Frog Brainstem Research Articles

Plasticity in the Functional Properties of NMDA Receptors Improves Network Stability during Severe Energy Stress.

Brain energy stress leads to neuronal hyperexcitability followed by a rapid loss of function and cell death. In contrast, the frog brainstem switches into a state of extreme metabolic resilience that allows them to maintain motor function during hypoxia as they emerge from hibernation. NMDA receptors (NMDARs) are Ca2+-permeable glutamate receptors that contribute to the loss of homeostasis during hypoxia. Therefore, we hypothesized that hibernation leads to plasticity that reduces the role of NMDARs within neural networks to improve function during hypoxia. To test this, we assessed a circuit with a large involvement of NMDAR synapses, the brainstem respiratory network of female bullfrogs, Lithobates catesbeianus Contrary to our expectations, hibernation did not alter the role of NMDARs in generating network output, nor did it affect the amplitude, kinetics, and hypoxia sensitivity of NMDAR currents. Instead, hibernation strongly reduced NMDAR Ca2+ permeability and enhanced desensitization during repetitive stimulation. Under severe hypoxia, the normal NMDAR profile caused network hyperexcitability within minutes, which was mitigated by blocking NMDARs. After hibernation, the modified complement of NMDARs protected against hyperexcitability, as disordered output did not occur for at least one hour in hypoxia. These findings uncover state-dependence in the plasticity of NMDARs, whereby multiple changes to receptor function improve neural performance during metabolic stress without interfering with their normal role during healthy conditions.

Methods for frequency and correlation analyses of neurograms

Many physiological functions are based on motor rhythmic activities, among them breathing is a vital issue. The method presented here, or ‘temporal grid extraction’, aims at characterizing the temporal organization of such an activity. Beyond the measurement of the fundamental frequency, defining the successive cycles, some signal processing tools are helpful in order to look for the presence of higher frequency components that potentially structure these cycles. The method is applied to neurograms recorded from frog brainstem preparations, where two cycle types, buccal and lung cycles, may alternate. It relies on:•Continues Wavelet Transform (CWT) for time-frequency maps and frequency profiles•Crosscorrelation analysis for amplitude maps and amplitude profiles•Cycle-by-cycle autocorrelation analysis for autocorrelation maps and autocorrelation profilesUsing this method, the maps and profiles have revealed that a common high frequency clock drives both buccal and lung cycles.

Putative Sympathetic Oscillator in the Thoracic Spinal Cord of the Bullfrog

BACKGROUNDCardiorespiratory control is essential for survival of all vertebrates, yet our understanding of the neuronal circuitry involved is rudimentary ‐‐ in part because there is little data beyond mammals to guide us. Neuronal oscillators are discrete neural circuits located within the central nervous system that are capable of generating rhythmic outputs without phasic input. These circuits are found throughout the animal kingdom and are often critical for regulating overt rhythmic behaviours such breathing. Previously, we found three oscillators in the frog brainstem that control ventilation: one for buccal ventilation, two for lung. Three respiratory oscillators have subsequently been found in mammals. Central neuronal oscillators within the sympathetic nervous system of frogs and mammals have also been suspected, but these oscillators have yet to be precisely located.FINDINGSUsing extracellular recording and transection techniques in the frog superfused, isolated brainstem and spinal cord preparation, we discovered a robust, yet previously unreported buccal‐like rhythm in the third spinal nerve (SNIII). Unlike the ventilatory rhythms we normally study, the SNIII rhythm demonstrates poor bilateral synchrony. Our data also suggest that this rhythm is: (a) not coupled to ventilatory rhythms recorded in cranial nerves; (b) has distinct responses to pharmacological stimulation compared to ventilatory rhythms; (c) does not require the brainstem; and (d) persists in a chunk of spinal cord centered around SNIII. These data suggest an additional neuronal oscillator in the frog spinal cord located at the level of SNIII. However, removing the brainstem alters the frequency, increases variability and degrades left‐right synchrony of the rhythm, suggesting brainstem connections are important for normal function.SIGNIFICANCEThe literature has long debated the existence of central neuronal oscillators that modulate sympathetic nervous system activity in vertebrates. We propose that the bursting activity recorded from the SNIII in frog is the output of such an oscillator, discovery of which could prove critical in shaping our current understanding of the function and evolution of the sympathetic nervous system.Support or Funding InformationNSERC and HBI.

Unbuckling the Buccal oscillator in the American Bullfrog

The American Bullfrog is a remarkable model organism to study rhythm generation underlying breathing. It exhibits a breathing pattern that can be divided into four distinct ventilatory phases: lung‐priming, lung‐powerstroke, buccal‐dilation, and buccal‐constriction. We recently established that lung‐priming and lung‐powerstroke are generated by two separate burst generating substrates in the brainstem—the Priming area and Powerstroke area—located in rhombomere 4–5. The neural origin of the two phases of buccal, on the other hand, remains elusive. Our previous experiments suggest that a Buccal area located in rhombomere 7 is responsible, at least in part, for generating the biphasic buccal rhythm; however, whether any additional burst generating substrates are involved is yet unknown.The objective of this study was to characterize areas in the frog brainstem that generate the biphasic buccal rhythm. We utilized the isolated frog brainstem preparation and recorded fictive respiratory motor output from the trigeminal and facial cranial nerves using extracellular suction electrodes. We progressively transected the brainstem in both directions (caudal‐to‐rostral, and rostral‐to‐caudal) to identify regions where transection eliminated one or both buccal burst phases.Our preliminary results suggest that both phases of the buccal rhythm are generated by substrates located at the same level as the previously identified Buccal area. Nevertheless, using our current methodology, we are unable to discern whether multiple substrates or a single substrate is generating the buccal rhythm. To address this question, we developed a ‘buccal slice’ preparation at the level of the Buccal area which, when exposed to 100nM AMPA, produces buccal‐like bursts. We continue to develop this preparation as it holds promise for further dissecting the properties of this system and exploring it at the cellular and molecular levels.Our analysis suggests that the Buccal area is an evolutionary homolog of the mammalian preBötzinger complex. Both are located in rhombomere 7, are resilient oscillators, being staunchly insensitive to CO2, and co‐opted for sniffing. We anticipate that having two comparable preparations, i.e. ‘buccal slice’ and ‘preBötC slice’, will allow for more direct comparisons between these oscillators, further testing their homology and thus take us closer towards understanding the evolution of breathing.Support or Funding InformationNational Science and Engineering Council of Canada (NSERC) and Alberta Innovates Health Solutions (AIHS) provided funding for this study.

Three brainstem areas involved in respiratory rhythm generation in bullfrogs.

Ventilation in mammals consists of at least three distinct phases: inspiration, post-inspiration and late-expiration. While distinct brainstem rhythm generating and pattern forming networks have long been assumed, recent data suggest the mammalian brainstem contains two coupled neuronal oscillators: one for inspiration and the other for active expiration. However, whether additional burst generating ability is required for generating other phases of ventilation in mammals is controversial. To investigate brainstem circuit architectures capable of producing multiphasic ventilatory rhythms, we utilized the isolated frog brainstem. This preparation produces two types of ventilatory motor patterns, buccal and lung bursts. Lung bursts can be divided into two phases, priming and powerstroke. Previously we identified two putative oscillators, the Buccal and Lung Areas. The Lung Area produces the lung powerstroke and the Buccal Area produces buccal bursts and - we assumed - the priming phase of lung bursts. However, here we identify an additional brainstem region that generates the priming phase. This Priming Area extends rostral and caudal of the Lung Area and is distinct from the Buccal Area. Using AMPA microinjections and reversible synaptic blockade, we demonstrate selective excitation and ablation (respectively) of priming phase activity. We also demonstrate that the Priming Area contains neurons active selectively during the priming phase. Thus, we propose that three distinct neuronal components generate the multiphase respiratory motor pattern produced by the frog brainstem: the buccal, priming and powerstroke burst generators. This raises the possibility that a similar multi-burst generator architecture mediates the three distinct phases of ventilation in mammals.

Persistent lung oscillator response to CO2 after buccal oscillator inhibition in the adult frog

The automatic ventilatory drive in amphibians depends on two oscillators interacting with each other, the gill/buccal and lung oscillators. The lung oscillator would be homologous to the mammalian pre-Bötzinger complex and the gill/buccal oscillator homologous to the mammalian parafacial respiratory group/retrotrapezoid nucleus (pFRG/RTN). Dysfunction of the pFRG/RTN has been involved in the development of respiratory diseases associated to the loss of CO2 chemosensitivity such as the congenital central hypoventilation syndrome. Here, on adult in vitro isolated frog brainstem, consequences of the buccal oscillator inhibition (by reducing Cl−) were evaluated on the respiratory rhythm developed by the lung oscillator under hypercapnic challenges. Our results show that under low Cl− concentration (i) the buccal oscillator is strongly inhibited and the lung burst frequency and amplitude decreased and (ii) it persists a powerful CO2 chemosensitivity. In conclusion, in frog, the CO2 chemosensitivity depends on cellular contingent(s) whose the functioning is independent of the concentration of Cl− and origin remains unknown.

Assessment of central chemosensitivity through simultaneous recording of single‐unit and whole‐nerve responses to CO2

The isolated frog brainstem is an established preparation to quantify respiratory drive and the role of central CO2 sensitivity in control of breathing. Here, we establish a technique to quantify neuronal response to high CO2 (hypercapnia) and compare it to the concomitant response by the intact respiratory network. Recorded neurons were subsequently juxtacellularly labeled, facilitating identification of location and phenotype of respiratory CO2‐ sensitive neurons. Neurograms representing buccal and lung breathing were obtained with suction electrodes recording whole‐nerve activity in cranial nerves 5 and 7. Simultaneously, extracellular electrodes recorded single neurons in established CO2‐sensitive sites of the frog brainstem. Neural activity was recorded while brainstems were exposed to normocapnia and hypercapnia (1.5 and 5.0% CO2, balance O2). Neurons were then entrained to an injected current and juxtacellularly labeled with biotinamide. After electrophysiology experiments, brainstem slices were stained with streptavidin‐AlexaFluor and the recorded cells were imaged. Our results validate this technique, which is the first reported capacity to simultaneously assess CO2 sensitivity of the central network that controls breathing and a single neuron embedded in the network. We expect to use this technique to elucidate neural mechanisms responsible for respiratory drive. NSF IOS‐1022442

Identification of lung priming area in frog brainstem, adjacent to the lung oscillator, distinct from the buccal oscillator: homologous to RTN/pFRG?

Data from mammals and frogs suggest tetrapods have an anatomically‐discrete inspiratory oscillator, necessary and sufficient for expression of the powerstroke phase of lung inflation (preBötzinger Complex in mammals; Lung Area in frogs). In mammals a second Pre‐Inspiratory / late‐phase expiratory oscillator has been hypothesized; this oscillator likely resides in the retrotrapezoid/parafacial respiratory group (RTN/pFRG) and is “conditional”, recruited during high respiratory demand. In isolated frog brainstems, lung bursts often have a powerstroke and priming phase. Though the priming phase is always observed with a subsequent powerstroke, the priming phase is “conditional”: powerstrokes can occur without a priming phase.Here we identify a region of the frog brainstem necessary and sufficient for the priming phase. This priming area is adjacent to the area that produces the powerstroke (between CNVII‐IX) and distinct from the buccal area (caudal of CN X). Using AMPA microinjections to locally excite the priming area, we demonstrate ectopic priming bursts uncoupled from powerstroke bursts. We propose the priming and powerstroke areas are homologous to the PreI and PreBötC, respectively. We further postulate that rhombomeric differences may be explained by a “gene cassette” for air breathing rhythmogenesis, turned on in different rhombomeres in different clades. Work funded by NSERC.

Molecular organization of perineuronal net of the oculomotor neurons in the frog

Event Abstract Back to Event Molecular organization of perineuronal net of the oculomotor neurons in the frog Botond Ágoston Gaál1, 2*, Eva Rácz1, Gabor Veres1, Gyorgy Szekely1, 2 and Klara Matesz1, 2 1 Department of Anatomy, University of Debrecen, Hungary 2 University of Debrecen, Hungary The perineuronal net (PN) is a condensation of extracellular matrix macromolecules (ECM) around the perikaryon, proximal dendrites and the axon hillock. It is generally accepted that in mammalian species the major components of the PN are the chondroitin-sulfate proteoglycans (CSPG) that bind to a variety of molecules such as the hyaluronan (HA) and tenascin-R. Since the motoneurons of the brainstem show different response for the axotomy, we suppose that it is associated with different molecular organization of their PN. This study was undertaken to examine the chemical components of the PN around the oculomotor neurons of the frog by immunohistochemical labeling. For identifying neurons, we used Neuron Specific Enolase (NSE) antibody in each reaction, meaning double labeling. Reactions were carried on paraffin embedded sections, treated with St. Marie’s fixative. The HA reaction was positive around the motoneurons showing the strongest intensity. The Wisteria floribunda reaction, the general marker of the CSPG, was negative similarly to the results of the immunohistochemical reaction for the individual PG molecules, i.g. versican and neurocan. Our result suggests that the structure of the PN in the frog brainstem and spinal cord motoneurons is less organized than that of the PN in the vestibular nuclear complex of the frog or in mammalian species. We suppose that in the motoneuronal PN of the frog the function of the CSPG is provided by the phylogenetically ancient heparan-sulfate proteoglycans. This work was supported by OTKA K 67641 and MTA-TKI 242. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Developmental neurobiology and subcortical functions Citation: Gaál B, Rácz E, Veres G, Szekely G and Matesz K (2009). Molecular organization of perineuronal net of the oculomotor neurons in the frog. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.055 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Feb 2009; Published Online: 27 Feb 2009. * Correspondence: Botond Ágoston Gaál, Department of Anatomy, University of Debrecen, Debrecen, Hungary, botond@chondron.anat.dote.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Botond Ágoston Gaál Eva Rácz Gabor Veres Gyorgy Szekely Klara Matesz Google Botond Ágoston Gaál Eva Rácz Gabor Veres Gyorgy Szekely Klara Matesz Google Scholar Botond Ágoston Gaál Eva Rácz Gabor Veres Gyorgy Szekely Klara Matesz PubMed Botond Ágoston Gaál Eva Rácz Gabor Veres Gyorgy Szekely Klara Matesz Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Respiratory neuronal activities of the frog brainstem visualized in vitro

Respiratory neuronal activities of the frog brainstem visualized in vitro

Immunohistochemical distribution of enkephalin, substance P, and somatostatin in the brainstem of the leopard frog, Rana pipiens.

The brainstems of frogs contain many of the neurochemicals that are found in mammals. However, the clustering of nuclei near the ventricles makes it difficult to distinguish individual cell groups. We addressed this problem by combining immunohistochemistry with tract tracing and an analysis of cell morphology to localize neuropeptides within the brainstem of Rana pipiens. We injected a retrograde tracer, Fluoro-Gold, into the spinal cord, and, in the same frog, processed adjacent sections for immunohistochemical location of antibodies to the neuropeptides enkephalin (ENK), substance P (SP), and somatostatin (SOM). SOM+ cells were more widespread than cells containing immunoreactivity (ir) to the other substances. Most reticular nuclei in frog brainstem contained ir to at least one of these chemicals. Cells with SOM ir were found in nucleus (n.) reticularis pontis oralis, n. reticularis magnocellularis, n. reticularis paragigantocellularis, n. reticularis dorsalis, the optic tectum, n. interpeduncularis, and n. solitarius. ENK-containing cell bodies were found in n. reticularis pontis oralis, n. reticularis dorsalis, the nucleus of the solitary tract, and the tectum. The midbrain contained most of the SP+ cells. Six nonreticular nuclei (griseum centrale rhombencephali, n. isthmi, n. profundus mesencephali, n. interpeduncularis, torus semicircularis laminaris, and the tectum) contained ir to one or more of the substances but did not project to the spinal cord. The descending tract of V, and the rubrospinal, reticulospinal, and solitary tracts contained all three peptides as did the n. profundus mesencephali, n. isthmi, and specific tectal layers. Because the distribution of neurochemicals within the frog brainstem is similar to that of amniotes, our results emphasize the large amount of conservation of structure, biochemistry, and possibly function that has occurred in the brainstem, and especially in the phylogenetically old reticular formation.

Characterization of respiratory-related neurons in the isolated brainstem of the frog

Using intra- and extracellular recording techniques we examined the spontaneous discharge and membrane properties of respiratory-related neurons in isolated brainstem preparations of the frogs Rana catesbeiana and Rana pipiens that display spontaneous respiratory related activity in vitro. We observed neurons that depolarize during the fictive lung ventilation cycle as well as neurons that depolarize during the non-lung ventilation phase. Respiratory-related neurons demonstrated significant decreases in membrane input resistance during the fictive lung ventilation cycle but showed no evidence of voltage-dependent membrane conductances activated near resting membrane potential. Furthermore, respiratory neurons showed little spike frequency adaptation, their oscillatory activity was not dissociated from the global respiratory motor output following imposed changes in membrane potential, and spontaneous fluctuations in membrane potential were not observed following reversible interruption of respiratory burst activity by application of solutions low in calcium and high in magnesium. Taken together these results suggest that bulbar respiratory neurons in the isolated frog brainstem sampled in our study do not display endogenous bursting characteristics. Rather, they are strongly influenced by synaptic input.

Strychnine eliminates reciprocation and augmentation of respiratory bursts of the in vitro frog brainstem

We have recorded rhythmic bursts of efferent action potentials from nerves of respiratory muscles in the frog ( Rana pipiens), using a modified in vitro preparation, in which the brainstem lies in situ in the ventral half of the skull. The burst in the sternohyoid branch of the hypoglossal nerve (Hsh) was augmenting, and alternated with a relatively brief augmenting burst in the main branch of the hypoglossal nerve (Hm). The laryngeal branch of the vagus nerve (Xl) displayed a biphasic burst, beginning before peak activity of Hsh and spanning the Hm burst. The spatio-temporal patterns of these bursts closely resemble those recorded from the same nerves in intact and in decerebrate frogs, indicating that the bursting rhythm of this in situ preparation constitutes fictive breathing. The nature of neurotransmission responsible for burst reciprocity and augmentation was investigated by applying the glycine receptor blocker, strychnine. Low levels of strychnine (1 and 5 M) increased the frequency of fictive breathing without changing the shape or timing of Hsh, Hm and Xl bursts; at higher doses (10 and 20 M) the bursts in all nerves abruptly changed shape and timing to become synchronous and decrementing. The strychnine-induced changes were associated with the appearance of a prominent peak (10–20 Hz) on the spectral analysis of the nerve discharge, possibly indicating a fundamental change in neurogenesis of the respiratory pattern. We conclude that the burst augmentation and reciprocation discharge characteristics of fictive breathing in the frog require strychnine-sensitive inhibitory networks.

Uncrossed disynaptic inhibition of second-order vestibular neurons and its interaction with monosynaptic excitation from vestibular nerve afferent fibers in the frog.

1. Eighth nerve evoked responses in central vestibular neurons (n = 146) were studied in the isolated brain stem of frogs. Ninety percent of these neurons responded with a monosynaptic excitatory postsynaptic potential (EPSP) after electrical stimulation of the ipsilateral VIIIth nerve. In 5% of these neurons, the EPSP was truncated by a disynaptic inhibitory postsynaptic potential (IPSP), and in 5% of these neurons a pure disynaptic IPSP was evoked. 2. Disynaptic IPSPs superimposed upon apparently pure EPSPs were revealed by bath application of the glycine receptor antagonist strychnine (0.5-5 microM) or of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline (0.5-2 microM). The evoked EPSP increased in most central vestibular neurons (strychnine: 15 out of 16 neurons; bicuculline 26 out of 29 neurons). At higher stimulus intensities, the evoked spike discharge increased from 2 to 3 spikes before up to 8-10 spikes per electrical pulse during the application of blocking agents. The unmasked disynaptic inhibitory component increased with stimulus intensity to a different extent in different neurons. 3. Lesion studies demonstrated that these inhibitory components were generated ipsilaterally with respect to the recording side. The disynaptic strychnine-sensitive inhibition was mediated by neurons located either in the ventral vestibular nuclear complex (VNC) or in the adjacent reticular formation. The spatial distribution of the disynaptic inhibition was investigated by simultaneous recordings of VIIIth nerve-evoked field potentials at different rostrocaudal locations of the VNC. A significant strychnine-sensitive component was detected in the middle and caudal parts but not in the rostral part of the VNC. A bicuculline-sensitive component was detected in the rostral and in the caudal parts but not in the middle part of the VNC. In view of a similar rostrocaudal distribution of glycineor GABA-immunoreactive neurons in the VNC of frogs, our results suggest that part of the disynaptic inhibition is mediated by local interneurons with a spatially restricted projection area. 4. The monosynaptic EPSP of second-order vestibular neurons was mediated in part by N-methyl-D-aspartate (NMDA) and in part by non-NMDA receptors. The relative contribution of the NMDA receptor-mediated component of the EPSP decreased with stronger stimuli. This negative correlation could have resulted from a preferential activation of NMDA receptors via thick vestibular nerve afferent fibers. Alternatively, the activation of NMDA receptors became disfacilitated at higher stimulus intensities due to the recruitment of disynaptic inhibitory inputs. Comparison of data obtained in the presence and in the absence of these glycine and GABAA receptor blockers indicates a preferential activation of NMDA receptors via larger-diameter vestibular nerve afferent fibers. 5. The kinetics of NMDA receptors (delay, rise time) activated by afferent nerve inputs were relatively fast. These fast kinetics were independent of superimposed IPSPs. The association of these receptors with large-diameter vestibular nerve afferent fibers suggests that fast NMDA receptor kinetics might be matched to the more phasic response dynamics of the large diameter vestibular afferent neurons to natural head accelerations.

Size-related properties of vestibular afferent fibers in the frog: Differential synaptic activation of N-methyl- d-aspartate and non- N-methyl- d-aspartate receptors

Vestibular afferent fibers exhibit a specific, cell size-related uptake of aspartate and glycine [Straka H. et al. (1995) Neuroscience 70, 685–696]. A similar, size-related coexistence of glycine and glutamate had been reported earlier for these fibers [Reichenberger I. and Dieringer N. (1994) J. comp. Neurol. 349, 603–614]. Taken together, these results suggest a size-related co-release of both amino acids and the activation of different glutamate receptors in second order vestibular neurons. To test this hypothesis we stimulated the VIIIth nerve and recorded the responses of central vestibular neurons in the isolated brainstem of frogs before and during the application of the N-methyl- d-aspartate antagonists (7-chlorokynurenic acid and d-(−)-2-amino-5-phosphonovaleric acid). The presence of either one of these antagonists provoked a dose-dependent and Mg 2+-sensitive partial block of the monosynaptic responses recorded extra- or intracellularly. This implies that afferent-evoked responses in central vestibular neurons are composed of N-methyl- d-aspartate and non- N-methyl- d-aspartate receptor-mediated components. In most of the intracellularly recorded neurons (21 out of 24) the relative amplitude of the N-methyl- d-aspartate receptor-mediated component decreased with an increase in stimulus intensity. Since electric stimulation recruits thick afferents at a lower current intensity than thin afferent fibers, our results imply a co-activation of N-methyl- d-aspartate and non- N-methyl- d-aspartate receptors by thick vestibular afferents. At a given stimulus intensity the amplitude of the N-methyl- d-aspartate receptor-mediated component differed between neurons. The results of this study extend the list of known anatomical, histochemical and physiological properties that distinguish thick from thinner vestibular afferent fibers. In spite of this detailed knowledge, however, the physiological role of thick vestibular afferents is so far unclear. The novel concept of a size-related co-activation of N-methyl- d-aspartate and non- N-methyl- d-aspartate receptors by vestibular afferent fibers establishes the basis for more specific physiological hypotheses.

Two regions in the isolated brainstem of the frog that modulate respiratory-related activity.

Using microinjection techniques, we have explored the isolated, complete midline sectioned brainstem of the frog (Rana catesbeiana) to identify regions that influence the endogenous respiratory-related motor activity. Ten-nanoliter injections of lidocaine (1%), GABA (100mM) and glutamate (10 and 100 mM) into discrete regions of the rostral and the caudal brainstem produced different effects on the phasic neural discharge. In the rostral site lidocaine, GABA and glutamate injections altered neural burst frequency with little or no effect on burst amplitude. In the caudal site, responses to lidocaine and GABA injections consisted primarily of decreases in neural burst amplitude, often, but not always associated with minor decreases in burst frequency. In the same region, the response to glutamate was characterized by a temporary interruption of the rhythmic neural burst activity. The largest responses to substance injection in both regions were obtained at sites ranging between 200 and 500 microns from the ventral surface, in the ventral medullary reticular formation. The results reveal the existence of two areas in the frog brainstem that influence respiratory motor output, one related to the respiratory burst frequency and the other related to the amplitude of the motor output.

Fictive respiratory rhythm in the isolated brainstem of frogs

Spontaneous rhythmically bursting activity was recorded from the trigeminal, vagal and hypoglossal nerve roots of the isolated brainstem from the frogs Rana catesbeiana and Rana pipiens superfused with a bicarbonate-free HEPES-buffer solution. Burst frequency, burst duration and the activity profile of the spontaneous neural discharges in vitro resembled those of a less radical preparation, the decerebrate, fictively breathing frog. After complete midsagittal section, each half of the isolated brainstem generated its own rhythmic neural activity which resembled that of the intact isolated brainstem. The spontaneous activity generated within each half of the brainstem is probably coordinated by decussating axons or by groups of neurons located along the midline of the brainstem Our results suggest that these coordinating entities extend the length of the brainstem (in a rostro-caudal dimension) and the degree of contact rather than the location of the contact between the two halves of the brainstem determines the synchronization of the right and left halves. Burst frequency of both the intact and hemisected brainstem preparation was decreased by alkaline challenge and increased by acid challenge. We conclude that this endogenous rhythmic activity represents the efferent motor output underlying lung ventilation in these animals.

Fictive respiratory rhythm in the isolated brainstem of frogs

Fictive respiratory rhythm in the isolated brainstem of frogs

Mode of synaptic transmission between vestibular afferents and neurons of the vestibular nucleus in the frog

Excitatory postsynaptic potentials (EPSPs) were evoked in vestibular neurons of the isolated frog brainstem by stimulation of the ipsilateral vestibular nerve or by direct intra-axonal activation of single vestibular fibers. Composite as well as single-fiber EPSPs usually displayed two components. A Ca 2+-deficient, Mn 2+-containing solution abolished the delayed chemical components of the EPSPs, but did not affect the short latency responses suggesting a dual (electrical-chemical) mode of transmission between some vestibular afferents and vestibular neurons.

Species differences in epinephrine concentration and norepinephrine n-methyltransferase activity in hypothalamus and brain stem

1. The concentration of epinephrine, norepinephrine and dopamine, and the activity of norepinephrine N-methyltransferase, the epinephrine-forming enzyme, were determined in hypothalamus and brain stem in several species. 2. Epinephrine concentration in hypothalamus, a nerve terminal region, varied in the order frog > turtle > chicken > cat > dog > pigeon > rat > ferret > hamster > mouse, with concentrations being undetectable in rabbits, horses and guinea pigs. 3. Epinephrine concentration was lower than norepinephrine concentration in all species except the frog. 4. NMT activity was detected in all species except guinea pigs. 5. Epinephrine concentration was lower in brain stem, a cell body region, than in hypothalamus in all species. Only in the frog brain stem was there more epinephrine than norepinephrine. 6. No epinephrine or NMT activity was detected in either brain region in guinea-pigs.