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PubMed2002

Identification of orcokinins in single neurons in the stomatogastric nervous system of the crayfish, Cherax destructor.

The orcokinins are a highly conserved family of crustacean peptides that enhance hindgut contractions in the crayfish Orconectes limosus (Stangier et al. [1992] Peptides 13:859-864). By combining immunocytochemical and mass spectrometrical analysis of the stomatogastric nervous system (STNS) in the crayfish Cherax destructor, we show that multiple orcokinins are synthesized in single neurons. Immunocytochemistry demonstrated orcokinin-like immunoreactivity in all four ganglia of the STNS and in the pericardial organs, a major neurohaemal organ. Identified neurons in the STNS were stained, including a pair of modulatory interneurons (inferior ventricular nerve neuron, IVN), a neuron with its cell body in the stomatogastric ganglion that innervates cardiac muscle c6 via the anterior median nerves (AM-c6), and a sensory neuron (anterior gastric receptor neuron). Five orcokinin-related peptides were identified by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) post source decay fragmentation in samples of either the stomatogastric ganglion or the pericardial organs. Four of these peptides are identical to peptides derived from the cloned Procambarus clarkii precursor (Yasuda-Kamatani and Yasuda [2000] Gen. Comp. Endocrinol. 118:161-172), including the original [Asn(13)]-orcokinin (NFDEIDRSGFGFN, [M+H](+) = 1,517.7 Da), [Val(13)]-orcokinin ([M+H](+) = 1,502.7 Da), [Thr(8)-His(13)]-orcokinin ([M+H](+) = 1,554.8 Da), and FDAFTTGFGHS ([M+H](+) = 1,186.5 Da). The fifth peptide is a hitherto unknown orcokinin variant: [Ala(8)-Ala(13)]-orcokinin ([M+H](+) = 1,458.7 Da). The masses of all five peptides were also detected in the inferior ventricular nerve of C. destructor, which contains the cell bodies and axons of the IVNs as well as the axons of two other orcokinin-like immunoreactive neurons. In the oesophageal nerve, in which all the orcokinin-like immunoreactivity derives from the IVNs, at least two of the orcokinins were detected, indicating that multiple orcokinins are synthesized in these neurons. Similarly, all four orcokinin masses were detected in the anterior median nerves, in which all the orcokinin-like immunoreactivity derives from the AM-c6 neuron. This study therefore lays the groundwork to investigate the function of the orcokinin peptide family using single identified neurons in a well-studied system.

Animals↗
PubMed2002

Remodeling of the proximal segment of crayfish motor nerves following transection.

Transected crustacean motor axons consist of a soma-endowed proximal segment that regenerates and a soma-less distal segment that survives for up to a year. We report on the anatomical remodeling of the proximal segment of phasic motor nerves innervating the deep flexor muscles in the abdomen of adult crayfish following transection. The intact nerve with 10 phasic axons and its two branches with subsets of 6 and 7 of these 10 axons undergo several remodeling changes. First, the transected nerve displays many more and smaller axon profiles than the 6 and 7 axons of the intact nerve, approximately 100 and 300 profiles in the two branches of a preparation transected 8 weeks previously. Serial images of the transected nerve denote that the proliferation of profiles is due to several orders of axon sprouting primary, secondary, and tertiary branches. The greater proliferation of axon sprouts, their smaller size, and the absence of intervening glia in the one nerve branch compared with the other branch denote that sprouting is more advanced in this branch. Second, the axon sprouts are regionally differentiated; thus, although in most regions the sprouts are basically axon-like, with a cytoskeleton of microtubules and peripheral mitochondria, in some regions they appear nerve terminal-like and are characterized by numerous clear synaptic vesicles, a few dense-core vesicles, and dispersed mitochondria. Both regions possess active zone dense bars with clustered synaptic vesicles found opposite other sprouts, glia, hemocytes, and connective tissue, but because the opposing membranes are not differentiated into a synaptic contact, the active zones are extrasynaptic. Third, some of the transected axons display a glial cell nucleus denoting assimilation of an adaxonal glial cell by the transected axons. Fourth, within the nerve trunk are a few myocytes and muscle fibers. These most likely originate from adjoining and intimately connected hemocytes, because such transformation occurs during muscle repair. In a crustacean nerve, however, where muscle is clearly misplaced, its presence implies an instructive role for motor nerves in muscle formation.

Animals↗
PubMed2001

Dichotomy in phasic-tonic neuromuscular structure of crayfish inhibitory axons.

Crustacean muscles are unique in their innervation by both excitatory and inhibitory neurons; therefore, they exhibit polyneuronal and multiterminal innervation. Because excitatory motoneurons are broadly divided into phasic and tonic types, we hypothesized that inhibitory neurons would follow a similar dichotomy. The abdominal extensor muscles in crayfish are separated into parallel deep and superficial bundles; the former has fast muscle fibers innervated by phasic excitatory motoneurons, and the latter has slow fibers supplied by tonic excitatory motoneurons. Each muscle also is innervated by a single, separate inhibitory neuron that uses gamma-aminobutyric acid (GABA) as the inhibitory neurotransmitter. The pattern of axonal branching by the separate inhibitory axons in phasic and tonic abdominal extensor muscles was visualized with confocal microscopy in preparations labeled for GABA-like immunoreactivity. Initial observations indicated that the phasic muscle was covered by extensive GABAergic, filiform axon terminals, whereas innervation of the tonic muscle was comprised of more localized and varicose terminals. With quantitative analyses, we found that the phasic axon has a more highly branched nature than the tonic in first- and second-order branches. The phasic axon branches also were significantly longer than the tonic branches in the second- and third-order branches. Synaptic varicosities in the phasic branches were smaller and less frequent than those in the tonic branches. The fine structure of the inhibitory nerve terminals near synaptic contacts examined with thin-serial-section electron microscopy revealed distinct differences between the phasic system and the tonic system. The phasic terminals were smaller in cross-sectional area than the tonic terminals, and they had smaller synapses and fewer mitochondria. The presynaptic active zone dense bodies were similar in length and number between phasic and tonic synapses. However, their number per synaptic area was two-fold higher in phasic synapses compared with tonic synapses because of the smaller size of the phasic synapses. Thus, within the same neuromuscular system, inhibitory synaptic terminals revealed unique phasic and tonic identities similar to those observed for the excitatory axons.

Animals↗
PubMed2003

Parasol cells of the hemiellipsoid body in the crayfish Procambarus clarkii: dendritic branching patterns and functional implications.

Multimodal, higher-order sensory integration in decapod crustaceans occurs in local interneurons (parasol cells) within a structure in the lateral protocerebrum, the hemiellipsoid body, which is located dorsal to the terminal medulla. The hemiellipsoid body is targeted by projection neuron inputs by means of the olfactory globular tract from bilateral deutocerebral neuropils, the accessory lobes, which receive secondary visual, mechanosensory, and olfactory inputs. Parasol cell dendrites arborize extensively within the two neuropils of the hemiellipsoid body and possibly have some neurites within another neuropil at its base. The two neuropils of the hemiellipsoid body, neuropils I and II, are known to receive asymmetrical inputs from the contralateral and ipsilateral accessory lobes, and our current study addresses the question of the distribution of parasol cells within these two neuropils. Three anatomic methods were used to analyze this distribution: intracellular filling of cells with neurobiotin and visualization of the cells by using either a fluorescent or a peroxidase avidin conjugate, or placement of a fluorescent lipophilic tracer within a lobe of the hemiellipsoid body. All of these methods demonstrated that single parasol cells exclusively arborize within one of the two lobes of the hemiellipsoid body, but not in both lobes. Electrophysiological recordings from pairs of parasol cells with dendrites in the same or different lobes confirm a functional separation between neuropils I and II. Comparisons are made between insect and crustacean systems, emphasizing the inputs to the hemiellipsoid body and the mushroom body and similarities between extrinsic cells in insects and parasol cells in decapod crustaceans.

Animals↗
PubMed2003

Differential dye coupling reveals lateral giant escape circuit in crayfish.

The lateral giant (LG) escape circuit of crayfish mediates a coordinated escape triggered by strong attack to the abdomen. The LG circuit is one of the best understood of small systems, but models of the circuit have mostly been limited to simple ball-and-stick representations, which ignore anatomical details of contacts between circuit elements. Many of the these contacts are electrical; here we use differential dye coupling, a technique which could help reveal connection patterns in many neural circuits, to reveal in detail the circuit within the terminal abdominal ganglion. Sensory input from the tailfan forms a somatotopic map on the projecting LG dendrites, which together with interafferent coupling mediates a lateral excitatory network that selectively amplifies strong, phasic, converging input to LG. Mechanosensory interneurons contact LG at sites distinct from the primary afferents and so maximize their summated effect on LG. Motor neurons and premotor interneurons are excited near the initial segments of the LGs and innervate muscles for generating uropod flaring and telson flexion. Previous research has shown that spatial patterns of input are important for signal integration in LG; this map of electrical contact points will help us to understand synaptic processing in this system.

Action Potentials↗
PubMed2003

Regenerating crayfish motor axons assimilate glial cells and sprout in cultured explants.

Phasic and tonic motor nerves originating from crayfish abdominal ganglia, in 2-3-day-old cultured explants, display at their transected distal ends growth zones from which axonal sprouts arise. The subcellular morphology of this regenerative response was examined with thin serial-section electron microscopy and reveals two major remodeling features. First, the external sprouts that exit the nerve are a very small part of a much more massive sprouting response by individual axons comprising several orders of internal sprouts confined to the nerve. Both internal and external sprouts have a simple construction: a cytoskeleton of microtubules and populations of mitochondria, clear synaptic vesicles, membranous sacs, and extrasynaptic active zone dense bars, features reminiscent of motor nerve terminals. Close intermingling of the sprouts of several axons give rise to a neuropil-like arbor within the nerve. Thus, extensive sprouting is an intrinsic response of crayfish motor axons to transection. Second, an equally dramatic remodeling feature is the appearance of nuclei, which resemble those of adjacent glial cells, within the motor axons. These nuclei often appear where the adjoining membranes of the axon and glial cell are disrupted and where free-standing lengths of the double membrane are present. These images signify a breakdown of the dividing membranes and assimilation of the glial cell by the axon, the nucleus being the most visible sign of such assimilation. Thus, crayfish motor axons respond to transection by assimilating glial cells that may provide regulatory and trophic support for the sprouting response.

Abdomen↗
PubMed2003

Presynaptic membrane of inhibitory crayfish axon terminals is stained by antibodies raised against mammalian GABA(A) receptor subunits alpha3 and beta(2/3).

The opener muscle of the dactyl of the walking leg of crayfish is innervated by one excitatory axon releasing glutamate and one inhibitory axon releasing GABA. Functional GABA(A) receptors are present postsynaptically on the muscle and presynaptically on terminals and release boutons of the excitatory axon, whereas presynaptic GABA(A) autoreceptors have not been reported on terminals or release boutons of the inhibitory axon. Using antibodies raised against mammalian GABA(A) receptor subunits alpha3 and beta(2/3), we obtained highly specific staining of the presynaptic membrane of the inhibitory bouton and of the postsynaptic membrane of the muscle. Using pre- and postembedding techniques, staining was localized to only presynaptic and postsynaptic membranes of synaptic active zones. We also found extrasynaptic receptor subunit immunoreactivity near (up to 100 nm) to the active zones. Staining with antibodies for the alpha3 and beta(2/3) subunits showed colocalization of particles of the two subunits. We suggest that presynaptic inhibitory boutons of the crayfish possess GABA(A)-like autoreceptors composed of at least the alpha3 and beta(2/3) subunits.

Animals↗
PubMed2003

Local commissural interneurons integrate information from intersegmental coordinating interneurons.

The information that coordinates movements of swimmerets on different segments of the crayfish abdomen is conducted by interneurons that originate in each abdominal ganglion. These interneurons project axons to neighboring ganglia and beyond. To discover the anatomy of these axons in their target ganglia, we used Neurobiotin and dextran-Texas Red microelectrodes to fill them near their targets. Coordinating axons coursed through these target ganglia close to the midline and extended only a few short branches that did not approach the lateral neuropils. Two of the three types of coordinating axons made direct synaptic connections with a class of local commissural interneurons that relayed the information to targets in the swimmeret pattern-generating circuits. These commissural interneurons, named here ComInt 1 neurons, followed a particular route to cross the midline and reach their targets. ComInt 1 neurons were nonspiking; they received EPSPs from the coordinating axons near the midline and transmitted this information to their targets in the lateral neuropils using graded transmission. The output of each ComInt 1 was restricted to a single local circuit and had opposite effects on the power-stroke and return-stroke motor neurons driven by that circuit. ComInt 1 neurons were direct postsynaptic targets of both descending and ascending coordinating axons that originated in other anterior and posterior ganglia. Because of phase differences in the impulses in these different coordinating axons, their signals arrived simultaneously at each ComInt 1. We discuss these findings in the context of alternative models of the intersegmental coordinating circuit.

Animals↗
PubMed2003

Immunocytochemical evidence for nitric oxide- and carbon monoxide-producing neurons in the stomatogastric nervous system of the crayfish Cherax quadricarinatus.

Nitric oxide (NO) and carbon monoxide (CO) have been shown to serve neuromodulatory roles in both vertebrates and invertebrates. Here, we use antibodies to their respective biosynthetic enzymes, nitric oxide synthase (NOS) and heme oxygenase 2 (HO-2), to map the distribution of putative gas-producing neurons in the stomatogastric nervous system (STNS) of the crayfish Cherax quadricarinatus. In this species, NOS immunolabeling is found in the neuropil of the stomatogastric ganglion (STG). This staining originates from two immunopositive axons that project to the STG through the superior oesophageal and stomatogastric nerves, presumably from cell bodies located in the commissural ganglia (CoGs). HO-2 immunoreactivity is present in small diameter fibers and varicosities in the periphery of nerves located in the anterior portion of the STNS. This labeling originates from approximately 12 somata in each CoG. Transmission electron microscopy done on the nerves of the anterior STNS shows they contain a neuroendocrine plexus. Collectively, our results indicate that NO- and CO-producing neurons are likely to exist in the crayfish STNS. Moreover, these gases appear to be produced by distinct subsets of the neurons present there. The localization of NO to the STG neuropil suggests that it serves as a locally released modulator or is involved in the local release of other substances within this ganglion. The presence of CO in the neurohemal plexus of the anterior STNS suggests that it serves as a circulating hormone or is involved in the control of neuroendocrine release from this plexus.

Animals↗
PubMed2001

Quantitative analyses of anatomical and electrotonic structures of local spiking interneurons by three-dimensional morphometry in crayfish.

We quantitatively investigated the three-dimensional structure of the dendrites of local spiking interneurons using a confocal laser scanning microscope in the terminal abdominal ganglion of crayfish. We also studied their passive membrane properties electrophysiologically using the single-electrode current clamp techniques to analyze their electrotonic structure. All of the local spiking interneurons examined in this study lacked distinctive axonal structure and had a monopolar cell body that was connected with a fine primary process to a thick main segment. Numerous fine secondary processes projected from the main segment in the ganglionic neuropile. The average anatomical length of a secondary process from the main segment to its terminal was 261.9 +/- 15.2 microm. The average input resistance and membrane time constant of local spiking interneurons, obtained from their voltage responses to intracellular injection of step current pulses in the main segment, were 15.2 +/- 1.6 MOmega and 13.9 +/- 1.9 msec, respectively. Calculation of the electrotonic length of dendritic processes based on morphological and physiological data obtained in this study revealed that the average electrotonic length of secondary processes in local spiking interneurons was significantly longer than in local nonspiking interneurons, although both types of local interneurons showed apparently similar anaxonic structure. The steady-state voltage attenuation factors for the secondary processes of local spiking interneurons were significantly greater than those of local nonspiking interneurons in both centrifugal and centripetal directions. The larger electrotonic structure of local spiking interneurons compared to that of nonspiking interneurons appears to be compensated for by their excitable dendritic membrane.

Action Potentials↗
PubMed2004

Morphology and connections of the abdominal accessory neurons of the crayfish Cherax destructor.

Associated with the abdominal muscle receptor organs of crayfish are accessory neurons that inhibit the activity of the stretch receptors. Cobalt infusion into their cut axons reveals four accessory somata associated with each hemiganglion in the abdomen of the crayfish Cherax destructor. These conform to the pattern described previously for these neurons: The cell bodies are in the ganglion posterior to the one from which they exit. We recorded intracellularly from the largest accessory neurons, Acc-1 and Acc-2, and stained them with intracellular dye to establish unambiguously the characteristics defining their identity and structure. We describe their branching patterns in the ganglion of origin and the ganglion of exit. This morphological information permitted us to distinguish all four accessory neurons in preparations with dye infused through their cut axons, and we propose a revised, unambiguous nomenclature for the two smaller ones. Our intracelluar recordings allowed us to reexamine the physiological relationships of Acc-1 and Acc-2, the only accessory neurons for which there are data in the literature. In general, the connections and inputs described in previous studies were substantiated, although there has clearly been confusion between the two, and they differ in a number of significant ways. We found that they are seldom active together, have different firing patterns, and may operate with different clusters of extensor and flexor motorneurons. The results illustrate the level at which the accessory neurons operate within the abdominal control system but do not distinguish between competing hypotheses concerning their role in behavior. The data are consistent with the view that accessory neurons assist in timing between adjacent segments.

Abdomen↗
PubMed2001

Neural pathways connecting the deutocerebrum and lateral protocerebrum in the brains of decapod crustaceans.

The olfactory and accessory lobes of eureptantian decapod crustaceans are bilateral brain neuropil regions located within the deutocerebrum. Although the olfactory lobe seems to receive only primary olfactory inputs, the accessory lobe receives higher-order multimodal (including olfactory) inputs. The output pathways from both the olfactory and accessory lobes are provided by the axons of a large population of projection neurons, whose somata lie adjacent to the lobes. The axons of these neurons form a large tract that projects bilaterally to the medulla terminalis and hemiellipsoid body in the lateral protocerebrum. To gain insights into the ways in which olfactory information is processed on leaving the deutocerebrum, we examined the neuroanatomy of the projection neuron pathways of three species of eureptantian decapod crustaceans: the freshwater crayfish, Procambarus clarkii and Orconectes rusticus, and the clawed lobster, Homarus americanus. Projection neurons were labeled by focal injections of the lipophilic tracers DiI and DiA into the olfactory and accessory lobes. In all three species, projection neurons innervating the accessory lobe were found to exclusively innervate the neuropils of the hemiellipsoid body. In contrast, projection neurons innervating the olfactory lobes primarily target neuropil regions of the medulla terminalis. The results of this study indicate, therefore, that the projection neuron pathways from the olfactory and accessory lobes project to separate, largely nonoverlapping regions of the lateral protocerebrum. The implications of these findings for our understanding of the processing of olfactory information in the brains of decapod crustaceans are discussed.

Animals↗
PubMed2002

Enkephalinergic control of the secretory activity of neurons producing stereoisomers of crustacean hyperglycemic hormone in the eyestalk of the crayfish Orconectes limosus.

A subgroup of neurons in the classical X organ sinus gland neuroendocrine system of the crayfish (Orconectes limosus) eyestalk produces two chiral forms of the crustacean hyperglycemic hormone (CHH) in two different types of neurons: CHH in 22 cells and D Phe(3) CHH in eight cells. Previous reports have demonstrated that release of CHH from the sinus gland is inhibited by enkephalins. Here, we have addressed the questions of 1) whether this inhibition affects one or both types of CHH neurons, 2) where the site of enkephalinergic control of CHH and/or D Phe(3) CHH is, and 3) whether the inhibitory effect is due to direct or indirect interactions of enkephalinergic neurons with CHH cells. In vitro incubations of neurosecretory complexes followed by immunoassays of CHH isoforms indicated that both methionine and leucine enkephalins inhibit release of the two CHH isoforms from crayfish eyestalks, by a receptor mediated process. Whole mount double or triple immunofluorescence labelings combined with confocal microscopy revealed enkephalin immunostaining in all neuropils of the eyestalk, except in the sinus gland. Virtual thin confocal sections showed many close appositions between terminals of enkephalinergic neurons and dendritic arborizations of specific CHH immunoreactive cells in the medulla terminalis neuropil. This provides the first evidence for direct inputs from enkephalinergic neurons into dendrites of both CHH cell types, which suggests that enkephalins inhibit release of both CHH isoforms via synaptic contacts.

Animals↗
PubMed2004

A crustacean serotonin receptor: cloning and distribution in the thoracic ganglia of crayfish and freshwater prawn.

Serotonin (5-HT) is involved in regulating important aspects of behavior and a variety of systemic physiological functions in both vertebrates and invertebrates. These functions are mediated through binding to 5-HT receptors, of which approximately 13 have been characterized in mammals. In crustaceans, important model systems for the study of the neural basis of behaviors, 5-HT is also linked with higher-order behaviors, associated with different 5-HT receptors that have been identified at the physiological and pharmacological levels. However, no crustacean 5-HT receptors have been identified at the molecular level. We have cloned a putative 5-HT(1) receptor (5-HT(1crust)) from crayfish, prawn, and spiny lobster and have raised antibodies that recognize this protein in all three organisms. 5-HT(1crust) immunoreactivity (5-HT(1crust)ir) was observed surrounding the somata of specific groups of neurons and as punctate staining within the neuropil in all thoracic ganglia of crayfish and prawn. In the crayfish, 5-HT(1crust)ir was also found in boutons surrounding the first and second nerves of each ganglion and on the 5-HT cells of T1-4. In the prawn, 5-HT(1crust)ir was also found in axons that project across the ganglia and along the connectives. We found examples of colocalization of 5-HT(1crust) with 5-HT, consistent with the short-term modulatory role of 5-HT, as well as cases of serotonergic staining in the absence of a 5-HT(1crust) signal, which might imply that other 5-HT receptors are found at these locations. We also observed receptors that did not possess counterpart 5-HT staining, suggesting that these may also mediate long-term neurohormonal functions of serotonin.

Amino Acid Sequence↗
PubMed2004

Distribution of glutamatergic immunoreactive neurons in the terminal abdominal ganglion of the crayfish.

Using an antiserum directed against glutamate, we have analyzed the distribution of glutamate-like immunoreactive neurons in the terminal abdominal ganglion of the crayfish Procambarus clarkii. Approximately 160 central neurons (157 +/- 8; mean +/- SEM, n = 8) showed positive glutamate-like immunoreactivity, which represents approximately 25% of the total number of neurons in the terminal ganglion. Using a combination of intracellular staining with the marker Lucifer yellow and immunocytochemical staining has shown that most excitatory motor neurons are glutamatergic and that glutamate acts as an excitatory transmitter at peripheral neuromuscular junctions. Seven of 10 identified spiking local interneurons and only 2 of 19 identified ascending interneurons, showed positive immunoreactivity. Our observation that inhibitory spiking interneurons were immunopositive, whereas excitatory ascending interneurons were immunonegative, indicates that glutamate is likely to act as an inhibitory neurotransmitter within the central nervous system. Local pressure injection of L-glutamate into the neuropil of the ganglion caused a hyperpolarization of the membrane potentials of many interneurons. gamma-Aminobutyric acid (GABA)ergic posterolateral nonspiking interneurons and the bilateral nonspiking interneuron LDS showed no glutamate-like immunoreactivity, whereas non-GABAergic anterolateral III nonspiking interneurons showed glutamate-like immunoreactivity. Thus, not only GABA but also glutamate are used in parallel as inhibitory neurotransmitters at central synapses.

Abdomen↗
PubMed2004

Projection and local interneurons in the sixth abdominal ganglion of the sand crab Emerita analoga (Hippidae).

Hippid crabs are adapted for life in the surf zone of exposed sandy beaches, and their tailfan differs from the tailfans of other crustaceans with respect to morphology and motor control and in having nonspiking stretch receptors (NSR). To investigate how these crabs' mechanosensory systems are adapted to this turbulent environment, I used axonal back-filling and intracellular recording with dye-filled microelectrodes to describe afferent projections from the telson and morphologies and physiological responses of intersegmental and local neurons in abdominal ganglion 6 (A6) in Emerita analoga, then compared them with descriptions of corresponding neurons in A6 of crayfish. The density of afferent terminals and the proportion of projection neuron somata is lower in anterior A6 of E. analoga than in crayfish, perhaps correlated with a reduction in hydrodynamic setae. Many interneurons responded to afferent nerve stimulation and displayed activity correlated with levels of A6 motor output. NSR stretch depolarizes unilateral local neurons and terminals of axons entering A6 from the connective and hyperpolarizes bilateral local and projection neurons. The timing and duration of this inhibition would suppress mechanosensory input from the telson during uropod beating (homologue of crayfish's nongiant tail-flipping). Suppression of reafference during uropod beating may have been pivotal for evolution of hippids' ability to move rapidly across the water-sand interface in the slosh zone of sandy beaches. Homologies between A6 neurons in E. analoga and crayfish, suggested by morphological and physiological similarities, indicate that the NSRs connect to a neuronal network regulating exteroceptive input that was inherited from their tail-flipping ancestors.

Abdomen↗
PubMed2005

Integration and segregation of inputs to higher-order neuropils of the crayfish brain.

Information about the input and output pathways of higher-order brain neuropils is essential for gaining an understanding of their functions. The present study examines the connectivity of two higher-order neuropils in the central olfactory pathway of the crayfish: the accessory lobe and its target neuropil, the hemiellipsoid body. It is known that the two subregions of the accessory lobe, the cortex and medulla, receive different inputs; the medulla receives visual and tactile inputs, whereas the cortex receives neither (Sandeman et al. [1995] J Comp Neurol 352:263-279). By using dye injections into the olfactory lobe, we demonstrate that the accessory lobe cortex and medulla also have differing connections with the olfactory lobe. These injections show that local interneurons joining the olfactory and accessory lobes branch primarily within the cortex with only limited branching within the medulla. Injections of different dyes into the two subregions of the hemiellipsoid body, HBI and HBII, show that the accessory lobe cortex and medulla also have separate output pathways. HBI is innervated by the output pathway from the cortex while HBII is innervated by the output pathway from the medulla. These injections also show that HBI and HBII are innervated by separate populations of local interneurons with differing connections to higher-order neuropils in the olfactory and visual pathways. These results suggest a segregation of olfactory and multimodal (including olfactory) inputs within both the accessory lobe and the hemiellipsoid body and provide evidence of important functional subdivisions within both neuropils.

Animals↗
PubMed2005

Immunocytochemical mapping and quantification of expression of a putative type 1 serotonin receptor in the crayfish nervous system.

Serotonin is an important neurotransmitter that is involved in modulation of sensory, motor, and higher functions in many species. In the crayfish, which has been developed as a model for nervous system function for over a century, serotonin modulates several identified circuits. Although the cellular and circuit effects of serotonin have been extensively studied, little is known about the receptors that mediate these signals. Physiological data indicate that identified crustacean cells and circuits are modulated via several different serotonin receptors. We describe the detailed immunocytochemical localization of the crustacean type 1 serotonin receptor, 5-HT1crust, throughout the crayfish nerve cord and on abdominal superficial flexor muscles. 5-HT1crust is widely distributed in somata, including those of several identified neurons, and neuropil, suggesting both synaptic and neurohormonal roles. Individual animals show very different levels of 5-HT1crust immunoreactivity (5-HT(1crust)ir) ranging from preparations with hundreds of labeled cells per ganglion to some containing only a handful of 5-HT(1crust)ir cells in the entire nerve cord. The interanimal variability in 5-HT(1crust)ir is great, but individual nerve cords show a consistent level of labeling between ganglia. Quantitative RT-PCR shows that 5-HT1crust mRNA levels between animals are also variable but do not directly correlate with 5-HT(1crust)ir levels. Although there is no correlation of 5-HT1crust expression with gender, social status, molting or feeding, dominant animals show significantly greater variability than subordinates. Functional analysis of 5-HT1crust in combination with this immunocytochemical map will aid further understanding of this receptor's role in the actions of serotonin on identified circuits and cells.

Animals↗