Cardiovascular responses to electrical stimulation of the recurrent laryngeal nerve in conscious toads (Bufo marinus)

Summary Cardiovascular responses to electrical stimulation of the cut central end of the recurrent laryngeal nerve (rLN) were recorded in 19 conscious toads (Bufo marinus). Low intensity stimulation of the rLN (3.4±0.5 V, 1 ms, 10 Hz) elicited a slow 18–22% fall in heart rate and systolic and diastolic aortic arterial blood pressures (N=18), but had little or no effect upon ventilation (N=6). This low threshold depressor response (LTDR) was considered to represent the expression of the previously demonstrated pulmocutaneous baroreflex. Bilateral stimulation of the rLNs elicited greater LTDRs than did either left or right unilateral rLN stimulation. Blood pressure and heart rate responses to bilateral stimulation were 69–77% of the sum of responses to unilateral stimulation, and the mean summation was significant for the reduction in heart rate. Stimulus intensities of >4.7±0.7 V caused an immediate cessation of cardiac activity for up to 6.5±1.3 s (N=17) and a concomitant apnoea (N=6), which were followed by a lesser bradycardia and hypotension. This response was termed a high threshold depressor response (HTDR). During continued stimulation at intensities of >9.1±1.4 V, aortic blood pressure (Pa) and ventilation were rapidly restored, and aortic blood pressure continued to rise above control values (N=14). In some cases this high threshold pressor response (HTPR) was associated with an increase in heart rate. All responses to rLN stimulation were abolished by pithing (N=9) or by pentobarbital (40 mg/kg, i.p.,N=4), but LTDS and HTPRs could be elicited in urethanized (1.5–2.0 g/kg,N=4) toads.During depressor responses, aortic arterial resistance fell by 18% in 18 of 20 trials in 5 toads, whereas pulmocutaneous arterial resistance increased by 76% in 12 of 15 trials in 4 toads. During the HTPR, aortic arterial resistance increased 40%, while pulmocutaneous arterial resistance remained unchanged. We suggest that depressor responses may actively redistribute blood flow from the pulmocutaneous to the aortic circulation, whereas the reverse should occur during HTPRs.Abbreviations HTDR high threshold depressor response - HTPR high threshold pressor response - rLN recurrent laryngeal nerve - LTDR low threshold depressor response - Pa aortic blood pressure - PCA pulmocutaneous artery - Pd diastolic aortic pressure - Ppca pulmocutaneous blood pressure - PRU peripheral resistance unit - Ps systolic aortic pressure - Pv venous blood pressure - Ra aortic arterial resistance - Rpca pulmocutaneous arterial resistance     

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

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

Catecholamine and blood pressure regulation by gonadotropin-releasing hormone analogs in amphibians

Analogs of gonadotropin-releasing hormone (GnRH) occur in the brain, plasma, and sympathoadrenal system of anuran amphibians. The present experiments studied the effects of GnRH and [Trp7, Leu8]-GnRH on plasma catecholamines and cardiovascular function in conscious adult bullfrogs (Rana catesbeiana) and cane toads (Bufo marinus). Both GnRH analogs elicited dose-dependent (0.1-1 nmol.kg-1) increases in arterial norepinephrine, epinephrine, and blood pressure levels when injected intravenously into toads. In bullfrogs, [Trp7, Leu8]-GnRH (1 nmol.kg-1) increased arterial norepinephrine concentration approximately 10-fold without affecting the concentrations of norepinephrine sulfate, norepinephrine glucuronide, epinephrine, epinephrine sulfate, or epinephrine glucuronide. The noradrenergic response of bullfrogs to [Trp7, Leu8]-GnRH was specific to the neurohormone because it could be inhibited by [D-pGlu1, D-Phe2, D-Trp3,6]-GnRH. The sympathomimetic activities of the GnRH analogs did not depend on changes in temperature, which occur seasonally in natural habitats, because similar noradrenergic responses were observed at 4 and 22 degrees C. GnRH and [Trp7, Leu8]-GnRH (0.01-10 nmol.kg-1) did not raise arterial blood pressure in bullfrogs despite their pressor actions in toads. This interspecific difference was remarkable because cardiovascular responses to norepinephrine, angiotensin II, and vasotocin in bullfrogs were similar to those in toads. The parallels between catecholamine and blood pressure responses suggest that epinephrine is the principal mediator of the blood pressure response to native GnRH analogs in toads. In bullfrogs, [Trp7, Leu8]-GnRH mobilizes norepinephrine but not epinephrine, and the noradrenergic effect is insufficient to raise blood pressure. These observations are consistent with a physiological role for native GnRH analogs in the regulation of the sympathoadrenal system in anuran amphibians.     

Autonomic variations caused by stimulation of the rhombencephalic visceral sensory zone in anesthetized toads

Electrical stimulation of the visceral sensory zone od the rhombencephalon in anesthetized toads (Bufo paracnemis) elicited hyper- and hypotensive responses depending on stimulus frequency.Carbachol injected into this region generally produced hypertensive responses.Peripheral blockage of the hypertensive responses was obtained with phentolamine.Central pretreatment with atropine blocked the hypertensive response obtained with carbachol.The pressure rises were accompanied by increased oscillatory gorge movements, which were not abolished by the peripheral nor by the central blocking agents.It is suggested that muscarinic cholinergic mediators may possibly be involved in the hypertensive response participating in the chemoreceptor reflex.     

The jamming avoidance response ofEigenmannia: properties of a diencephalic link between sensory processing and motor output

Summary Brain regions participating in the control ofEigenmannia's electric organ discharge frequency were localized by electrical microstimulation and anatomically identified by means of horseradish peroxidase deposition. A diencephalic region was found which, when stimulated, caused electric organ discharge (EOD) frequency increases of similar magnitude and time course as the frequency increases seen during the jamming avoidance response. Single unit recordings from this region revealed one cell type which preferentially responded to stimuli that cause the acceleration phase of the jamming avoidance response (electric organ discharge frequency increase). A second cell type responded preferentially to stimuli which cause EOD frequency decrease, and both cell types were tuned to stimuli which evoked maximal jamming avoidance behaviors.The results of the horseradish peroxidase experiments showed that the recording and stimulation sites correspond to the previously described nucleus electrosensorius. Our results confirm the earlier finding that this nucleus receives output from the torus semicircularis and we also found that the N. electrosensorius projects to the mesencephalic prepacemaker nucleus. The prepacemaker projects to the medullary pacemaker nucleus which generates the commands that evoke electric organ discharges.The anatomical and physiological results described here establish this diencephalic region as a link between the major sensory processing region for the jamming avoidance response, the torus semicircularis, and a mesencephalic pre-motor region, the prepacemaker nucleus.Abbreviations AM amplitude modulation - DF Delta F - ELLL electrosensory lateral line lobe - EOD electric organ discharge - JAR jamming avoidance response - NE nucleus electrosensorius - PPN prepacemaker nucleus - PN pacemaker nucleus     

Native Australian frogs avoid the scent of invasive cane toads

Invasive species can affect the ecosystems they colonize by modifying the behaviour of native taxa; for example, avoidance of chemical cues from the invader may modify habitat use (shelter site selection) by native species. In laboratory trials, we show that metamorphs of most (but not all) native frog species on a tropical Australian floodplain avoid the scent of invasive cane toads (Bufo marinus Linnaeus 1758). Cane toads also avoid conspecific scent. This response might reduce vulnerability of metamorph frogs and toads to larger predatory toads. However, similar avoidance of one type of pungency control (garlic), and the presence of this avoidance behaviour in frogs at the toad invasion front (and hence, with no prior exposure to toads), suggest that this may not be an evolved toad‐specific response. Instead, our data support the simpler hypothesis that the metamorph anurans tend to avoid shelter sites that contain strong and unfamiliar scents. Temporal and spatial differences in activity of frogs versus toads, plus the abundance of suitable retreat sites during the wet season (the primary time of frog activity), suggest that avoiding toad scent will have only a minor impact on the behaviour of native frogs. However, this behavioural impact may be important when environmental conditions bring toads and frogs into closer contact.     

Behavioural responses of carnivorous marsupials (Planigale maculata) to toxic invasive cane toads (Bufo marinus)

The arrival of a toxic invasive species may impose selection on local predators to avoid consuming it. Feeding responses may be modified via evolutionary changes to behaviour, or via phenotypic plasticity (e.g. learning, taste aversion). The recent arrival of cane toads (Bufo marinus) in the Northern Territory of Australia induced rapid aversion learning in a predatory marsupial (the common planigale, Planigale maculata). Here, we examine the responses of planigales to cane toads in north‐eastern Queensland, where they have been sympatric for over 60 years, to investigate whether planigale responses to cane toads have been modified by long‐term exposure. Responses to toads were broadly similar to those documented for toad‐naïve predators. Most Queensland planigales seized (21 of 22) and partially consumed (11 of 22) the first toad they were offered, but were likely to ignore toads in subsequent trials. However, unlike their toad‐naïve conspecifics from the Northern Territory, the Queensland planigales all survived ingestion of toad tissue without overt ill effects and continued to attack toads in a substantial proportion of subsequent trials. Our data suggest that (i) learning by these small predators is sufficiently rapid and effective that selection on behaviour has been weak; and (ii) physiological tolerance to toad toxins may be higher in planigales after 60 years (approximately 60 generations) of exposure to this toxic prey.     

Configurational pattern discrimination responsible for dishabituation in common toads Bufo bufo (L.): Behavioral tests of the predictions of a neural model

Summary Recently, a neural model of visual pattern discrimination for stimulus-specific habituation was developed, based on previous behavioral studies which demonstrated that toads exhibit a dishabituation hierarchy for different worm-like stimuli. The model suggests that visual objects are represented by temporal coding and predicts that the dishabituation hierarchy changes when the stimulus/background contrast direction is reversed or the stimulus size is varied. The behavioral experiments reported in this paper were designed to test these predictions, (1) For a pair of stimuli from the contrast reversal prediction, the experimental results validated the theory. (2) For a pair of stimuli from the size reduction prediction, the experimental results failed to validate the theory. Further experiments concerning size effects suggest that configurai visual pattern discrimination in toads exhibits size invariance. (3) Inspired by the Groves-Thompson account of habituation, we found that dishabituation by a second stimulus has a separate process from habituation to a first stimulus. This paper serves as an example of a fruitful dialogue between experimentation and modeling, crucial for understanding brain functions.Abbreviations a-h worm-like stimulus patterns - AT anterior thalamus - ERF excitatory receptive field - IRF inhibitory receptive field - RF receptive field - R2 to R4 retinal ganglion cell types - vMP posterior ventromedial pallium     

Multimodal interneurons in the cricket brain: properties of identified extrinsic mushroom body cells

Summary 322 neurons were recorded intracellularly within the central part of the insect brain and 150 of them were stained with Lucifer Yellow or cobaltous sulphide. Responses to mechanical, olfactory, visual and acoustical stimulation were determined and compared between morphologically different cell types in different regions of the central brain. Almost all neurons responded to multimodal stimulation and showed complex responses. It was not possible to divide the cells into different groups using physiological criteria alone.Extrinsic neurons with projections to the calyces connect the mushroom bodies with the deutocerebrum and also with parts of the diffuse protocerebrum. These cells probably give input to the mushroom body system. The majority are multimodal and they often show olfactory responses. Among those cells that extend from the antennal neuropil are neurons that respond to non-antennal stimulation (Figs. 1, 2).Extrinsic neurons with projections in the lobes of the mushroom bodies often project to the lateral protocerebrum. Anatomical and physiological evidence suggest that they form an output system of the mushroom bodies. They are also multimodal and often exhibit long lasting after discharges and changes in sensitivity and activity level, which can be related to specific stimuli or stimulus combinations (Figs. 3, 4).Extrinsic neurons, especially those projecting to the region where both lobes bifurcate, exhibit stronger responses to multimodal stimuli than other local brain neurons. Intensity coding for antennal stimulation is not different from other areas of the central protocerebrum, but the signal-tonoise ratio is increased (Fig. 5).Abbreviation AGT antenno-glomerular tract     

Behavior of larval Hemigrapsus sanguineus (de Haan) in response to gravity and pressure

Hemigrapsus sanguineus is an invasive species of crab (family: Grapsidae) in the north Atlantic basin. The species has spread rapidly since it was first discovered in North America in the late 1980s; however, the mechanisms of this range expansion remain unclear. This study attempts to predict the vertical distribution and, thus, ultimate transport of H. sanguineus larvae by examining larval responses to gravity and pressure. Geotaxis was determined by measuring the response of individual larvae to gravity in the absence of other tactic stimuli. Barokinesis was determined by measuring changes in swimming speed of larvae upon step-wise changes in pressure. Geotactic response of the larvae changes ontogenetically; early stage larvae are negatively geotactic (orienting towards the surface), while late stage larvae are positively geotactic (orienting towards the bottom). Larvae show a response to pressure that would aid in depth regulation. Early-stage larvae increase activity upon a change in pressure and orient their movement to gravity. However, the larvae show a relatively low sensitivity to pressure change. The evidence predicts an export-and-return model of larval transport, similar to that of Uca spp. in the Middle Atlantic Bight. This model supports the hypothesis that H. sanguineus larvae have the potential for high dispersal and will continue to invade new regions through larval transport.     

Behavioural responses of native predators to an invasive toxic prey species

One important impact of invasive species may be to modify the behaviour of native taxa. For example, the invasion of highly toxic cane toads (Bufo marinus) kills many anurophagous native predators, but other predators learn to recognize and avoid the toxic invader. We exposed native fish (northern trout gudgeons, Mogurnda mogurnda) and Dahl's aquatic frogs (Litoria dahlii) to cane toad tadpoles, then monitored the predator's responses during subsequent trials. Both the frogs and fish initially attacked toad tadpoles, but rapidly learned not to do so. Fish and adult frogs retained their aversion for at least a week, whereas recently metamorphosed frogs did not. Clearly, the spread of cane toads through tropical Australia can modify feeding responses of native aquatic predators. For predators capable of rapid avoidance learning, the primary impact of cane toads may be on foraging behaviour rather than mortality.     

Neuromodulatory Control of a Goal-Directed Decision

Many cost-benefit decisions reduce to simple choices between approach or avoidance (or active disregard) to salient stimuli. Physiologically, critical factors in such decisions are modulators of the homeostatic neural networks that bias decision processes from moment to moment. For the predatory sea-slug Pleurobranchaea, serotonin (5-HT) is an intrinsic modulatory promoter of general arousal and feeding. We correlated 5-HT actions on appetitive state with its effects on the approach-avoidance decision in Pleurobranchaea. 5-HT and its precursor 5-hydroxytryptophan (5-HTP) augmented general arousal state and reduced feeding thresholds in intact animals. Moreover, 5-HT switched the turn response to chemosensory stimulation from avoidance to orienting in many animals. In isolated CNSs, bath application of 5-HT both stimulated activity in the feeding motor network and switched the fictive turn response to unilateral sensory nerve stimulation from avoidance to orienting. Previously, it was shown that increasing excitation state of the feeding network reversibly switched the turn motor network response from avoidance to orienting, and that 5-HT levels vary inversely with nutritional state. A simple model posits a critical role for 5-HT in control of the turn network response by corollary output of the feeding network. In it, 5-HT acts as an intrinsic neuromodulatory factor coupled to nutritional status and regulates approach-avoidance via the excitation state of the feeding network. Thus, the neuromodulator is a key organizing element in behavioral choice of approach or avoidance through its actions in promoting appetitive state, in large part via the homeostatic feeding network.     

Temporal discharge patterns of tectal and medullary neurons chronically recorded during snapping toward prey in toads Bufo bufo spinosus

In freely moving toads, the temporal discharge patterns of tectal and medullary neurons were observed during prey-catching.

1. Tectal T5.2 and T8.1 neurons displayed a premotor warming up firing that in the former was addressed specifically to prey orienting or snapping and in the latter generally to almost any kind of body movement.
2. The temporal discharge patterns of T5.2 neurons during snapping were different from those during orienting toward prey. Snapping started in the peak phase of warming up; firing was immediately terminated during the snap; thereafter some rebound activity was observed. Orienting started after the premotor warming up in the declining phase whilst the neuron kept on firing during orienting and then settled when the orienting movement was completed.
3. In toads which were not motivated to catch prey — comparabl to immobilized ones — the discharge frequency of T5.2 neurons toward a prey stimulus revealed no such warming up.
4. Because it is known that prey-selective T5.2 neurons are controlled by pretectal inhibitory influences, the following experiment was conducted: during recording a T5.2 neuron a pretectal lesion was applied ipsilaterally to the recording site. After a few seconds, the neuron showed a strong premotor wanning up in response to any kind of moving object, followed by prey-catching.
5. In the medulla oblongata, different H-type neurons of the hypoglossal nucleus displayed specific discharge patterns which resembled the tongue protractor and retractor muscle activities; a third type resembled the activity of the genio/sterno-hyoid muscle, which are suggested to stabilize the hyoid bone during snapping.
6. There were medullary M8-type neurons with properties similar to T8.1.
7. Snapping could be triggered by electrical stimulation of the optic tectum in the representation of the frontal visual field, but not by stimulation in the hypoglossal nucleus or the adjacent medial reticular formation.
8. A concept of a neuronal circuit for the coordination of tongue muscle contractions in response to prey is proposed.

     

The organization of plurisegmental mechanosensitive interneurons in the central nervous system of the wandering spider Cupiennius salei

Summary In spiders the bulk of the central nervous system (CNS) consists of fused segmental ganglia traversed by longitudinal tracts, which have precise relationships with sensory neuropils and which contain the fibers of large plurisegmental interneurons. The responses of these interneurons to various mechanical stimuli were studied electrophysiologically, and their unilateral or bilateral structure was revealed by intracellular staining. Unilateral interneurons visit all the neuromeres on one side of the CNS. They receive mechanosensory input either from a single leg or from all ipsilateral legs via sensory neurons that invade leg neuromeres and project into specific longitudinal tracts. The anatomical organization of unilateral interneurons suggests that their axons impart their information to all ipsilateral leg neuromeres. Bilateral interneurons are of two kinds, symmetric and asymmetric neurons. The latter respond to stimulation of all legs on one side of the body, having their dendrites amongst sensory tracts of the same side of the CNS. Anatomical evidence suggests that their terminals invade all four contralateral leg neuromeres. Bilaterally symmetrical plurisegmental interneurons have dendritic arborizations in both halves of the fused ventral ganglia. They respond to the stimulation of any of the 8 legs. A third class of cells, the ascending neurons have unilateral or bilateral dendritic arborizations in the fused ventral ganglia and show blebbed axons in postero-ventral regions of the brain. Their response characteristics are similar to those of other plurisegmental interneurons. Descending neurons have opposite structural polarity, arising in the brain and terminating in segmental regions of the fused ventral ganglia. Descending neurons show strong responses to visual stimulation. Approximately 50% of all the recorded neurons respond exclusively to stimulation of a single type of mechanoreceptor (either tactile hairs, or trichobothria, or slit sensilla), while the rest respond to stimulation of a variety of sensilla. However, these functional differences are not obviously reflected by the anatomy. The functional significance of plurisegmental interneurons is discussed with respect to sensory convergence and the coordination of motor output to the legs. A comparison between the response properties of certain plurisegmental interneurons and their parent longitudinal tracts suggests that the tracts themselves do not reflect a modality-specific organization.Abbreviations BPI bilateral plurisegmental interneuron - CNS central nervous system - FVG fused ventral ganglia - LT longitudinal tract - PI plurisegmental interneuron - PSTH peristimulus timehistogram - UPI unilateral plurisegmental interneuron     

Non‐Selective and Time‐Dependent Behavioural Responses of Common Toads (Bufo bufo) to Predator Acoustic Cues

Acoustic predator recognition has rarely been studied in anurans, in spite of the fact that hearing is widespread in these animals and that it has been demonstrated to play an important role in both arthropods and other vertebrates. Using field playback experiments, we tested the hypothesis that adult common toads (Bufo bufo) are capable of recognizing natural vocalizations of a common predator, the Eurasian otter (Lutra lutra), and show antipredator responses. We found that toads exposed to both natural (two types of otter sounds) and synthetic stimuli [white noise (WN) and otter sound‐based amplitude modulated WN] increased time allocated to locomotion and escape behaviour. These responses were correlated with time elapsed from sunset to the onset of testing and were independent from the type of acoustic signal, toad features and other environmental factors monitored. We conclude that B. bufo has not developed a selective recognition of predator vocalizations, suggesting that low‐frequency or seismic sounds associated with predator movements may provide anurans with better cues about an approaching risk. We propose that the time‐dependent response to acoustic stimuli of common toads represents a case of threat‐sensitivity and demonstrates that it can occur even when the response to the threat is not predator specific.     

Cardiovascular actions of l-cysteine and l-cysteine sulfinic acid in the nucleus tractus solitarius of the rat

The sulfur-containing excitatory amino acid (EAA) l-cysteine sulfinic acid (CSA), a neurotransmitter candidate, is endogenously synthesized from l-cysteine (Cys). Exogenous Cys administration into the brain produces cardiovascular effects; these effects likely occur via synaptic stimulation of central nervous system (CNS) neurons that regulate peripheral cardiovascular function. However, the cardiovascular responses produced by CNS Cys administration could result from CSA biosynthesized in synapse. The present study examined the role of CSA in Cys-induced cardiovascular responses within the nucleus tractus solitarius (NTS) of anesthetized rats. The NTS receives input from various visceral afferents that gate autonomic reflexes, including cardiovascular reflexes. Within the NTS, both Cys and CSA microinjections produced decrease responses in arterial blood pressure and heart rate that were similar to those produced by l-glutamate. Co-injection of the ionotropic EAA receptor antagonist kynurenic acid abolished Cys-, but not CSA-, induced cardiovascular responses. This finding suggests that only Cys-induced cardiovascular responses are mediated by kynurenate-sensitive receptors. This study provides the first demonstration that Cys- and CSA-induced cardiovascular responses occur via different mechanisms in the NTS of rats. Further, this study also indicates that Cys-induced cardiovascular responses do not occur via CSA. Thus, within the NTS, endogenous Cys and/or CSA might be involved in cardiovascular regulation.     

Responses of the Toad Bufo bufo (L.) to Stationary Prey Stimuli1

In the present work toads (Bufo bufo) are shown to respond with prey catching to stationary dummies without previous or accompanying visual or olfactory stimulation. The subjects very rarely showed jerky head movements which, therefore, cannot be necessary for perception of stationary objects. Size preference with respect to stationary stimuli is about the same as in experiments with moving stimuli. However, differences exist between the effects of stationary and moving stimuli with respect to shape and orientation. If a square measuring 10 times 10 mm and a rectangle measuring 5 times 20 mm, oriented either horizontally or vertically, are presented within the frontal-vertical plane, the square is preferred to the rectangles, and among these the horizontal rectangle is to the vertical one. This latter preference is due to the negative effect of the vertical extension: If the vertical rectangle is reduced in length, it becomes more effective as compared to the horizontal rectangle. In the horizontal (X-Z) plane the square and the rectangle oriented parallel to the Z-axis are equally superior to the bar oriented parallel to the X-axis. At presentation of a pair of stimuli in both planes, the one in the frontal-vertical plane is always preferred to that in the horizontal plane. Correspondences and differences of these results to those from experiments with moving prey dummies are discussed.     

Reflex cardiovascular responses originating in exercising muscles of mice.

The cardiovascular responses induced by exercise are initiated by two primary mechanisms: central command and reflexes originating in exercising muscles. Although our understanding of cardiovascular responses to exercise in mice is progressing, a murine model of cardiovascular responses to muscle contraction has not been developed. Therefore, the purpose of this study was to characterize the cardiovascular responses to muscular contraction in anesthetized mice. The results of this study indicate that mice demonstrate significant increases in blood pressure (13.8 +/- 1.9 mmHg) and heart rate (33.5 +/- 11.9 beats/min) to muscle contraction in a contraction-intensity-dependent manner. Mice also demonstrate 23.1 +/- 3.5, 20.9 +/- 4.0, 21.7 +/- 2.6, and 25.8 +/- 3.0 mmHg increases in blood pressure to direct stimulation of tibial, peroneal, sural, and sciatic hindlimb somatic nerves, respectively. Systemic hypoxia (10% O(2)-90% N(2)) elicits increases in blood pressure (11.7 +/- 2.6 mmHg) and heart rate (42.7 +/- 13.9 beats/min), while increasing arterial pressure with phenylephrine decreases heart rate in a dose-dependent manner. The results from this study demonstrate the feasibility of using mice to study neural regulation of cardiovascular function during a variety of autonomic stimuli, including exercise-related drives such as muscle contraction.     

Serotonin-mediated cardiovascular responses to electrical stimulation of the raphe nuclei in the rat.

The dorsal and median raphe nuclei in rats were electrically stimulated and blood pressure and heart rate were recorded. Stimulation of each raphe nucleus caused an increase in blood pressure without affecting heart rate. The size of the increase in blood pressure depended upon the stimulus-intensity.Significant increases were already obtained with 5 sec. trains of 0.3 msec., 200 μA stimuli given at a frequency of 50 Hz. The increases in blood pressure could be obtained with electrodes within the raphe nuclei.Pretreating rats with para-chlorophenylalanine (pCPA, 100 mg/kg.day for 3 days) significantly diminished the increases in blood pressure obtained during electrical stimulation of the median raphe nucleus. However, similar pretreatment did not affect blood pressure rises induced by dorsal raphe stimulation.These data are discussed in relation to the role of central serotoninergic mechanisms in cardiovascular control.     

Respiratory effects of brief baroreceptor stimuli in the anesthetized dog

To quantify the immediate isocapnic respiratory response to baroreceptor stimulation, pressure in the isolated externally perfused carotid sinuses (CS) of 24 vagotomized alpha-chloralose-anesthetized dogs was increased selectively during either inspiration or expiration as a step (from time of onset to end of respiratory phase) or a pulse (500 ms). The rise time (150 ms), base-line pressure (80 mmHg), and stimulus magnitude (40 mmHg) were similar for the two stimuli. The time of stimulus onset (delay), expressed as a percent of control time of inspiration (TI) or expiration (TE), was varied. TI, TE, and tidal volume (VT) were expressed as percent changes from control. Stimuli delivered early in inspiration lengthened TI [23.5 +/- 6.4% (SE) for step and 11.7 +/- 6.3% for pulse stimuli at 5% delay] more effectively than late stimuli. VT was essentially unaltered. In contrast, step stimuli delivered during expiration caused a lengthening of TE (32.7 +/- 6.3% at 5% delay) that did not depend on the delay (up to 75%). Very late (85%) pulse stimuli lengthened TE (15.2 +/- 5.7%) more effectively than early stimuli. For both stimuli, the expiratory VT was unaltered. When the responses are compared before and after separation of the blood supply of the carotid bodies from the CS region and when they are compared before and after inhibition of reflex systemic hypotension by ganglionic blockade, the observed responses were shown to be due solely to CS baroreceptor stimulation and not to alterations in carotid body blood flow or reflex changes in systemic cardiovascular variables.