Tritocerebral Commissure Research Articles

Ontogeny and development of the tritocerebral commissure giant (TCG): an identified neuron in the brain of the grasshopper Schistocerca gregaria.

The tritocerebral commissure giant (TCG) of the grasshopper Schistocerca gregaria is one of the best anatomically and physiologically described arthropod brain neurons. A member of the so-called Ventral Giant cluster of cells, it integrates sensory information from visual, antennal and hair receptors, and synapses with thoracic motor neurons in order to initiate and regulate flight behavior. Its ontogeny, however, remains unclear. In this study, we use bromodeoxyuridine incorporation and cyclin labeling to reveal proliferative neuroblasts in the region of the embryonic brain where the ventral giant cluster is located. Engrailed labeling confirms the deutocerebral identity of this cluster. Comparison of soma locations and initial neurite projections into tracts of the striate deutocerebrum help identify the cells of the ventral cluster in both the embryonic and adult brain. Reconstructions of embryonic cell lineages suggest deutocerebral NB1 as being the putative neuroblast of origin. Intracellular dye injection coupled with immunolabeling against neuron-specific horseradish peroxidase is used to identify the VG1 (TCG) and VG3 neurons from the ventral cluster in embryonic brain slices. Dye injection and backfilling are used to document axogenesis and the progressive expansion of the dendritic arbor of the TCG from mid-embryogenesis up to hatching. Comparative maps of embryonic neuroblasts from several orthopteroid insects suggest equivalent deutocerebral neuroblasts from which the homologous TCG neurons already identified in the adult brain could originate. Our data offer the prospect of identifying further lineage-related neurons from the cluster and so understand a brain connectome from both a developmental and evolutionary perspective.

The presence of abalone egg-laying hormone-like peptide in the central nervous system and ovary of the blue swimming crab, Portunus pelagicus, and its effect on ovarian maturation

Egg-laying hormone (ELH) is a neuropeptide secreted from the neural ganglia of mollusks that can stimulate the egg-laying and associated behaviors. In the present study, using a polyclonal antibody against an abalone, H asinina, ELH (aELH) we could detect the aELH-like immunoreactivity (aELH-l-ir) in the central nervous system (CNS) and ovary of the blue swimming crab Portunus pelagicus. In protocerebrum, aELH-l-ir was detected in the small- and medium- sized neurons of cluster 6, anterior/posterior medial protocerebral neuropils, protocerebral bridge and central body. In deutocerebrum, the aELH-l-ir was observed in small-sized neurons of cluster 9, fibers between small-sized neurons of cluster 10, medium-sized neurons of cluster 11, olfactory neuropil and medial/lateral antenna I neuropils. In tritocerebrum, the medium- sized neurons of cluster 16, the tritocerebral commissure, and tegumental neuropil showed strong aELH-l-ir. In the ventral nerve cord, the aELH-l-ir was detected in the small- and medium-sized neurons of dorsolateral clusters of subesophageal ganglion. There was no aELH-l- ir in neurons of thoracic ganglion, but aELH-l-ir exhibited a dot-like structure in the subcapsular space around the thoracic neuropils. In abdominal ganglion, the aELH-l-ir was detected in some medium-sized neurons and abdominal neuropils. In the ovary, the aELH-l-ir was detected in the cytoplasm of oogonia, and all steps of developing oocytes. The effect of aELH on ovarian maturation in the crabs was examined by bioassay. When mature female crabs were injected with a dose of 500ng/g body weight per crab, the ovarian maturation was accelerated as indicated by the rising of gonado-somatic index and levels of vitellin in the ovarian tissue and hemolymph, which was confirmed by histological studies. The aELH also enhanced the proliferation of follicular cells as indicated by the increased number of BrdU-labeled nuclei. In addition, the aELH also significantly induced the 17β-estradiol and progesterone secretion in the cultured ovarian explant. In conclusion, this study demonstrated the existence of an aELH-liked-peptide in the CNS and ovary of the P. pelagicus, and it can induce the ovarian 17β-estradiol and progesterone production resulting in early ovarian maturation in this crab.

Architecture of the nervous system in mystacocarida (Arthropoda, crustacea)—An immunohistochemical study and 3D reconstruction

Mystacocarida is a species-poor group of minute crustaceans with unclear phylogenetic affinities. Previous studies have highlighted the putative "primitiveness" of several mystacocarid features, including the architecture of the nervous system. Recent studies on arthropod neuroarchitecture have provided a wealth of characters valuable for phylogenetic reconstructions. To permit and facilitate comparison with these data, we used immunohistochemical labeling (against acetylated alpha-tubulin, serotonin and FMRFamide) on the mystacocarid Derocheilocaris remanei, analyzing it with confocal laser-scanning microscopy and 3D reconstruction. The mystacocarid brain is fairly elongated, exhibiting a complicated stereotypic arrangement of neurite bundles. However, none of the applied markers provided evidence of structured neuropils such as a central body or olfactory glomeruli. A completely fused subesophageal ganglion is not present, all segmental soma clusters of the respective neuromeres still being delimitable. The distinct mandibular commissure comprises neurite bundles from more anterior regions, leading us to propose that it may have fused with an ancestral posterior tritocerebral commissure. The postcephalic ventral nervous system displays a typical ladder-like structure with separated ganglia which bears some resemblance to larval stages in other crustaceans. Ganglia and commissures are also present in the first three limbless "abdominal" segments, which casts doubt on the notion of a clear-cut distinction between thorax and abdomen. An unpaired longitudinal median neurite bundle is present and discussed as a potential tetraconate autapomorphy. Additionally, a paired latero-longitudinal neurite bundle extends along the trunk. It is connected to the intersegmental nerves and most likely fulfils neurohemal functions. We report the complete absence of serotonin-ir neurons in the ventral nervous system, which is a unique condition in arthropods and herein interpreted as a derived character.

Ventral veins lacking is required for specification of the tritocerebrum in embryonic brain development of Drosophila

The homeotic or Hox genes encode a network of conserved transcription factors which provide axial positional information and control segment morphology in development and evolution. During embryonic brain development of Drosophila, the Hox gene labial (lab) is essential for tritocerebral neuromere specification; lab loss of function results in tritocerebral cells that fail to adopt a neuronal identity, causing axonal pathfinding defects. Here we present evidence that the POU-homeodomain DNA-binding protein ventral veins lacking (vvl) acts genetically downstream of lab in the specification of the tritocerebral neuromere. In the embryonic brain, vvl expression is seen in all brain neuromeres, including the tritocerebral lab domain. Lab mutant analysis shows that vvl expression in the tritocerebrum is dependent on lab activity. Loss-of-function analysis focussed on the tritocerebrum reveals that inactivation of vvl results in patterning defects which are comparable to the brain phenotype caused by null mutation of lab. In the absence of vvl, mutant tritocerebral cells are generated and positioned correctly, but these cells fail to express neuronal markers indicating defects in neuronal differentiation. Moreover, longitudinal axon pathways in the tritocerebrum are severely reduced or absent and the tritocerebral commissure is missing in the vvl mutant brain. Genetic rescue experiments show that vvl is able to partially replace lab in the specification of the tritocerebral neuromere. Our results indicate that vvl acts downstream of the Hox gene lab and regulates specific aspects of neuronal differentiation within the tritocerebral neuromere during embryonic brain development of Drosophila.

Neurophysiological studies of flight-related density-dependent phase characteristics in locusts.

Locusts show an extreme example of density-dependent phase polymorphism, demonstrating within the species differences in morphology as well as biology, dependent on the population density. Behavior is the primary density-dependent change which facilitates the appearance of various morphological and physiological phase characteristics. We have studied density dependent differences in flight related sensory and central neural elements in the desert locust Schistocerca gregaria. Wind generated high frequency spiking activity in the tritocerebral commissure giant (TCG, an identified interneuron that relay inputs from head hair receptors to thoracic motor centers) that was much less intense in solitary locusts, compared to gregarious ones. In addition the solitary locusts' TCG demonstrated much stronger adaptation of its response. In cases when flight was initiated high frequency TCG activity was independent of the locust phase. The tritocerebral commissure dwarf (TCD) is a GABAergic flight related interneuron that is sensitive to ambient illumination intensity. An increase in the TCD spontaneous activity under dark vs. light conditions was significantly higher in gregarious locusts then in solitary ones, implying a flight-related inhibitory mechanism that is far more active in gregarious locusts under dark conditions. Thus, density-dependent phase differences in interneuron activity pattern and properties well reflect and may be at least partially responsible to behavioral flight-related characteristics.

Commissure formation in the embryonic insect brain

The primary axon scaffold of the insect brain is established early in embryogenesis and comprises a preoral protocerebral commissure, a postoral tritocerebral commissure and longitudinal fiber pathways linking the two. In both grasshopper and fly its form is approximately orthogonal and is centered around the stomodeum. We show how pioneer fibers from the protocerebrum and tritocerebrum cross the brain midline directly via their respective commissures. The deutocerebrum, however, lacks its own commissure and we describe how deutocerebral pioneers circumnavigate the gut to cross the midline either via the protocerebral commissure or the tritocerebral commissure. In contrast to all other commissures of the central nervous system, the protocerebral commissure persists, albeit in reduced form, in the commissureless mutation in the fly. Besides the com gene, a further, as yet unidentified, mechanism must regulate this commissure. The formation of the tritocerebral commissure involves labial, a member of the Hox gene group. Genetic rescue experiments in labial mutants reveal that the formation of this commissure can be rescued by all other Hox genes except Abdominal-B. However, only in the labial and Deformed null mutants are the commissures associated with the respective expression domains (tritocerebral, mandibular, respectively) absent. This suggests that the molecular mechanisms regulating postoral brain commissure formation are distinct from those in the neuromeres of the ventral nerve cord.

The jing gene is required for embryonic brain development in Drosophila [corrected

Loss- and gain-of-function studies have demonstrated a crucial role for the jing zinc finger transcription factor in neuronal and glial differentiation and survival in the embryonic central nervous system midline of Drosophila. Here, we have studied the role of jing during embryonic brain development. Proper jing function is required for the formation of the primary brain axon scaffold. In homozygous jing (3) mutant embryos the preoral commissure is not pioneered and never forms. Other axon pathways are pioneered but subsequently do not form properly, including the postoral tritocerebral commissure, the circumesophageal connectives and the pathways that connect the brain with the ventral nerve cord. To understand the cellular basis of the axon phenotype the jing expression pattern in the brain was characterized using a jing-lacZ enhancer trap. jing-lacZ enhancer trap expression occurs in glia and neurons in the brain midline and lateral clusters as determined by co-localization of the lacZ gene product with Repo and Castor, respectively. In addition, the jing-lacZ enhancer trap and the basic helix-loop-helix-PAS gene, single-minded ( sim), are expressed in the only glial midline cluster present in stage-14 wild-type embryos. jing function is required for the differentiation of Repo-, Castor- and Sim-positive cells in the embryonic brain as each of these populations contain a reduced number of cells in homozygous jing (3) mutant embryos. We further find that jing is required for neuronal and glial survival as repo- and castor-expressing cells undergo cell death in homozygous jing (3) mutant embryos, as revealed by double labeling with Tunel. Expression of jing in sim-expressing cells in the brain disrupts the entire axon scaffold but most significantly results in loss of the preoral and postoral tritocerebral commissures. In addition, circumesophageal connectives are repelled after expression of two copies of UAS- jing in sim-expressing cells, suggesting the activation of axon repellent molecules. Over-expression of sim in the brain is also associated with loss of preoral and postoral tritocerebral commissures. Therefore, the proper dosage of jing and sim in the brain is critical for the formation of the primary axon scaffold. These results show that an important role for jing in the developing brain is the regulation of neuronal and glial differentiation and survival.

Labial acts to initiate neuronal fate specification, but not axon pathfinding, in the embryonic brain of Drosophila

Drosophila embryos lacking the homeotic gene labial (lab) show two types of defects in brain development: (1) cells in the brain lab domain do not express neuronal markers or extend axons, and (2) axons originating from outside the lab domain stop at this region or project ectopically. A severe disruption of neuronal patterning and axon scaffolding is the net result. It is not clear how the absence of Lab can result in both neuronal fate defects and axon pathfinding defects. I have expressed Lab in short pulses in lab loss-of- function embryos, and this gave almost complete rescue; for example, the tritocerebral commissure was restored. Rescue only occurred when Lab was provided at the time when cells in the brain are adopting a neuronal fate. Lab expression later, when the first axons are seen in the lab domain, did not give rescue. I conclude that Lab expression helps to establish neuronal identity in the lab domain, and these neurons act as a permissive substrate for axon extension. However, Lab itself is not required at the time of axon pathfinding through this region.

Localization of octopaminergic neurones in insects

This paper reviews data on the localization of octopaminergic neurons revealed by immunocytochemistry in insects, primarily the locusts Schistocerca gregaria and Locusta migratoria, cricket Gryllus bimaculatus, and cockroach Periplaneta americana. Supporting evidence for their octopaminergic nature is mentioned where available. In orthopteran ventral ganglia, the major classes of octopamine-like immunoreactive (-LI) neurones include: (1) efferent dorsal and ventral unpaired median (DUM, VUM) neurones; (2) several intersegmentally projecting DUM interneurones in the suboesophageal ganglion; other DUM interneurones are probably GABAergic; (3) a pair of anterior median cells in the prothoracic ganglion; (4) a single pair of ventral cells in most thoracic and some other ganglia; these appear to be plurisegmentally projecting interneurones. Eight categories of octopamine-LI neurones occur in the orthopteran brain. The basic projections of three types are described here: one class project to the optic lobes to form wide field projections. Another type descends to cross into the tritocerebral commissure and may invade the contralateral brain hemisphere. A further class is the median neurosecretory cells with axons in the nervi corpori cardiaci I. Available data for the honey bee Apis mellifera and moth Manduca sexta indicate that the octopamine-LI cell types found in orthopterans also occur in holometabolous insects. Immunocytochemical evidence suggests that some octopaminergic DUM cells contain an FMRFamide-related peptide and the amino acid taurine as putative cotransmitters.

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 giant 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.

Axogenesis in the embryonic brain of the grasshopper Schistocerca gregaria: an identified cell analysis of early brain development.

Axogenesis in the embryonic brain was studied at the single cell level in the grasshopper Schistocerca gregaria. A small set of individually identifiable pioneer neurons establishes a primary axon scaffold during early embryogenesis. At the beginning of scaffold formation, pioneering axons navigate along and between glial borders that surround clusters of proliferating neuroblasts. In each brain hemisphere, an axonal outgrowth cascade involving a series of pioneer neurons establishes a pathway from the optic ganglia to the brain midline. At the midline the primary preoral commissural interconnection in the embryonic brain is pioneered by a pair of midline-derived pioneer neurons. A second preoral commissural connection is pioneered by two pairs of pars intercerebralis pioneer neurons. Descending tracts are pioneered by the progeny of identified neuroblasts in the pars intercerebralis, deutocerebrum and tritocerebrum; the postoral tritocerebral commissure is pioneered by a pair of tritocerebral neurons. All of the pioneering brain neurons express the cell adhesion molecule fasciclin I during initial axon outgrowth and fasciculation. Once established, the primary axon scaffold of the brain is used for fasciculation by subsequently differentiating neurons and, by the 40% stage of embryogenesis, axonal projections that characterize the mature brain become evident. The single cell analysis of grasshopper brain development presented here sets the stage for manipulative cell biological experiments and provides the basis for comparative molecular genetic studies of embryonic brain development in Drosophila.

Ontogenetic studies of flight initiation in Locusta: Wind response of an identified interneurone (TCG)

The tritocerebral commissure giant (TCG) wind-sensitive interneurone is involved in initiation and maintenance of flight in adult locusts. In this paper we study this interneurone in the imago and non-flying larval instars. Cobalt fills show that the TCG establishes its adult morphology by the first larval instar. An accompanying axon, apparently representing the peculiar tritocerebral commissure “dwarf” (TCD) is present, too, at least for the last preimaginal instars. Physiological tests show similar responses of the TCG to wind stimuli in the 4th, 5th instar and adult stages. Spike activity, however, is usually higher in adult compared to larval instars. It is possible that all interneurones, involved in adult-specific motor patterns (such as flight), are present in preimaginal stages and can be activated independently of the function of the final motor system.

Temperature compensation in the nervous system of the grasshopper

Abstract The wind‐sensitive head hair neurones of the grasshopper Schistocerca americana (Drury) are influenced by temperature, increasing the number of spikes fired in response to a given hair deflection as temperature increases. Because these neurones show similar increases in spike output for greater hair deflections, an interneurone which receives their input would not be able to distinguish changes in stimulus strength from changes in temperature, unless the effects of temperature were compensated or independently measured. This study examines the effects of temperature on the output of the tritocerebral commissure giant (TCG), an interneurone that receives wind hair input. Some wind hairs provide excitatory input to the TCG, while others are inhibitory (Bacon & Möhl, 1983). Temperature variations similar to those measured in freely moving animals were applied to the wind hairs and TCG while the interneurone's spike output was recorded. Two manipulations resulted in temperature compensated outputs from the TCG: (1) When both excitatory and inhibitory hair fields were stimulated simultaneously, the temperature sensitivity of the interneurone's spike output was significantly lower than when the excitatory hairs alone were stimulated. (2) The spike output of the TCG showed very little sensitivity to temperature changes which occurred only at its wind hair inputs, the temperature of the interneurone itself remaining constant. It is therefore possible for the output of a neural circuit to be temperature compensated even though the circuit itself may be composed of temperature‐sensitive units. Possible mechanisms by which temperature compensation may be produced in the TCG are discussed, and the behavioural relevance of the conditions under which TCG output is temperature compensated is considered.

GABA-like immunoreactivity in the suboesophageal ganglion of the locust Schistocerca gregaria

Neurones in the suboesophageal ganglion of the locust Schistocerca gregaria were stained with an antiserum raised against gamma amino butyric acid (GABA). This ganglion consists of the fused mandibular, maxillary and labial neuromeres. Immunoreactive cell bodies of similar size and distribution occur in the lateral, ventral and middorsal regions of all three neuromeres. Approximately 200 cell bodies stain in both the mandibular and maxillary neuromeres and 270 in the labial neuromere. A few distinctly larger cells occur in the ventral groups and one large pair occurs in the lateral group of the maxillary neuromere. Dorsal commissures DCIV and DCV are composed mainly of stained fibres, while DCI–DCIII are largely unstained. A ventral commissure also stains in the maxillary neuromere. All longitudinal tracts contain both stained and unstained fibres. Many processes within the neuropil are also immunoreactive. A stained axon is found in the posterior tritocerebral commissure which enters the anterior dorsal region of the mandibular neuromere. The salivary branch of the 7th nerve contains one stained axon and two axons stain in nerve 8 which innervates neck muscles.

The tritocerebral commissure 'dwarf' (TCD): a major GABA-immunoreactive descending interneuron in the locust.

The minor branch of the tritocerebral commissure of the locust, Locusta migratoria, contains only two axons which are from interneurons in the brain descending to the ventral cord ganglia. The smaller of these two neurons, the tritocerebral commissure dwarf (TCD), is immunoreactive to GABA, suggesting that it may be an inhibitory interneuron. We have exploited the accessibility of its axon in the commissure, first, to fill it with cobalt to define its morphology, and second, to record its input characteristics. It has a cell body and arborization of fine branches in the deutocerebrum of the brain, its axon passes contralateral through the tritocerebral commissure and it forms bilateral arborizations in the suboesophageal and three thoracic ganglia. It receives mechanosensory input from many regions of the ipsilateral body and head, and it is sensitive to illumination levels, generally showing greater spontaneous activity in the dark. It is one of the largest GABA-immunoreactive descending interneurons in the locust, suggesting it plays a prominent role in behaviour. Since it is easily accessible for physiological recording, its roles in circuits for particular components of behaviour should be amenable to investigation.

Course correction circuitry translates feature detection into behavioural action in locusts

Like other flying animals, locusts must maintain course stability despite turbulence and motor errors. Accordingly, they must detect course deviations and then correct them. The compound eyes, the ocelli and the cephalic wind hairs all detect different sensory consequences of flight instability1–3,and descending interneurones bring this information to the thorax4–9. One such interneurone of this population (the tritocerebral commissure giant neurone) is known to elicit correctional steering10.Here we characterize three additional pairs of descending deviation detector neurones and show how their information is translated into altered drive to the flight motoneurones. The central pattern generator for flight11–13,modulated by proprioceptive feedback14, gates the signal of the detector neurones in thoracic premotor interneurones9,ensuring that the flight motoneurones are affected only during flight. Further, the gating process transforms the phase-independent information of the deviation detectors into a phase-dependent signal modulated at wing-beat frequency, and transfers it to those flight motoneurones active at the time and appropriate to the corrective action required.

The development of projections and connections from transplanted locust sensory neurons

Neurons innervating wind-sensitive hairs on the locust head form characteristic projections and connections within the CNS. These depend on intrinsic properties of the epidermis from which the hair and its neuron are formed (Anderson & Bacon, 1979; Bacon & Anderson, 1984). To investigate further these intrinsic properties and also extrinsic factors involved in guiding axon growth and determining synaptic connectivity, pieces of epidermis from the head were transplanted to the posterior head, prothorax, or mesothorax. Thus wind-sensitive neurons developing from the grafts were caused to grow into foreign parts of the CNS. The neuronal projections from the graft hairs were examined by filling the axons with cobalt, and their connectivity with an identified interneuron, the Tritocerebral Commissure Giant, was examined by recording electrophysiologically the activity of the interneuron during stimulation of the graft hairs. The results show that the neuronal projections are confined to one tract, the median ventral tract, and to one arborization area, the ventral association centre, in all ganglia; in all ganglia, neurons from different epidermal regions preserve their location-specific properties of forming ipsilateral or additional contralateral projections; the extent of their projection in the CNS is not interpretable in terms of intrinsic instructions only; in foreign ganglia, they fail to form connections with their normal target interneuron.

Short Communications Initiation of Flight By an Identified Wind Sensitive Neurone (Tcg) in The Locust

ABSTRACT When the tarsi are not in contact with the ground, brief wind stimuli applied to the wind sensitive hairs on the head elicit flight in the locust (Weis-Fogh, 1949; Camhi, 1969). The descending interneurones mediating this reaction have not been identified but some likely candidates have been reported (Bacon & Tyrer, 1978; Simmons, 1980, 1981). The most extensively studied is the tritocerebral commissure giant (TCG) (Bacon & Tyrer, 1978; Bacon & Möhl, 1979). This large wind sensitive interneurone descends from the brain, crosses to the contralateral side of the nerve cord via the tritocerebral commissure, and makes excitatory connections with some flight motor neurones in the thoracic ganglia (Bacon & Tyrer, 1979). The location of the TCG’s axon in the tritocerebral commissure makes this neurone easily accessible for recording and stimulation in almost intact, freely moving animals. Recordings during flight, for example, have shown that the TCG discharges one or two spikes during each cycle (Bacon & Möhl, 1979). The spike activity results from rhythmic air turbulences caused by flapping of the wings and head movements during flight. This rhythmic activity may play a role in regulating motor output during flight manoeuvres, such as yaw (B. Möhl & J. Bacon, in preparation). It seems unlikely however that this is the only function for the TCG since it is capable of discharging in very high frequency bursts quite unlike those occurring in flying animals. Here we present evidence that the TCG also functions to facilitate the initiation of flight following a jump.

The tritocerebral commissure giant (TCG): A bimodal interneurone in the locust,Schistocerca gregaria

A large interneurone responding to stimulation both by wind on the head and to light is described in the locust,Schistocerca gregaria. The neurone has been filled with cobalt and intensified with silver. Its cell body lies in the brain. There is a tuft of fine branches in the tritocerebrum which receives input from the primary sensory projections of the sensory hairs on the head. The neurone descends to the suboesophageal and thoracic ganglia via the tritocerebral commissure and branches extensively in each ganglion on the side contralateral to the projection in the brain. The response of the neurone to both stimulus modes has been recorded at the tritocerebral commissure.

Isolation of three chromatophorotropic hormones from the eyestalk of the shrimp Crangon crangon

The hormones present in the water extract of the eyestalks of Crangon crangon (L.) were separated by gel filtration on Sephadex G-25 fine in 0.1 M acetic acid. Chromatophorotropic activity was present in 3 separate fractions. Peak II (Fig. 1) contained Black Pigment Dispersing Hormone (BPDH); a concentrating activity, especially towards the pigment of leucophores, was present in fraction IIIA (WPCH). Peak IV contained Red Pigment Concentrating Hormone (RPCH). Combining BPDH with RPCH in the ratio 5:1, effects of lightening of the body and darkening of the telson and uropods were observed. A similar effect was produced when BPDH and WPCH were combined in the ratio 1:1. Such effects have not been previously described for eyestalk hormones, but only for the hormones of the tritocerebral commissure. In the crude water extract of the eyestalk, BPDH is inhibited by the remaining 2 hormones (WPCH and RPCH), and shows no dispersing effect when tested on eyestalkless C. crangon.