Octopamine enhances neuromuscular transmission in developing and adult moths, Manduca sexta

The effect of octopamine on neuromuscular transmission was examined in developing and adult Manduca sexta. Intracellular recordings were made from the dorsal longitudinal muscle (DLM), superfused with solutions containing DL-octopamine or other amines. In untreated adult moths and pharate adults nearly ready to enclose (stage Day 19), stimulation of the motor nerve evokes a large excitatory junction potential (EJP), an active membrane response, and a twitch. In adults and Day 19 animals DL-octopamine (10(-7) to 10(-4)M) has no effect on the amplitude and rise-time of the electrical response in normal saline, but 10(-6) to 10(-4) M DL-octopamine increases the amplitude of the excitatory junction potential recorded in saline containing one-third the normal calcium concentration. Immature (Day 16) muscle, which normally produces only small EJPs following stimulation of its motor nerve, responds to 10(-6) to 10(-4) M DL-octopamine by an increase in the EJP above threshold for an active membrane response and a contraction. When the muscle has developed sufficiently to spike and contract in response to nerve stimulation in the absence of exogenous octopamine (Days 17 and 18), application of DL-octopamine increases the maximum rate at which the muscle contracts in response to each stimulus in a train (designated the maximum following frequency, MFF). The threshold dose for an effect on the MFF of Day 18 immature moths is less than 10(-10) M. At this stage 10(-8) M DL-octopamine increases the MFF four-fold. The effect on the MFF is dose-dependent over the range 10(-10) M to 10(-6) M. The biogenic amines DL-epinephrine, DL-norepinephrine, tyramine, DL-phenylethanolamine, 2-phenylethylamine, and dopamine, applied at concentrations of 10(-8) or 10(-4) M, do not change the MFF. Both DL-synephrine (10(-8) M) and serotonin (10(-7) M) mimic the action of 10(-10) M DL-octopamine on the MFF. The action of DL-octopamine (10(-7) M) is blocked by phentolamine (10(-4)M) but not by propranolol (10(-4)M). The octopamine content of hemolymph was determined with a radioenzymtic assay. The concentration of octopamine in the hemolymph increases 3.6-fold, from 5 X 10(-8) M on Day 18 (duration of adult development is 19 days) to 1.85 X 10(-7) M one day following eclosion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Octopamine receptors in the molluscan aortic bulb: effects of clozapine and chlordimeform

The presence of specific, stereo-selective octopamine receptors has been demonstrated in the non-spontaneously beating accessory ventricle (aortic bulb) of the clam Tapes watlingi. Analogues of octopamine with a single chloro group in either the para or meta positions of the benzene ring were 10 times less potent than octopamine in their agonist activity. In low concentrations (less than 200 microM), phentolamine, chlordimeform and clozapine were octopamine antagonists. In high concentrations (greater than 200 microM), clozapine, clonidine and chlordimeform induced changes in aortic tone similar to that produced by p-octopamine. This activity may result from the chloro-substituted phenamidine skeleton in both clozapine and chlordimeform.     

Pre-imaginal flight motor pattern in Locusta

In a wind stream, larval stages of Locusta usually show a tonic muscle activity but they can also exhibit a rhythmic motor output. With ageing such a pattern can be released sooner, the trains become longer. The basic rhythm of 10 Hz does not change. The initial co-contraction of specific muscles is substituted later in development by an antagonistic recruitment. This activity resembles the flight motor pattern of young locusts which lack phasic sensory feedback from the wing region. Azadirachtin, an insect growth regulator, has been used to produce a permanent 5th larval instar. However, the extension of the last larval stage does not lead to a further development of the motor pattern to a level comparable to mature animals.     

Oxytocin and vasopressin enhance responsiveness to infant stimuli in adult marmosets

The neuropeptides oxytocin (OT) and arginine-vasopressin (AVP) have been implicated in modulating sex-specific responses to offspring in a variety of uniparental and biparental rodent species. Despite the large body of research in rodents, the effects of these hormones in biparental primates are less understood. Marmoset monkeys (Callithrix jacchus) belong to a clade of primates with a high incidence of biparental care and also synthesize a structurally distinct variant of OT (proline instead of leucine at the 8th amino acid position; Pro⁸-OT). We examined the roles of the OT and AVP systems in the control of responses to infant stimuli in marmoset monkeys. We administered neuropeptide receptor agonists and antagonists to male and female marmosets, and then exposed them to visual and auditory infant-related and control stimuli. Intranasal Pro⁸-OT decreased latencies to respond to infant stimuli in males, and intranasal AVP decreased latencies to respond to infant stimuli in females. Our study is the first to demonstrate that Pro⁸-OT and AVP alter responsiveness to infant stimuli in a biparental New World monkey. Across species, the effects of OT and AVP on parental behavior appear to vary by species-typical caregiving responsibilities in males and females.     

Maturation of the flight motor pattern without movement inManduca sexta

The development of the flight motor pattern was studied by recording acutely with fine wire electrodes inserted in the thoracic muscles of pharate moths of known age and by recording chronically for up to 8 days with implanted electrodes. Externally visible morphological characteristics by which the age of a pharateManduca sexta can be established were identified (Table 1). Bouts of activity lasting approximately 30 min to 2 h and alternating with inactive periods of similar duration were recorded as early as the ninth day after pupation and on all successive days until early on the day of eclosion, typically 19 days after pupation (Figs. 1,5). During the 3 days preceding the day of eclosion a rhythmic flight motor pattern was produced (Fig. 2). The rhythmic activity ceased 5^1/2–10^1/2 h before eclosion and only an occasional, large potential change was recorded from the thoracic muscles during this time (Fig. 3). During the 3 days of rhythmic activity the percent-age of time that the animal was active did not change (Fig. 4). The flight motor pattern matured, in that the cycle-time decreased and became less variable (Fig. 6). The approximate flight phase relationship between an elevator muscle and the dorsal longitudinal depressor muscle did not become less variable as the cycle-time improved. The flight motor pattern produced by pharate moths caused neither movement of the scutum nor an increase in thoracic temperature in marked contrast to the consequences of adult motor activity (Fig. 7). Intracellular recording from the dorsal longitudinal muscle of pharate moths 20–30 h before eclosion showed that, after repeated stimulation of the motor nerve at 2/s, only small junctional potentials were elicited (Fig. 8). A burst of 6 stimuli at 50/s elicited 2–5 active membrane responses and a contraction. These observations explain the absence of thoracic movement in immature animals producing the flight motor pattern and the presence of movement in immature animals stimulated to eclose. They also show that the neuromuscular junction matures rapidly during the day before eclosion.     

Manipulation of the endocrine system ofLocusta and the development of the flight motor pattern

Journal of Comparative Physiology A - By chemical allatectomy (precocenetreatment) or implantation of corpora allata, precocious adults (adultiforms) and supernumerary larval instars respectively...     

Dipteran flight motor pattern: Invariabilities and changes during postlarval development

For Calliphora the wingbeat frequency and the underlying motoneuronal activity were recorded during adult life. Wingbeat frequency increases during the ten days following last molt. The activity of motoneurons serving four selected flight muscles (nonfibrillar and fibrillar ones) also increases with age. The motoneuronal activity of young and old flies was analyzed statistically (serial and cross-correlograms, latency and phase histograms). In addition, several wing manipulations were carried out to evaluate the significance of sensory feedback on pattern generation during maturation. These ontogenetic studies suggest a centrally generated motor pattern that (1) is essentially complete with the molt to adulthood, (2) shows a progressive increase in intrinsic activity, and (3) is modulated by sensory feedback from the wing region by the same amount irrespective of age. Similarities in the postlarval development of the flight pattern of neurogenic and myogenic flyers are discussed.     

Specification of synaptic connections between sensory and motor neurons in the developing spinal cord

Experimental studies of mechanisms underlying the specification of synaptic connections in the monosynaptic stretch reflex of frogs and chicks are described. Sensory neurons innervating the triceps brachii muscles of bullfrogs are born throughout the period of sensory neurogenesis and do not appear to be related clonally. Instead, the peripheral targets of these sensory neurons play a major role in determining their central connections with motoneurons. Developing thoracic sensory neurons made to project to novel targets in the forelimb project into the brachial spinal cord, which they normally never do. Moreover, these foreign sensory neurons make monosynaptic excitatory connections with the now functionally appropriate brachial motoneurons. Normal patterns of neuronal activity are not necessary for the formation of specific central connections. Neuromuscular blockade of developing chick embryos with curare during the period of synaptogenesis still results in the formation of correct sensory-motor connections. Competitive interactions among the afferent fibers also do not seem to be important in this process. When the number of sensory neurons projecting to the forelimb is drastically reduced during development, each afferent still makes central connections of the same strength and specificity as normal. These results are discussed with reference to the development of retinal ganglion cells and their projections to the brain. Although many aspects of the two systems are similar, patterned neural activity appears to play a much more important role in the development of the visual pathway than in the spinal reflex pathway described here.     

Vibrissal inputs into the motor cortex of adult and developing rats

Field potentials (FP) and responses of single neurones to electrical stimulation of vibrissal pads have been recorded in motor cortex in the albino mature and developing rats. The FPs were characterized by 3-phasic shape and high stability in mature rats. The FPs evoked by contralateral stimuli have a range of onset latency of 4 to 24 ms (peak of distribution 8-11 ms); those to ipsilateral stimuli have a latency of 4 to 23 ms (peak of distribution 12-16 ms). Responses of single neurones were evoked with a latency of 9 to 20 ms. Usually, the FPs were evoked by both contralateral and ipsilateral stimulation, and in some tracks were effective only ipsilateral stimuli in the developing rats beginning from the 11th day of life. The FPs in such animals were less stable and more fatigable. During 2-4 weeks of life, FPs evoked by contralateral stimulation appeared with a latency of 15 to 46 ms; during the same period, a latency of single unit responses ranged between 20 to 33 ms. The FPs to ipsilateral stimuli appeared with a latency of 18 to 47 ms, a latency of single unit responses of 27 to 47 ms. The results indicate functional immaturity of vibrissal system up to the end of the first month of rat life.     

The motor pattern of locusts during visually induced rolling in long-term flight

Desert locusts (Schistocerca gregaria F.), mounted in a wind tunnel on a low-mechanical-impedance torque meter, flew for at least 30 min in the posture typical of long-term flight. As they flew, they were induced to rotate about their long axis (roll) by rotation of an artificial horizon. All maintained departures from the horizontal attitude were brought about actively, by the animal's own efforts. In the roll maneuver, the hindlegs and abdomen were bent toward the side ipsilateral to the direction of rotation. However, these rudderlike movements were not adequate to initiate and maintain a constant roll angle.During a roll, there was a change in the pattern of excitation of all the wing muscles that were monitored: the depressorsM81, 97, 99, 112, 127, and 129, and the elevatorsM83, 84, 89, 113, 118, 119 (numbering according to Snodgrass 1929). Hence all 12 muscles probably not only provide power for the flight but also steer it. Evidently, then, for these muscles a rigid distinction between power and steering muscles is not appropriate.The period of the contraction cycle changed in correlation with the roll angle, but was not a parameter for control of the roll maneuver, because the changes were the same in all muscles (Fig. 2).Even with constant burst length, the phase shifts between the muscles changed. These changes were the main control parameter for rolling (Figs. 3–9).There was a latency coupling between elevators and the following depressors (Fig. 3).The changes in phase shift were tonic or phasic (sometimes phasic-tonic) in different muscle pairs (Fig. 4).When a roll angle of ca. 15° was adopted, the phase shifts between depressor muscles in a given fore- or hindwing (e.g.,M127R vs.M129R) changed by about 5 ms, whereas the elevators changed by less than 1 ms (Fig. 6).The phase shifts between the anterior elevators and depressors of a given wing, as well as the posterior elevators and depressors, changed by ca. 5 ms (in some cases with different time courses) when the animal rolled to an angle of ca. 15° (Fig. 7).The changes in phase shift between muscles of the fore-and hindwing on one side of the body amounted, as a rule, to about 4 ms at ca. 15° roll (Fig. 8).Corresponding muscles on the two sides of the body change in phase with respect to one another by as much as 10 ms (Fig. 9). The phase shifts of all such contralateral muscle pairs except for the posterior basalar muscles,M127, have the same sign, such that the muscle ipsilateral to the direction of rotation becomes active sooner.     

Analysis of zigzagging flight in moths: a correction

In 1978 we reported the results of an analysis of the zigzagging behaviour of male Plodia interpunctella flying up a plume of sex pheromone (Marsh et al. , 1978). Since then we have discovered that, owing to two technical faults, we used an incorrect time base in analysing the videotape records of the moths' tracks. The original tapes have now been re-analysed and a full revision paper is being prepared which shows that only one important conclusion must be changed. Meanwhile that incorrect conclusion has been cited at least twice (Schöne, 1980, p.236; Murlis & Jones, 1981) so we here summarize the correction to be made.     

The pattern of sensory discharge can determine the motor response in young Xenopus tadpoles

Young Xenopus tadpoles were used to test whether the pattern of discharge in specific sensory neurons can determine the motor response of a whole animal. Young Xenopus tadpoles show two main rhythmic behaviours: swimming and struggling. Touch-sensitive skin sensory neurons in the spinal cord of immobilised tadpoles were penetrated singly or in pairs using microelectrodes to allow precise control of their firing patterns. A single impulse in one Rohon-Beard neuron (= light touch) could sometimes trigger “fictive” swimming. Two to six impulses at 30–50 Hz (= a light stroke) reliably triggered fictive swimming. Neither stimulus evoked fictive struggling. Twenty-five or more impulses at 30–50 Hz (= pressure) could evoke a pattern of rhythmic bursts, distinct from swimming and suitable to drive slower, stronger movements. This pattern showed some or all the characteristics of “fictive” struggling. These results demonstrate clearly that sensory neurons can determine the pattern of motor output simply by their pattern of discharge. This provides a simple form of behavioural selection according to stimulus. Accepted: 28 November 1996     

Control of respiratory motor pattern by sensory neurons in spinal cord of lamprey

Summary Extracellular stimulation over the dorsal funiculus in the spinal cord of lampreys was found to selectively activate prolonged episodes of fictive arousal respiration (Figs. 1, 3). The induced episodes showed comparable increases in cycle frequency and motoneuron burst duration to the spontaneous arousal pattern observed in isolated brain preparations (Fig. 2). Intracellular stimulation of primary sensory neurons with axons in the dorsal funiculus, called dorsal cells, also elicited the arousal pattern (Fig. 4). Mechanoreceptive dorsal cells respond to cutaneous stimulation. When mechanical stimuli were applied to the skin of intact lampreys (Fig. 6) or to lampreys with ipsilateral vagotomy, arousal respiration was induced (Figs. 7, 8). Bilateral, but not unilateral, trigeminal lesion blocked dorsal cell induction of the arousal response (Fig. 5). Spontaneous arousal respiration was recorded from intact, unrestrained lampreys (Fig. 9). These results suggest that fictive arousal respiration is the in vitro correlate of natural arousal respiration in lampreys, and that one mechanism leading to arousal respiration may be the activity of sensory dorsal cells. A model for respiratory motor pattern switching in lamprey is proposed. The model suggests that the normal and arousal patterns are produced by separately engaging rostral or caudal pattern generators in the medulla, rather than by modifying one pattern generator (Fig. 10).     

Flight duration and flight muscle ultrastructure of unfed hawk moths

Flight muscle breakdown has been reported for many orders of insects, but the basis of this breakdown in insects with lifelong dependence on flight is less clear. Lepidopterans show such muscle changes across their lifespans, yet how this change affects the ability of these insects to complete their life cycles is not well documented. We investigated the changes in muscle function and ultrastructure of unfed aging adult hawk moths (Manduca sexta). Flight duration was examined in young, middle-aged, and advanced-aged unfed moths. After measurement of flight duration, the main flight muscle (dorsolongitudinal muscle) was collected and histologically prepared for transmission electron microscopy to compare several measurements of muscle ultrastructure among moths of different ages. Muscle function assays revealed significant positive correlations between muscle ultrastructure and flight distance that were greatest in middle-aged moths and least in young moths. In addition, changes in flight muscle ultrastructure were detected across treatment groups. The number of mitochondria in muscle cells peaked in middle-aged moths. Many wild M. sexta do not feed as adults; thus, understanding the changes in flight capacity and muscle ultrastructure in unfed moths provides a more complete understanding of the ecophysiology and resource allocation strategies of this species.     

Daily flight activity of moths in the continuous daylight of the arctic summer

The daily onset of flight and the lime of activity of moths were studied at an arctic and a subarctic locality in midsummer under natural light conditions but with all other factors kept constant. The daily variation of light intensity is much smaller than at temperate latitudes, and the illumination is continuously at levels that normally inhibit the activity of moths. In spite of this, the investigated species showed a distinct daily periodicity with the activity occurring at about the same time of day as in the same or related species from lower latitudes. It is suggested that this is the result of a process of acclimatization to high light intensities.
A number of species show a diurnal activity pattern, and it is suggested that this is connected with their high temperature requirements. In the field, Anarta zetterstedti Staud. thermoregulates by settling frequently on dark rocks which can reach high temperatures when the sun is shining. This species can not fly unless its body temperature is above 30°C and it prefers an ambient temperature of about 36°C.