Michael Hörner

The function of auditory neurons in cricket phonotaxis

SummaryIn order to examine the role of particular identified auditory neurons of the cricket,Gryllus bimaculatus, in orientation to a sound source, a method has been developed by which intracellular recordings can be made while the animal walks on an air-suspended sphere, which is rotated by the leg movements (Fig. 1). The angular velocities of sphere rotation were found to depend on the direction of incident sound, on its intensity and frequency and on the temporal pattern of the sound stimulus (Figs. 2, 3).While the cricket was walking, auditory neurons discharged extra action potentials, not correlated with the sound stimulus, and the neuronal response to the sound itself was reduced (Figs. 4, 5).Suppressing the spike activity by hyperpolarization of a local neuron in the prothoracic ganglion (ON1) reduced in some animals the tendency to turn toward the sound source on the side of the ear that excites the ON1 (Figs. 6–8). Hyperpolarization of a neuron that ascends from the prothoracic ganglion into the brain (AN1), while sound was presented to the ear that excites this neuron, caused all animals to reverse direction; that is, they turned away from the sound source and from the side of the inactivated AN1 (Figs. 9, 10). Hyperpolarization of another ascending neuron (AN2) caused a reduction in turning velocity in half of the animals; but this effect occurred only with high sound pressure levels, and the direction of walking was not reversed (Figs. 11, 12).From the influences on turning tendency observed in these experiments, it appears that the paired AN1s (and possibly the AN2s at high intensities) may provide inputs to a central comparator that dictates turning tendency in phonotaxis.

Octopamine-immunoreactive neurons in the central nervous system of the cricket, Gryllus bimaculatus

SummaryThe distribution of octopamine-immunoreactive neurons is described using whole-mount preparations of all central ganglia of the cricket, Gryllus bimaculatus. Up to 160 octopamine-immunoreactive somata were mapped per animal. Medial unpaired octopamine-immunoreactive neurons occur in all but the cerebral ganglia and show segment-specific differences in number. The position and form of these cells are in accordance with well-known, segmentally-organized clusters of large dorsal and ventral unpaired medial neurons demonstrated by other techniques. In addition, bilaterally arranged groups of immunoreactive somata have been labelled in the cerebral, suboesophageal and terminal ganglia. A detailed histological description of octopamine-immunoreactive elements in the prothoracic ganglion is given. Octopamine-immunoreactive somata and axons correspond to the different dorsal unpaired medial cell types identified by intracellular single-cell staining. In the prothoracic ganglion, all efferent neurons whose primary neurites are found in the fibre bundle of dorsal unpaired cells are immunoreactive. Intersegmental octopamine-immunoreactive neurons are also present. Collaterals originating from dorsal intersegmental fibres terminate in different neuropils and fibre tracts. Fine varicose fibres have been located in several fibre tracts, motor and sensory neuropils. Peripheral varicose octopamine-immunoreactive fibres found on several nerves are discussed in terms of possible neurohemal releasing sites for octopamine.

Prothoracic DUM neurons of the cricket Gryllus bimaculatus - responses to natural stimuli and activity in walking behavior

SummaryResponses to sensory stimuli and spike activity uring walking were investigated in bilaterally symmetrical dorsal unpaired median (DUM) neurons of the cricket. Intracellular recordings within the prothoracic ganglion were made either in restrained animals or in stationary walking specimens whilst parameters of their intended locomotion were measured. Three types of DUM cells were distinguished morphologically and physiologically. DUMa neurons send axons through segmental nerves. They often generated spontaneously large action potentials with low frequencies. Most DUMa neurons showed multimodal sensitivity, preferentially to cereal wind puffs and 15 kHz sound. Mean latencies ranged from 25 to 349 ms. Their large intraindividual variability could be correlated with behavioral modes during walking. Generally, the spike frequency increased with increased forward speed, while it was not related to turning. DUMb neurons projected either through the anterior or posterior connectives, but seemed physiologically similar to DUMa neurons. DUMc neurons were H-shaped with axons in both pairs of connectives. No external stimulus led to discrete spikes, but the regular spontaneous activity was modulated following cereal wind puffs to a restrained animal. During wind evoked escape the spike activity of another DUMc cell was modulated in phase with the rhythmic running behavior. The possibly different functions of DUMa and DUMc neurons during walking are discussed.

Cytoarchitecture of histamine-, dopamine-, serotonin- and octopamine-containing neurons in the cricket ventral nerve cord.

The present article provides a comparative neuroanatomical description of the cellular localization of the biogenic amines histamine, dopamine, serotonin and octopamine in the ventral nerve cord of an insect, namely the cricket, Gryllus bimaculatus. Generally, different immunocytochemical staining techniques reveal a small number of segmentally distributed immunoreactive (‐IR) amine‐containing neurons allowing single cell reconstruction of prominent elements. Aminergic neurons share common morphological features in that they innervate large portions of neurophil and often connect different neuromeres by intersegmental ‘wide‐field’ projections of varicose appearance. In many cases aminergic terminals are also found on the surface of peripheral nerves suggesting additional neurohemal release sites.

Octopamine immunoreactive neurons in the fused central nervous system of spiders

Using antisera directed against octopamine (OA), we identified and mapped octopamine-immunoreactive (OA-ir) neurons and their projections in the fused, central ganglion complex of wandering spiders, Cupiennius salei. Labeled cell bodies are concentrated in the subesophageal ganglion complex (SEG) where they are arranged serially in ventral, midline clusters. OA-ir processes from these cells project dorsally. Some neurites end close to segmental septa; others merge into longitudinal tracts connecting the neuromeres. Labeled collaterals leaving these tracts project into peripheral neuropil. In the brain, OA-ir somata were found only in the two cheliceral hemiganglia, where a cluster of 4-5 relatively large cells (soma diameter 25 microns) lies next to a group of small somata (diameter < 10 microns). Neurites originating from the large somata descend into the SEG and merge into longitudinal tracts. The central body of the brain contains profuse ascending projections. Except for fine varicosities that are confined to the roots of nerves, we found no OA-ir fibers leaving the central nervous system (CNS). Within the CNS, however, OA-ir varicosities are concentrated in neuropil and near hemolymph spaces. This distribution suggests that OA acts as a neurotransmitter and/or local neuromodulator at central synapses, while it is also released into the hemolymph and presumably acts hormonally at peripheral sites. Using high-pressure liquid chromatography measurements, the hemolymph was in fact found to contain 12-40 nM of free octopamine.

The distribution of neurones immunoreactive for β-tyrosine hydroxylase, dopamine and serotonin in the ventral nerve cord of the cricket, Gryllus bimaculatus

The cellular localization of the biogenic amines dopamine and serotonin was investigated in the ventral nerve cord of the cricket, Gryllus bimaculatus, using antisera raised against dopamine, β-tyrosine hydroxylase and serotonin. Dopamine-(n<-70) and serotonin-immunoreactive (n<-120) neurones showed a segmental arrangement in the ventral nerve cord. Some neuromeres, however, did not contain dopamine-immunoreactive cell bodies. The small number of stained cells allowed complete identification of brain and thoracic cells, including intersegmentally projecting axons and terminal arborizations. Dopamine-like immunostaining was found primarily in plurisegmental interneurones with axons descending to the soma-ipsilateral hemispheres of the thoracic and abdominal ganglia. In contrast, serotonin-immunostaining occurred predominantly in interneurones projecting via soma-contralaterally ascending axons to the thorax and brain. In addition, serotonin-immunoreactivity was also present in efferent cells and afferent elements. Serotonin-immunoreactive, but no dopamine-immunoreactive, varicose fibres were observed on the surface of some peripheral nerves. Varicose endings of both dopamine-and serotonin-immunoreactive neurones occurred in each neuromere and showed overlapping neuropilar projections in dorsal and medial regions of the thoracic ganglia. Ventral associative neuropiles lacked dopamine-like immunostaining but were innervated by serotonin-immunoreactive elements. A colocalization of the two amines was not observed. The topographic representation of neurone types immunoreactive for serotonin and dopamine is discussed with respect to possible modulatory functions of these biogenic amines in the central nervous system of the cricket.

The distribution of histamine-immunoreactive neurons in the ventral nerve cord of the cricket, Gryllus bimaculatus

Abstract.The present study demonstrates the immunocytochemical localisation of the biogenic amine, histamine (HA), in interneurons within the ventral nerve cord of the cricket, Gryllus bimaculatus. Analysis of whole-mount preparations combined with histology of serial sections reveals a constant number of HA-immunoreactive (HA-ir) neurons in the suboesophageal (n=8), thoracic (n=4) and abdominal ganglia (females/males n=24/20). Except for the suboesophageal and prothoracic ganglion, each thoracic and abdominal neuromere contains one pair of bilateral-symmetric HA-ir somata in a medio-ventral position. Axons from HA-ir cells in the thorax extend anteriorly and share common projection areas in thoracic associative neuropils; they terminate in the brain. HA-ir cells also display efferent descending axons. Extending posteriorly, these axons give rise to varicose HA-ir fibre plexuses on the surface of nerve 1 of the abdominal ganglia. In the suboesophageal ganglion, processes from a bilateral symmetric group of clustered HA-ir cells ascend into the tritocerebrum of the brain and further project into the frontal ganglion and the recurrent nerve. Ultrastructural analysis reveals dense-core vesicles, indicative of non-synaptic secretion, in HA-ir elements within the stomatogastric nervous system. Arborisations of HA-ir neurons are present in all major neuropil regions of the ventral nerve cord and display characteristic varicose structures also detected in other types of amine-containing cells. Central HA-ir varicose projections in dorsal and ventral neuropils are located in close apposition to the ganglionic surface. The wide-spread innervation of all neuromeres by HA-ir interneurons and the identification of possible neurohemal release sites suggest a general role of HA as a neuroactive substance, including neuromodulatory and neurohormonal functions.

A comparison of spontaneous and wind-evoked running modes in crickets and cockroaches

Abstract We studied the effects of repetitive wind pulses on the escape behaviour of tethered male cockroaches and crickets walking on a styrofoam ball (open-loop stimulation). The movements of this sphere were recorded to measure duration, forward and turning speed of walking and standing phases during the insects intended locomotion. All tested parameters were quantitatively similar for spontaneous walking in both species. During stimulation crickets generated a sequence of running bouts very regular both in duration and forward speed. Interposed were standing phases the mean duration of which was inversely correlated with the wind puff frequency. The mean distance run per period varied only between 100 and 150 mm for the tested frequencies. Cockroaches often showed continuous high speed running for seconds, variable in duration and followed by variable standing phases. Both parameters together with the mean forward speed of walking phases depended on the stimulus frequency in a non-linear manner. Therefore, the longest distance per period was run during stimulation with medium frequencies. Crickets were much better than cockroaches in turning away from the wind source in the range of 5–10 Hz stimulation. In cockroaches, the escape reaction was partly retained after cercus ablation, but ceased completely when the styli were also removed.

Synaptic Connectivity of Amine-Containing Neurosecretory Cells of Lobsters: Inputs to 5HT- and OCT- Containing Neurons

Biogenic amines, such as serotonin (5HT) and octopamine (OCT), the invertebrate counterpart of norepinephrine in vertebrates, function as neuromodulators capable of influencing vital behaviors in a wide variety of animal species (Hen 1992; Cases et al. 1995; Weiger 1997; Edwards and Kravitz 1997; Shiah and Yatham 1998; Horner 1999a; Monastirioti 1999; Kravitz 2000). Amine actions have been examined at organizational levels ranging from behavioral, through systems, and ultimately to cellular and subcellular levels. Invertebrate preparations are used extensively for such studies because of their unique advantages: with these models the analyses can be brought to the level of identified neurons likely to be important in the behavior. In crustaceans, for example, individual identified 5HT and OCT neurons are readily accessible for electrophysiological, pharmacological, and even molecular studies aimed at defining their function in complex behaviors like aggression.

Intrinsic Properties of Amine-Containing Neurosecretory Cells of Lobsters: Spontaneous Activity and Autoinhibition

Amines, peptides and steroid hormones exert a wide range of physiological actions on central neurons and peripheral tissues to play important roles in regulating or controlling aspects of the behavioral repertoire of animals. In lobsters and other crustaceans the amines serotonin (5 HT), octopamine (OCT) and dopamine (DA) modulate: muscular contractions in neuromuscular preparations (Kravitz et al. 1976; Florey and Rathmayer 1978; Lingle 1981); the rhythmic activity generated by the stomatogastric ganglion (Flamm and Harris-Warrick 1986); and the central circuitries concerned with postural regulation, olfactory, and mechanosensory processing, and other CNS functions (Livingstone et al. 1980; Pasztor and Bush 1987; Ma et al. 1992; Sandeman et al. 1995). Pharmacological, physiological and behavioral studies suggest that 5HT and OCT may serve opposite functional roles in aggression and the control of agonistic behavior including the establishment and maintenance of dominance relationships (Livingstone et al. 1980; Harris-Warrick and Kravitz 1984; Kravitz 1988; Huber et al. 1997; Edwards and Kravitz 1997).