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M S Siniaia

Publications and source records attributed to M S Siniaia.

At least 19 recordsLinked to original sources
PubMed2000

High-pass filtering of carotid-vagal influences on expiration in rat: role of N-methyl-D-aspartate receptors.

Repetitive electrical stimulation of the carotid sinus nerve or vagus nerve in rats elicited abrupt reflex shortening or prolongation, respectively, of the inter-burst interval of phrenic nerve activity followed by exponential decay from the initial response. Removal of the stimuli resulted in transient post-stimulus rebound excitation or inhibition that mirrored the corresponding stimulus-evoked responses. The biphasic responses to these complementary inputs approximate the on- and off-transients of full-wave differentiators or high-pass filters. Blockade of N-methyl-D-aspartate (NMDA) receptors abolished the post-stimulus rebounds and transformed both signal pathways into integrators or low-pass filters, thus switching off part or all of the high-pass filters. We suggest that such NMDA receptor-dependent high-pass filtering effects may serve to increase the dynamic range and response speed of sensory neurotransmission to the brain, thereby enhancing closed-loop stability of sensorimotor reflex.

Animals↗
PubMed2000

Habituation and desensitization of the Hering-Breuer reflex in rat.

1. Many processes in mammalian and invertebrate central nervous systems exhibit habituation and/or sensitization of their responses to repetitive stimuli. Here, we studied the adaptive behaviours of the respiratory pattern generator in rat on repetitive vagal-afferent stimulation and compared these behaviours obtained in vivo with the reported effects of such stimuli on synaptic transmission in the corresponding signal pathway in vitro. 2. Sustained (1 min) electrical pulsed stimulation of the vagus nerve elicited the classic Hering-Breuer (HB) reflex slowing of the respiratory rhythm followed by a bi-exponential recovery, and a post-stimulus rebound (PR). The recovery from the HB reflex satisfied the classic criteria of habituation. 3. The fast component of the recovery and the PR were abolished by systemic administration of an NMDA receptor antagonist or electrolytic lesioning of the pontine Kolliker-Fuse nucleus. The characteristics of the fast recovery and PR suggest a vagally induced desensitization of the NMDA receptor-dependent pontine input to the respiratory pattern generator. 4. The slow component of recovery persist after both experimental interventions and accounted for the habituation to the vagal input. The characteristics of the slow recovery in vivo were reminiscent of the reported synaptic accommodation in vitro in the medullary region where vagal afferents terminate. 5. The habituation of vagal input and desensitization of pontine input act in concert to offset the HB reflex. Such simultaneous habituation-desensitization in parallel neural pathways with differing sensitivities to NMDA receptor activation represent a hitherto unknown pairing of dual non-associative learning processes in the mammalian brain.

Animals↗
PubMed2000

Plasticity of cardiorespiratory neural processing: classification and computational functions.

Neural plasticity, or malleability of neuronal structure and function, is an important attribute of the mammalian forebrain and is generally thought to be a kernel of biological intelligence. In this review, we examine some reported manifestations of neural plasticity in the cardiorespiratory system and classify them into four functional categories, integral; differential; memory; and statistical-type plasticity. At the cellular and systems level the myriad forms of cardiorespiratory plasticity display emergent and self-organization properties, use- and disuse-dependent and pairing-specific properties, short-term and long-term potentiation or depression, as well as redundancy in series or parallel structures, convergent pathways or backup and fail-safe surrogate pathways. At the behavioral level, the cardiorespiratory system demonstrates the capability of associative and nonassociative learning, classical and operant conditioning as well as short-term and long-term memory. The remarkable similarity and consistency of the various types of plasticity exhibited at all levels of organization suggest that neural plasticity is integral to cardiorespiratory control and may subserve important physiological functions.

Animals↗
PubMed1999

Short-term potentiation of carotid chemoreflex: an NMDAR-dependent neural integrator.

Repetitive stimulation of the carotid sinus nerve (CSN) elicits a short-term potentiation (STP) of the reflex response in respiratory motor output in mammals. The input-output transformation approximates a leaky integrator with a time constant of several seconds. Here, we showed that STP induced by CSN stimulation in rats was manifested in the reflex response in the amplitude of rhythmic phrenic nerve activity as well as its duration. Moreover, pharmacological blockade of NMDA receptors (NMDAR) resulted in marked increases in the time constants of the equivalent neural integrator in both the STP induction phase (by 10- to 20-fold) and recovery phase (by 1- to 5-fold). Thus, NMDAR serves as a molecular switch that facilitates the integrative processing of CSN inputs by STP.

Animals↗
PubMed1998

Recovery of retching after lesions involving the nucleus of the solitary tract.

The nucleus of the solitary tract (NTS) in the caudal brainstem receives various inputs that trigger vomiting. Chemical (kainic acid) NTS lesions in decerebrate, paralyzed cats temporarily suppressed fictive vomiting induced by different emetics. Subsequently, retching but not expulsion, resumed in 2-3.5 h. Since the NTS does not appear essential for retching, antiemetic drugs targeted at the NTS may not completely suppress vomiting.

Animals↗
PubMed1996

Vestibular effects on upper airway musculature.

The vestibular system produces a variety of compensatory responses to accelerations of the head, which include reflex responses recorded from respiratory muscle nerves of the thorax and abdomen. In order to better understand the functional significance of vestibulo-respiratory reflexes, we investigated the extent to which such responses are also present on muscle nerves of the upper airway. Experiments were conducted on adult cats that were decerebrated, paralyzed, and artificially ventilated. Electrical stimulation of the vestibular nerve using short trains of current pulses evoked reflex responses on the following nerves: recurrent laryngeal, superior laryngeal, pharyngeal branch of the vagus, glossopharyngeal, and hypoglossal. The responses were bilateral and occurred on average within about 15 ms after stimulus onset. The medial and inferior vestibular nuclei were shown to be essential for the reflex, since the responses were abolished by injections of the neurotoxin kainic acid into these nuclei. The widespread presence of vestibular-evoked responses recorded from respiratory muscle nerves of the upper airway. as well as from those of the thorax and abdomen, suggests that one function of vestibulo-respiratory reflexes is to provide adjustments in breathing and airway patency during movements and changes in posture.

Animals↗
PubMed1996

Role of ventral respiratory group bulbospinal expiratory neurons in vestibular-respiratory reflexes.

1. Activation of the vestibular system produces reflex modulation of expiratory muscle activity. The purpose of the present study was to investigate the possible role of bulbospinal expiratory (E) neurons located in the caudal ventral respiratory group (VRG) in mediating vestibulo-respiratory reflexes. Experiments were carried out in decerebrated, paralyzed, and artificially ventilated cats. 2. Electrical stimulation of the vestibular nerve (VN), using short trains of current pulses, elicited bilateral reflex responses on abdominal muscle nerves (ABDNs). This response was not affected by lesions of the cochlear nuclei made by kainic acid injections. The ABDN response typically consisted of a combination of short-latency excitation and long-latency inhibition on the ipsilateral side and, in contrast, a combination of short-latency inhibition and long-latency excitation on the contralateral side. 3. Extracellular recordings were made from 43 caudal VRG bulbospinal E neurons that were activated antidromically from the contralateral upper lumbar spinal cord. More than 80% of these neurons responded to either ipsi- and/or contralateral VN stimulation. The neuronal response consisted of either a combination of excitation and inhibition or only inhibition. The majority of neurons had response patterns appropriate to contribute to the response observed on the contralateral ABDN; however, the latency of the VRG E neuron response was too long to initiate the ABDN response. 4. To further evaluate the contribution of caudal VRG E neurons to the vestibulo-abdominal reflex, ABDN responses were compared before and after sectioning the axons of caudal VRG bulbospinal E neurons where they cross the midline between the obex and first cervical spinal segment. These midsagittal lesions abolished expiratory modulation of ABDN discharge. The lesions also decreased the amplitude of the vestibular-evoked ABDN response but could not abolish the response. The postlesion amplitude was decreased on average to approximately 70% of prelesion values. 5. In conclusion, although the present results indicate that the majority of caudal VRG bulbospinal E neurons respond appropriately to contribute to the vestibulo-abdominal reflex, the reflex largely is unaffected by the removal of caudal VRG E input. The additional descending inputs that are important for mediating the reflex remain to be investigated and may include vestibulospinal and/or reticulospinal tracts.

Abdominal Muscles↗
PubMed1995

Multifunctional ventral respiratory group: bulbospinal expiratory neurons play a role in pudendal discharge during vomiting.

Pudendal motoneurons are activated in phasic bursts during the retching and expulsion phases of vomiting. The resulting contraction of the anal and urethral sphincters serves to maintain continence during the large increase in abdominal pressure that occurs during vomiting. We evaluated the contribution of bulbospinal expiratory neurons located in the portion of the ventral respiratory group (VRG) caudal to the obex (nucleus retroambigualis) to the control of pudendal motoneurons during fictive vomiting in decerebrate, paralyzed cats. Pudendal nerve discharge is abolished by cutting the axons of caudal VRG expiratory neurons as they cross the midline between the obex and C1 before descending in the spinal cord. All caudal VRG expiratory neurons that were antidromically activated from the sacral spinal cord, where the pudendal motor pool (nucleus of Onuf) is located, discharged strongly during the end of the expulsion phase of vomiting. However, only a small proportion of these neurons was active in phase with pudendal discharge during the retching phase. The apparent involvement of caudal VRG expiratory neurons in the control of pudendal motoneurons during vomiting is another example of the multifunctional role that can be played by respiratory-related neurons in the mammalian nervous system.

Animals↗
PubMed1995

Descending pathways necessary for vestibular influences on sympathetic and inspiratory outflow.

The objective of this study was to determine which brain stem regions that have projections to sympathetic preganglionic neurons or phrenic motoneurons ae necessary for vestibulosympathetic or vestibulorespiratory responses in decerebrate cats. Bilateral kainic acid injections into the rostral ventrolateral medulla abolished splanchnic nerve responses to electrical stimulation of the vestibular nerve, suggesting that this region is critical for the production of vestibulosympathetic responses. In contrast, injections into the caudal medullary raphe nuclei had no apparent effect on the responses. Neither the dorsal nor the ventral respiratory group appears to be necessary for mediating vestibular influences on the phrenic nerve, suggesting that nonrespiratory neurons (such as vestibulospinal neurons) may be important for producing vestibulorespiratory responses.

Animals↗
PubMed1995

Ventral respiratory group bulbospinal inspiratory neurons participate in vestibular-respiratory reflexes.

1. The vestibular system responds to accelerations of the head and produces reflex responses that serve a variety of compensatory functions. The neuronal circuitry that mediates vestibulo-respiratory reflexes is largely unknown. The purpose of the present study was to investigate the possible role of bulbospinal inspiratory neurons located in the para-ambigual region of the ventral respiratory group (VRG) in mediating these reflexes. Experiments were carried out in cats that were decerebrated, paralyzed, and artificially ventilated. 2. Activation of the vestibular nerve by electrical stimulation produced prominent bilateral reflex responses recorded from the phrenic nerve, which supplies the diaphragm. The responses could be complex and consisted of a decrease and/or increase in nerve discharge. 3. Extracellular recordings were made from 35 VRG inspiratory neurons that were antidromically activated from the upper cervical spinal cord. Almost one-half of these neurons (15/35, 43%) responded to vestibular stimulation. The neuronal response patterns were consistent with VRG inspiratory neurons contributing to the vestibular reflex response simultaneously recorded from the phrenic nerve. 4. The present results indicate that approximately one-half of VRG bulbospinal inspiratory neurons contribute to vestibulo-respiratory reflexes. These findings are in contrast to our recent neuroanatomic and electrophysiological studies which revealed a paucity of vestibular inputs to the dorsal respiratory group (DRG) located in the ventrolateral nucleus of the solitary tract. Thus there appears to be a difference between inspiratory neurons in the DRG and VRG in regard to participating in vestibulo-respiratory reflexes.

Animals↗
PubMed1991

[The compensatory plasticity of the brain when it is damaged].

A new test for determination of the degree of the compensatory processes after brain damage was proposed in experiments in the cats with one-sided transection of the hemisphere and children with one-sided cerebral palsy. The process of habituation of the skin galvanic reaction was used for this aim.

Adaptation, Physiological↗
PubMed1989

[Functional reorganization in the system of corticotectal connections after unilateral deafferentation of the cortex].

The responses of the cat's collicular neurons to direct stimulation (DCR) of contralateral neocortex were studied in various periods after unilateral dissection of cortico-subcortical connections. The data obtained suggest that, in intact cat's brain, during early hours of postoperative period, and within 1-2 years after the operation, functional specifics of contralateral motor and sensory projections to superior colliculus played a major part in determining basic features of compensatory shifts of the impulse activity of collicular neurons.

Adaptation, Physiological↗
PubMed1985

[Patterns in the development of habituation in the cortical area of the visceral analyzer].

In anesthetized cats, a gradual decrement of direct cortical responses was studied in associative and SII cortical areas, in neuronally isolated and in intact cortex. The habituation of direct cortical responses was more rapid in associative area of the intact cortex after deafferentiation of the cerebral hemisphere than in the neuronally isolated cortex. The mechanism of habituation in intact cortex of animals with neuronally isolated cortex is discussed.

Animals↗