Head Ganglia Research Articles

Effects of neck and circumoesophageal connective lesions on posture and locomotion in the cockroach

Few studies in arthropods have documented to what extent local control centers in the thorax can support locomotion in absence of inputs from head ganglia. Posture, walking, and leg motor activity was examined in cockroaches with lesions of neck or circumoesophageal connectives. Early in recovery, cockroaches with neck lesions had hyper-extended postures and did not walk. After recovery, posture was less hyper-extended and animals initiated slow leg movements for multiple cycles. Neck lesioned individuals showed an increase in walking after injection of either octopamine or pilocarpine. The phase of leg movement between segments was reduced in neck lesioned cockroaches from that seen in intact animals, while phases in the same segment remained constant. Neither octopamine nor pilocarpine initiated changes in coordination between segments in neck lesioned individuals. Animals with lesions of the circumoesophageal connectives had postures similar to intact individuals but walked in a tripod gait for extended periods of time. Changes in activity of slow tibial extensor and coxal depressor motor neurons and concomitant changes in leg joint angles were present after the lesions. This suggests that thoracic circuits are sufficient to produce leg movements but coordinated walking with normal motor patterns requires descending input from head ganglia.

Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8 days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.

Mass spectrometric analysis of head ganglia and neuroendocrine tissue of larval Galleria mellonella (Arthropoda, Insecta)

A brain-retrocerebral complex-subesophageal ganglion acidified methanolic extract of 100 larval Galleria mellonella (greater wax moth) was prepared for the isolation and identification of (neuro)peptides. To reduce sample complexity, the isolated peptides were roughly separated using a single, conventional chromatographic separation step. Subsequently, screening of these fractions with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in combination with nanoflow electrospray ionization quadrupole time-of-flight tandem mass spectrometry resulted in the identification of 12 lepidopteran peptides. None of these had been previously isolated or characterized within this species. VIFTPKLamide encoded by the diapause hormone-pheromone biosynthesis activating neuropeptide precursor was for the first time isolated and biochemically identified in a tissue extract, providing irrefutable evidence of its expression in larval nervous tissue. Another pentapeptide, AMVRFamide, with no resemblance to other lepidopteran peptides, was de novo sequenced and is most related to the neuropeptide F peptide family.

Further exploration into the adaptive design of the arthropod “microbrain”: I. Sensory and memory-processing systems

Arthropods have small but sophisticated brains that have enabled them to adapt their behavior to a diverse range of environments. In this review, we first discuss some of general characteristics of the arthropod "microbrain" in comparison with the mammalian "megalobrain". Then we discuss about recent progress in the study of sensory and memory-processing systems of the arthropod "microbrain". Results of recent studies have shown that (1) insects have excellent capability for elemental and context-dependent forms of olfactory learning, (2) mushroom bodies, higher olfactory and associative centers of arthropods, have much more elaborated internal structures than previously thought, (3) many genes involved in the formation of basic brain structures are common among arthropods and vertebrates, suggesting that common ancestors of arthropods and vertebrates already had organized head ganglia, and (4) the basic organization of sensori-motor pathways of the insect brain has features common to that of the mammalian brain. These findings provide a starting point for the study of brain mechanisms of elaborated behaviors of arthropods, many of which remain unexplored.

Wasp manipulates cockroach behavior by injecting venom cocktail into prey central nervous system.

The parasitoid wasp Ampulex compressa induces behavioral changes in the cockroach prey by injecting venom into its central nervous system. In contrast to most other venomous predators, the wasp's sting does not induce paralysis. Rather, the two consecutive stings in the thoracic and head ganglia induce three stereotypic behavioral effects. The prey behavior is manipulated in a way beneficial to the wasp and its offspring by providing a living meal for its newborn larva. The first sting in the thorax causes a transient front leg paralysis lasting a few minutes. This paralysis prevents the cockroach from fighting with its front legs, thereby facilitating the second sting in the head. A postsynaptic block of central synaptic transmission mediates this leg paralysis. Following the head sting, dopamine identified in the venom induces 30 minutes of intense grooming that appears to prevent the cockroach from straying until the last and third behavioral effect of hypokinesia commences. In this lethargic state that lasts about three weeks, the cockroach does not respond to various stimuli nor does it initiates movement. However, other specific behaviors of the prey are unaffected. We propose that the venom represses the activity of head ganglia neurons thereby removing the descending excitatory drive to specific thoracic neurons.

Diapausing Colorado potato beetles are devoid of short neuropeptide F I and II

An extract of head ganglia and retrocerebral complexes of nondiapausing and diapausing Leptinotarsa decemlineata was prepared to characterize regulatory neuropeptides involved in adult diapause by using a differential peptidomics approach. To reduce sample complexity, both extracts were roughly separated by means of an identical chromatographic step. MALDI-TOF MS led to the identification of proctolin, an adipokinetic hormone, and short neuropeptide F I and II in the extract of nondiapausing beetles. In combination with nano-ESI-Q-TOF MS 2 evidence was found for the presence of three pyrokinins, the first to be identified in a coleopteran species. Pyrokinins, involved in the induction of embryonic diapause in Bombyx mori, were present in both physiological conditions suggesting that they are of minor importance in the regulation of adult diapause in the Colorado potato beetle. A striking difference, detected by the differential peptidomics approach, between both neuropeptide profiles was the absence of ions corresponding to the short neuropeptide F (sNPF) related peptides, also known as Led-NPF-I and -II, in the extract of diapausing animals. Therefore, we postulate that “short NPFs” are involved in the regulation of adult diapause, displayed by the Colorado potato beetle.

Effects of aging on behavior and leg kinematics during locomotion in two species of cockroach

Aging is often associated with locomotor deficits. Behavior in aged Blaberus discoidalis cockroaches was analyzed during horizontal walking, climbing, righting and inclined walking. Adult animals showed a decrease in spontaneous locomotion with increasing age. Tarsal abnormalities, termed 'tarsus catch', were often present in aged individuals. In 'tarsus catch', the prothoracic leg catches on the mesothoracic leg during the swing phase. This deficit causes alterations of the gait, but animals are able to regain a tripod gait after the perturbation. The tibio-tarsal joint angle in individuals with 'tarsus catch' was significantly less than in intact animals. Structural defects were consistently associated with 'tarsus catch'. The tracheal tubes in the tarsus and around the tibio-tarsal joint were often discolored and the tarsal pads were hardened in aged cockroaches. All aged individuals were able to climb. However, prior to climbing, some animals with 'tarsus catch' failed to show postural changes that are normally seen in young animals. Aged individuals can right as rapidly as 1-week-old adults. However, animals with 'tarsus catch' take longer to right than aged intact individuals. Old cockroaches have difficulty climbing an incline of 45 degrees, and leg slipping is extensive. Slipping may be caused by tarsal degeneration, but animals that are unsuccessful in inclined walking often show uncoordinated gaits during the attempt. Escape behavior was examined in aged American cockroaches (Periplaneta americana). They do not show normal escape. However, after decapitation, escape movements return, suggesting that degeneration in head ganglia may actually interfere with escape. These findings provide evidence for age-related changes both in the periphery and in the central nervous system of cockroaches and stress the importance of multi-level approaches to the study of locomotion.

Wasp uses venom cocktail to manipulate the behavior of its cockroach prey.

The sting of the parasitoid wasp Ampulex compressa is unusual, as it induces a transient paralysis of the front legs followed by grooming behavior and then by a long-term hypokinesia of its cockroach prey. Because the wasp's goal is to provide a living meal for its newborn larva, the behavioral changes in the prey are brought about by manipulating the host behavior in a way beneficial to the wasp and its offspring. To this end, the wasp injects its venom cocktail with two consecutive stings directly into the host's central nervous system. The first sting in the thorax causes a transient front leg paralysis lasting a few minutes. This paralysis is due to the presence of a venom component that induces a postsynaptic block of central cholinergic synaptic transmission. Following the head sting, dopamine identified in the venom appears to induce 30 min of intense grooming. During the long-term hypokinesia that follows the grooming, specific behaviors of the prey are inhibited while others are unaffected. We propose that the venom represses the activity of head ganglia neurons thereby removing the descending excitatory drive to the thoracic neurons.

Mass spectrometric analysis of the perisympathetic organs in locusts: identification of novel periviscerokinins

A mass spectrometric analysis carried out to determine the peptidome of the abdominal perisympathetic organs in the locust species Locusta migratoria and Schistocerca gregaria yielded a number of predominant ion peaks, among which are Lom-PVK (AAGLFQFPRVamide) and Scg-MT-2 (TSSLFPHPRLamide). In addition, three novel peptides were identified: Lom-PVK-2 (identical in Schistocerca): GLLAFPRVamide, Lom-PVK-3: DGGEPAAPLWFGPRVamide, and Scg-PVK-3: DGAETPGAAASLWFGPRVamide. An extensive mass spectrometric study of the central nervous system showed that the periviscerokinins (-PRVamides) and Scg-MT-2 (-FXXPRLamide) are restricted to the abdominal ganglia and their perisympathetic organs, while the pyrokinins (-FXPRLamides) are present only in the brain–retrocerebral complex. Sequence comparison with the Drosophila genes supports a conserved gene structure whereby a capability-like gene encodes the periviscerokinins that are expressed in the abdominal ganglia and stored in the perisympathetic organs, while a hugin-like gene encodes the pyrokinins that are expressed in the head ganglia and stored in the retrocerebral complex.

Cerebral-abdominal interganglionic coordinating neurons in Aplysia.

Three cerebral-abdominal interneurons (CAIs), CC2, CC3, and CC7, were identified in the cerebral ganglion C cluster. The cells send their axons to the abdominal ganglion via the pleural-abdominal connective. CC2 and CC3 are bilaterally symmetrical cells, whereas CC7 is a unilateral cell. CC3 is immunopositive for serotonin and may be the same cell (CB-1) previously described as located in the B cluster rather than the C cluster. We suggest that the full designation of CC3, be CC3(CB-1). All three cells respond to feeding-related inputs. Each CAI has a monosynaptic connection to at least one abdominal ganglion neuron involved in the control of various nonsomatic organs. The CAIs also exert widespread polysynaptic actions in the abdominal and head ganglia. The results suggest that the CAIs may act as interneurons that coordinate visceral responses mediated by the abdominal ganglion, with behaviors such as feeding and head withdrawal, that are controlled by neurons located in the head ganglia of the animal.

Immunocytochemical localization of putative γ-aminobutyric acid receptor subunits in the head ganglia of Periplaneta americana using an anti-RDL C-terminal antibody

A polyclonal antibody raised against a 17 amino acid polypeptide (the predicted C-terminal sequence of the cloned Drosophila melanogaster γ-aminobutyric acid (GABA) receptor subunit, RDL) was used to investigate the distribution of GABA receptor subunit(s) of this type in the nervous system of the cockroach Periplaneta americana. Intense staining was detected in the calyces of the mushroom bodies, glomeruli of the antennal lobes, lower central body, the corpora cardiaca and several cell layers of the medulla and the lobula regions of the optic lobe. The most intense immunocytochemical staining was in the suboesophageal ganglion. Control sections pre-incubated with the primary antibody and conjugated peptide were not stained. Thus, it appears that a GABA receptor subunit of the RDL type is located in cockroach brain regions involved in the processing of visual, olfactory and mechanosensory inputs to the nervous system. Since the corpora cardiaca reacted to this antiserum, this type of GABA receptor may also be involved in the regulation of neurosecretory activity.

New ways to look at axons inCaenorhabditis elegans

In the nematode Caenorhabditis elegans, a well-established model organism for the analysis of nervous system development and function, nerve processes can be labelled in the intact animal with markers based on the "Green Fluorescent Protein" (GFP). The generation of GFP variants with improved brightness and modified emission spectra potentiated the use of this marker for in vivo labelling of subcellular structures. This made it possible to label different groups of neurons and their axons in the same animal with GFP variants of different spectral characteristics. Here I show with double labelling experiments that spatial relationships of axons in small axon bundles can now be resolved at the light microscopic level. In the future this will largely circumvent the need for time-consuming electron microscopic reconstructions to detect local defects in axon outgrowth. Furthermore, I demonstrate that neuronal processes can now be traced even in the head ganglia, an area of the nervous system that was previously almost inaccessible for analysis due to the compact arrangement of cell bodies and axons.

Localization of the site of effect of a wasp's venom in the cockroach escape circuitry

The parasitic wasp Ampulex compressa stings a cockroach Periplaneta americana in the neck, toward the head ganglia (the brain and subesophageal ganglion). In the present study, our aim was to identify the head ganglion that is the target of the venom and the mechanisms by which the venom blocks the thoracic portion of the escape neuronal circuitry. Because the escape responses elicited by a wind stimulus in brainless and sham-operated animals were similar, we propose that the venom effect is on the subesophageal ganglion. Apparently, the subesophageal ganglion modulates the thoracic portion of the escape circuit. Recordings of thoracic interneuron responses to the input from the abdominal giant interneurons showed that the thoracic interneurons receive synaptic drive from these interneurons in control and in stung animals. Unlike normal cockroaches, which use both fast and slow motoneurons for producing rapid escape movements, stung animals activate only the slow motoneuron. However, we show that in stung animals, the fast motoneuron still can be recruited with bath application of pilocarpine, a muscarinic agonist. These results indicate that the descending control from the subesophageal ganglion is presumably exerted on the premotor thoracic interneurons to motoneurons connection of the thoracic escape circuitry.

Neuronal Nicotinic Receptors in the Locust Locusta migratoria: CLONING AND EXPRESSION

We have identified five cDNA clones that encode nicotinic acetylcholine receptor (nAChR) subunits expressed in the nervous system of the locust Locusta migratoria. Four of the subunits are ligand-binding alpha subunits, and the other is a structural beta subunit. The existence of at least one more nAChR gene, probably encoding a beta subunit, is indicated. Based on Northern analysis and in situ hybridization, the five subunit genes are expressed. localpha1, localpha3, and locbeta1 are the most abundant subunits and are expressed in similar areas of the head ganglia and retina of the adult locust. Because Loc<alpha3 binds alpha-bungarotoxin with high affinity, it may form a homomeric nAChR subtype such as the mammalian alpha7 nAChR. Localpha1 and Locbeta1 may then form the predominant heteromeric nAChR in the locust brain. localpha4 is mainly expressed in optic lobe ganglionic cells and localpha2 in peripherally located somata of mushroom body neurons. localpha3 mRNA was additionally detected in cells interspersed in the somatogastric epithelium of the locust embryo, suggesting that this isoform may also be involved in functions other than neuronal excitability. Transcription of all nAChR subunit genes begins approximately 3 days before hatching and continues throughout adult life. Electrophysiological recordings from head ganglionic neurons also indicate the existence of more than one functionally distinct nAChR subtype. Our results suggest the existence of several nAChR subtypes, at least some of them heteromeric, in this insect species.

Characterization of indolamine N-acetyltransferase activity from the head ganglia of the American cockroach, Periplaneta americana

More than 90% of indolamine N-acetyltransferase (NAT) activity was recovered in the supernatant of centrifuged homogenate of the head ganglia of the American cockroach, Periplaneta americana. NAT activity increased at temperatures of up to 40°C with serotonin (5HT) and up to 45°C with tryptamine (TP) as the substrates. The pH-activity curve with 5HT resembled that with TP, both showing two activity maxima, one at pH 7.0 and the other at 8.5-9.0. Na+ and K+ ions stimulated the enzymatic activity up to 200 mM, after which a further increase in the concentrations reduced the enzyme activity. Cu2+ suppressed the activity at least up to 0.5 mM. One millimolar Mg2+ stimulated the activity but a further increase in the concentration suppressed the activity. Ca2+ also stimulated the activity up to 2 mM, but a further increase suppressed the activity. The secondary plot of the ordinate intercepts of a series of Lineweaver-Burk plots against fixed concentrations of acetyl-CoA showed that the enzymatic mechanism of indolamine NAT from the head ganglia of P. americana proceeds according to the kinetics known as the ping pong Bi-Bi mechanism. The apparent Kms and Vmax with TP and acetyl-CoA were 19.3 μM and Vmax 3.64 nmol product/mg protein/min, respectively, while the Km for acetyl-CoA was 28.0 μM and Vmax the same as that for TP. The Km for 5HT was 106 μM, Vmax being 2.16 nmol product/mg protein/min, while the Km for acetyl-CoA was 19.7 μM, Vmax being the same as that for 5HT.

Anatomical pathways connecting lip sensory structures and central nervous system in hirudinid leeches visualized by carbocyanine dyes and laser scanning confocal microscopy.

Chemoreception in Hirudo medicinalis is thought to be mediated by ciliated cells grouped in sensory structures, the sensilla, arranged in bands on the animal's dorsal lip (Elliott, 1986; Zipser et al., 1994). Furthermore, chemical and/or thermal stimulation of the dorsal lip in reduced preparations evokes changes in the electrical activity of the cephalic nerves that connect the head with the central nervous system. However, the complete trajectory by which the sensory afferents reach the cerebral ganglia has not been demonstrated anatomically. In this study, we traced these pathways following retrograde and/or anterograde transport of carbocyanine dyes (DiI, DiA and DiD) in the cephalic nerves of Hirudo medicinalis and a closely related species, Macrobdella decora. While information regarding Macrobdella's chemoreception is scarce, the two species show some differences with regard to their chemical preferences. Dyes were applied to the sensillar structures along the dorsal lip, or to the cut ends of individual cephalic nerves in fixed preparations that included the lip and attached nerves with or without the head ganglia. After a two week incubation, specimens were mounted and imaged using a confocal microscope. The results show that the axons of the sensory neurons in the sensilla project through the four pairs of cephalic nerves. The sensillar projections are however more numerous in the dorsal nerves than they are in the ventral ones. In addition, the organization of the sensillar bands, the morphology of the pathways and the sensory structures themselves appear to be identical for Hirudo and Macrobdella and therefore the behavioral differences in response to appetitive stimuli cannot be readily explained by differences in morphology.

Cellular Organization of an Antennal Mechanosensory Pathway in the Cockroach,Periplaneta americana

Escape responses of cockroaches, Periplaneta americana, can be triggered by wind and mediated by a group of "giant interneurons" that ascend from cercal mechanoreceptors to motor centers. Recently it has been observed that escape also can be triggered by tactile stimulation of the antennae, and it is then independent of the giant interneurons. Here we identify a descending antennal mechanosensory pathway that may account for escape. Cobalt backfills demonstrated that a limited number of cells in the head ganglia have axons that project through all three thoracic ganglia. Comparison with known wind-sensory pathways indicated that wind is not a reliable stimulus for activating descending antennal pathways. However, direct touch stimulation of an antenna reliably evoked short-latency responses in cells with axons in the cervical connectives. Intracellular recording and dye injection revealed members of this pathway, referred to as descending mechanosensory interneurons (DMIs). The two axons of largest diameter in the cervical connectives were found to belong to DMIs, and these large-caliber interneurons were studied in detail. One had a soma in the supraesophageal ganglion, and the other in the subesophageal ganglion. Both had extensive neuritic arborizations at the same level as the soma and axonal arbors in all three thoracic ganglia. Each of these DMIs exhibited short-latency responses to small antennal movements, demonstrated a degree of directional sensitivity, and rapidly conducted impulses to thoracic levels. These cells have properties suggesting that they play a role in a short-latency behavior such as touch-evoked escape.

Effects of Temperature on Reproductive Neuroendocrine Function inAplysia californica

Egg laying in the gastropod molluskAplysia californicais a temperature-dependent behavior, facilitated by warm temperature and attenuated by cold. The purpose of this work was to determine which components of the reproductive axis controlling egg laying are affected by temperature. There were three neural/reproductive tissues investigated: (1) the head ganglia that transmit neural signals to the neuroendocrine bag cells, (2) the bag cells that synthesize and secrete egg-laying hormone (ELH), and (3) the ovotestis that extrudes eggs into the hermaphroditic duct in response to ELH. There was no significant effect of temperature on the ability of ELH to stimulate egg laying, suggesting that temperature does not alter responsiveness of the ovotestis to hormonal stimulation. There was evidence that the bag cells play a secondary role in mediating the effects of temperature on egg-laying behavior, that is, using both bioassays and radioimmunoassay for detection or measurement of ELH, hormone secretion was shown to be inhibited by cooler temperatures in some preparations. However, the inconsistency of this response suggested that the primary effect of temperature is upstream from the bag cells. Results from an experiment in which the head ganglia were chemically stimulated to activate bag cell electrical activity suggested that the primary site of temperature regulation lies within the head ganglia.

Replication and Tissue Tropism of the Alphavirus Sindbis in the Mosquito Aedes albopictus

We have examined the replication and tissue distribution of the alphavirus Sindbis in the mosquito Aedes albopictus. Parenteral inoculation of virus resulted in an acute infection accompanied by rapid virus replication and a persistent infection, during which total virus production was reduced. Acute and persistent phase virus RNA synthesis, virus production, and organ-specific distribution of infection were determined over an 18-day incubation period. Organs were classified as refractory (ovarioles, Malpighian tubules), cleared (head ganglia), transient (salivary glands, anterior midgut, posterior midgut, and thoracic muscle), or persistent (fat bodies-hemolymph, hindgut, and tracheole-associated cells) according to the onset, peak, and duration of Sindbis virus antigens within that particular organ. Virus was identified in respiratory tissue by immunological and ultrastructural methods. This represents a novel tropism for an alphavirus. These findings demonstrate that the cells of mature insect organs respond differently to virus infection. Correlations among virus replication, virus RNA synthesis, and organ-specific clearing of a pantropic infection were observed. We suggest that the underlying temporal and spatial kinetics that characterize this virus-invertebrate interaction may reflect a mechanism for the modulation of the arbovirus titer seen in the mosquito host.

Anatomy of the neurosecretory cells in the cerebral and subesophageal ganglia of the female European corn borer moth, Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae)

The anatomy of the neurosecretory cells in the brain-subesophageal ganglion complex of female European corn borer moth Ostrinia nubilalis (Lepidoptera: Pyralidae) was studied using histological and cobalt backfilling techniques. Histological staining revealed the presence of 2 median and one lateral neurosecretory cell groups in the brain. These brain neurosecretory cells are made up of mainly type A cells with a few type B cells in the median group. Three type C neurosecretory cell clusters occupy the apparent mandibular, maxillary, and labial neuromeres at the ventral median aspect of the subesophageal ganglion. Axonal pathways of the neurosecretory cell groups were delineated by retrograde cobalt filling from the corpora cardiaca. Fibers of the 3 brain neurosecretory cell groups merged to form a distinct axonal tract that exits the brain via the fused nervi corporis cardiaci-1 + 2. Cobalt backfilling from the corpora cardiaca filled 4 groups of cell bodies in the subesophageal ganglion. The presence in the subesophageal ganglion of extensive dendritic arborizations derived from the brain suggests interactions between neurosecretory cell groups in the 2 head ganglia.