EOG responses in anesthetized freely breathing rats

In mammals, access of odor molecules to the olfactory receptor neurons is controlled by respiratory activity. Thus, anesthetized, freely breathing rats were used to record from the olfactory mucosa in the intact nasal cavity (electroolfactogram or EOG) so as to study global response characteristics to odor stimuli. During alternation of the inspiratory phases of odor sampling and expiratory phases, the response was a succession of individual EOG events synchronized with respiration. These were characterized by a steep decrease that started approximately 100-150 ms after the beginning of inhalation, reached its maximum at the transition between inspiration and expiration and was followed by a slower rise until the next inhalation. They were greater during the first respiratory cycles following odor stimulation onset. Thereafter their amplitudes decreased throughout odor delivery, but a significant EOG signal was still present at the end of short (10 s) and long (60 s) odor presentations. Amplitude increased with odor concentration, but much less than expected from concentration changes. Lastly, for some odors EOG responses persisted well beyond the end of stimulation. These results are in agreement with the respiratory synchronization of mitral cell activities observed during short odor presentations and long duration odor exposures. They underline again the importance of taking into account the respiratory activity in studies on the functioning of the olfactory system.     

Behavioural and cardiovascular responses to electrical stimulation of the medulla oblongata of the cat

Effects of stimulation of the nucleus tractus solitarii, the dorsal motor nucleus of the vagus, the nucleus reticularis paramedianus, and the nucleus cuneatus were studied in free-moving cats. Stimulation of the medullary nuclei that are known to be involved in the central nervous control of cardiovascular functions might activate preprogrammed motor responses such as licking and sniffing, and induce complex behavioural response patterns such as sleep or flight reaction. Moreover, both lever-pressing for rewarding brain stimulation, and eating in food deprived cats might be modulated by these stimulations. In a shuttle box the cats showed no tendency toward shuttling during stimulation, except the stimulation of the nucleus reticularis paramedianus which produced aversion. The cardiovascular and respiratory effects varied parallel with the behavioural responses. It is concluded that the medullary nuclei related to visceral functions are capable of affecting somatomotor behaviour either directly on the motor system, or by inducing complex response patterns in which somatomotor and visceral responses are integrated.     

Synaptic responses of medulla oblongata neurons to stimulation of the spinal stepping atria in the cat

Synaptic responses of medulla oblongata (bulbar) neurons to microstimulation of stepping points in the spinal dorsolateral funiculi were recorded in decrebrate cats. Upon stimulation of the stepping point both in the ipsi- and contralateral funiculi, 40% of the neurons generated synaptic responses; the remaining cells responded to stimulation of only one stepping point. A part of the bulbar neurons responds to stimulation of stepping points both at the C₂ and Th₁₂ level. The latent periods of the synaptic responses of the bulbar neurons to stimulation of the stepping point at the C₂ level were in the 2–10 msec range. The data obtained indicate that bulbar neurons, along with propriospinal neurons, can participate in evoking locomotion upon stimulating the stepping point.Institute of Information Transmission Problems, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 328–333, May–June, 1991.     

Ventrolateral medulla mechanisms involved in cardiorespiratory responses to central chemoreceptor activation in rats

A rise in arterial Pco(2) stimulates breathing and sympathetic activity to the heart and blood vessels. In the present study, we investigated the involvement of the retrotrapezoid nucleus (RTN) and glutamatergic mechanisms in the B?tzinger/C1 region (B?tz/C1) in these responses. Splanchnic sympathetic nerve discharge (sSND) and phrenic nerve discharge (PND) were recorded in urethane-anesthetized, sino-aortic-denervated, vagotomized, and artificially ventilated rats subjected to hypercapnia (end-expiratory CO(2) from 5% to 10%). Phrenic activity was absent at end-expiratory CO(2) of 4%, and strongly increased when end-expiratory CO(2) reached 10%. Hypercapnia also increased sSND by 103 ± 7%. Bilateral injections of the GABA-A agonist muscimol (2 mM) into the RTN eliminated the PND and blunted the sSND activation (Δ = +56 ± 8%) elicited by hypercapnia. Injections of NMDA receptor antagonist AP-5 (100 mM), non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 100 mM) or metabotropic glutamate receptor antagonist (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG; 100 mM) bilaterally into the B?tz/C1 reduced PND (Δ = +43 ± 7%, +52 ± 6% or +56 ± 11%, respectively). MCPG also reduced sSND (Δ = +41 ± 7%), whereas AP-5 and DNQX had no effect. In conclusion, the increase in sSND caused by hypercapnia depends on increased activity of the RTN and on metabotropic receptors in the B?tz/C1, whereas PND depends on increased RTN activity and both ionotropic and metabotropic receptors in the B?tz/C1.     

Immunohistochemical mapping of adrenomedullin in the human medulla oblongata

We studied by immunocytochemistry the expression of adrenomedullin (AM) in the human medulla oblongata, sampled from 13 adult subjects (mean age: 38 years), whose medical history was negative for neurological and neurovascular pathologies. Immunoreactive neurons were found in the medulla oblongata with statistically significant differences among the various nuclei (one-way ANOVA, P < 0.001). The hypoglossal nucleus showed higher AM expression than that of the spinal tract of the trigeminal nerve (P < 0.05), solitary tract nucleus (P < 0.05), nucleus intercalatus (P < 0.05), and area postrema (P < 0.05). The arcuate nucleus and inferior olivary nuclear complex showed lower AM expression than the hypoglossal nucleus (P < 0.001), vestibular nuclei (P < 0.01), cuneate and gracile nuclei (P < 0.05), lateral column of the reticular formation (P < 0.05), and nucleus ambiguous (P < 0.05). Furthermore the nuclei were grouped with reference to their function, into somatic sensitive nuclei, somatic motor nuclei, visceral nuclei, reticular formation, and nuclei involved in cerebellar functions. The ANOVA revealed statistically significant differences (P < 0.001) in mean AM scores among the different groups. Nuclei involved in cerebellar function showed the lowest mean AM score (P < 0.05). The difference in AM score between somatic motor nuclei and visceral nuclei was also statistically significant (P < 0.05). Widespread AM immunoreactivity in the nuclei of the medulla oblongata may account for the role of the peptide in neuronal function and regulation of regional blood flow. Differences in the expression of AM in the nuclei studied indicate the different involvement of AM in neurotransmission and neuromodulation.     

Response of respiratory neurons of the medulla oblongata to the septum stimulation in hypoxia

In the oxygen deficiency conditions, we studied influence of irritation of ventral (BNST), lateral (LSN) and medial (MSN) nuclei of the septum on the impulse activity of the bulbar respiratory neurons and on respiration. Phases of hypoxia were the model of experiment. In conditions of normal atmospheric pressure, the electrical stimulation of BNST, LSN and MSN nuclei of the septum exerted inhibiting as well as activating influence with the inhibiting influence prevailing. In difficult conditions of hypoxia (7.5-8 thousand meters) on the reduction of the impulse activity of neurons, stimulation of septum nucleuses induced uncharacteristic reactions of those neurons.     

Substance P in the ventrolateral medulla oblongata regulates ventilatory responses.

Local injection of substance P (SP) into the ventral portion of the nucleus gigantocellularis, nucleus reticularis lateralis, and nucleus retrofacialis of the ventrolateral medulla oblongata (VLM) or direct application on the ventral surface of the medulla oblongata caused marked stimulation of tidal volume (VT) and/or minute ventilation (VE). The ventilatory response to hypoxia was significantly blunted after SP in the VLM but not in the dorsal medulla oblongata (DM) (nucleus tractus solitarius). The SP antagonist [D-Pro2,D-Trp7,9]SP almost completely inhibited this response when applied locally to a wide area of the superficial layer of the VLM but not of the DM. Unilateral or bilateral application of 0.3-1.5 nmol of the SP antagonist in the VLM (corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment) markedly attenuated the response to a 5% CO2 inhalation. The inhibition of the CO2 response was seen after [D-Pro2,D-Trp7,9]SP in the rostral areas of the medulla oblongata corresponding to the corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment of the cervical cord. Electric somatosensory-induced ventilatory stimulation could be depressed by approximately 70% by [D-Pro2,D-Trp7,9]SP locally applied on the surface of the VLM. We conclude that SP is involved in the hypoxic, hypercapnic, and somatosensory ventilatory responses in the rat. However, these respiratory reflexes are mediated via different neuronal pools in the medulla oblongata, mainly the VLM.     

Effects of focal cooling of medulla oblongata structures on quiet breathing in cats

Experiments were carried out on 16 anaesthetized, non-paralysed cats to determine the effects of unilateral, successive focal cooling of the nuclei of the dorsal and ventral respiratory groups (DRG, VRG) of the medulla oblongata on quiet breathing parameters. The results of cold block tests of the respiratory nuclei showed that: 1. Compared with the control state, cooling of the ventrolateral part of the nucleus solitarii (vl. NTS) and the rostral part of the nucleus retroambigualis (r. NRA) to 20 degrees C or 15 degrees C decreased the respiration rate (p less than 0.001), prolonged the inspiration time (p less than 0.01 and p less than 0.001 respectively) and the development of apneustic breathing. A decrease in the inspiratory pleural pressure values (p less than 0.01) was found after cooling the r. NRA region to 15 degrees C. In 45% of the cases of cooling of the vl. NTS and 66.7% of cooling of the r. NRA to 15 degrees C, an incidence of short inspiratory efforts was observed. 2. Focal cooling of the nucleus retrofacialis (nucl. RF) region to 20 degrees C always arrested rhythmic respiration. 3. The effects of unilateral focal cooling of the respiratory nuclei were always bilaterally symmetrical and, after discontinuing cooling, reversible. 4. The findings indicate that the inspiratory neurones of the r. NRA participate more in regulation of the intensity of inspiration than those of the vl. NTS, while the nucl. RF region may be a part of central regulatory mechanisms essential for the maintenance of rhythmic breathing in cats.     

大鼠延髓尾端加压区微量注射L—精氨酸对血压、心率和肾灌流压的影响

目的：研究NO前体L-Arg微量注入大鼠延髓尾端加压区（CPA）对心血管活动的影响。并探讨其可能的机制。方法：采用延髓腹外侧部微量满面主射法,以整体灌流肾为模型观察与NO代谢有关的试剂对心血管活动的影响。结果：（1）CPA内微量注入L-Arg(60-100nmodl)。动脉血压与心率呈剂量依赖性下降,肾灌流压下降,与生理盐水对照,差异有显著意义;（2）预先在CPA内注入鸟苷酸环化酶抑制剂甲基蓝可取消L-Arg的降压降肾灌流压作用;（3）CPA内注入lu,AP上升,如预先注入L-Arg后5min再注入L-Glu,L-Glu的升压效应被衰减,期衰减程度与L-Arg是剂量依赖性关系。结论：CPA内的L-Arg-NO通路参与延髓心血管中枢对AP的调控,其机制之一可能是通过cGMP抑制CPA内谷氨酸能神经突触。     

Evoked potentials of the medulla oblongata of the skate in response to stimulation of lateral line nerves

The characteristics of the bioelectrical reactions of structures of the medulla oblongata connected with lateral line electro- and mechanoreceptor were investigated in acute experiments on skates under urethane anesthesia. The parameters of the evoked potentials (EP) are characteristic of each of the lateral line nerves studied. A comparison of the characteristics of the fast and slow components of the EP obtained by stimulation of nerves of the medulla oblongata makes it possible to state a hypothesis concerning the presynaptic origin of the fast and the postsynaptic origin of the slow components of the EP. A dependence of the magnitude of the EP on the amplitude of the stimulus and on the location of the active electrode was found. The location of the focus of maximum activity was determined for each of the nerves investigated. A correlation was established between some parameters of the bioelectrical reactions of the medulla oblongata and the morphophysiological properties of the fibers which make up the nerves studied. The results obtained make it possible to assume the presence in the medulla oblongata of spatially arranged structures responsible for the development of the bioelectrical effects in response to stimulation of the lateral line nerves of fish.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 284–292, May–June, 1971.     

Comparison of identified mitral and tufted cells in freely breathing rats: II. Odor-evoked responses

Mitral and tufted cells are the 2 types of output neurons of the main olfactory bulb. They are located in distinct layers, have distinct projection patterns of their dendrites and axons, and likely have distinct relationships with the intrabulbar inhibitory circuits. They could thus be functionally distinct and process different aspects of olfactory information. To examine this possibility, we compared the odor-evoked responses of identified single units recorded in the mitral cell layer (MCL units), in the core of the external plexiform layer (not at the glomerular border tufted cells), or at the glomerular border of this layer (GB tufted cells) of the entire olfactory bulb. Differences between mitral and tufted cells were observed only when subtle aspects of the responses were explored, such as the firing rate per respiratory cycle or the distribution of firing activity along the respiratory cycle. By contrast, more clear differences were found when the 2 subtypes of tufted cells were examined separately. GB units were significantly more responsive, had significantly higher firing activity, and showed greater activity at the transition between inspiration and expiration. The projection-type tufted cells situated closer to the entrance of the olfactory bulb may thus form a distinct physiological class of output neurons and differ from mitral cells and other tufted cells in the manner of processing olfactory information.     

Influence of the stimulation of central chemoreceptors on the gastric mucosal blood flow in artificially ventilated and spontaneously breathing rats.

Respiratory failure coincides frequently with the occurrence of gastric ulceration. In advanced respiratory insufficiency hypoxemia is often accompanied by hypercapnia, which is the stimulus for central chemoreceptors as well as for carotid body chemoreceptors. The purpose of the work was to investigate the reflex effect of stimulation of central chemoreceptors on gastric mucosal blood flow (GMBF) in the rat. Central chemoreceptors were stimulated by a gas mixture composed of 10% carbon dioxide, 50% oxide and 40% nitrogen. In artificially ventilated and spontaneously breathing animals, the stimulation of central chemoreceptors caused a significant increase in gastric mucosal vascular resistance, accompanied by a marked decline in blood flow. We hypothesize that in patients with respiratory insufficiency accompanied by hypercapnia, the reflex impairment of GMBF may contribute to gastric ulceration.