Barbara S. Beltz

Distribution and functional anatomy of amine-containing neurons in decapod crustaceans.

One of the lessons learned from studying the nervous systems of phylogenetically distant species is that many features are conserved. Indeed, aminergic neurons in invertebrate and vertebrate systems share a multitude of common characteristics. In this review, the varied roles of serotonin, octopamine, dopamine, and histamine in decapod crustaceans are considered, and the distributions of the amine‐containing cells are described. The anatomy of these systems reinforces the idea that amine neurons are involved in widespread modulation and coordination within the nervous system. Many aminergic neurons have long projections, linking multiple regions with a common input, and therefore are anatomically perfected as “gain setters.” The developmental patterns of appearance of each amine in the crustacean nervous system are described and compared. The developmental picture suggests that transmitter acquisition is distinctive for each amine, and that the pace of acquisition may be co‐regulated with target maturation. The distinctive roles that transmitters play during specific developmental periods may, ultimately, provide important clues to their functional contributions in the mature organism. Microsc. Res. Tech. 44:105–120, 1999.

CRUSTACEAN HYPERGLYCEMIC HORMONE IN THE LOBSTER NERVOUS SYSTEM : LOCALIZATION AND RELEASE FROM CELLS IN THE SUBESOPHAGEAL GANGLION AND THORACIC SECOND ROOTS

Crustacean hyperglycemic hormones (CHHs) are neuropeptides involved in the regulation of hemolymph glucose. The primary source of CHHs has been identified as the neurosecretory neurons of the eyestalk X‐organ and its associated neurohemal organ, the sinus gland. We have identified another source of CHH‐like peptides in the nervous system. With the use of immunocytochemistry, cells in the second roots of the thoracic ganglia have been observed to stain positively for CHH‐reactive material. We also identified a pair of cells in the subesophageal ganglion that contain large amounts of CHH‐reactive material. Depolarization of these cells with elevated potassium mediates a calcium‐dependent release of CHH‐like material from the ganglion as quantified with an enzyme‐linked immunosorbent assay (ELISA). J. Comp. Neurol. 414:50–56, 1999.

Physiological identification, morphological analysis, and development of identified serotonin-proctolin containing neurons in the lobster ventral nerve cord

Amines and peptides exert a wide range of physiological actions on both central neurons and peripheral tissues. Among these actions, serotonin and octopamine are known to trigger contrasting postures when injected into freely moving lobsters. Immunocytochemical studies of lobster ganglia have identified presumptive serotonergic neurons, their central and peripheral projections, and their terminal fields of arborization. More than 100 neurons that show serotonin-like immunoreactivity have been found in the lobster nervous system (Beltz and Kravitz, 1983). From immunocytochemical studies it appears that varicosities within peripheral neurosecretory structures and endings in certain central neuropil regions arise from the same 2 pairs of large cells located in the fifth thoracic (T5) and first abdominal (A1) ganglia. Because we believed that such cells could account for the central and peripheral actions of serotonin on the postural system, we chose to study these 2 pairs of neurons in greater detail. In the previous paper, Siwicki et al. (1987) report that these neurons contain the pentapeptide proctolin in addition to serotonin. In this communication, we report that these cells can be identified reliably in living preparations; they have large fields of innervation projecting anteriorly into at least 4 segmental ganglia; these neurons are the origin of the fibers that form the thoracic second root neurosecretory regions; they are generally spontaneously active neurons that have overshooting action potentials in their cell bodies; and the serotonin and proctolin immunoreactivities are first expressed in these cells at widely different times in development.

Adult Neurogenesis: A Common Strategy Across Diverse Species

Adult neurogenesis, the generation of new neurons from adult precursor cells, occurs in the brains of a phylogenetically diverse array of animals. In the higher (amniotic) vertebrates, these precursor cells are glial cells that reside within specialized regions, known as neurogenic niches, the elements of which both support and regulate neurogenesis. The in vivo identity and location of the precursor cells responsible for adult neurogenesis in nonvertebrate taxa, however, remain largely unknown. Among the invertebrates, adult neurogenesis has been particularly well characterized in freshwater crayfish (Arthropoda, Crustacea), although the identity of the precursor cells sustaining continuous neuronal proliferation in these animals has yet to be established. Here we provide evidence suggesting that, as in the higher vertebrates, the precursor cells maintaining adult neurogenesis in the crayfish Procambarus clarkii are glial cells. These precursor cells reside within a specialized region, or niche, on the ventral surface of the brain, and their progeny migrate from this niche along glial fibers and then proliferate to form new neurons in the central olfactory pathway. The niche in which these precursor cells reside has many features in common with the neurogenic niches of higher vertebrates. These commonalities include: glial cells functioning as both precursor and support cells, directed migration, close association with the brain vasculature, and specialized basal laminae. The cellular machinery maintaining adult neurogenesis appears, therefore, to be shared by widely disparate taxa. These extensive structural and functional parallels suggest a common strategy for the generation of new neurons in adult brains. J. Comp. Neurol. 500:574–584, 2007.

A new look at embryonic development of the visual system in decapod crustaceans: neuropil formation, neurogenesis, and apoptotic cell death.

In recent years, comparing the structure and development of the central nervous system in crustaceans has provided new insights into the phylogenetic relationships of arthropods. Furthermore, the structural evolution of the compound eyes and optic ganglia of adult arthropods has been discussed, but it was not possible to compare the ontogeny of arthropod visual systems, owing to the lack of data on species other than insects. In the present report, we studied the development of the crustacean visual system by examining neurogenesis, neuropil formation, and apoptotic cell death in embryos of the American lobster, Homarus americanus, the spider crab, Hyas araneus, and the caridean shrimp, Palaemonetes argentinus, and compare these processes with those found in insects. Our results on the patterns of stem cell proliferation provide evidence that in decapod crustaceans and hemimetabolous insects, there exist considerable similarities in the mechanisms by which accretion of the compound eyes and growth of the optic lobes is achieved, suggesting an evolutionary conservation of these mechanisms.

The well-modulated lobster: The roles of serotonin, octopamine, and proctolin in the lobster nervous system

Abstract Two amines, serotonin and octopamine, and a pentapeptide, proctolin, function as neurohormones in the lobster nervous system. This review article summarizes findings from this laboratory on: (i) the biosynthesis and further metabolism of the amines; (ii) the localization of amines at a cellular level using immunocytochemical methods; (iii) the physiological effects of the amines and proctolin on exoskeletal muscles and preliminary studies of the molecular basis of these effects; and (iv) explorations on the actions of amines on motoneurons of the ventral nerve cord that show that amines direct the readout of central motor programs for flexion and extension.

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. J. Comp. Neurol. 441:9–22, 2001.

Ecological, evolutionary, and functional correlates of sensilla number and glomerular density in the olfactory system of decapod crustaceans

One of the features common among olfactory systems for vertebrate and invertebrate species is the division of the primary processing area into distinct clumps of synaptic neuropil, called glomeruli. The olfactory glomeruli appear to serve as functional units of olfaction and are the location of the primary processing between chemosensory afferents and second‐order neurons. Although glomeruli are found across all phyla, their numbers and size appear to be characteristic for each species, giving rise to the speculation that there is a relationship between glomerular number and function. It has been hypothesized, for example, that animals with more glomeruli may be able to resolve a wider range of odors. Crustacean species are distributed among freshwater, marine, and terrestrial habitats in arctic, temperate, and tropical climates. They also exhibit a variety of lifestyles and behaviors in which olfaction may play a dominant role. Feeding, for example, ranges from carnivorous, through subaquatic and terrestrial omnivorous scavenging, to filter feeding. Mating and territorial behaviors also are known to involve chemical signals. The current study examines glomerular numbers in the olfactory lobes of 17 crustacean species from six of the seven taxa now included in the reptantian decapods. Estimates of the glomerular numbers were obtained from the analysis of sectioned material treated immunocytochemically with an antibody against synapsin that labels proteins contained in neuronal terminals. The numbers of glomeruli found in the different species were then compared with the volume of the glomerular neuropil, numbers of olfactory sensilla, life styles, habitat, and phylogenetic affinities. The picture that emerges from these correlations is that the decapod crustaceans have exploited various strategies in the construction of their olfactory systems in which the problems of size, sensitivity, and selectivity have all interacted. We find a continuum across the groups ranging from those that favor a high convergence of receptor neurons onto a few glomeruli to those that share a small number of receptor neurons among many glomeruli. The potential functional consequences of these differences are discussed. J. Comp. Neurol. 455:260–269, 2003.

Amines and peptides in the brain of the American lobster: immunocytochemical localization patterns and implications for brain function

Abstract.The distributions of serotonin- (5HT-), substance P- (SP-), small cardioactive peptideb- (SCPb-), and histamine- (HA-) like immunoreactivities were examined in the adult lobster supraesophageal ganglion. Vibratome sections were labeled using avidin-biotin-peroxidase immunocytochemical methods. The localization patterns for each substance were assessed in 21 regions within the median protocerebrum, deutocerebrum, and tritocerebrum. Each immunoreactivity has a unique distribution within the brain; however, most regions are immunoreactive for more than one neurotransmitter. Of particular interest are SP-immunoreactive protocerebral neurons that contact olfactory projection neurons and appear homologous to those found in other crustaceans. Regional differences in immunolabeling within the deutocerebral olfactory and accessory lobes suggest that specific areas within individual olfactory lobe glomeruli serve distinct functions in olfactory processing, and that subpopulations of accessory lobe glomeruli are innervated by different groups of neurons. This detailed comparison of the labeling patterns also has allowed us to define the anatomical connectivity between several cell body clusters, fiber tracts, and neuropil areas in the lobster brain.

Regulation of life-long neurogenesis in the decapod crustacean brain

This article provides an overview of our understanding of life-long neurogenesis in the decapod crustacean brain, where the proliferation of sensory and interneurons is controlled by many of the same factors as is neurogenesis in the mammalian brain. The relative simplicity, spatial organization and accessibility of the crustacean brain provide opportunities to examine specific neuronal pathways that regulate neurogenesis and the sequence of gene expression that leads to neuronal differentiation.