Crustacean cardioactive peptide-immunoreactive neurons innervating brain neuropils,retrocerebral complex and stomatogastric nervous system of the locust,Locusta migratoria

The distribution and morphology of crustacean cardioactive peptide-immunoreactive neurons in the brain of the locust Locusta migratoria has been determined. Of more than 500 immunoreactive neurons in total, about 380 are interneurons in the optic lobes. These neurons invade several layers of the medulla and distal parts of the lobula. In addition, a small group of neurons projects into the accessory medulla, the lamina, and to several areas in the median protocerebrum. In the midbrain, 12 groups or individual neurons have been reconstructed. Four groups innervate areas of the superior lateral and ventral lateral protocerebrum and the lateral horn. Two cell groups have bilateral arborizations anterior and posterior to the central body or in the superior median protocerebrum. Ramifications in subunits of the central body and in the lateral and the median accessory lobes arise from four additional cell groups. Two local interneurons innervate the antennal lobe. A tritocerebral cell projects contralaterally into the frontal ganglion and appears to give rise to fibers in the recurrent nerve, and in the hypocerebral and ingluvial ganglia. Varicose fibers in the nervi corporis cardiaci III and the corpora cardiaca, and terminals on pharyngeal dilator muscles arise from two subesophageal neurons. Some of the locust neurons closely resemble immunopositive neurons in a beetle and a moth. Our results suggest that the peptide may be (1) a modulatory substance produced by many brain interneurons, and (2) a neurohormone released from subesophageal neurosecretory cells.     

Octopamine-like immunoreactive neurones in locust genital abdominal ganglia

Using a well characterized anti-serum, the distribution of octopamine-like immunoreactive neurones is described in the locust seventh abdominal (A7) and terminal ganglia (TG), which are associated with genital organs. Apart from 4 paired ventral somata occasionally observed in the TG, all labelled cells could be identified as efferent dorsal- and ventral unpaired median (DUM/VUM) neurones by virtue of the characteristic large size and position of their somata, projections of their primary neurites in DUM-cell tracts, and bifurcating axons which arise from dorsal T-junctions and enter peripheral nerves. For the examined ganglia our data indicate that the whole population of efferent DUM and VUM-cells, defined here as progeny of the segment specific unpaired median neuroblast with peripheral axons, are octopaminergic, and that equal numbers of these cells occur in both sexes: 8 in A7 and 11 in TG. Sex-specific differences are probably restricted to the axonal projections of 5 octopamine-like immunoreactive DUM-somata in A7, and 5 in TG, which in females project into their segment specific sternal nerves, but in males into the genital nerve of the TG. Numerous intersegmentally projecting octopamine-like immunoreactive fibres traverse both ganglia. The majority probably stem from previously described octopamine-like immunoreactive neurones in the thoracic and suboesophageal ganglia.     

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     

GABA and glutamate-like immunoreactivity at synapses received by dorsal unpaired median neurones in the abdominal nerve cord of the locust

Dorsal unpaired median (DUM) neurones in the abdominal ganglia of the locust were impaled with microelectrodes and some were injected intracellularly with horseradish peroxidase so that their synapses could be identified in the electron microscope. Simultaneous recordings from DUM neurones in different abdominal ganglia revealed that they received common postsynaptic potentials from descending interneurones. Post-embedding immunocytochemistry using antibodies against GABA and glutamate was carried out on ganglia containing HRP-stained neurones. GABA-like immunoreactivity was found in 39% (n=82) of processes presynaptic to abdominal DUM neurones and glutamate-like immunoreactivity in 21% (n=42) of presynaptic processes. Output synapses from the DUM neurites were rarely observed within the neuropile. Structures resembling presynaptic dense bars but not associated with synaptic vesicles, were seen in some large diameter neurites.     

Localization of Lom-AG-myotropin I-like substances in the male reproductive and nervous tissue of the locust,Locusta migratoria

Summary Lom-AG myotropin I (Lom-AG-MTI) was the first peptide to be isolated from the male accessory reproductive glands of the locust, Locust migratoria. It shows no sequence similarity to any of the peptides identified from vertebrate or invertebrate tissues. A polyclonal antiserum was used to localize Lom-AG-MTI-like material in the male reproductive system and nervous system of the locust. Immunoreactivity was found in two of the hyaline gland tubules. In the brain, cell bodies were detected in the proto- and deuterocerebrum as well as the frontal ganglion. Nerve fibers were stained in the neuropils of the brain and throughout the labial nerves into the recurrent nerve. Thoracic and last abdominal ganglia contained neurons which could be stained with Lom-AG-MTI antiserum. The pronounced reactivity in the central nervous system suggests a possible neuroregulatory function of the peptide.     

Postembryonic development of leucokinin I-immunoreactive neurons innervating a neurohemal organ in the turnip moth Agrotis segetum

Summary In the abdominal ganglia of the turnip moth Agrotis segetum, an antibody against the cockroach neuropeptide leucokinin I recognizes neurons with varicose fibers and terminals innervating the perisympathetic neurohemal organs. In the larva, the abdominal perisympathetic organs consist of a segmental series of discrete neurohemal swellings on the dorsal unpaired nerve and the transverse nerves originating at its bifurcation. These neurohemal structures are innervated by varicose terminals of leucokinin I-immunoreactive (LKIR) fibers originating from neuronal cell bodies located in the preceding segment. In the adult, the abdominal segmental neurohemal units are more or less fused into a plexus that extends over almost the whole abdominal nerve cord. The adult plexus consists of peripheral nerve branches and superficial nerve fibers beneath the basal lamina of the neural sheath of the nerve cord. During metamorphosis, the LKIR fibers closely follow the restructuration of the perisympathetic organs. In both larvae and adults the LKIR fibers in the neurohemal structures originate from the same cell bodies, which are distributed as ventrolateral bilateral pairs in all abdominal ganglia. The transformation of the series of separated and relatively simple larval neurohemal organs into the larger, continuous and more complex adult neurohemal areas occurs during the first of the two weeks of pupal life. The efferent abdominal LKIR neurons of the moth Agrotis segetum thus belong to the class of larval neurons which persist into adult life with substantial peripheral reorganization occurring during metamorphosis.     

The distribution of glutamate-like immunoreactivity in the thoracic and abdominal ganglia of the locust (Schistocerca gregaria)

The distribution of glutamate-like immunore-activity in the thoracic and abdominal ganglia of the locust was studied using two polyclonal antibodies against glutamate. Because glutamate is a precursor of the inhibitory transmitter -amino butyric acid (GABA) the distribution of immunostaining by antibodies against glutamate and GABA was closely compared in adjacent serial sections. When the antibodies were used at optimal dilutions there was no overlap in the distribution of immunostaining for glutamate and GABA. In the pro- and mesothoracic ganglia 360–400 somata are immunoreactive for glutamate, while in the metathoracic ganglion about 600 somata were stained. These range in diameter from 10–100 m in diameter and include the majority of the large somata in these ganglia. Bundles of primary neurites emerging from these large somata can be traced through the neuropile. Most of the bundles correspond to the known paths of motor neurone primary neurites. In addition the T-tract is also immunolabelled. The free abdominal ganglia each contain 80–100 somata ranging in size from 10–45 m while the terminal ganglion contains about 250 somata, 10–60 m in diameter.     

GABA-like immunoreactivity of identified interneurons in the flight system of the locust,Locusta migratoria

Summary The transmitter content of identified inhibitory interneurons in the flight system of the locust, Locusta migratoria, has been characterized using antibodies raised against protein-conjugated gamma aminobutyric acid. Identified flight neurons were filled with the fluorescent dye, Lucifer Yellow. Serial sections of dye-filled neurons were incubated with an antibody to gamma aminobutyric acid which was subsequently tagged with a fluorescent marker. Excitatory motoneurons to wing muscles and 13 flight interneurons (3 excitatory, 7 inhibitory, and 3 with unknown synaptic effect) were examined. Neither the moto-neurons nor any of the 3 excitatory interneurons contained immunoreactive material. Six of the 7 inhibitory interneurons did contain immunoreactive material. All the neurons which contained immunoreactive material and whose synaptic effect is known were inhibitory. We conclude that most of the inhibitory flight interneurons which have been described use gamma aminobutyric acid as their transmitter. Interestingly, at least 1 set of interneurons known to be inhibitory does not use gamma aminobutyric acid. We predict that the 2 interneurons which do contain immunoreactive material and whose synaptic effect is not yet known will be found to have inhibitory roles in the operation of the flight circuitry.     

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust,Locusta migratoria

Summary Using a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A₁ cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A₂ cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.     

Immunochemical analysis of the distribution of the new ovary maturating neurohormone during development of the African locust,Locusta migratoria

Summary Following our prior identification of a gonadotropic neurohormone isolated from the neurosecretory lobe of the corpora cardiaca of the African locust, we have raised a polyclonal antiserum against this new molecule. In the present paper, we characterize this antiserum using enzyme-linked immunosorbent assay and Western blotting. The latter procedure reveals that the immune serum specifically recognizes the neurohormone, which we have termed ovary maturating parsin. Immunohistochemistry, enzyme-linked immunosorbent assay and Western blotting were used to analyze the distribution of this gonadotropic neurohormone throughout the central nervous system during development. It is produced only by the type-B neurosecretory cells of the pars intercerebralis-corpora cardiaca system and is present both in males and females throughout life from embryo to adult. This permanent expression suggests that the neurohormone may have functions other than its primary direct gonadotropic role in females.     

The morphology of suboesophageal ganglion cells innervating the nervus corporis cardiaci III of the locust

Summary The nervus corporis cardiaci III (NCC III) of the locust Locust migratoria was investigated with intracellular and extracellular cobalt staining techniques in order to elucidate the morphology of neurons within the suboesophageal ganglion, which send axons into this nerve. Six neurons have many features in common with the dorsal, unpaired, median (DUM) neurons of thoracic and abdominal ganglia. Three other cells have cell bodies contralateral to their axons (contralateral neuron 1–3; CN 1–3). Two of these neurons (CN2 and CN3) appear to degenerate after imaginal ecdysis. CN3 innervates pharyngeal dilator muscles via its anterior axon in the NCC III, and a neck muscle via an additional posterior axon within the intersegmental nerve between the suboesophageal and prothoracic ganglia. A large cell with a ventral posterior cell body is located close to the sagittal plane of the ganglion (ventral, posterior, median neuron; VPMN). Staining of the NCC III towards the periphery reveals that the branching pattern of this nerve is extremely variable. It innervates the retrocerebral glandular complex, the antennal heart and pharyngeal dilator muscles, and has a connection to the frontal ganglion.Abbreviations AH antennal heart - AN antennal nerves - AO aorta - AV antennal vessel - CA corpus allatum - CC corpus cardiacum - CN1, CN2, CN3 contralateral neuron 1–3 - DIT dorsal intermediate tract - DMT dorsal median tract - DUM dorsal, unpaired, median - FC frontal connective - FG frontal ganglion - HG hypocerebral ganglion - LDT lateral dorsal tract - LMN, LSN labral motor and sensory nerves - LN+FC common root of labral nerves and frontal connective - LO lateral ocellus - MDT median dorsal tract - MDVR ventral root of mandibular nerve - MVT median ventral tract - NCA I, II nervus corporis allati I, II - NCC I, II, III nervus corporis cardiaci I, III - NR nervus recurrens - NTD nervus tegumentarius dorsalis - N8 nerve 8 of SOG - OE oesophagus - OEN oesophageal nerve - PH pharynx - SOG suboesophageal ganglion - T tentorium - TVN tritocerebral ventral nerve - VLT ventral lateral tract - VIT ventral intermediate tract - VMT ventral median tract - VPMN ventral, posterior, median neuron - 1–7 peripheral nerves of the SOG - 36, 37, 40–45 pharyngeal dilator muscles     

Distribution of SchistoFLRFamide-like immunoreactivity in the adult ventral nervous system of the locust,Schistocerca gregaria

SchistoFLRFamide (PDVDHVFLRF-NH₂) is one of the major endogenous neuropeptides of the FMRF-amide family found in the nervous system of the locust,Schistocerca gregaria. To gain insights into the potential physiological roles of this neuropeptide we have examined the distribution of SchistoFLRFamide-like immunoreactivity in the ventral nervous system of adult locusts by use of a newly developed N-terminally specific antibody. SchistoFLRFamide-like immunoreactivity in the ventral nerve cord is found in a subgroup of the neurones that are immunoreactive to an antiserum raised against bovine pancreatic polypeptide (BPP). In the suboesophageal ganglion three groups of cells stain, including one pair of large posterior ventral cells. These cells are the same size, in the same location in the ganglion and have the same branching pattern as a pair of BPP immunoreactive cells known to innervate the heart and retrocerebral glandular complex of the locust. In the thoracic and abdominal ganglia two and three sets of cells, respectively, stain with both the SchistoFLRFamide and BPP antisera. In the abdominal ganglia the immunoreactive cells project via the median nerves to the intensely immunoreactive neurohaemal organs.     

In vitro peptidergic neurons from the adult locust pars intercerebralis: Morphological and immunocytological studies

Primary cell cultures were prepared from a major neurosecretory center of the adult locust brain, the pars intercerebralis, in order to characterize neurosecretory cells growingin vitro. Individual pars intercerebralis could be removed free of surrounding tissue and dissociated by mechanical treatment. Mature neurosecretory neurons of different sizes regenerate new neurites during the initial three daysin vitro in serum-free medium. They show a tendency to sprout one primary neurite from which fine processes develop. By means of electron microscopy, we observed the integrity of the cellular organelles, indicating that cultured neurons are healthy, and we were able to distinguish three types of neurosecretory neurons on the basis of the ultrastructural aspects of the neurosecretory material. These three types have the same ultrastructural characteristics asin situ neuroparsin, ovary maturing parsin and locust insulin related peptide neurons. Immunogold labelling at the electron microscopic level, using the two available specific antibodies, anti-neuroparsin and anti-ovary maturing parsin, confirms the morphological characterization of neuroparsin and ovary maturing parsin cells. These results show for the first time that cultured locust neurosecretory neurons behave like thosein vivo, in terms of their ultrastructure and immunocytochemistry. Moreover, the presence of recently-formed neurosecretory material both in the Golgi zone of the perikaryon and in the neuronal processes indicates that cultured neurons have functional capacity since they are able to synthesizede novo and to transport the neurosecretory material along the neurite. Thus our well-characterized culture system provides a suitable invitro model to investigate the secretory mechanism of locust neurosecretory neurons.     

Distribution of FMRFamide-like immunoreactive neurons in the central nervous system of the snail Helix pomatia

Summary The distribution of FMRFamide-like immunoreactive (FLI) neurons and their morphological characteristics have been investigated in the central nervous system of the snail, Helix pomatia L. Approximately phageal ganglion complex. More than 50% of the FLI neurons were located in the cerebral ganglia. The FLI neurons could be divided into four groups according to size: (i) giant neurons (over 100 m); (ii) large neurons (80–100 m); (iii) medium-sized neurons (40–70 m); (iv) small neurons (12–30 m). They were distributed i) in groups or clusters, typical of small neurons and ii) in solitary form or in groups comprising 2–3 cells, typical of large and giant neurons. Giant and large neurons revealed only limited arborizations in the neuropil, but rich branching towards and in the peripheral nerves. Some of the small neurons had extensive arborizations of varicose fibers in the neuropil. They may therefore play some role in integratory processes. Varicose FLI fibers were visualized in the cell body layer of the different ganglia, and in the neural sheath of both the ganglia and the peripheral nerves. We propose a multifunctional involvement of FLI neurons and FMRFamide-like neuropeptides in the Helix nervous system: (i) a synaptic or modulatory role in axo-axonic interactions in the neuropil; (ii) a direct influence on neuronal cell bodies in the cortical layer, (iii) innervation of different peripheral organs; and (iv) remote neurohormonal control of peripheral events through the neural sheath.     

Neuronal connections between central and enteric nervous system in the locust, Locusta migratoria

The number and location of neurons, in the central nervous system, that project into the frontal connective was studied in the locust by using retrograde neurobiotin staining. Staining one frontal connective revealed some 70 neurons in the brain. Most of these were located within both tritocerebral lobes. Additional groups of neurons were located within the deutocerebrum and protocerebrum. Some 60 neurons were labelled in the suboesophageal ganglion. These formed nine discernable populations. In addition, two neurons were located in the prothoracic ganglion and two neurons in the first abdominal neuromere of the metathoracic ganglion. Thus, some 250 neurons located within the head ganglia, and even neurons in thoracic ganglia, project into the ganglia of the enteric nervous system. This indicates that the coordination between the central and enteric ganglia is much more complex than previously thought. With the exception of some previously described dorsal unpaired median neurons and a few motor neurons in the head ganglia, the identity and function of most of these neurons is as yet unknown. Possible functions of the neurons in the thoracic ganglia are discussed.     

Complex innervation of three neck muscles by motor and dorsal unpaired median neurons in crickets

Summary In the crickets, Gryllus campestris and Gryllus bimaculatus, the innervation of the dorso-ventral neck muscles M62, M57, and M59 was examined using cobalt staining via peripheral nerves and electrophysiological methods. M62 and M57 are each innervated by two motoneurons in the suboesophageal ganglion. The four motoneurons project into the median nerve to bifurcate into the transverse nerves of both sides. M62 and M57 are the only neck muscles innervated via this route. These bifurcating axon-projections are identical to those of the spiracular motoneurons in the prothoracic ganglion innervating the opener and closer muscle of the first thoracic spiracle in the cricket. The morphology of their branching pattern is described. The neck muscle M57 and the opener muscle of the first thoracic spiracle are additionally innervated by one mesothoracic motoneuron each, with similar morphology. These results suggest, that in crickets, the neck muscles M57 and M62 are homologous to spiracular muscles in the thoracic segments. The two neck muscles M62 and M59 (the posterior neighbour of M57) receive projections from a prothoracic dorsal unpaired median (DUM) neuron that also innervates dorsal-longitudinal neck muscles but not M57. In addition, one or two mesothoracic DUM neurons send axon collaterals intersegmentally to M59. This is the first demonstration of the innervation of neck muscles by DUM neurons.     

Neurons projecting from the brain to the corpora allata in orthopteroid insects: anatomy and physiology

Retrograde and orthograde labeling of neurons projecting to the corpus allatum was performed in locust, grasshopper, cricket, and cockroach species in order to identify brain neurons that may be involved in the regulation of juvenile hormone production. In the acridid grasshopper Gomphocerus rufus L., and the locusts Locusta migratoria (R.&F.) and Schistocerca gregaria Forskal, the corpora allata are innervated by two morphologically distinguishable types of brain neurons. One group of 9–13 neurons (depending on species) with somata in the pars lateralis extend axons via the nervus corporis cardiaci 2 and nervus corporis allati 1 to the ipsilateral corpus allatum, whereas two cells in each pars lateralis have bilateral projections and innervate both glands. No direct connection between the pars intercerebralis and corpus allatum has been found. In contrast, neurons with paired axons innervating both glands are not present in Periplaneta americana (L.) and Gryllus bimaculatus de Geer. Instead, two cells in each pars lateralis project only to the gland contralateral to their somata. Electrophysiological experiments on acridid grasshoppers have confirmed the existence of a direct conduction pathway between the two glands via the paired axons of four cells that have been identified by neuroanatomy. These cells are not spontaneously active under experimental conditions. Ongoing discharges in the left and right nerves are unrelated, suggesting that the corpora allata receive independent neuronal inputs from the brain.     

Central projections of sensory cells of the midleg of the locust,Schistocerca gregaria

The central projections of trichoid hairs and of some scolopidial organs of the mesothoracic leg of the locust Schistocerca gregaria were studied by using nickel chloride backfilling and single cell recording. Trichoid hair sensilla on different parts of the legs project somatotopically in the ventral part of the ipsilateral neuropile of the mesothoracic ganglion. Generally, distally located receptors have their terminal arborizations in ventro-lateral areas of the neuropile, and proximally located receptors in ventro-medial areas. The axons of the subgenual organ and tarsal chordotonal organs project into the intermediate neuropile.     

The generation of DPOAEs in the locust ear is contingent upon the sensory neurons

Tympanal organs of insects emit distortion-product otoacoustic emissions (DPOAEs) that are indicative of nonlinear ear mechanics. Our study sought (1) to define constraints of DPOAE generation in the ear of Locusta migratoria, and (2) to identify the sensory structures involved. We selectively destroyed the connection between the (peripheral) sensory ganglion and the tympanal attachment points of the “d-cell” dendrites; d-cells are most sensitive to sound frequencies above 12 kHz. This led to a decrease of DPOAEs that were evoked by f ₂ frequencies above 15 kHz (decrease of 15–40 dB; mean 28 dB; n = 12 organs). DPOAEs elicited by lower frequencies remained unchanged. Such frequency-specific changes following the exclusion of one scolopidial sub-population suggest that these auditory scolopidia are in fact the source of DPOAEs in insects. Electrical stimulation of the auditory nerve (with short current pulses of 4–10 μA or DC-currents of 0.5 μA) reversibly reduced DPOAEs by as much as 30 dB. We assume that retrograde electrical stimulation primarily affected the neuronal part of the scolopidia. Severing the auditory nerve from the central nervous system (CNS) did not alter the DPOAE amplitudes nor the effects of electrical stimulation.     

The distribution of GABA-like immunoreactivity in the thoracic nervous system of the locust Schistocerca gregaria

Summary An antiserum raised against gamma aminobuyric acid (GABA) was used to stain the thoracic nervous system of the locust. It stained both neuronal somata and processes within the neuropile. Among the stained somata, those of the three pairs of common inhibitory motor neurones could be identified in each of the three thoracic ganglia. In the pro- and mesothoracic ganglia five discrete groups of somata are stained, four ventral and one dorsal. In the metathoracic neuromere, an additional second dorsal group can be identified. In the abdominal neuromeres of the metathoracic ganglion both dorsal and ventral somata are stained but the latter cannot be divided into discrete populations. In each ganglion, dorsal commissures (DC) IV and V are composed of stained neurites, DCVII, the supramedian commissure, the perpendicular tract, and all the longitudinal tracts contain both stained and unstained neurites. DCI, II, III and VI, the T and I tracts are unstained. An abundance of GABA-like immunoreactive processes is found throughout the neuropile except for the anterior ventral association centre where stained processes are sparser. Some of the stained cell groups contain neurones that have been studied physiologically. The function of these neurones is discussed.Beit Memorial Fellow