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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.

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.

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.

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.

The convergence of visceral and somatic afferent systems in the secondary somatosensory areas of the cat cortex was studied by means of evoked potentials. The suprathreshold stimulation of the sciatic and brachial plexus nerves depressed the test potentials evoked by the pelvic and mesenteric nerves stimulation. Maximal depression was observed at paired stimulation of visceral nerves. Comparison of the data obtained with mono- and bimodal stimulation suggests that duration of the response restoration period depends on the functional groups of neurons.

Reactions of neurons without background activity ("silent" neurons) on long-lasting stimulation of mesenteric nerves were studied in cats anesthetized with chloralose 65-70 mg/kg) and paralyzed with flaxedile. It is shown that the "silent" neurons of the parietal and first projections areas are characterized by habituation during long-lasting stimulation of visceral nerves. Habituation developed faster in the parietal cortex and in the focus of maximal activity of the first somatosensory areas as compared to the second somatosensory area. The particularities of neuronal habituation in the cortex on visceral stimulation are discussed.

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.

Interaction of visceral and somatic afferents and changes of neuronal discharges in focus of maximal activity of cerebral cortex on repetitive stimulation of visceral afferents were studied in anesthetized immobilized cats. Habituation was shown to develop in the cortex. Visceral and somatic impulses appeared to converge on cortical neurons in the S1. Simultaneous stimulation of the visceral and somatic afferents revealed domination of visceral influences. The elements of cortex seem to have unequal plasticity which can provide premises for learning process.

Arterial blood pressure, heart rate and dynamic of neuronal activity in the cerebral cortex and medulla oblongata were selected as indices of the visceral habituation to stimulation of the splanchnic and mesenteric nerves. The habituation was more rapid in primary projection zones of the cerebral cortex rather than in the medulla oblongata nuclei and more obvious in unspecific structures of the brain (associative cortex, gigantocellular, reticular and ventral nuclei of the medulla oblongata). Evoked potentials recorded in the area S1 during long-term stimulation of the pelvic nerve revealed development of the habituation in immobilized cats.

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.