Neuromodulation for behavior in the locust frontal ganglion

Allatostatin A Signalling: Progress and New Challenges From a Paradigmatic Pleiotropic Invertebrate Neuropeptide Family

Neuropeptides have gained broad attraction in insect neuroscience and physiology, as new genetic tools are increasingly uncovering their wide-ranging pleiotropic functions with high cellular resolution. Allatostatin A (AstA) peptides constitute one of the best studied insect neuropeptide families. In insects and other panarthropods, AstA peptides qualify as brain-gut peptides and have regained attention with the discovery of their role in regulating feeding, growth, activity/sleep and learning. AstA receptor homologs are found throughout the protostomia and group with vertebrate somatostatin/galanin/kisspeptin receptors. In this review, we summarise the current knowledge on the evolution and the pleiotropic and cell-specific non-allatostatic functions of AstA. We speculate about the core functions of AstA signalling, and derive open questions and challengesfor future research on AstA and invertebrate neuropeptides in general.

K+ absorption by locust gut and inhibition of ileal K+ and water transport by FGLamide allatostatins

The Scanning Ion-Selective Electrode Technique (SIET) was utilized for the first time in Locusta migratoria to characterize K+ transport along the digestive tract and to determine the effect of two locust FGLamide allatostatins (FGLa/ASTs) on K+ transport: a previously sequenced FGLa/AST from Schistocerca gregaria (Scg-AST-6; ARPYSFGL-NH2) and a newly sequenced FGLa/AST from L. migratoria (Locmi-FGLa/AST-2; LPVYNFGL-NH2). Regional differences in K+ fluxes along the gut were evident, where K+ efflux in vitro (or absorption into the hemolymph in vivo) was greatest at the anterior ileum, and lowest at the colon. Ileal K+ efflux was inhibited by both Scg-AST-6 and Locmi-FGLa/AST-2, with maximal inhibition at 10-10 and 10-11 M, respectively. Both FGLa/ASTs also inhibited cAMP-stimulated K+ efflux from the ileum. Locmi-FGLa/AST-2 also inhibited efflux of water across the ileum. Locusts are terrestrial insects living in dry climates, risking desiccation and making water conservation a necessity. The results suggest that FGLa/ASTs may be acting as diuretics by increasing K+ excretion and therefore increasing water excretion. Thus, it is likely that FGLa/ASTs are involved in the control of hemolymph water and ion levels during feeding and digestion, to help the locust deal with the excess K+ load (and subsequently fluid) when the meal is processed.

The effect of octopamine on the locust stomatogastric nervous system

Octopamine (OA) is a prominent neuromodulator of invertebrate nervous systems, influencing multiple physiological processes. Among its many roles in insects are the initiation and maintenance of various rhythmic behaviors. Here, the neuromodulatory effects of OA on the components of the locust stomatogastric nervous system were studied, and one putative source of OA modulation of the system was identified. Bath application of OA was found to abolish the endogenous rhythmic output of the fully isolated frontal ganglion (FG), while stimulating motor activity of the fully isolated hypocerebral ganglion (HG). OA also induced rhythmic movements in a foregut preparation with intact HG innervation. Complex dose-dependent effects of OA on interconnected FG-HG preparations were seen: 10⁻⁵ M OA accelerated the rhythmic activity of both the HG and FG in a synchronized manner, while 10⁻⁴ M OA decreased both rhythms. Intracellular stimulation of an identified octopaminergic dorsal unpaired median neuron in the subesophageal ganglion was found to exert a similar effect on the FG motor output as that of OA application. Our findings suggest a mechanism of regulation of insect gut patterns and feeding-related behavior during stress and times of high energy demand.

Peptidergic control of food intake and digestion in insects 1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Like all heterotrophic organisms, insects require a strict control of food intake and efficient digestion of food into nutrients to maintain homeostasis and to fulfill physiological tasks. Feeding and digestion are steered by both external and internal signals that are transduced by a multitude of regulatory factors, delivered either by neurons innervating the gut or mouthparts, or by midgut endocrine cells. The present review gives an overview of peptide regulators known to control feeding and digestion in insects. We describe the discovery and functional role in these processes for insect allatoregulatory peptides, diuretic hormones, FMRFamide-related peptides, (short) neuropeptide F, proctolin, saliva production stimulating peptides, kinins, and tachykinins. These peptides control either gut myoactivity, food intake, and (or) release of digestive enzymes. Some peptides exert their action at multiple levels, possibly having a biological function that depends on their site of delivery. Many regulatory peptides have been physically extracted from different insect species. However, multiple peptidomics, proteomics, transcriptomics, and genome sequencing projects have led to increased discovery and prediction of peptide (precursor) and receptor sequences. In combination with physiological experiments, these large-scale projects have already led to important steps forward in unraveling the physiology of feeding and digestion in insects.

The neural and peptidergic control of gut contraction in Locusta migratoria: the effect of an FGLa/AST

The regulation of insect gut physiology is complex and involves the interactions of a number of mechanisms, including the neural regulation of gut contraction by altering neural input and the modulation of gut contractions by neuropeptides directly affecting the muscle. The FGLa-type allatostatins (FGLa/ASTs) are known brain/gut peptides with numerous physiological roles, including modulation of gut contraction and neural input. To further investigate the pleiotropic roles of FGLa/AST peptides in Locusta migratoria, we have examined the role of a locust FGLa/AST (Scg-AST-6) in the gut. Proctolin and Scg-AST-6 have opposing effects on gut contraction, where proctolin dose-dependently increases gut muscle tension, while Scg-AST-6 inhibits both muscle tension and spontaneous and neurogenic contractions in a dose-dependent manner. Results from neurophysiological recordings indicate that there may be a central pattern generator (CPG) within the ventricular ganglia regulated by descending inhibition, and the addition of Scg-AST-6 dose-dependently modulates this ventricular ganglion CPG. This work provides a comprehensive picture of how FGLa/ASTs may modulate and coordinate each region of the locust gut, and shows that FGLa/ASTs have both central effects, on the ventricular ganglion CPG, and peripheral effects on the gut muscle. Overall, this work shows how FGLa/ASTs contribute to the complex regulation and fine tuning of gut contraction.

Neuroanatomy and neurophysiology of the locust hypocerebral ganglion

The insect stomatogastric ganglia control foregut movements. Most previous work on the system has concentrated on the frontal ganglion (FG), including research into the role of the FG in feeding as well as molting-related behavior, mostly in locusts, but also in other insect species. The stomatogastric system exerts its physiological actions by way of careful interaction and coordination between its different neural centers and pattern-generating circuits. One such hitherto unstudied neural center is the hypocerebral ganglion (HG), which is connected to the FG via the recurrent nerve. It sends two pairs of nerves along the esophagus and to the posterior region of the crop, terminating in the paired ingluvial ganglia. Very little is known about the neuroanatomy and neurophysiology of the insect HG. Here we investigate, for the first time, the neuronal composition of the locust HG, as well as its motor output. We identify rhythmic patterns endogenous to the isolated HG, demonstrating the presence of a central pattern-generating network. Our findings suggest interactions between the HG and FG rhythm-generating circuits leading to complex physiological actions of both ganglia. This work will serve as a basis for future investigation into the physiology of the HG and its role in insect behavior.

Neural substrate and allatostatin-like innervation of the gut of Locusta migratoria

Allatostatin-like immunoreactivity (ALI) is widely distributed in processes and varicosities on the fore-, mid-, and hindgut of the locust, and within midgut open-type endocrine-like cells. ALI is also observed in cells and processes in all ganglia of the central nervous system (CNS) and the stomatogastric nervous system (SNS). Ventral unpaired median neurons (VUMs) contained ALI within abdominal ganglia IV-VII. Neurobiotin retrograde fills of the branches of the 11th sternal nerve that innervate the hindgut revealed 2-4 VUMs in abdominal ganglia IV-VIIth, which also contain ALI. The VIIIth abdominal ganglion contained three ventral medial groups of neurons that filled with neurobiotin and contained ALI. The co-localization of ALI in the identified neurons suggests that these cells are the source of ALI on the hindgut. A retrograde fill of the nerves of the ingluvial ganglia that innervate the foregut revealed numerous neurons within the frontal ganglion and an extensive neuropile in the hypocerebral ganglion, but there seems to be no apparent co-localization of neurobiotin and ALI in these neurons, indicating the source of ALI on the foregut comes via the brain, through the SNS.

Rhythmic behaviour and pattern-generating circuits in the locust: key concepts and recent updates

There is growing recognition that rhythmic activity patterns are widespread in our brain and play an important role in all aspects of the functioning of our nervous system, from sensory integration to central processing and motor control. The study of the unique properties that enable central circuits to generate their rhythmic output in the absence of any patterned, sensory or descending, inputs, has been very rewarding in the relatively simple invertebrate preparations. The locust, specifically, is a remarkable example of an organism in which central pattern generator (CPG) networks have been suggested and studied in practically all aspects of their behaviour. Here we present an updated overview of the various rhythmic behaviours in the locust and aspects of their neural control. We focus on the fundamental concepts of multifunctional neuronal circuits, neural centre interactions and neuromodulation of CPG networks. We are certain that the very broad and solid knowledge base of locust rhythmic behaviour and pattern-generating circuits will continue to expand and further contribute to our understanding of the principles behind the functioning of the nervous system and, indeed, the brain.

The brain can eat: establishing the existence of a central pattern generator for feeding in third instar larvae of Drosophila virilis and Drosophila melanogaster

To establish the existence of a central pattern generator for feeding in the larval central nervous system of two Drosophila species, the gross anatomy of feeding related muscles and their innervation is described, the motor units of the muscles identified and rhythmic motor output recorded from the isolated CNS. The cibarial dilator muscles that mediate food ingestion are innervated by the frontal nerve. Their motor pathway projects from the brain through the antennal nerves, the frontal connectives and the frontal nerve junction. The mouth hook elevator and depressor system is innervated by side branches of the maxillary nerve. The motor units of the two muscle groups differ in amplitude: the elevator is always activated by a small unit, the depressor by a large one. The dorsal protractors span the cephalopharyngeal skeleton and the body wall hence mediating an extension of the CPS. These muscles are innervated by the prothoracic accessory nerve. Rhythmic motor output produced by the isolated central nervous system can simultaneously be recorded from all three nerves. The temporal pattern of the identified motor units resembles the sequence of muscle contractions deduced from natural feeding behavior and is therefore considered as fictive feeding. Phase diagrams show an almost identical fictive feeding pattern is in both species.

Allatostatin immunoreactivity in the honeybee brain

Information transmission and processing in the brain is achieved through a small family of chemical neurotransmitters and neuromodulators and a very large family of neuropeptides. In order to understand neural networks in the brain it will be necessary, therefore, to understand the connectivity, morphology, and distribution of peptidergic neurons, and to elucidate their function in the brain. In this study we characterize the distribution of substances related to Dip-allatostatin I in the honeybee brain, which belongs to the allatostatin-A (AST) peptide family sharing the conserved c-terminal sequence -YXFGL-NH(2). We found about 500 AST-immunoreactive (ASTir) neurons in the brain, scattered in 18 groups that varied in their precise location across individuals. Almost all areas of the brain were innervated by ASTir fibers. Most ASTir neurites formed networks within functionally distinct areas, e.g., the antennal lobes, the mushroom bodies, or the optic lobes, indicating local functions of the peptide. A small number of very large neurons had widespread arborizations and neurites were found in the corpora cardiaca and in the cervical connectives, suggesting that AST also has global functions. We double-stained AST and GABA and found that a subset of ASTir neurons were GABA-immunoreactive (GABAir). Double staining AST with backfills of olfactory receptor neurons or mass fills of neurons in the antennal lobes and in the mushroom bodies allowed a more fine-grained description of ASTir networks. Together, this first comprehensive description of AST in the bee brain suggests a diverse functional role of AST, including local and global computational tasks.

Peptidomic survey of the locust neuroendocrine system

Neuropeptides are important controlling agents in animal physiology. In order to understand their role and the ways in which neuropeptides behave and interact with one another, information on their time and sites of expression is required. We here used a combination of MALDI-TOF and ESI-Q-TOF mass spectrometry to make an inventory of the peptidome of different parts (ganglia and nerves) of the central nervous system from the desert locust Schistocerca gregaria and the African migratory locust Locusta migratoria. This way, we analysed the brain, suboesophageal ganglion, retrocerebral complex, stomatogastric nervous system, thoracic ganglia, abdominal ganglia and abdominal neurohemal organs. The result is an overview of the distribution of sixteen neuropeptide families, i.e. pyrokinins, pyrokinin-like peptides, periviscerokinins, tachykinins, allatotropin, accessory gland myotropin, FLRFamide, (short) neuropeptide F, allatostatins, insulin-related peptide co-peptide, ion-transport peptide co-peptide, corazonin, sulfakinin, orcokinin, hypertrehalosaemic hormone and adipokinetic hormones (joining peptides) throughout the locust neuroendocrine system.

From behavior to fictive feeding: anatomy, innervation and activation pattern of pharyngeal muscles of Calliphora vicina 3rd instar larvae

A description of the muscles and nerves involved in feeding of larval Calliphora vicina is given as a prerequisite to establish fictive feeding patterns recorded from the isolated central nervous system. Feeding Diptera larvae show a repetitive sequence of pro- and retraction of the cephalopharyngeal skeleton (CPS), elevation and depression of the mouth hooks and food ingestion. The corresponding pharyngeal muscles are protractors, mouth hook elevators and depressors, the labial retractor and cibarial dilator muscles. These muscles are innervated by the prothoracic accessory nerve (PaN), maxillary nerve (MN) and antennal nerve (AN) as shown electrophysiologically by recording action potentials from the respective nerve that correlate to post-synaptic potentials on the muscles. All three nerves show considerably more complex branching patterns than indicated in the literature. Extracellular recordings from the stumps of PaN, MN and AN connected to an isolated CNS show spontaneous rhythmic motor patterns that reflect the feeding sequence in intact larvae. Variability of the feeding pattern observed in behavioral experiments is also evident from the level of motor output from an isolated CNS. The data obtained from Calliphora will facilitate electrophysiological investigations dealing with the genetic background of feeding behavior in Drosophila larvae.

Innexin genes and gap junction proteins in the locust frontal ganglion

Gap junctions (GJs) belong to one of the most conserved cellular structures in multicellular organisms. They probably serve similar functions in all Metazoa, providing one of the most common forms of intercellular communication. GJs are widely distributed in embryonic cells and tissues and have been attributed an important role in development, modulating cell growth and differentiation. These channels have been also implicated in mediating electrical synaptic signaling; Coupling through GJs is now accepted as a major pathway that supports network behavior and contributes to physiological rhythms. Here we focus on the physiology and molecular biology of GJs in a recently established model for the study of rhythm-generating networks and their role in behavior: the frontal ganglion (FG) of the desert locust, Schistocerca gregaria. Four novel genes of the invertebrate GJs (innexin) gene family were found to be expressed in the FG: Sg-inx1, Sg-inx2, Sg-inx3 and Sg-inx4. Immunohistochemistry revealed that some of the neurons in the FG express at least one innexin protein, INX1. We also established the presence of functional gap junction proteins in the FG and demonstrated functional electrical coupling between the neurons in the FG. This study forms the basis for further investigation of the role of GJs in network development and behavior.

Interactions of suboesophageal ganglion and frontal ganglion motor patterns in the locust

Although locust feeding has been well studied, our understanding of the neural basis of feeding-related motor patterns is still far from complete. This paper focuses on interactions between the pattern of rhythmic movements of the mouth appendages, governed by the suboesophageal ganglion (SOG), and the foregut movements, controlled by the frontal ganglion (FG), in the desert locust. In vitro simultaneous extracellular nerve recordings were made from totally isolated ganglia as well as from fully interconnected SOG-FG and brain-SOG-FG preparations. SOG-confined bath application of the nitric oxide donor, SNP, or the phosphodiesterase antagonist, IBMX, each followed by the muscarinic agonist pilocarpine, consistently induced robust fictive motor patterns in the SOG. This was observed in both isolated and interconnected preparations. In the brain-SOG-FG configuration the SOG-confined modulator application had an indirect excitatory effect on spontaneous FG rhythmic activity. Correlation between fictive motor patterns of the two ganglia was demonstrated by simultaneous changes in burst frequency. These interactions were found to be brain-mediated. Our results indicate the presence of intricate neuromodulation-mediated circuit interactions, even in the absence of sensory inputs. These interactions may be instrumental in generating the complex rhythmic motor patterns of the mandibles and gut muscles during locust feeding or ecdysis-related air swallowing.

How to innervate a simple gut: familiar themes and unique aspects in the formation of the insect enteric nervous system

Like the vertebrate enteric nervous system (ENS), the insect ENS consists of interconnected ganglia and nerve plexuses that control gut motility. However, the insect ENS lies superficially on the gut musculature, and its component cells can be individually imaged and manipulated within cultured embryos. Enteric neurons and glial precursors arise via epithelial-to-mesenchymal transitions that resemble the generation of neural crest cells and sensory placodes in vertebrates; most cells then migrate extensive distances before differentiating. A balance of proneural and neurogenic genes regulates the morphogenetic programs that produce distinct structures within the insect ENS. In vivo studies have also begun to decipher the mechanisms by which enteric neurons integrate multiple guidance cues to select their pathways. Despite important differences between the ENS of vertebrates and invertebrates, common features in their programs of neurogenesis, migration, and differentiation suggest that these relatively simple preparations may provide insights into similar developmental processes in more complex systems.

Octopamine mediates thermal preconditioning of the locust ventilatory central pattern generator via a cAMP/protein kinase A signaling pathway

We investigated the role of biogenic amines in generating thermoprotection of the ventilatory motor pattern circuitry in Locusta migratoria. Levels of octopamine (OA) and dopamine (DA) in the metathoracic ganglion decreased during heat stress. We measured the thermosensitivity of central pattern generation in response to a ramped increase of temperature in semi-intact preparations. OA, DA, and tyramine (TA) were either bath applied or injected into the locust hemocoel 4-8 h before testing. Neither TA nor DA modified the thermotolerance of ventilatory motor pattern generation. However, OA treatment by bath applications (10(-4) M OA) or by injections into the hemocoel (2 microg/10 microl OA) mimicked heat shock preconditioning and improved the thermotolerance of the motor pattern by increasing the failure temperature and by decreasing the time taken to recover operation after a return to room temperature. Heat shock-induced thermoprotection was eradicated in locusts preinjected with epinastine (Oct betaR antagonist). Neuropil injections of the cAMP agonist and protein kinase A (PKA) activator, Sp-cAMPs, both conferred thermoprotection in control locusts and rescued thermoprotection in epinastine-treated HS locusts. Similar injections of the PKA inhibitor Rp-cAMPs blocked the thermoprotective effect of bath-applied OA. Octopamine-mediated thermoprotection was also abolished with neuropil injections of cycloheximide or actinomycin D, indicating a requirement for transcription and translation. We conclude that OA has a crucial role in triggering protein synthesis-dependent physiological adaptations to protect CNS function during heat stress by activating a cAMP/PKA pathway.

The control of anterior foregut motility during a larval molt of the moth Manduca sexta involves the modulation of presynaptic activity

In the moth, Manduca sexta, anterior foregut motility is modulated during the larval–larval molts in order to control the timing of molting fluid (MF) ingestion. MF is the enzymatic mixture that destroys the outer cuticle so that it can be shed at the end of the molt. The onset of the larval–larval molt is characterized by a dramatic decline in the amplitude of the anterior foregut contractions so that MF is not prematurely ingested. As the end of the molt approaches, the robust contractions of the anterior foregut return and the MF is ingested, enabling the larva to free itself from its old cuticle. In the present study we examine possible mechanisms involved in modulating anterior foregut motility during a larval–larval molt. Our results reveal that the release of a blood-borne factor plays a role in the decline in anterior foregut peristaltic activity during the molt. This blood-borne factor reduces the efficacy of the presynaptic endings of the motorneurons, resulting in a reduction in the amplitude of the excitatory junctional potential (EJP) recorded from the anterior foregut musculature. We also present evidence that crustacean cardioactive peptide (CCAP) targets the motorneuron terminals and its actions are sufficient to trigger the dramatic increase in EJP amplitude and anterior foregut contractions. Finally, the surgical ablation of the subesophageal ganglion, which has been previously described to be a source of CCAP neurons and the CCAP projections to the anterior foregut region, blocks both the increase in anterior foregut motility and the ingestion of MF that normally occur at the end of a larval–larval molt.

Neuromodulation of the locust frontal ganglion during the moult: a novel role for insect ecdysis peptides

In insects, continuous growth requires the periodic replacement of the exoskeleton during the moult. A moulting insect displays a stereotypical set of behaviours that culminate in the shedding of the old cuticle at ecdysis. Moulting is an intricate process requiring tightly regulated physiological changes and behaviours to allow integration of environmental cues and to ensure the proper timing and sequence of its components. This is under complex hormonal regulation, and is an important point of interaction between endocrine and neural control. Here, we focus on the locust frontal ganglion (FG), an important player in moulting behaviour, as a previously unexplored target for ecdysis peptides. We show that application of 10(-7) mol l(-1) ecdysis-triggering hormone (ETH) or 10(-7) mol l(-1) and 10(-6) mol l(-1) Pre-ecdysis-triggering hormone (PETH) to an isolated FG preparation caused an increase in bursting frequency in the FG, whereas application of 10(-6) mol l(-1) eclosion hormone (EH) caused an instantaneous, though temporary, total inhibition of all FG rhythmic activity. Crustacean cardioactive peptide (CCAP), an important peptide believed to turn on ecdysis behaviour, caused a dose-dependent increase of FG burst frequency. Our results imply a novel role for this peptide in generating air-swallowing behaviour during the early stages of ecdysis. Furthermore, we show that the modulatory effects of CCAP on the FG motor circuits are dependent on behavioural state and physiological context. Thus, we report that pre-treatment with ETH caused CCAP-induced effects similar to those induced by CCAP alone during pre-ecdysis. Thus, the action of CCAP seems to depend on pre-exposure to ETH, which is thought to be released before CCAP in vivo.

Proctolin-like immunoreactivity in the central and peripheral nervous systems of the locust, Locusta migratoria

Proctolin-like immunoreactivity (PLI) was widely distributed in the locust, Locusta migratoria, within the central, peripheral and stomatogastric nervous systems, as well as the digestive system and retrocerebral complex. Proctolin-like immunoreactivity was observed in cells and processes of the brain and all ganglia of the ventral nerve cord. Of interest, PLI was found in the lateral neurosecretory cells, which send axons within the paired nervi corporis cardiaci II (NCC II) to the corpus cardiacum (CC). The CC contained extensive processes displaying PLI, which continued on within the paired nervi corporis allata (NCA) to the paired corpora allata (CA) where the axons entered and branched therein. The frontal and hypocerebral ganglia of the stomatogastric nervous system contained PLI within processes, resulting in a brightly staining neuropile. Each region of the gut contained PLI in axons and processes of varying patterns and densities. The paired ingluvial ganglia contained PLI, including an extensively stained neuropile and immunoreactive axons projecting through the nerves to the foregut. The hindgut contained PLI within longitudinal tracts, with lateral projections originating from the 8th abdominal ganglion via the proctodeal nerve. The midgut contained PLI in a regular latticework pattern with many varicosities and blebs. No difference in PLI in cells and processes of the central nervous system (CNS) was found between males and females.

Dopamine modulation of spike dynamics in bursting neurons

The pyloric network of the lobster stomatogastric ganglion is a prime example of an oscillatory neural circuit. In our previous study on the firing patterns of pyloric neurons we observed characteristic temporal structures termed 'interspike interval (ISI) signatures' which were found to depend on the synaptic connectivity of the network. Dopamine, a well-known modulator of the pyloric network, is known to affect inhibitory synapses so it might also tune the fine temporal structure of intraburst spikes, a phenomenon not previously investigated. In the recent work we study the DA modulation of ISI patterns of two identified pyloric neurons in normal conditions and after blocking their glutamatergic synaptic connections. Dopamine (10-50 microM) strongly regularizes the firing of the lateral pyloric (LP) and pyloric dilator (PD) neurons by increasing the reliability of recurrent spike patterns. The most dramatic effect is observed in the LP, where precisely replicated spike multiplets appear in a normally 'noisy' neuron. The DA-induced regularization of intraburst spike patterns requires functional glutamatergic inputs to the LP neuron and this effect cannot be mimicked by simple intracellular depolarization. Inhibitory synaptic inputs arriving before the bursts are important factors in shaping the intraburst spike dynamics of both the PD and the LP neurons. Our data reveal a novel aspect of chemical neuromodulation in oscillatory neural networks. This effect sets in at concentrations lower than those affecting the overall burst pattern of the network. The sensitivity of intraburst spike dynamics to preceding synaptic inputs also suggests a novel method of temporal coding in neural bursters.