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A technique to identify and quantitate simultaneously more than 30 compounds in individual neurons is described. The method uses nanoliter volume sampling, capillary electrophoresis separation, and wavelength-resolved native fluorescence detection. Limits of detection (LODs) range from the low attomole to the femtomole range, with 5-hydroxytryptamine (or serotonin [5-HT]) LODs being approximately 20 attomoles. Although the cellular sample matrix is chemically complex, the combination of electrophoretic migration time and fluorescence spectral information allows positive identification of aromatic monoamines, aromatic amino acids and peptides containing them, flavins, adenosine- and guanosine-nucleotide analogs, and other fluorescent compounds. Individual identified neurons from Aplysia californica and Pleurobranchaea californica are used to demonstrate the applicability and figures of merit of this technique.

Hunger͞satiation state interacts with appetitive and noxious stimuli to determine feeding and avoidance responses. In the predatory marine snail Pleurobranchaea californica, food chemostimuli induced proboscis extension and biting at concentration thresholds that varied directly with satiation state. However, food stimuli also tended to elicit avoidance behavior (withdrawal and avoidance turns) at concentration thresholds that were relatively low and fixed. When the feeding threshold for active feeding (proboscis extension with biting) was exceeded, ongoing avoidance and locomotion were interrupted and suppressed. Noxious chemostimuli usually stimulated avoidance, but, in animals with lower feeding thresholds for food stimuli, they often elicited feeding behavior. Thus, sensory pathways mediating appetitive and noxious stimuli may have dual access to neural networks of feeding and avoidance behavior, but their final effects are regulated by satiation state. These observations suggest that a simple costbenefit computation regulates behavioral switching in the animal's foraging behavior, where food stimuli above or below the incentive level for feeding tend to induce feeding or avoidance, respectively. This decision mechanism can weigh the animal's need for nutrients against the potential risk from other predators and the cost of relative energy outlay in an attack on prey. Stimulation of orienting and attack by low-level noxious stimuli in the hungriest animals may reflect risk-taking that can enhance prey capture success. A simple, hedonically structured neural network model captures this computation.T o optimize foraging behavior, animals often must make decisions based on the likely costs and benefits of a feeding attempt. One way in which they may do so is by integrating the percepts of a potential food source with their own internal state. That is, the predicted gains and losses of a feeding attempt, in terms of nutrient gain, energy expenditure, and risks from noxious prey defense and predation while foraging, are weighed against the organism's nutrient need as represented in terms of hunger. How animals do this must be basic to their ecosystem interactions and a major organizing factor in strategies of optimal foraging. However, the computational mechanisms animals use to decide between expression of feeding and avoidance behaviors are not well understood.In the carnivorous opisthobranch snail Pleurobranchaea californica, feeding and avoidance behaviors are largely exclusive of each other, as is the case for most animals. For instance, induction of active feeding behavior (rhythmic biting) suppresses avoidance withdrawal to a mechanical stimulus (1). Escape swimming, a stereotypic predator avoidance behavior, takes precedence over most other behaviors, including feeding (2, 3). Some data indicate that the transitions between feeding and avoidance behaviors can be modulated by experience, such that the feeding response to a food stimulus is replaced by withdrawal and avoidance turns after associative condit...

Escape swimming in the notaspid opisthobranch Pleurobranchaea is an episode of alternating dorsal and ventral body flexions that overrides all other behaviors. We have explored the structure of the central pattern generator (CPG) in the cerebropleural ganglion as part of a study of neural network interactions underlying decision making in normal behavior. The CPG comprises at least eight bilaterally paired interneurons, each of which contributes and is phase-locked to the swim rhythm. Dorsal flexion is mediated by hemiganglion ensembles of four serotonin-immunoreactive neurons, the As1, As2, As3, and As4, and an electrically coupled pair, the A1 and A10 cells. When stimulated, A10 commands fictive swimming in the isolated CNS and actual swimming behavior in whole animals. As1-4 provide prolonged, neuromodulatory excitation enhancing dorsal flexion bursts and swim cycle number. Ventral flexion is mediated by the A3 cell and a ventral swim interneuron, IVS, the soma of which is yet unlocated. Initiation of a swim episode begins with persistent firing in A10, followed by recruitment of As1-4 and A1 into dorsal flexion. Recurrent excitation within the As1-4 ensemble and with A1/A10 may reinforce coactivity. Synchrony among swim interneuron partners and bilateral coordination is promoted by electrical coupling among the A1/A10 and As4 pairs, and among unilateral As2-4, and reciprocal chemical excitation between contralateral As1-4 groups. The switch from dorsal to ventral flexion coincides with delayed recruitment of A3, which is coupled electrically to A1, and with recurrent inhibition from A3/IVS to A1/A10. The alternating phase relation may be reinforced by reciprocal inhibition between As1-4 and IVS. Pleurobranchaea's swim resembles that of the nudibranch Tritonia; we find that the CPGs are similar in many details, suggesting that the behavior and network are primitive characters derived from a common pleurobranchid ancestor.

4,5-Diaminofluorescein (DAF-2) is widely used for detection and imaging of NO based on its sensitivity, noncytotoxicity, and specificity. In the presence of oxygen, NO and NO-related reactive nitrogen species nitrosate 4,5-diaminofluorescein to yield the highly fluorescent DAF-2 triazole (DAF-2T). However, as reported here, the DAF-2 reaction to form a fluorescent product is not specific to NO because it reacts with dehydroascorbic acid (DHA) and ascorbic acid (AA) to generate new compounds that have fluorescence emission profiles similar to that of DAF-2T. When DHA is present, the formation of DAF-2T is attenuated because the DHA competes for DAF-2, whereas AA decreases the nitrosation of DAF-2 to a larger extent, possibly because of additional reducing activity that affects the amount of available N 2 O 3 from the NO. The reaction products of DAF-2 with DHA and AA have been characterized using capillary electrophoresis with laser-induced fluorescence detection and electrospray mass spectrometry. The reactions of DAF-2 with DHA and AA are particularly significant because DHA and AA often colocalize with nitric-oxide synthase in the central nervous, cardiovascular, and immune systems, indicating the importance of understanding this chemistry.NO is involved in a variety of important biological functions in the cardiovascular system, the central and peripheral nervous system, the reproductive system, and the immune system (1-6). NO is normally generated via an enzymatically regulated pathway with the conversion of L-arginine to citrulline by a family of at least three distinct nitric-oxide synthase (NOS) 1 enzymes, the neuronal, inducible, and endothelial NOS forms (or NOS-I, -II, and -III) (7-9). Endothelial and neuronal NOS, also named constitutive NOS, are calcium-dependent. Although cells expressing constitutive NOS generally produce small amounts of NO (submicromolar at the cellular level), inducible NOS, which is synthesized in immune-competent cells when stimulated by cytokines, endotoxins, and other biologically active compounds, is calcium-independent and produces NO at higher levels (1-10 M in microphages) (10). Although in situ and immunohistochemical techniques allow one to determine whether NOS is present in a particular tissue, whether the NOS is actively producing NO under specific conditions and the amount of NO produced are important questions to answer to understand the physiological roles of NOS.Direct detection (or imaging) of NO production in a biological system was unsatisfactory until the development of a series of fluorescent indicators for NO, the diaminofluoresceins (DAFs) in 1998 by the Nagano group (11). In the presence of oxygen, NO nitrosates DAFs to produce the highly fluorescent triazofluoresceins. DAFs provide the advantages of sensitivity (detection limits of 5 nM), simple protocols, and noncytotoxicity, and they are also believed to offer high specificity to NO. Since then, an increasing number of researchers have used them for NO detection and NO imaging (10, 12).The specificity...

Serotonergic systems of invertebrate and vertebrate central nervous systems (CNS) are functionally similar in multiple characters. Serotonin (5-HT) neurons dispersed throughout the CNS of lophotrochozoan invertebrates (molluscs and leeches) are analogous to vertebrate 5-HT neurons concentrated in the raphe nuclei of mid- and hindbrain: they innervate specific central pattern generators and other circuits of the CNS, receive feedback from them, and support general behavioral arousal. In both groups 5-HT regulates excitatory gain of CNS circuitry and uses similarly diverse 5-HT receptors. Marked contrast, however, exists for roles of 5-HT in regulation of appetite. Where invertebrate 5-HT neurons promote an appetitive state, this role is supplanted in the vertebrates by a peptidergic network centered around orexins/hypocretins, to which the role of 5-HT in arousal is subordinate. In the vertebrates, 5-HT has appetite-suppressant properties. This is paralleled by differing complexities of mechanisms that bring about satiety. Lophotrozoans appear to rely on simple stretching of the gut, with no obvious feedback from true nutrient stores. In contrast, vertebrate appetite is regulated by hypothalamic sensitivity to hormonal signals reporting separately on the status of fat cells and digestive activity, and to blood glucose, in addition to gut stretch. The simple satiety mechanism of a mollusc can be used in value-based foraging decisions that integrate hunger state, taste, and experience (Gillette and others 2000). For vertebrates, where appetite and arousal are regulated by signals from long-lived nutrient stores, decisions can be based on resource need going far beyond simple gut content, enabling value estimation and risk assessment in the longer-term. Thus, connection of nutrient storage depots to CNS circuitry mediating appetite may supply critical substrate for evolving complexity in brain and behavior. This hypothesis may be tested in expanded comparative studies of 5-HT and peptidergic functions in appetite and arousal.

The central nervous systems of the marine molluscs Pleurobranchaea californica (Opisthobranchia: Notaspidea) and Tritonia diomedea (Opisthobranchia: Nudibranchia) were examined for serotonin-immunoreactive (5-HT-IR) neurons and processes. Bilaterally paired clusters of 5-HT-IR neuron somata were distributed similarly in ganglia of the two species. In the cerebropleural ganglion complex, these were the metacerebral giant neurons (both species), a dorsal anterior cluster (Pleurobranchaea only), a dorsal medial cluster including identified neurons of the escape swimming network (both species), and a dorsal lateral cluster in the cerebropleural ganglion (Pleurobranchaea only). A ventral anterior cluster (both species) adjoined the metacerebral giant somata at the anterior ganglion edge. Pedal ganglia had the greatest number of 5-HT-IR somata, the majority located near the roots of the pedal commissure in both species. Most 5-HT-IR neurons were on the dorsal surface of the pedal ganglia in Pleurobranchaea and were ventral in Tritonia. Neither the buccal ganglion of both species nor the visceral ganglion of Pleurobranchaea had 5-HT-IR somata. Afew asymmetrical 5-HT-IR somata were found in cerebropleural and pedal ganglia in both species, always on the left side. The clustering of 5-HT-IR neurons, their diverse axon pathways, and the known physiologic properties of their identified members are consistent with a loosely organized arousal system of serotonergic neurons whose components can be generally or differentially active in expression of diverse behaviors.

1. The white, bilaterally paired A1 interneurons of the cerebropleural ganglion of Pleurobranchaea californica fire rhythmic bursts of action potentials during escape swimming behavior. We studied the role of the A1s in swimming behavior and pattern generation in whole animal and isolated CNS preparations. 2. The escape swim is a cyclic sequence of dorsal and ventral flexions of the body. During the swim, A1 bursts precede and accompany the dorsal flexion phase of the cycle. Hyperpolarization of A1 to prevent spike activity interrupts swimming behavior in the whole animal and fictive swimming in the isolated CNS. Stimulated A1 activity was not observed to cause swimming in whole animals, and was only occasionally sufficient to trigger fictive swimming activity in the isolated CNS. 3. In quiescent whole animal preparations, stimulation of a single A1 normally causes a single dorsal flexion followed by body flexion to the side contralateral to the stimulated cell; characteristically, A1 spike activity stimulates feedback inhibition coinciding with the end of dorsal flexion and the onset of contralateral flexion. 4. A1 spike activity suppresses feeding behavior and causes proboscis retraction in whole animal preparations induced to feed. A1 activity also suppresses fictive feeding driven by stimulation of the critical phasic paracerebral neurons (PCps) of the motor network of feeding in the isolated CNS. Concomitantly, A1 spikes cause potent inhibition of the PCp interneurons. 5. The A1s are specifically excited by noxious mechanical and chemical stimuli, but are not affected by feeding stimuli or the occurrence of feeding behavior. 6. We conclude that the A1 neurons are elements of an escape swimming pattern generator, and that they are probably homologous to the similar C2 neurons of the nudibranch Tritonia diomedea. One of their functions outside of generating the swim pattern may be the suppression of feeding behavior in response to noxious stimulation. These observations provide a neural mechanism for the original observations of the dominance of escape swimming behavior over feeding.