical organ of a trochophore larva is discussed. A distinctive longitudinal rod, the chordoid organ, consists of vacuolized cells with circular myofilaments. The organ is comparable to a similar structure in gastrotrichs. In the discussion of the phylogenetic position of Cycliophora among protostomians, important morphological observations that are described in the present study indicate that, despite some dissimilarities, the chordoid larva is a modified trochophore. © 1996 Wiley-Liss, Inc.

Anatomical pathways connecting lip sensory structures and central nervous system in hirudinid leeches visualized by carbocyanine dyes and laser scanning confocal microscopy.

Chemoreception in Hirudo medicinalis is thought to be mediated by ciliated cells grouped in sensory structures, the sensilla, arranged in bands on the animal's dorsal lip (Elliott, 1986; Zipser et al., 1994). Furthermore, chemical and/or thermal stimulation of the dorsal lip in reduced preparations evokes changes in the electrical activity of the cephalic nerves that connect the head with the central nervous system. However, the complete trajectory by which the sensory afferents reach the cerebral ganglia has not been demonstrated anatomically. In this study, we traced these pathways following retrograde and/or anterograde transport of carbocyanine dyes (DiI, DiA and DiD) in the cephalic nerves of Hirudo medicinalis and a closely related species, Macrobdella decora. While information regarding Macrobdella's chemoreception is scarce, the two species show some differences with regard to their chemical preferences. Dyes were applied to the sensillar structures along the dorsal lip, or to the cut ends of individual cephalic nerves in fixed preparations that included the lip and attached nerves with or without the head ganglia. After a two week incubation, specimens were mounted and imaged using a confocal microscope. The results show that the axons of the sensory neurons in the sensilla project through the four pairs of cephalic nerves. The sensillar projections are however more numerous in the dorsal nerves than they are in the ventral ones. In addition, the organization of the sensillar bands, the morphology of the pathways and the sensory structures themselves appear to be identical for Hirudo and Macrobdella and therefore the behavioral differences in response to appetitive stimuli cannot be readily explained by differences in morphology.

The chordoid larva of Symbion pandora (Cycliophora) is a modified trochophore

Developmental and free-living stages of the chordoid larva of the cycliophoran species, Symbion pandora Funch and Kristensen 1995, were studied using light and electron microscopy. In the free-living stage of the larva, about 200 μm long, four ciliated areas are found: two anterior bands, a ventral ciliated field, and a posterior unit on the ventral side of the foot. The nervous system consists of a dorsal brain and a pair of ventral longitudinal nerves. A gut is absent. A pair of protonephridia, each with a single multiciliated terminal cell and at least one duct cell, is present. Nephridiopores are not localized. A pair of corsal ciliated organs is posterior to the brain. The homology between these and the apical organ of a trochophore larva is discussed. A distinctive longitudinal rod, the chordoid organ, consists of vacuolized cells with circular myofilaments. The organ is comparable to a similar structure in gastrotrichs. In the discussion of the phylogenetic position of Cycliophora among protostomians, important morphological observations that are described in the present study indicate that, despite some dissimilarities, the chordoid larva is a modified trochophore. © 1996 Wiley-Liss, Inc.