Norbert Elsner

The stridulatory movements of acridid grasshoppers recorded with an opto-electronic device

Summary(i)The singing movements of acridid grasshoppers are recorded opto-electronically: a small retroflective “Scotchlite” sheeting (Ø2mm) is attached to the tip of the stridulating femur and illuminated via a semi-transmissive mirror mounted at 45° to the optical axis in front of a photographic object lens. The light retroflected through this mirror is focused by the lens on the surface of a position-sensing photo-detector from which the co-ordinates of the light spot are tapped off instantaneously. Using this principle and having one recording device on each side the stridulatory movements of both hindlegs are monitored simultaneously.(ii)The grasshoppersChorthippus biguttulus (L.) andChorthippus mollis (Charp.) and their hybrids are studied by this method. Each of the two hindlegs performs a different Stridulatory pattern, the movements being considerably phase-shifted. The legs change their patterns from time to time. In the pure species the two patterns are very tightly coupled. Although in the hybrids in principle the same close relationships exist between the two lateral sub-systems, the couplings of the two patterns can be temporarily loosened. In the extreme, one hindleg may stridulate aCh. mollis song-pattern, whereas the other produces aCh. biguttulus pattern.

A role for muscarinic excitation: Control of specific singing behavior by activation of the adenylate cyclase pathway in the brain of grasshoppers

Muscarinic acetylcholine receptors exert slow and prolonged synaptic effects in both vertebrate and invertebrate nervous systems. Through activation of G proteins, they typically decrease intracellular cAMP levels by inhibition of adenylate cyclase or stimulate phospholipase C and the turnover of inositol phosphates. In insects, muscarinic receptors have been credited with two main functions: inhibition of transmitter release from sensory neuron terminals and regulation of the excitability of motoneurons and interneurons. Our pharmacological studies with intact and behaving grasshoppers revealed a functional role for muscarinic acetylcholine receptors as being the basis for specific arousal in defined areas of the brain, underlying the selection and control of acoustic communication behavior. Periodic injections of acetylcholine into distinct areas of the brain elicited songs of progressively increasing duration. Coinjections of the muscarinic receptor antagonist scopolamine and periodic stimulations with muscarine identified muscarinic receptor activation as being the basis for the underlying accumulation of excitation. In contrast to reports from other studies on functional circuits, muscarinic excitation was apparently mediated by activation of the adenylate cyclase pathway. Stimulation of adenylate cyclase with forskolin and of protein kinase A with 8-Br-cAMP mimicked the stimulatory effects of muscarine whereas inhibition of adenylate cyclase with SQ22536 and of protein kinase A with H-89 and Rp-cAMPs suppressed muscarine-stimulated singing behavior. Activation of adenylate cyclase by muscarinic receptors has previously been reported from studies on membrane preparations and heterologous expression systems, but a physiological significance of this pathway remained to be demonstrated in an in vivo preparation.

Pharmacological brain stimulation releases elaborate stridulatory behaviour in gomphocerine grasshoppers – conclusions for the organization of the central nervous control

Abstract. Grasshoppers produce a variety of sounds generated by complex movements of the hindlegs. Stridulation, performed in the context of partner finding, mating and rivalry, can be released by pressure injection of cholinergic agonists into the protocerebrum. Particularly stimulation with muscarinic agonists induced long-lasting stridulation that resembled the natural behaviour to an astonishing degree, not only with respect to their temporal structure and right/left coordination, but also to changes in the song sequences according to the progress of courtship stridulation, even including accessory movements of other parts of the body. According to the complexity of their stridulatory behaviour ten gomphocerine species were chosen for this comparative study. The results indicate that the protocerebrum fulfils two important tasks in the control of stridulation: (1) it integrates sensory input relevant to stridulation that represents a certain behavioural situation and internal state of arousal, and (2) it selectively activates and deactivates the thoracic networks that generate the appropriate movement and sound patterns. With the knowledge of the natural behaviour and the accessibility to pharmacological and electrophysiological studies, the cephalic control system for stridulation in grasshoppers appears to be a suitable model for how the brain selects and controls appropriate behaviours for a given situation.

Nitric oxide/cyclic guanosine monophosphate signaling in the central complex of the grasshopper brain inhibits singing behavior.

Grasshopper sound production, in the context of mate finding, courtship, and rivalry, is controlled by the central body complex in the protocerebrum. Stimulation of muscarinic acetylcholine receptors in the central complex has been demonstrated to stimulate specific singing in various grasshoppers including the species Chorthippus biguttulus. Sound production elicited by stimulation of muscarinic acetylcholine receptors in the central complex is inhibited by co‐applications of various drugs activating the nitric oxide/cyclic guanosine monophosphate (cGMP) signaling pathway. The nitric oxide‐donor sodium nitroprusside caused a reversible suppression of muscarine‐stimulated sound production that could be blocked by 1H‐[1,2,4]oxadiazolo‐[4,3‐a]quinoxaline‐1‐one (ODQ), which prevents the formation of cGMP by specifically inhibiting soluble guanylyl cyclase. Furthermore, injections of both the membrane‐permeable cGMP analog 8‐Br‐cGMP and the specific inhibitor of the cGMP‐degrading phosphodiesterase Zaprinast reversibly inhibited singing. To identify putative sources of nitric oxide, brains of Ch. biguttulus were subjected to both nitric oxide synthase immunocytochemistry and NADPH‐diaphorase staining. Among other areas known to express nitric oxide synthase, both procedures consistently labeled peripheral layers in the upper division of the central body complex, suggesting that neurons supplying this neuropil contain nitric oxide synthase and may generate nitric oxide upon activation. Exposure of dissected brains to nitric oxide and 3‐(5′hydroxymethyl‐2′‐furyl)‐1‐benzyl indazole (YC‐1) induced cGMP‐associated immunoreactivity in both the upper and lower division. Therefore, both the morphological and pharmacological data presented in this study strongly suggest a contribution of the nitric oxide/cGMP signaling pathway to the central control of grasshopper sound production. J. Comp. Neurol. 488:129–139, 2005.

Neuropharmacological evidence for inhibitory cephalic control mechanisms of stridulatory behaviour in grasshoppers

Abstract In gomphocerine grasshoppers the neuromuscular patterns of stridulatory hindleg movements are produced by metathoracic rhythm generators under the control of cephalic command neurons. Injections of cholinergic agonists into the protocerebrum activate this command system which induces the performance of stridulatory sequences, resembling natural species specific movements. Injections of GABA, glycine and picrotoxin into the central protocerebrum of the species Omocestus viridulus, Chorthippus mollis and Ch. biguttulus revealed a contribution of inhibitory mechanisms to the control of the stridulatory behaviour. The experiments suggest that inhibition interferes with the cephalic command systems at three levels: (1) sustained inhibition through picrotoxin sensitive receptors acting on all command units while grasshoppers are at rest, and during stridulation on all command units except the one activating the pattern generators of the currently performed movements; (2) premature termination of song sequences, experimentally induced by injections of GABA and glycine; and (3) coupling of a timing mechanism that terminates a song sequence or its subunits with a particular movement pattern after specific durations. These results together with those from previous studies on the pharmacological activation of stridulatory behaviour suggest that a balance of inhibitory and excitatory inputs to the command system selects the appropriate song type and controls its performance.

The interference of sound and movement stimuli in tympanal receptors ofLocusta migratoria

Summary1.With glass microelectrodes in the metathoracic ganglion ofLocusta migratoria, the activity of auditory receptors in Müllers organ was recorded and the fibers were stained with Lucifer Yellow (part D of Figs. 3–6). Responses to (i) acoustic stimuli, (ii) movement stimuli and (iii) the two stimuli in combination were recorded.2.Sound pulses (10 ms, 10/s, 70 dB, 4 or 12 kHz) elicited the typical response, ca. 1–4 action potentials for each pulse, with a latency of 8–11 ms (parts A and F of Figs. 3–6).3.Sinusoidal rotation of the hindleg ipsilateral to the tympanal organ, with a frequency of 2.5–20 Hz and an amplitude of 1–5 mm at the femur tip (Fig. 1), elicited activity phase-coupled to the movement in a manner depending on the individual receptor (parts B and E of Figs. 3–6). When acoustic and movement stimuli were presented simultaneously, reciprocal effects on the responses to the two kinds of stimuli were observed. The auditory response could be greatly reduced, and even almost suppressed in certain phases of the movement (parts C, G and I of Figs. 3–6). When an auditory response occurred, the subsequent movement response could be diminished or eliminated altogether (part I of Figs. 3–6).

Can spectral cues contribute to species separation in closely related grasshoppers

Abstract The acridid grasshoppers Chorthippus biguttulus and Ch. mollis, which are closely related and often sympatric species, were compared intra- and interspecifically with regard to the spectra of their calling and courtship songs and of the sound-induced vibrations of the tympanal membrane, as well as the threshold curves of the tympanal nerve. In the low-frequency range but not in the ultrasound region, the maxima of these various curves fall at distinctly different frequencies in the two species. It is shown that the low-frequency sensitivity of the auditory system in both species, especially in females, is well matched to the conspecific song spectra but not to those of the heterospecific songs. Whether these characteristics actually contribute to species discrimination remains to be determined by behavioural tests.

MICROINJECTION OF NEUROACTIVE SUBSTANCES INTO BRAIN NEUROPIL CONTROLS STRIDULATION IN THE CRICKET GRYLLUS BIMACULATUS (DE GEER)

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Central nervous control of hindleg coordination in stridulating grasshoppers

Abstract Stridulation in many gomphocerine grasshoppers is characterized by specific phase shifts between the two hindlegs as well as different movement patterns produced by the left and the right leg. The underlying neuronal excitation patterns are generated by networks on either side of the metathoracic ganglion. The role of the intraganglionic commissures in right-left coordination and the production of differing movement patterns was investigated by transecting the metathoracic ganglion mediosagittally in Omocestus viridulus, Chorthippus biguttulus and Chorthippus mollis. In all three species, after this operation both hindlegs produced the same pattern and no longer different movements. The effects of transection on coordination differed: rapid movement rhythms, like those typical of Ch. biguttulus and the vibratory parts of the song of Ch. mollis, on the two sides drifted with respect to one another. In contrast, the slow rhythms characteristic of O. viridulus and the song subunits of Ch. mollis were completely synchronized. It is inferred that in intact animals the pathways for coordination of the rapid stridulatory rhythms are exclusively intraganglionic, whereas the phase relations of the slow rhythms are additionally influenced by way of anterior right-left connections, perhaps within the suboesophageal ganglion.

Biophysical and Neurophysiological Effects of Respiration on Sound Reception in the Migratory Locust Locusta Migratoria

The influence of ventilatory pressure changes in the tracheal system on sound reception has been analysed by laservibrometry and tympanal nerve recordings. During rapid and high-amplitude pressure changes enhancements or reductions of the membrane response do occur, depending on the frequency of the acoustic stimulus. These changes are in general also reflected in the activity of the tympanal receptor cells.