A neurobehavioral model for rapid actions of corticosterone on sensorimotor integration.

Stress-induced corticosterone (CORT) secretion that causes a rapid blockade of courtship clasping by male roughskin newts (Taricha granulosa) is mediated by a specific neuronal membrane receptor for CORT. Amplectic clasping, which can be triggered by pressure on the ventral body surface and cloaca, is controlled by the influence of medullary neurons on the spinal cord. Using clasping as a simple neurobehavioral model, we have focused our analysis of CORT effects on clasping by examining the steroid's effects on neurophysiological properties of medullary neurons, especially medullary reticulospinal neurons, the principal output cells from the brain to the spinal cord. Systemic CORT caused, within 3 min of injection, diverse reductions in reticulospinal neuron excitability. Another rapid CORT effect on medullary neurons was to depress responsiveness to pressure on the cloaca. Experiments with chronically implanted, freely moving newts revealed that the rapid CORT effects are quite specific to neural processes related to clasping. CORT injections rapidly blocked clasping in response to cloacal stimuli and concurrently depressed neuronal responses to cloacal pressure and firing associated with clasping. Activity of reticulospinal neurons was often associated with nonclasping movements and this activity was rarely altered by CORT. Thus, CORT mainly affected aspects of neuronal function related to clasping. In other neurophysiological experiments, we found that the neuropeptides vasotocin and corticotropin-releasing hormone modified the neural effects of CORT. Prior exposure of medullary neurons to either of these neuropeptides caused systemic CORT administration to rapidly potentiate neuronal responses to cloacal stimuli, indicating that the direction and potency of CORT effects depend critically on the prevailing neuroendocrine state of the brain.     

Rapid corticosterone-induced impairment of amplectic clasping occurs in the spinal cord of roughskin newts (taricha granulosa)

Courtship clasping, a reproductive behavior in male roughskin newts (Taricha granulosa), is rapidly blocked by an action of corticosterone (CORT) at a specific neuronal membrane receptor. The CORT-induced impairment of clasping in behaving newts appears to be mediated partly by an elimination of clasping-related activity in medullary reticulospinal neurons. Previous studies of rapid CORT actions in Taricha have focused on the brain, so existence of CORT action in the spinal cord or peripheral nervous system has not been assessed. The present study used newts with a high cervical spinal transection to examine potential spinal or peripheral CORT effects on clasping by the hindlimbs in response to pressure on the cloaca. Spinal transection causes clasps elicited by cloacal stimulation to be very sustained beyond the termination of the eliciting stimulus. In spinally transected newts, CORT caused a dose-dependent depression in the duration as well as quality of the clasp that appeared within 10 min of injection. CORT selectively impaired the usual sustained maintenance of a clasp after termination of cloacal stimulation, but not clasp elicitation during stimulation. These effects were not produced by dexamethasone, a synthetic glucocorticoid that binds poorly to the CORT membrane receptor. The CORT effect on clasp maintenance but not clasp elicitation implies selective action on an intraspinal generator for clasping but not on sensory or efferent neuromuscular aspects of the response. These results indicate the presence in the newt spinal cord of the CORT membrane receptor that exerts functional effects distinctly different from those on the brainstem.     

Corticosteroid actions from neuronal membrane to behavior: neurophysiological mechanisms underlying rapid behavioral effects of corticosterone.

Investigation of the rapid suppression of male courtship clasping behavior by corticosterone in roughskin newts (Taricha granulosa) has led to the identification of a specific neuronal membrane receptor for this stress steroid. This paper describes studies of the neurophysiological effects of the rapid, membrane receptor mediated action of corticosterone on neurons that are involved in the control of clasping. In freely behaving newts, medullary neurons, including reticulospinal neurons, process clasp-triggering sensory signals and participate in control of clasping movements. Corticosterone injection causes these brainstem neurons to show selective depression of clasping-related sensorimotor function. These corticosterone effects appear in 3-10 min and are closely associated with the simultaneous depression of clasping. In addition to these functionally specific effects, corticosterone simultaneously causes widespread, primarily depressive effects on neuronal activity and excitability in the medulla and elsewhere in the brain. Thus, the membrane actions of corticosterone lead to diverse neural effects, including changes in membrane excitability as well as specific, network-level actions that are apparent only during behavior. These rapid corticosterone effects strongly interact with actions of the neuropeptides vasotocin and corticotropin-releasing factor, such that the form and magnitude of the steroid's effects depend on the prevailing neuroendocrine state of the brain.     

Brainstem reticulospinal neurons are targets for corticotropin-releasing factor-Induced locomotion in roughskin newts

Stress-induced release or central administration of corticotropin-releasing factor (CRF) enhances locomotion in a wide range of vertebrates, including the roughskin newt, Taricha granulosa. Although CRF's stimulatory actions on locomotor behavior are well established, the target neurons through which CRF exerts this effect remain unknown. To identify these target neurons, we utilized a fluorescent conjugate of CRF (CRF-TAMRA 1) to track this peptide's internalization into reticulospinal and other neurons in the medullary reticular formation (MRF), a region critically involved in regulating locomotion. Epifluorescent and confocal microscopy revealed that CRF-TAMRA 1 was internalized by diverse MRF neurons, including reticulospinal neurons retrogradely labeled with Cascade Blue dextran. In addition, we immunohistochemically identified a distinct subset of serotonin-containing neurons, located throughout the medullary raphé, that also internalized the fluorescent CRF-TAMRA 1 conjugate. Chronic single-unit recordings obtained from microwire electrodes in behaving newts revealed that intracerebroventricular (icv) administration of CRF-TAMRA 1 increased medullary neuronal firing and that appearance of this firing was associated with, and strongly predictive of, episodes of CRF-induced locomotion. Furthermore, icv administered CRF-TAMRA 1 produced behavioral and neurophysiological effects identical to equimolar doses of unlabeled CRF. Collectively, these findings provide the first evidence that CRF directly targets reticulospinal and serotonergic neurons in the MRF and indicate that CRF may enhance locomotion via direct effects on the hindbrain, including the reticulospinal system.     

Corticosterone suppresses vasotocin-enhanced clasping behavior in male rough-skinned newts by novel mechanisms interfering with V1a receptor availability and receptor-mediated endocytosis

In rough-skinned newts, Taricha granulosa, exposure to an acute stressor results in the rapid release of corticosterone (CORT), which suppresses the ability of vasotocin (VT) to enhance clasping behavior. CORT also suppresses VT-induced spontaneous activity and sensory responsiveness of clasp-controlling neurons in the rostromedial reticular formation (Rf). The cellular mechanisms underlying this interaction remain unclear. We hypothesized that CORT blocks VT-enhanced clasping by interfering with V1a receptor availability and/or VT-induced endocytosis. We administered a physiologically active fluorescent VT conjugated to Oregon Green (VT–OG) to the fourth ventricle 9 min after an intraperitoneal injection of CORT (0, 10, 40 μg/0.1 mL amphibian Ringers). The brains were collected 30 min post-VT–OG, fixed, and imaged with confocal microscopy. CORT diminished the number of endocytosed vesicles, percent area containing VT–OG, sum intensity of VT–OG, and the amount of VT-V1a within each vesicle; indicating that CORT was interfering with V1a receptor availability and VT-V1a receptor-mediated endocytosis. CORT actions were brain location-specific and season-dependent in a manner that is consistent with the natural and context-dependent expression of clasping behavior. Furthermore, the sensitivity of the Rf to CORT was much higher in animals during the breeding season, arguing for ethologically appropriate seasonal variation in CORT's ability to prevent VT-induced endocytosis. Our data are consistent with the time course and interaction effects of CORT and VT on clasping behavior and neurophysiology. CORT interference with VT-induced endocytosis may be a common mechanism employed by hormones across taxa for mediating rapid context- and season-specific behavioral responses.     

Brainstem neuronal and behavioral activation by corticotropin-releasing hormone depend on the behavioral state of the animal

Central administration of corticotropin-releasing hormone (CRH) is known to enhance locomotion across a wide range of vertebrates, including the roughskin newt, Taricha granulosa. The present study aimed to identify the CRH effects on locomotor-controlling medullary neurons that underlie the peptide's behavioral stimulating actions. Single neurons were recorded from the rostral medullary reticular formation before and after intraventricular infusion of CRH in freely behaving newts and newts paralyzed with a myoneural blocking agent. In behaving newts, most medullary neurons showed increased firing 3-23 min after CRH infusion. Decreases in firing were less common. Of particular importance was the finding that in behaving newts, medullary neurons showed a cyclic firing pattern that was strongly associated with an increase in the incidence of walking bouts, an effect blocked by pretreatment with the CRH antagonist, alpha-helical CRH and not seen following vehicle administration. In contrast, the majority of medullary neurons sampled in immobilized newts lacked temporal cyclicity in their firing patterns following intraventricular infusion of CRH. That is, there was no evidence for a fictive locomotor activity pattern. Our results indicate that the actual expression of locomotion is a critical factor in regulating the behavior-activating effects of CRH and underscore the importance of using an awake, unrestrained animal for analysis of a hormone's neurobehavioral actions.     

Neuroendocrinology of context-dependent stress responses: vasotocin alters the effect of corticosterone on amphibian behaviors

The ability of an animal to respond with appropriate defensive behaviors when confronted with an immediate threat can affect its survival and reproductive success. In the roughskin newt (Taricha granulosa), exogenous corticosterone (CORT) rapidly blocks and vasotocin (VT) enhances reproductive behaviors (mainly clasping behavior). Electrophysiological studies have shown that pretreatment of male Taricha with VT counteracts the inhibitory effects of CORT on neuronal activity in the medulla. To test whether similar interactions between VT and CORT influence reproductive behaviors in Taricha, we recorded the time spent and incidence of clasping in males injected with VT or vehicle at 60 min and then CORT or vehicle at 5 min before presentation of a female. This study found that clasping behavior is suppressed in males that received vehicle and then CORT, but is not suppressed in males that received VT and then CORT. Considering these results and the possibility that the performance of clasping behaviors might cause increases in endogenous VT activity, we tested whether the suppressive effects of CORT administration on clasping behavior would occur in males that had recently clasped females. The study found that, in contrast to males that had been isolated from females, CORT administration did not suppress clasping behavior in males that had been allowed to clasp females for 60 min prior to the hormone injection. Our results suggest that, at least in this amphibian and perhaps in other animals, the neuroendocrine regulation of alternative behavioral responses to threats involves functional interactions between corticosteroids and VT-like peptides.     

Role of the reticular formation in motor control. Study of some intrareticular mechanisms and functional properties of the reticulospinal system

Participation of the reticular formation and descending reticulospinal system in the motor control functions of the spinal cord is examined. The data indicate that the reticular formation may participate in the regulation of specific motor actions. This is shown by the results of experiments to analyze the properties of membranes of reticulospinal neurons and the principles of organization of cortico-reticular monosynaptic relays, and to the investigation of characteristics of responses of "ensembles" of reticular neurons in cats, and also by data obtained in a study of correlation of unit activity in the reticular formation with movements elaborated in rats. The functional role of differential characteristics of the reticular formation is discussed and prospects for future research into reticular membranous, neurochemical, and neuronal mechanisms as a step toward the understanding of reticular control of motor functions are described.Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 16, No. 5, pp. 637–651, September–October, 1984.     

The effects of sex steroids and vasotocin on behavioral responses to visual and olfactory sexual stimuli in ovariectomized female roughskin newts

Previous studies have found that vasotocin (AVT) administration to male roughskin newts (Taricha granulosa) enhances courtship clasping as well as appetitive responses to specific sexual stimuli and that treating female newts with androgens plus AVT induces the expression of male-typical courtship clasping (the selective clasping of females). However, the unique and/or interactive effects of sex steroids and AVT on appetitive responses to specific sexual stimuli have not yet been determined. To first identify male-typical, sexually dimorphic appetitive responses to female sexual stimuli, we tested intact newts during the breeding season and found that males, but not females, are attracted to female visual and pheromonal sexual stimuli. We then used ovariectomized (ovx) females implanted with empty silastic capsules (Blk) or with capsules containing testosterone (T), dihydrotestosterone (DHT), or estradiol (E2) and then injected with either saline or AVT to determine the effects of steroids and AVT, alone or in combination with each other, on male-typical behavioral responses to those stimuli. E2 treatment depressed responses toward female visual stimuli independently of AVT. On the other hand, only T-implanted, AVT-injected females displayed male-typical behavioral responses toward female olfactory stimuli, preferring to spend more time in proximity to female-scented than unscented newt models and selectively clasping the female-scented models. Together, these results support the conclusion that sex steroids and AVT influence behavioral responses to sexual stimuli via sensory-specific mechanisms. Furthermore, they suggest that T and AVT interact within the brain to influence sensorimotor processing in the pathways that integrate olfactory sexual stimuli into male-typical courtship behaviors.     

The modulation of sensory transmission through the medullary dorsal horn during cortically driven mastication

During mastication, reflexes are modulated and sensory transmission is altered in interneurons and ascending pathways of the rostral trigeminal sensory complex. The current experiment examines the modulation of sensory transmission through the most caudal part of the trigeminal sensory system, the medullary dorsal horn, during fictive mastication produced by cortical stimulation. Extracellular single unit activity was recorded from the medullary dorsal horn, and multiple unit activity was recorded from the trigeminal motor nucleus in anesthetized, paralyzed rabbits. The masticatory area of sensorimotor cortex was stimulated to produce rhythmic activity in the trigeminal motor nucleus (fictive mastication). Activity in the dorsal horn was compared in the presence and absence of cortical stimulation. Fifty-two percent of neurons classified as low threshold and 83% of neurons receiving noxious inputs were influenced by cortical stimulation. The cortical effects were mainly inhibitory, but 21% of wide dynamic range and 6% of low threshold cells were excited by cortical stimulation. The modulation produced by cortical stimulation, whether inhibitory or excitatory, was not phasically related to the masticatory cycle. It is likely that, when masticatory movements are commanded by the sensorimotor cortex, the program includes tonic changes in sensory transmission through the medullary dorsal horn.     

Role of Acetylcholine in the Modulation of Activity of Neocortical Neurons in Awake Animals Performing an Instrumental Conditioned Reflex

We studied modulatory effects of the cholinergic system on the activity of sensorimotor cortex neurons related to realization of an instrumental conditioned placing reflex. Experiments were carried out on awake cats; multibarrel glass microelectrodes were used for extracellular recording of impulse activity of neurons in the sensorimotor cortex and iontophoretic application of synaptically active agents within the recording region. The background and reflex-related activity was recorded in the course of realization of conditioned movements, and then changes of spiking induced by applications of the testing substances were examined. Applications of acetylcholine and carbachol resulted in increases in the intensity of impulse reactions of neocortical neurons evoked by presentation of an acoustic signal and in simultaneous shortening of the response latencies. An agonist of muscarinic receptors, pylocarpine, exerted a similar effect on the evoked activity of sensorimotor cortex neurons. Blockers of muscarinic receptors, atropine and scopolamine, vice versa, sharply suppressed impulse reactions of cortical neurons to afferent stimulation and simultaneously increased latencies of these responses. Applications of an agonist of nicotinic receptors, nicotine, was accompanied by suppression of impulse neuronal responses, an increase in the latency of spike reactions to presentation of a sound signal, and a corresponding increase in the latency of a conditioned motor reaction. In contrast, application of an antagonist of nicotinic receptors, tubocurarine, significantly intensified neuronal spike responses and shortened their latency. The mechanisms underlying the effects of antagonists of membrane muscarinic and nicotinic cholinoreceptors and the role of activation of these receptors in the modulation of activity of pyramidal and non-pyramidal neocortical neurons related to realization of the instrumental motor reflex are discussed.     

Androgens and male mating behavior in rough-skinned newts, Taricha granulosa

Cyproterone acetate was administered either orally or intraperitoneally to intact, adult male newts, Taricha granulosa. The number of males that exhibited the courtship behavior of clasping when tested with nuptial females was not altered by the antiandrogen treatments. In males which were unresponsive to nuptial females, the occurrence of clasping was not evoked by injections for 4 days of testosterone, dihydrotestosterone, or 11-ketotestosterone. Further, the incidence of clasping was not significantly elevated by injections of prolactin and/or testosterone for 30 days. The effect of sexual activity on testosterone and dihydrotestosterone levels in male newts was determined by radioimmunoassay of plasma collected from males which were: (1) isolated from females; (2) allowed to clasp a female for 2 min; or (3) allowed to clasp a female for 1 hr. The testosterone and dihydrotestosterone levels were unchanged during this period of clasping. In February and again in June, plasma androgen concentrations were measured in males which differed in their propensity to initiate courtship when paired with females. Androgen levels were similar for males that clasped a female and males that never attempted to clasp a female. Plasma androgen levels in the male newt are apparently not correlated with sexual responsiveness.     

Simulating Spinal Border Cells and Cerebellar Granule Cells under Locomotion – A Case Study of Spinocerebellar Information Processing

The spinocerebellar systems are essential for the brain in the performance of coordinated movements, but our knowledge about the spinocerebellar interactions is very limited. Recently, several crucial pieces of information have been acquired for the spinal border cell (SBC) component of the ventral spinocerebellar tract (VSCT), as well as the effects of SBC mossy fiber activation in granule cells of the cerebellar cortex. SBCs receive monosynaptic input from the reticulospinal tract (RST), which is an important driving system under locomotion, and disynaptic inhibition from Ib muscle afferents. The patterns of activity of RST neurons and Ib afferents under locomotion are known. The activity of VSCT neurons under fictive locomotion, i.e. without sensory feedback, is also known, but there is little information on how these neurons behave under actual locomotion and for cerebellar granule cells receiving SBC input this is completely unknown. But the available information makes it possible to simulate the interactions between the spinal and cerebellar neuronal circuitries with a relatively large set of biological constraints. Using a model of the various neuronal elements and the network they compose, we simulated the modulation of the SBCs and their target granule cells under locomotion and hence generated testable predictions of their general pattern of modulation under this condition. This particular system offers a unique opportunity to simulate these interactions with a limited number of assumptions, which helps making the model biologically plausible. Similar principles of information processing may be expected to apply to all spinocerebellar systems.     

Selection of Motor Programs for Suppressing Food Intake and Inducing Locomotion in the Drosophila Brain

Central mechanisms by which specific motor programs are selected to achieve meaningful behaviors are not well understood. Using electrophysiological recordings from pharyngeal nerves upon central activation of neurotransmitter-expressing cells, we show that distinct neuronal ensembles can regulate different feeding motor programs. In behavioral and electrophysiological experiments, activation of 20 neurons in the brain expressing the neuropeptide hugin, a homolog of mammalian neuromedin U, simultaneously suppressed the motor program for food intake while inducing the motor program for locomotion. Decreasing hugin neuropeptide levels in the neurons by RNAi prevented this action. Reducing the level of hugin neuronal activity alone did not have any effect on feeding or locomotion motor programs. Furthermore, use of promoter-specific constructs that labeled subsets of hugin neurons demonstrated that initiation of locomotion can be separated from modulation of its motor pattern. These results provide insights into a neural mechanism of how opposing motor programs can be selected in order to coordinate feeding and locomotive behaviors.     

Gaseous intermediates in the brain of the salmon Oncorhynchus masou

Distribution of nitroxidergic and H2S-producing neurons in the brain of the salmon Oncorhynchus masou was studied by methods of histochemical markering of NADPH-diaphorase and by immunohistochemical markering of the neuronal nitric oxide synthase and cystathionin beta-synthase (CBS). The established distribution of CBS and nNOS/NADPH-d of neurons and fibers in the salmon telencephalon, optic tectum, and cerebellum allows suggesting that the NO- and H2S-producing systems, represent individual, non-overlapping neuronal complexes performing specialized functions in the activity of local neuronal networks. In the brainstem part, the nNOS-ir and NADPH-d-positive neurons were detected in the composition of viscerosensor (V, VII, and IX-X) and visceromotor (III, IV, and VI) nuclei of craniocerebral nerves, octavolateral afferent complex, reticulospinal neurons, and medial reticular formation. CBS in the salmon medulla was revealed in neurons of the X nerve nucleus, reticulospinal neurons, and ventrolateral reticular formation. Distribution of NO-ergical and H2S-producing neurons in the salmon medulla nuclei indicates that NO in salmon is the predominant neuromodulator of medulla viscerosensory systems, while H2S seems to modulate only the descending motor systems. The results of the performed study allow suggesting that NI in the descending motor systems. The results of the performed study allow suggesting that NO in the salmon medulla periventricular area can act as a regulator of postnatal ontogenesis.     

An image-free opto-mechanical system for creating virtual environments and imaging neuronal activity in freely moving Caenorhabditis elegans

Non-invasive recording in untethered animals is arguably the ultimate step in the analysis of neuronal function, but such recordings remain elusive. To address this problem, we devised a system that tracks neuron-sized fluorescent targets in real time. The system can be used to create virtual environments by optogenetic activation of sensory neurons, or to image activity in identified neurons at high magnification. By recording activity in neurons of freely moving C. elegans, we tested the long-standing hypothesis that forward and reverse locomotion are generated by distinct neuronal circuits. Surprisingly, we found motor neurons that are active during both types of locomotion, suggesting a new model of locomotion control in C. elegans. These results emphasize the importance of recording neuronal activity in freely moving animals and significantly expand the potential of imaging techniques by providing a mean to stabilize fluorescent targets.     

Impact of Swimming Exercise Training on the Effects of Modulation of Mitochondrial Permeability Transition and NOS-1 Activation in Medullary Cardiovascular Neurons of Rats

Physical inactivity can be considered one of the major risk factors related to cardiovascular diseases. There are reasons to believe that the positive effect of exercise training is, to a large extent, mediated by modulation of the nervous control of the circulation system. In our previous studies, we showed that modulation of mitochondrial permeability transition in medullary cardiovascular neurons significantly contributes to the hemodynamic reactions in both the norm and a number of pathological states. In this study, we examined in acute experiments on urethane-anesthetized rats the hemodynamic effects mediated by either modulation of mitochondrial permeability transition in medullary neurons, or activation of neuronal NO synthase (NOS-1) in these neuronal populations after preliminary moderate exercise training (everyday swimming sessions of increased duration carried out for four weeks). It was shown that, after exercise training had been completed, the effects of injections of an inductor of mitochondrial permeability transition pore (MPTP) opening, phenylarsine oxide (PAO, 0.5 to 1.5 nmol), into populations of cardiovascular neurons in the medullary autonomic nuclei (nucl. tractus solitarius and paramedian and lateral reticular nuclei) were less expressed, as compared with those in control (untrained) animals. The data obtained suggest that exercise training can exert a protective action on functional activity of medullary neurons due to the decreased sensitivity of MPTPs to their opening. Injections of an inhibitor of MPTP opening, melatonin (0.7 to 2.1 nmol), into populations of medullary neurons under study in trained rats induced a decrease in the systemic arterial pressure (SAP), in contrast to untrained animals demonstrating mostly hypertensive responses following injections of melatonin into the above nuclei. Injections of an activator of neuronal NO synthase (NOS-1), L-arginine, into the medullary nuclei of swimming-trained rats resulted in more expressed hemodynamic shifts than in control animals, which suggests an increase in the activity of neuronal NO synthase in medullary neurons of such animals.     

Role of Sensory Experience in Functional Development of Drosophila Motor Circuits

Neuronal circuits are formed according to a genetically predetermined program and then reconstructed in an experience-dependent manner. While the existence of experience-dependent plasticity has been demonstrated for the visual and other sensory systems, it remains unknown whether this is also the case for motor systems. Here we examined the effects of eliminating sensory inputs on the development of peristaltic movements in Drosophila embryos and larvae. The peristalsis is initially slow and uncoordinated, but gradually develops into a mature pattern during late embryonic stages. We tested whether inhibiting the transmission of specific sensory neurons during this period would have lasting effects on the properties of the sensorimotor circuits. We applied Shibire-mediated inhibition for six hours during embryonic development (15–21 h after egg laying [AEL]) and studied its effects on peristalsis in the mature second- and third-instar larvae. We found that inhibition of chordotonal organs, but not multidendritic neurons, led to a lasting decrease in the speed of larval locomotion. To narrow down the sensitive period, we applied shorter inhibition at various embryonic and larval stages and found that two-hour inhibition during 16–20 h AEL, but not at earlier or later stages, was sufficient to cause the effect. These results suggest that neural activity mediated by specific sensory neurons is involved in the maturation of sensorimotor circuits in Drosophila and that there is a critical period for this plastic change. Consistent with a role of chordotonal neurons in sensory feedback, these neurons were activated during larval peristalsis and acute inhibition of their activity decreased the speed of larval locomotion.     

Pheromones enhance somatosensory processing in newt brains through a vasotocin-dependent mechanism

We tested whether the sex pheromones that stimulate courtship clasping in male roughskin newts do so, at least in part, by amplifying the somatosensory signals that directly trigger the motor pattern associated with clasping and, if so, whether that amplification is dependent on endogenous vasotocin (VT). Female olfactory stimuli increased the number of action potentials recorded in the medulla of males in response to tactile stimulation of the cloaca, which triggers the clasp motor reflex, as well as to tactile stimulation of the snout and hindlimb. That enhancement was blocked by exposing the medulla to a V1a receptor antagonist before pheromone exposure. However, the antagonist did not affect medullary responses to tactile stimuli in the absence of pheromone exposure, suggesting that pheromones amplify somatosensory signals by inducing endogenous VT release. The ability of VT to couple sensory systems together in response to social stimulation could allow this peptide to induce variable behavioural outcomes, depending on the immediate context of the social interaction and thus on the nature of the associated stimuli that are amplified. If widespread in vertebrates, this mechanism could account for some of the behavioural variability associated with this and related peptides both within and across species.     

Microfluidics for in vivo imaging of neuronal and behavioral activity in Caenorhabditis elegans

The nematode C. elegans is an excellent model organism for studying behavior at the neuronal level. Because of the organism's small size, it is challenging to deliver stimuli to C. elegans and monitor neuronal activity in a controlled environment. To address this problem, we developed two microfluidic chips, the 'behavior' chip and the 'olfactory' chip for imaging of neuronal and behavioral responses in C. elegans. We used the behavior chip to correlate the activity of AVA command interneurons with the worm locomotion pattern. We used the olfactory chip to record responses from ASH sensory neurons exposed to high-osmotic-strength stimulus. Observation of neuronal responses in these devices revealed previously unknown properties of AVA and ASH neurons. The use of these chips can be extended to correlate the activity of sensory neurons, interneurons and motor neurons with the worm's behavior.