The terminal abdominal ganglion of the wood cricket Nemobius sylvestris

The abdominal cerci of the wood cricket, Nemobius sylvestris, are covered by a variety of hair‐like sensilla that differ in length, thickness, and articulation. Fillings from the cercal nerves with cobalt chloride and fluorescent dyes revealed the projection of sensory axons into the terminal abdominal ganglion of the ventral nerve chain. Two projection areas on each side of the terminal abdominal ganglion midline could be identified: a posterior cercal glomerulus and an anterior bristle neuropil. Axons from some cercal sensilla ascend through the connectives to reach the metathoracic ganglionic mass. As their axons pass through each segmental abdominal ganglion, they project medial arborization. Cross‐sections of the terminal abdominal ganglion and retrograde fills with cobalt chloride and fluorescent dyes from connectives revealed several small cells and seven pairs of giant ascending interneurons organized symmetrically. Giant somata are located contralateral to their axons (diameters between 20 and 45 μm). The cercal projections overlap extensively with the dendritic fields of the giant interneurons. In the terminal abdominal ganglion, we identified nine longitudinal tracts, two major tracts, and seven smaller ones. The functional implications of the neuranatomical organization of the system are discussed on a comparative basis. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Intersegmental modulation of abdominal postural responses initiated by mechanostimulation of the swimmeret in lobster

In a multiganglionic preparation of the lobster abdominal nerve cord, composed of the first through fifth ganglia (A1-A5) and attached second swimmeret, tactile stimulation of the cuticular surface of the swimmeret initiates a postural motor program in A2 for abdominal extension, whereas deflection of feathered hair sensilla that fringe the swimmeret rami does not affect postural motor activity recorded from A2 (Kotak and Page, 1986a). This report demonstrates that partial isolation of A2 from adjacent abdominal ganglia by sectioning the A1-A2 or the A2-A3 connectives both increases the strength of the extension response evoked by cuticular stimulation and disinhibits a postural flexion inhibition response initiated by feathered hair stimulation. Complete isolation of A2, by cutting the A1-A2 and the A2-A3 connectives, further increases the strength of these postural responses. Intersegmental inhibition of these responses originates in the ganglia adjacent to A2, since mechanoresponsiveness of A2 is not affected by resection of a more distant connective (A3-A4). These results provide evidence for the presence in adjacent abdominal ganglia of intersegmental interneurons that regulate the access of swimmeret sensory activity to the postural motor neurons in A2.     

An electrophysiological study of sound sensitive neurons in the ‘Primitive ear’ of Acheta domesticus

Crickets have two types of mechanisms for the reception of environmental sounds: (1) the tympanal organs in the two forelegs and (2) the freely articulated setal receptors on the abdominal ceri. The cercal setal receptors have hitherto received much less experimental attention as decoders of biologically significant sounds than have the tympano-receptors. In the present study the cercal auditory system of Acheta domesticus was examined electrophysiologically to determine its auditory frequency sensitivity, the tuning characteristics of individual units, and the synchronization between nerve impulses and stimulus frequency. Both pre- and postsynaptic units were examined in the fifth abdominal ganglion; several of the observed response patterns were compared with those of homologous cercal sensory neurons in Periplaneta americana. The results show that (1) A. domesticus possesses an elaborate array of cercal receptors which are highly sensitive to sounds, (2) the cercal setal receptors are more sensitive and numerous in the cricket than in the cockroach, and (3) the cercal auditory system can decode stimulus information by narrow tuning in individual cells and by synchronous discharge patterns; firing frequencies range up to 300 Hz in presynaptic sensory units and 60 Hz in the postsynaptic giants. The response patterns were related to the structure of the receptor and the behavioural adaptations of the insect.     

Hypoxia inhibits abdominal expiratory nerve activity

Our purpose was to examine the influence of steady-state changes in chemical stimuli, as well as discrete peripheral chemoreceptor stimulation, on abdominal expiratory motor activity. In decerebrate, paralyzed, vagotomized, and ventilated cats that had bilateral pneumothoraces, we recorded efferent activity from a phrenic nerve and from an abdominal nerve (cranial iliohypogastric nerve, L1). All cats showed phasic expiratory abdominal nerve discharge at normocapnia [end-tidal PCO2 38 +/- 2 Torr], but small doses (2-6 mg/kg) of pentobarbital sodium markedly depressed this activity. Hyperoxic hypercapnia consistently enhanced abdominal expiratory activity and shortened the burst duration. Isocapnic hypoxia caused inhibition of abdominal nerve discharge in 11 of 13 cats. Carotid sinus nerve denervation (3 cats) exacerbated the hypoxic depression of abdominal nerve activity and depressed phrenic motor output. Stimulation of peripheral chemoreceptors with NaCN increased abdominal nerve discharge in 7 of 10 cats, although 2 cats exhibited marked inhibition. Four cats with intact neuraxis, but anesthetized with ketamine, yielded qualitatively similar results. We conclude that when cats are subjected to steady-state chemical stimuli in isolation (no interference from proprioceptive inputs), hypercapnia potentiates, but hypoxia attenuates, abdominal expiratory nerve activity. Mechanisms to explain the selective inhibition of expiratory motor activity by hypoxia are proposed, and physiological implications are discussed.     

Synaptic transmission in the sixth ganglion of the cockroach: action of 4-aminopyridine.

1. Study was made of the action of 4-aminopyridine (5 X 10(-5) M) on synaptic transmission in the last abdominal ganglion of Periplaneta americana. The 'oil-gap' technique was used to record postsynaptic events in a single giant axon. 2. 4-AP quickly increased the 'background' of postsynaptic activity, which consisted of 'spontaneous' unitary EPSPs and IPSPs. Postsynaptic spikes were also propagated. 3. Both evoked EPSPs (stimulation of cercal nerve XI) and evoked IPSPs (stimulation of cercal nerve X) were greatly increased in amplitude although their duration (half-time) was unaltered. 4. 4-AP triggered presynaptic action potentials in the cercal nerves (recorded with external electrodes). These 'antidromic' potentials appeared singly or sometimes repetitively, especially after electrical stimulation of the cercal nerves. They were often in monosynaptic correlation with unitary EPSPs. 5. Neither the resting potential nor the postsynaptic membrane resistance was modified. 6. There were no changes in the equilibrium potentials of the ions involved in postsynaptic events. 7. The results may be essentially explained by an increase in transmitter release after 4-AP treatment, which may be partly the result of a rise in presynaptic terminal excitability, and partly the result of a lengthening of the presynaptic action potentials.     

Cercal sensory regulation of acetylcholinesterase in nervous system of the cockroach, Periplaneta americana

Cercal ablation caused a significant loss in acetylcholinesterase (AChE) activity of the cercal nerves and terminal ganglion within 12 hr while a similar reduction in enzyme activity of connectives was noticed at least one day after cercectomy. The decrease in AChE activity of the nervous tissues showed a recovery toward control levels from 20 days of unilateral cercectomy whereas the bilateral cercectomy produced a continuous and irreversible decline in enzyme activity. These localized changes in AChE activity of the abdominal nervous system of the cockroach were attributed to be regulated by the cercal sensory innervation.     

Neural circuitry underlying linear representation of wind information in a nonspiking local interneuron of the cockroach

In the cercal system of the cockroach Periplaneta americana, primary sensory interneurons exhibiting a sharp directional sensitivity respond to wind in a linear manner whereas those exhibiting an omnidirectional sensitivity respond nonlinearly. For example, the wind-evoked response in an identifiable, nonspiking local interneuron, 101, which responds preferentially to wind from the left versus the right, is characterized exclusively by a differential first-order (linear) kernel. However, the slow potential response in a cercal giant interneuron, GI-1, is omnidirectional, and characterized by a second-order (nonlinear) kernel with an elongated depolarizing peak on the diagonal with two off-diagonal valleys. We here examined the neural circuitry underlying the linear and nonlinear representations of wind information by the deprivation of inputs from particular sets of cercal hair afferents. Electrical stimulation of the ipsilateral (related to the soma) cercal nerve elicited a depolarizing potential in 101, which was followed by delayed hyperpolarization. A continuous flow of 10^–4 M picrotoxin, which selectively blocked this delayed hyperpolarization, resulted in a significant change in the 101 response from linear to nonlinear. Because no frequency-doubling response was observed, the nonlinearity is due to signal compression (or rectification) that reflects the mechanical property of cercal afferents. This is consistent with the hypothesis that the linear representation in 101 is based on a subtraction process between two subsets of particular column hairs, whose best optimal directions are opposite to each other.Abbreviations GABA -aminobutyric acid - GI(s) giant interneuron(s) - GI-1, GI-2, GI-3, GI-4 giant interneuron 1,2,3,4 - ipsi ipsilateral - cont contralateral - MSE(s) mean square error(s)     

Attenuation of phrenic motor discharge by phrenic nerve afferents

Short latency phrenic motor responses to phrenic nerve stimulation were studied in anesthetized, paralyzed cats. Electrical stimulation (0.2 ms, 0.01-10 mA, 2 Hz) of the right C5 phrenic rootlet during inspiration consistently elicited a transient reduction in the phrenic motor discharge. This attenuation occurred bilaterally with an onset latency of 8-12 ms and a duration of 8-30 ms. Section of the ipsilateral C4-C6 dorsal roots abolished the response to stimulation, thereby confirming the involvement of phrenic nerve afferent activity. Stimulation of the left C5 phrenic rootlet or the right thoracic phrenic nerve usually elicited similar inhibitory responses. The difference in onset latency of responses to cervical vs. thoracic phrenic nerve stimulation indicates activation of group III afferents with a peripheral conduction velocity of approximately 10 m/s. A much shorter latency response (5 ms) was evoked ipsilaterally by thoracic phrenic nerve stimulation. Section of either the C5 or C6 dorsal root altered the ipsilateral response so that it resembled the longer latency contralateral response. The low-stimulus threshold and short latency for the ipsilateral response to thoracic phrenic nerve stimulation suggest that it involves larger diameter fibers. Decerebration, decerebellation, and transection of the dorsal columns at C2 do not abolish the inhibitory phrenic-to-phrenic reflex.     

Neural pathways to cardioaccelerator neurons in the isopod crustacean Bathynomus doederleini: Cholinergic activation by somatic movements

We investigated the excitatory and inhibitory input to cardioaccelerator (CA) and cardioinhibitor (CI) neurons located in the thoracic ganglia of the isopod crustacean Bathynomus doederleini by extracellular and intracellular recording. Electrical stimuli applied to the anterior and posterior connectives of single-ganglion preparations, containing either the 2nd or 3rd thoracic ganglion alone, and each of three paired ganglionic nerve roots produced excitatory postsynaptic potentials (EPSPs) in the cell body of a CA neuron. Artificial movements of appendages, such as the thoracic limbs and the swimmerets, also evoked EPSPs in the CA neuron. Electrical stimuli applied to the peripheral nerves running to appendages induced inhibitory postsynaptic potentials (IPSPs) in a CI neuron. Since artificial movements of the appendages caused decrease of CI impulse rate, these IPSPs in the CI neuron may be caused by mechanoproprioceptors in the appendages. Since tachycardia was accompanied by excitation of CA neurons and inhibition of CI neurons, activation of the mechanoproprioceptors may be responsible for tachycardia. EPSPs in CA neurons produced by stimulation of peripheral nerves were augumented by eserinization and blocked by curarization. The activation of CA neurons by ganglionic roots may be mediated by cholinergic processes ascending from mechanoproprioceptors.     

What are the so-called ‘cercal nerves’ in the cockroach Blabera craniifer?

The branching of the nerves which issue from the terminal abdominal ganglion and the structures innervated by these branches were studied in the cockroach Blabera craniifer. The results indicate in particular that the movor cercal nerve is only one branch of the tenth nerve (N 10b) and that the sensory cercal nerve is only one branch of the eleventh nerve (N 11c).     

Effects of oxygen on the cercal receptors of the cockroach Periplaneta americana

• 1.1. The activity of the cercal nerve XI and giant interneurons of the cockroach Periplaneta americana is much more intense in situ than in vitro, despite perfusion of the sixth abdominal ganglion by oxygenated saline.
• 2.2. The background cercal nerve activity increases in vitro upon oxygenation from a negligible level. It persists for about 10 min following cessation of oxygenation. The activity in situ remains unaffected.
• 3.3. Oxygenation also substantially increases the frequency of sensory spikes evoked during mechanical stimulation of cercal receptors in vitro, as well as the frequency of generated EPSPs in the interneurons which integrate the cercal activity. The latter effect is apparently due to the increased frequency of afferent spikes.
• 4.4. The intense activity detected in vitro in oxygenated preparations appears to be closer to that existing in situ.

     

Dendritic calcium accumulation regulates wind sensitivity via short‐term depression at cercal sensory‐to‐giant interneuron synapses in the cricket

An in vivo Ca²⁺ imaging technique was applied to examine the cellular mechanisms for attenuation of wind sensitivity in the identified primary sensory interneurons in the cricket cercal system. Simultaneous measurement of the cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and membrane potential of a wind‐sensitive giant interneuron (GI) revealed that successive air puffs caused the Ca²⁺ accumulation in dendrites and diminished the wind‐evoked bursting response in the GI. After tetanic stimulation of the presynaptic cercal sensory nerves induced a larger Ca²⁺ accumulation in the GI, the wind‐evoked bursting response was reversibly decreased in its spike number. When hyperpolarizing current injection suppressed the [Ca²⁺]_i elevation during tetanic stimulation, the wind‐evoked EPSPs were not changed. Moreover, after suprathreshold tetanic stimulation to one side of the cercal nerve resulted in Ca²⁺ accumulation in the GI's dendrites, the slope of EPSP evoked by presynaptic stimulation of the other side of the cercal nerve was also attenuated for a few minutes after the [Ca²⁺]_i had returned to the prestimulation level. This short‐term depression at synapses between the cercal sensory neurons and the GI (cercal‐to‐giant synapses) was also induced by a depolarizing current injection, which increased the [Ca²⁺]_i, and buffering of the Ca²⁺ rise with a high concentration of a Ca²⁺ chelator blocked the induction of short‐term depression. These results indicate that the postsynaptic Ca²⁺ accumulation causes short‐term synaptic depression at the cercal‐to‐giant synapses. The dendritic excitability of the GI may contribute to postsynaptic regulation of the wind‐sensitivity via Ca²⁺‐dependent depression. © 2001 John Wiley & Sons, Inc. J Neurobiol 46: 301–313, 2001     

Multiple feedback loops in the flying cockroach: excitation of the dorsal and inhibition of the ventral giant interneurons

1. In a tethered cockroach (Periplaneta americana) whose wings have been cut back to stumps, it is possible to elicit brief sequences of flight-like activity by puffing wind on the animal's body. 2. During such brief sequences, rhythmic bursts of action potentials coming from the thorax at the wingbeat frequency, descend the abdominal nerve cord to the last abdominal ganglion (A6). This descending rhythm is often accompanied by an ascending rhythm (Fig. 2). 3. Intracellular recording during flight-like activity from identified ascending giant interneurons, and from some unidentified descending axons in the abdominal nerve cord, shows that: (a) ventral giant interneurons (vGIs) remain silent (Fig. 3); (b) dorsal giant interneurons (dGIs) are activated at the onset of the flight-like activity and remain active sporadically throughout the flight sequence (Fig.4); (c) some descending axons in the abdominal nerve cord show rhythmic activity phase-locked to the flight rhythm (Fig. 5). 4. Also during such brief sequences, the cercal nerves, running from the cerci (paired, posterior, wind sensitive appendages) to the last abdominal ganglion, show rhythmic activity at the wingbeat frequency (Fig. 6). This includes activity of some motor axons controlling vibratory cercal movements and of some sensory axons. 5. More prolonged flight sequences were elicited in cockroaches whose wings were not cut and which flew in front of a wind tunnel (Fig. 1B). 6. In these more prolonged flight sequences, the number of ascending spikes per burst was greater than that seen in the wingless preparation (Fig. 8; compare to Fig. 2). Recordings from both ventral and dorsal GIs show that: in spite of the ongoing wind from both the tunnel and the beating wings, which is far above threshold for the vGIs in a resting cockroach, the vGIs are entirely silent during flight. Moreover, the vGIs response to strong wind puffs that normally evoke maximal GI responses is reduced by a mean of 86% during flight (Fig. 9). The dGIs are active in a strong rhythm (Figs. 11 and 12). 7. Three sources appear to contribute to the ascending dGI rhythm (1) the axons carrying the rhythmic descending bursts; (2) the rhythmic sensory activity resulting from the cercal vibration; and (3) the sensory activity resulting from rhythmic wind gusts produced by the wingbeat and detected by the cerci. The contribution of each source has been tested alone while removing the other two (Figs. 13 and 14). Such experiments suggest that all 3 feedback loops are involved in rhythmically exciting the dGIs (Fig. 15).     

Fictive locomotion and scratching inhibit dorsal horn neurons receiving thin fiber afferent input

In decerebrate paralyzed cats, we examined the effects of two central motor commands (fictive locomotion and scratching) on the discharge of dorsal horn neurons receiving input from group III and IV tibial nerve afferents. We recorded the impulse activity of 74 dorsal horn neurons, each of which received group III input from the tibial nerve. Electrical stimulation of the mesencephalic locomotor region (MLR), which evoked fictive static contraction or fictive locomotion, inhibited the discharge of 44 of the 64 dorsal horn neurons tested. The mean depth from the dorsal surface of the spinal cord of the 44 neurons whose discharge was inhibited by MLR stimulation was 1.77 +/- 0.04 mm. Fictive scratching, evoked by topical application of bicuculline to the cervical spinal cord and irritation of the ear, inhibited the discharge of 22 of the 29 dorsal horn neurons tested. Fourteen of the twenty-two neurons whose discharge was inhibited by fictive scratching were found to be inhibited by MLR stimulation as well. The mean depth from the dorsal surface of the cord of the 22 neurons whose discharge was inhibited by fictive scratching was 1.77 +/- 0.06 mm. Stimulation of the MLR or the elicitation of fictive scratching had no effect on the activity of 22 dorsal horn neurons receiving input from group III and IV tibial nerve afferents. The mean depth from the dorsal surface of the cord was 1.17 +/- 0.07 mm, a value that was significantly (P < 0.05) less than that for the neurons whose discharge was inhibited by either MLR stimulation or fictive scratching. We conclude that centrally evoked motor commands can inhibit the discharge of dorsal horn neurons receiving thin fiber input from the periphery.     

Postural interneurons in the abdominal nervous system of lobster

The multisegmented abdomen of crayfish and lobster assumes a variety of postures as components of different behavioral acts. Experimentally these postures can be maintained by activating any of a number of premotor positioning interneurons. The pathways by which the motor output in two or more segments is coordinated were here investigated for a small group of identified postural interneurons whose somata lie in the 2nd abdominal ganglion (A2). Stimulation of all postural interneurons examined evokes a motor output in other abdominal ganglia through which the axon of the neuron passes as well as in the ganglion of origin (ganglion containing the neuron's cell body). The spread of motor excitation away from the originating ganglion occurs via two general pathways. In the first pathway connections to postural motoneurons are made directly by processes of the postural interneuron which pass into ganglia distal to the originating ganglion. Examples of this are shown for two flexion producing interneurons (FPIs) 201 and 301. Each of these FPIs makes monosynaptic connections with motoneurons in A2 and with a homologous set of motoneurons in A3. All postural interneurons fired a set of corollary discharge interneurons (CDIs) whose activities were recorded from the abdominal connectives. Two FPIs, 202 and 301, and a third interneuron, 503, produced motor outputs in ganglia to which they did not project. The motor specificity established in A2 by stimulation of FPIs 202 and 301 (whose axons pass caudally) was preserved in more rostral ganglia, such as A1. Therefore, different sets of CDIs can be specifically recruited to spread the same motor program that is initiated in the originating ganglion to ganglia that do not receive projections from the stimulated postural interneuron. CDIs, in addition, have the capacity to elicit motor programs in distal ganglia that are markedly different from that expressed in the ganglion of origin. For example, although 503 produced an inhibitory output in the abdominal ganglia that it innervated (A1 and A2), a flexion response was generated by it in more caudal ganglia. The caudal flexion response was mediated in part through a monosynaptic activation of FPI 201 and through other unidentified CDIs. Thus, the interneuronal circuitry for postural control is composed of numerous components, some of which have regional control over different portions of the abdominal nerve cord. Depending upon the required movement, select components are coactivated, either serially or in parallel, to effect a variety of spatially distinct positions.     

A comparison of the effect of kainate and some related amino acids on locomotor activity in cockroaches and electrical activity recorded from locust ventral nerve cord

The ED50 for loss of righting behaviour of cockroaches induced by kainate (43 mumol/kg body weight) indicated the toxicity of kainate to be much greater than would have been predicted from the excitatory action of this amino acid at insect skeletal muscle fibres. N-Methyl-D-aspartate had little effect on righting behaviour (ED50 greater than 3500 mumol/g body weight). Electrical recordings from the locust ventral nerve cord showed kainate (0.1-2 mM) to have a depolarizing action on neurons within the metathoracic ganglion. The depolarizing action of kainate was partially resistant to tetrodotoxin. The kainate-induced abolition of rostrally evoked potentials recorded in the abdominal connectives from the metathoracic ganglion suggests that the giant fibres are sensitive to kainate. Domoic acid was 46 times more potent than kainate. The lack of effect of N-methyl-D-aspartate (2 mM), dihydrokainate (2 mM), quisqualate (2 mM) and L-glutamate (20 mM) on nerve cords in the present experiments suggests that the kainate receptors in this preparation show a chemical selectivity comparable to that observed at vertebrate central neurones.     

Mechanisms of sperm release from the receptaculum seminis of Schistocerca vaga Scudder (Orthoptera: Acrididae)

Release of spermatozoa from the receptaculum seminis of Schistocerca vaga was studied by means of electrical and mechanical stimulation. Electrical stimulation of the receptaculum nerve, or the ductus aperture nerve, leads to release of spermatozoa from the receptaculum seminis, provided the spermathecal innervation is intact. Mechanical stimulation of the ductus aperture in the genital chamber also leads to sperm release, provided the neural loop, ductus aperture/terminal abdominal ganglion/receptaculum seminis, has not been interrupted at any point. Ten somata in the terminal abdominal ganglion, including 6 dorsal unpaired medial (DUM) neurons, innervate the receptaculum seminis; some of these somata may be neurosecretory. Approximately 80 presumed sensory axons run from the ductus aperture to the same ganglion. On the basis of these neuroanatomical data and the results of electrical and mechanical stimulation, a schema of how the release mechanisms operate in S. vaga is proposed.     

The neuroethology of sound production in tiger moths (Lepidoptera,Arctiidae)

When stimulated either acoustically or tactually, certain species of arctiid moths rhythmically emit trains of clicks from metathoracic tymbals. The purpose of the experiments presented here was to determine the location within the central nervous system (CNS) of the proposed tymbal central pattern generator (CPG) in Cycnia tenera. Motor neuron impulses that underlie tymbal activation were recorded extracellularly from the tymbal nerve while moths were subjected to selective severing of the suboesophageal, prothoracic, pterothoracic and abdominal ganglia connectives. Motor output evoked by either acoustic or tactile stimulation originates from a common CPG because tymbal nerve spikes in both cases are similar in amplitude, waveform and rhythmicity. Our results showed: (1) removal of the CNS posterior of the second abdominal neuromere had no effect, (2) removal of the head decreased the responsiveness of the animal to acoustic stimulation and, (3) severing the connectives between the prothoracic and pterothoracic ganglia abolished responses to acoustic stimuli and diminished responses to tactile stimuli. We conclude that although the minimal circuitry sufficient for activating the tymbals resides in the pterothoracic ganglion, the prothoracic and cephalic ganglia are required for the normal, and in particular, auditory-evoked operation of the tymbal CPG.Abbreviations ASR acoustic startle response - CNS central nervous system - CPG central pattern generator - dB peSPL decibel peak equivalent sound pressure level (rms re 20 Pa) - ISI inter-spike interval     

Interaction of Distant Mechanoreceptor Systems under Conditions of Presentation of Conspecific Sound Signals to Normal and Allatectomized Male Crickets Gryllus bimaculatus

The character of interaction between the cercal and tympanal systems was studied in male crickets Gryllus bimaculatus. Experiments were carried out on non-copulated males at the age of 7 days (copulative period). A complex of directed motor reactions in response to stimulation of animals with conspecific acoustic signals was analyzed. Directed motor reactions of males without hormonal pathology and under conditions of experimental hormonal pathology (after ablation of corpora allata) as well as those before and after reversible inactivation of the cercal receptors were studied. Data are obtained on participation of male corpora allata hormones in providing effects of the cercal system on the ethological result of functioning of the tympanal system. A hypothesis is put forward about the existence of a neuroendocrine mechanism for realization of defensive and territorial acoustic behavior of the 7-day-old male crickets.     

Changes in cytoplasmic and vesicular acetylcholine content in insect ganglia during tetanic stimulation

Acetylcholine (ACh) content was reduced by about 30 pmol or 20% of the initial ACh content in the cockroach sixth abdominal ganglion in response to prolonged (30 min) tetanic stimulation at 40 Hz of the cercal nerves in the presence of 10⁻³ M hemicholinium-3 (HC-3). The reduction in ACh content in ganglia occurred in the cytoplasmic rather than the vesicular ACh fraction. The latter showed instead a transient increase followed by a gradual decrease to the previous level. Similar changes in ACh in the fractions were produced also by the stimulation, although the ACh content in ganglia did not change in a calcium-free saline, but was reduced in the presence of 50 μM dantrolene or 1–5 mM cobalt chloride. Synaptic transmission at the cercal nerve-giant nerve fiber synapses rapidly decreased and was abolished within a few minutes during tetanic stimulation at 40 Hz, but recovered on reducing the frequency to 0.1 Hz. The decline in transmission was not affected by HC-3, but a significant delay was observed in the recovery following 30 min of tetanic stimulation in the presence of HC-3.These results may suggest that the depletion of ACh as a functional store occurs in the cytoplasmic ACh fraction, rather than in the vesicular one, after prolonged stimulation in the presence of HC-3. The latter fraction shows and increase in the uptake of cytoplasmic ACh that depend on the presence of intracellular calcium ions during stimulation.