Central projections of the antennal cold receptor neurons and hygroreceptor neurons of the cockroach Periplaneta americana

The central projections of the cold receptor axons were examined by filling two types of cold receptive sensilla with cobalt lysine—a cold and hygroreceptive (C/H) sensillum and a cold receptive and olfactory (C/O) sensillum—on the antennae of the cockroach, Periplaneta americana L. When the dye filled a single C/H sensillum, four axons were stained. Three of these axons terminate in the ipsilateral antennal lobe, while the other branches in the ipsilateral dorsal lobe. One of the branches passed through the tritocerebrum to terminate in the suboesophageal ganglion, while the other branches end in the lobe. When a single C/O sensillum is dye filled, all axons of the four receptor neurons terminate exclusively in the ipsilateral antennal lobe. One axon from the C/H sensillum and one axon from the C/O sensillum terminate in a particular glomerulus in the ventroposterior region of the antennal lobe. Each of these axons also has a tuft in separate giomeruli situated just dorsal to the glomerulus in which both axons terminate. This set of three glomeruli have indistinct boundaries and appear to form a complex of glomeruli similar to the macroglomerular complex of male moths. Assuming modality-specific convergence of antennal afferents, these axons appear to belong to the cold receptor neurons, and the set of glomeruli appear to function in cold reception. Two other neurons stained from C/H sensilla always terminate in theglom-eruli distinct from the set of glomeruli mentioned earlier. These neurons are assigned to the pair of hygroreceptor neurons, and their glomeruli are thought to function in hygroreception. © 1995 Wiley-Liss, Inc.     

Functional dissection of the neural substrates for gravitaxic maze behavior in Drosophila melanogaster

In animals, sensing gravity is supported by mechanosensory neurons that send information to the central brain for integration along with other modalities. In Drosophila, candidate sensory organs for detecting the gravity vector were predicted from the results of a recent forward genetic screen. This analysis also suggested possible roles for the central complex and antennal system in Drosophila. Using the same vertical maze assay employed in the original screen, we investigated the roles of these candidate neural structures by spatial and temporal inactivation of synaptic transmission with the GAL4/UAS-shibire[ts1] system. We correlate changes in the maze behavior of flies with specific inhibition of synaptic transmission for key brain neuropil that includes the central complex and antenno-glomerular tract. Further, our results point toward a minimal, or nonexistent, role for the mushroom bodies.     

Unique accumulation of neuropeptides in an insect: FMRFamide-related peptides in the cockroach, Periplaneta americana

FMRFamides belong to the most extensively studied neuropeptides in invertebrates and exhibit diverse physiological effects on different target organs, such as muscles, intestine and the nervous system. This study on the American cockroach confirms for the first time that extended FMRFamides occur in non-dipteran insects. By means of tandem mass spectrometry, these neuropeptides were structurally elucidated, and sequence information was used for subsequent cloning of the cockroach FMRFamide gene. This precursor gene encodes for 24 putative peptides and shows sufficient similarity with the Drosophila FMRFamide gene. Of the 24 peptides, 23 were detected by mass spectrometric methods; it is the highest number of neuropeptide forms shown to be expressed from a single precursor in any insect. The expression was traced back to single neurons in the thoracic ganglia. The unique accumulation of these FMRFamide-related peptides in thoracic perisympathetic organs provides the definite evidence for a tagma-specific distribution of peptidergic neurohormones in neurohaemal release sites of the insect CNS. Excitatory effects of the cockroach FMRFamides were observed on antenna-heart preparations. In addition, the newly described FMRFamides reduce the spike frequency of dorsal-unpaired median neurons and reduce the intracellular calcium concentration, which may affect the peripheral release of the biogenic amine octopamine.     

Comprehensive classification of the auditory sensory projections in the brain of the fruit fly Drosophila melanogaster

We established a comprehensive projection map of the auditory receptor cells (Johnston's organ neurons: JONs) from the antennae to the primary auditory center of the Drosophila brain. We found 477 +/- 24 cell bodies of JONs, which are arranged like a "bottomless bowl" within the auditory organ. The target of the JONs in the brain comprises five spatially segregated zones, each of which is contributed by bundles of JON axons that gradually branch out from the antennal nerve. Four zones are confined in the antennal mechanosensory and motor center, whereas one zone further extends over parts of the ventrolateral protocerebrum and the subesophageal ganglion. Single-cell labeling with the FLP-out technique revealed that most JONs innervate only a single zone, indicating that JONs can be categorized into five groups according to their target zones. Within each zone, JONs innervate various combinations of subareas. We classified these five zones into 19 subareas according to the branching patterns and terminal distributions of single JON axons. The groups of JONs that innervate particular zones or subareas of the primary auditory center have their cell bodies in characteristic locations of the Johnston's organ in the antenna, e.g., in concentric rings or in paired clusters. Such structural organization suggests that each JON group, and hence each zone of the primary auditory center, might sense different aspects of sensory signals.     

Distribution of serotonin-containing neurons and their pathways in the supraoesophageal ganglion of the cockroach Periplaneta americana (L.) as revealed by immunocytochemistry

The distribution of serotonin (5-HT)-containing neurons in the supraoesophageal (cerebral) ganglion of the cockroach Periplaneta americana was studied using immunocytochemistry and the formaldehyde histofluorescence method ( Klemm , '83). In this material immunocytochemistry was more sensitive than the formaldehyde histofluorescence procedure. A relatively small number of 5-HT-immunoreactive cell bodies (220-280) were found. For the first time, their processes could be followed. They highly arborize and innervate many brain regions. Three patterns of monoamine innervation have been demonstrated: (1) 5-HT and catecholamine fibres ( Klemm , '83) occurring in the same region (e.g., outer lateral protocerebral neuropil, stratum caudale , mushroom body, fan-shaped body, olfactory lobe), but having certain differences with respect to the organization of their projection fields; (2) 5-HT fibres innervating a region lacking catecholamine-containing fibres (pons); and (3) catecholamine neurons innervating a region lacking 5-HT fibres (ellipsoid body). In the mushroom body only the extrinsic neurons contain 5-HT immunoreactivity. They form a commissural fibre system linking the left- and right-hand mushroom bodies and other brain regions. The pons is part of a 5-HT-neuron fibre system innervating many areas including the mushroom bodies. The present study demonstrates novel, complex, and widely distributed connections within the insect brain.     

Morphological analysis of the primary center receiving spatial information transferred by the waggle dance of honeybees

The waggle dancers of honeybees encodes roughly the distance and direction to the food source as the duration of the waggle phase and the body angle during the waggle phase. It is believed that hive‐mates detect airborne vibrations produced during the waggle phase to acquire distance information and simultaneously detect the body axis during the waggle phase to acquire direction information. It has been further proposed that the orientation of the body axis on the vertical comb is detected by neck hairs (NHs) on the prosternal organ. The afferents of the NHs project into the prothoracic and mesothoracic ganglia and the dorsal subesophageal ganglion (dSEG). This study demonstrates somatotopic organization within the dSEG of the central projections of the mechanosensory neurons of the NHs. The terminals of the NH afferents in dSEG are in close apposition to those of Johnston's organ (JO) afferents. The sensory axons of both terminate in a region posterior to the crossing of the ventral intermediate tract (VIT) and the maxillary dorsal commissures I and III (MxDCI, III) in the subesophageal ganglion. These features of the terminal areas of the NH and JO afferents are common to the worker, drone, and queen castes of honeybees. Analysis of the spatial relationship between the NH neurons and the morphologically and physiologically characterized vibration‐sensitive interneurons DL‐Int‐1 and DL‐Int‐2 demonstrated that several branches of DL‐Int‐1 are in close proximity to the central projection of the mechanosensory neurons of the NHs in the dSEG. J. Comp. Neurol. 521:2570–2584, 2013. © 2013 Wiley Periodicals, Inc.     

Neurosecretory neurons and their projections to the serotonin neurohemal system of the cockroach Periplaneta americana (L.), and identification of mandibular and maxillary motor neurons associated with this system

The neuroanatomy of a serotonin neurohemal system in the head of Periplaneta americana was studied by means of immunohistochemistry, cobalt backfilling, transmission electron microscopy, and nerve transection. This neurohemal system is supplied by bilateral groups of two or three neurons whose somata are located ventrally in the subesophageal ganglion, near the root of each mandibular nerve. Axons of these serotoninergic neurons extend into all of the nerves of the mouth parts but reach most of these nerves by a very circuitous route. Initially the axons extend from the subesophageal ganglion, through the ipsilateral mandibular nerve trunk, and into the third branch of the mandibular nerve. From here the axons extend into the second branch of the maxillary nerve by way of a link nerve, and then they project retrogradely to reenter the subesophageal ganglion. In the ganglion, branches of these axons extend into the labial nerves, and the axons run dorsally through the subesophageal ganglion, circumesophgeal connectives, and tritocerebrum to reach the labral nerves. In the nerves of the mouth parts the serotoninergic axons give rise to numerous secondary branches that form an extensive neurohemal system at the surface of these nerves. The relatively large surface and cephalic location of this system probably indicate that the timely release of relatively large amounts of serotonin plays an important role in the physiology of feeding in this insect. The somata, neurites, and dendritic fields of the serotonin neurohemal neurons and those of the motor neurons of the mandibular abductor muscle occur together, and some of the mandibular abductor motor neurons also stain for serotonin. In order to distinguish clearly between these neurohemal and motor neurons, the anatomy of the mandibular abductor motor neurons has also been determined. Similarly, in the course of this study it has been necessary to work out the anatomy of the motor neurons of the maxillary retractor and cardo rotator muscles in order to distinguish them from the serotoninergic neurons. A nonserotoninergic peripheral neuron is associated with the serotonin neurohemal system, and its soma is located on the mandibular-maxillary link nerve. This link nerve neuron appears to be neurosecretory.     

Synaptic connections between GABA-immunoreactive neurons and uniglomerular projection neurons within the antennal lobe of the cockroach,Periplaneta americana

Synapses within deutocerebral glomeruli between GABA-immunoreactive, putatively inhibitory local interneurons and uniglomerular projection (output) neurons were demonstrated by means of a combination of GABA-immunogold labeling and intracellular HRP injection. The following connections were identified. 1) GABA-immunoreactive (GABAir) neurons form output synapses in a dyadic fashion onto a uniglomerular projection neuron and, in addition, a second GABAir neuron. A uniglomerular projection neuron in turn forms dyadic output synapses onto two GABAir neurons. Several examples of reciprocal connections have been identified between, first, GABAir neurons and uniglomerular projection neurons, and, second, GABAir neurons themselves. 2) GABAir neurons are serially connected with uniglomerular projection neurons via interposed GABAir processes. In some cases, also the first GABAir process of such a polysynaptic connection formed an output synapse onto the projection neuron. Such serial connections may form the structural basis for both, the feedforward inhibition as well as the feedforward disinhibition of uniglomerular projection neurons by GABAergic neurons. The reciprocal contacts may serve as control devices that modulate the output activity of the projection neurons. Synapse 29:1–13, 1998. © 1998 Wiley-Liss, Inc.     

Immunocytochemical localization of a methionine-enkephalin-resembling neuropeptide in the central nervous system of the american cockroach,Periplaneta americana L

Using the peroxidase antiperoxidase immunocytochemical method, we were able to demonstrate within the brain and retrocerebral complex of Periplaneta americana several neuronal structures which were very specifically stained with an anti-methionine-enkephalin antiserum. From the precise localization of this immunoreactive material some speculations about its possible functions could be derived, such as a neurotransmitter- or neuromodulatorlike function and/or a neurohormonal role. These data present new evidence for the recently developed concept that opiate peptides, identical or related to those found in higher species, occur also in invertebrates.     

Sensillum-specific, topographic projection patterns of olfactory receptor neurons in the antennal lobe of the cockroach Periplaneta americana

In vertebrates and many invertebrates, olfactory signals detected by peripheral olfactory receptor neurons (ORNs) are conveyed to a primary olfactory center with glomerular organization in which odor-specific activity patterns are generated. In the cockroach, Periplaneta americana, ORNs in antennal olfactory sensilla project to 205 unambiguously identifiable antennal lobe (AL) glomeruli that are classified into 10 glomerular clusters (T1-T10 glomeruli) innervated by distinct sensory tracts. In this study we employed single sensillum staining techniques and investigated the topographic projection patterns of individual ORNs to elucidate the relationship between sensillum types and glomerular organization in the AL. Axons of almost all ORNs projected to individual glomeruli. Axons of ORNs in perforated basiconic sensilla selectively innervated the anterodorsal T1-T4 glomeruli, whereas those in trichoid and grooved basiconic sensilla innervated the posteroventral T5-T9 glomeruli. About 90% of stained ORNs in trichoid sensilla sent axons to the T5 glomeruli and more than 90% of ORNs in grooved basiconic sensilla innervated the T6, T8, and T9 glomeruli. The T5 and T9 glomeruli exclusively receive sensory inputs from the trichoid and grooved basiconic sensilla, respectively. All investigated glomeruli received convergent input from a single type of sensillum except F11 glomerulus in the T6 glomeruli, which was innervated from both trichoid and grooved basiconic sensilla. These results suggest that ORNs in distinct sensillum types project to glomeruli in distinct glomerular clusters. Since ORNs in distinct sensillum types are each tuned to distinct subsets of odorant molecules, the AL is functionally compartmentalized into groups of glomeruli.     

Histamine‐immunoreactive local neurons in the antennal lobes of the hymenoptera

Neural networks receive input that is transformed before being sent as output to higher centers of processing. These transformations are often mediated by local interneurons (LNs) that influence output based on activity across the network. In primary olfactory centers, the LNs that mediate these lateral interactions are extremely diverse. For instance, the antennal lobes (ALs) of bumblebees possess both γ‐aminobutyric acid (GABA)‐ and histamine‐immunoreactive (HA‐ir) LNs, and both are neurotransmitters associated with fast forms of inhibition. Although the GABAergic network of the AL has been extensively studied, we sought to examine the anatomical features of the HA‐ir LNs in relation to the other cellular elements of the bumblebee AL. As a population, HA‐ir LNs densely innervate the glomerular core and sparsely arborize in the outer glomerular rind, overlapping with the terminals of olfactory receptor neurons. Individual fills of HA‐ir LNs revealed heavy arborization of the outer ring of a single “principal” glomerulus and sparse arborization in the core of other glomeruli. In contrast, projection neurons and GABA‐immunoreactive LNs project throughout the glomerular volume. To provide insight into the selective pressures that resulted in the evolution of HA‐ir LNs, we determined the phylogenetic distribution of HA‐ir LNs in the AL. HA‐ir LNs were present in all but the most basal hymenopteran examined, although there were significant morphological differences between major groups within the Hymenoptera. The ALs of other insect taxa examined lacked HA‐ir LNs, suggesting that this population of LNs arose within the Hymenoptera and underwent extensive morphological modification. J. Comp. Neurol. 518:2917–2933, 2010. © 2010 Wiley‐Liss, Inc.     

Serotonin‐induced activation of the network for locomotion in adult spinal rats

The biogenic amine serotonin has been described in the literature as a powerful modulator of the spinal central pattern generator for locomotion. In the present study, we tested whether administration of serotonin or its agonist quipazine could restore motor activity in a model of paraplegia. One to three weeks after a complete transection of the spinal cord at a low thoracic level, rats were given either intrathecal injections of serotonin (5 mM, 15 μL) or intraperitoneal injections of quipazine (400–600 μg/kg). Both treatments allowed recovery of locomotor activity on a treadmill in response to tail pinching. As compared with the activity elicited before treatment, the locomotor activity produced by spinal animals was characterised by longer locomotor sequences with a larger number of successive steps, better body support, better interlimb coordination, and a higher amplitude of electromyographic bursts. These results suggest that serotonergic drugs could be used for the recovery of motor functions after lesions of the spinal cord. J. Neurosci. Res. 55:87–98, 1999. © 1999 Wiley‐Liss, Inc.     

The motor program and role of sensory feedback in claw extension of the crayfish

The motor program and role of the meropodite sensory organs (the chordotonal organs MC-1, MC-2 and the myochordotonal organ MCO) in extension of the merocarpodite (M-C) joint of the claw was examined during an antennal-evoked defense response. Recordings from the meropodite extensor muscle indicated that the tonic extensor motoneuron was primarily responsible for M-C joint extension. The phasic extensor motoneuron was co-activated with the tonic motoneuron in only 48% of the responses. Tonic motoneuron discharge was elevated in those responses in which the phasic motoneuron was active. Inactivation of individual meropodite sensory organs did not alter the tonic motoneuron response. Simultaneous inactivation of all 3 organs reduced tonic motoneuron discharge by 47%. Phasic motoneuron discharge was reduced following inactivation of the individual MC-1, MC-2 and MCO organs as well as in the sham operated group. Following inactivation of all 3 organs phasic motoneuron activity ceased. These results suggest that feedback from the M-C sensory organs during an active extension response is positive and redundant.     

Complete mapping of glomeruli based on sensory nerve branching pattern in the primary olfactory center of the cockroach Periplaneta americana

Glomeruli are structural and functional units in the primary olfactory center in vertebrates and insects. In the cockroach Periplaneta americana, axons of different types of sensory neurons housed in sensilla on antennae form dorsal and ventral antennal nerves and then project to a number of glomeruli. In this study, we identified all antennal lobe (AL) glomeruli based on detailed innervation patterns of sensory tracts in addition to the shape, size, and locations in the cockroach. The number of glomeruli is ∼205, and no sex‐specific difference is observed. Anterograde dye injections into the antennal nerves revealed that axons supplying the AL are divided into 10 sensory tracts (T1–T10). Each of T1–T3 innervates small, oval glomeruli in the anteroventral region of the AL, with sensory afferents invading each glomerulus from multiple directions, whereas each of T4–T10 innervates large glomeruli with various shapes in the posterodorsal region, with a bundle of sensory afferents invading each glomerulus from one direction. The topographic branching patterns of all these tracts are conserved among individuals. Sensory afferents in a sub‐tract of T10 had axon terminals in the dorsal margin of the AL and the protocerebrum, where they form numerous small glomerular structures. Sensory nerve branching pattern should reflect developmental processes to determine spatial arrangement of glomeruli, and thus the complete map of glomeruli based on sensory nerve branching pattern should provide a basis for studying the functional significance of spatial arrangement of glomeruli and its developmental basis. J. Comp. Neurol. 518:3907–3930, 2010. © 2010 Wiley‐Liss, Inc.     

Synaptic connection between olfactory receptor cells and uniglomerular projection neurons in the antennal lobe of the American cockroach,Periplaneta americana

Both antennal receptor cell axons and uniglomerular projection neurons of the antennal lobe were specifically labeled, and their synaptic relationship was studied at the fine structural level. The labelings were applied in different combinations: i) Experimentally induced anterograde degeneration of sensory-afferent axons was combined with injection of horseradish peroxidase into uniglomerular projection neurons. ii) Lucifer Yellow was injected into uniglomerular projection neurons, and receptor cell axons were anterogradely labeled with the lipophilic dye DiI. The fluorescent dyes were transformed by immuno- or photochemical treatment into electron-dense markers. In both types of preparations, a considerable number of monosynaptic output synapses from antennal receptor neurons onto processes of uniglomerular projection neurons were identified within the glomeruli of the lobe. In most cases, the receptor axon was connected in a dyadic fashion, firstly to a process of a projection neuron and secondly to a nonlabeled process. The results clearly demonstrate a direct connection between receptor cells and output neurons of the cockroach antennal lobe which exists in parallel to the already proposed and demonstrated polysynaptic connection via inhibitory local interneurons. © 1996 Wiley-Liss, Inc.     

Topographic organization of sensory afferents of Johnston's organ in the honeybee brain

Johnston's organ (JO) in insects is a multicellular mechanosensory organ stimulated by movement of the distal part of the antenna. In honeybees JO is thought to be a primary sensor detecting air-particle movements caused by the waggling dance of conspecifics. In this study projection patterns of JO afferents within the brain were investigated. About 720 somata, distributed around the periphery of the second segment of the antenna (pedicel), were divided into three subgroups based on their soma location: an anterior group, a ventral group, and a dorsal group. These groups sent axons to different branches (N2 to N4) diverged from the antennal nerve. Dye injection into individual nerve branches revealed that all three groups of afferents, having fine collaterals in the dorsal lobe, sent axons broadly through tracts T6I, T6II, and T6III to terminate ipsilaterally in the medial posterior protocerebral lobe, the dorsal region of the subesophageal ganglion, and the central posterior protocerebral lobe, respectively. Within these termination fields only axon terminals running in T6I were characterized by thick processes with large varicosities. Differential staining using fluorescent dyes revealed that the axon terminals of the three groups were spatially segregated, especially in T6I, showing some degree of somatotopy. This spatial segregation was not observed in axon terminals running in other tracts. Our results show that projection patterns of JO afferents in the honeybee brain fundamentally resemble those in the dipteran brain. The possible roles of extensive termination fields of JO afferents in parallel processings of mechanosensory signals are discussed.     

Central afferent projections of proprioceptive sensory neurons in Drosophila revealed with the enhancer-trap technique

We have used a GAL4 enhancer-trap line coupled with an upstream activation sequence (UAS)-linked lacZ reporter construct to visualise and describe the central projections of proprioceptive sensory neurons of the thorax and abdomen in Drosophila. In the legs, lacZ expression is restricted to sensory neurons associated with hair plates, a subset of campaniform sensilla, and with the femoral chordotonal organ; whereas, in the wing, expression is seen only in subsets of campaniform sensilla. In the abdomen, expression is seen in Wheeler's organ and in a segmentally repeated array of internal sensory neurons that have not been previously described. The central projections from all of these neurons are described. The results confirm and expand upon our knowledge of the organisation of sensory neuropils in insects. The enhancer-trap technique provides a potentially powerful tool for describing the organisation of the central nervous system of Drosophila. © 1996 Wiley-Liss, Inc.