The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is an important determinant of CO2-H+ sensitivity during wakefulness. Bilateral, stainless steel microtubules were implanted into the CFN (N = 9) for injection (0.5–10 μl) of the neurotoxin ibotenic acid. Two or more weeks after implantation of the microtubules, eupneic breathing and CO2-H+ sensitivity did not differ significantly (P > 0.10) from pre-implantation conditions. Injection of ibotenic acid (50 mM) did not significantly alter eupneic PaCO2 (P > 0.10). The coefficient of variation of eupneic PaCO2 was 4.0 ± 0.6 and 3.7 ± 0.4% over the 2 weeks before and after the lesion, respectively. CO2-H+ sensitivity expressed as inspired ventilation/PaCO2 decreased from 2.15 ± 0.17 pre-lesion to 1.58 ± 0.26 l/(min mmHg) 3–6 days post-lesion (P < 0.02, −27%). There was no significant (P > 0.10) recovery of sensitivity between 7 and 10 days post-lesion. The lesion also increased (P < 0.05) the day-to-day variability of this index by nearly 100%. When CO2 sensitivity was expressed as elevated inspired CO2/room air V˙I, values at 7%, but not 3 and 5% inspired CO2, were reduced and more variable (P < 0.05) after the ibotenic acid injections. We conclude that during wakefulness, the CFN contributes relatively more to overall ventilatory drive at high relative to low levels of hypercapnia.

Our objective in this study was to test the hypothesis that focal acidosis (FA) in the cerebellar fastigial nucleus (CFN) of awake goats arising from global brain acidosis induced by increasing inspired CO2 will increase breathing. FA was created by reverse microdialysis of mock cerebral spinal fluid, equilibrated with 6.4, 25, 50, or 80% CO2 through chronically implanted microtubules (cannula). Dialysis with 6.4% CO2 had no significant effects on any physiological parameters. However, microdialysis at higher levels of CO2 increased pulmonary ventilation (V(I)) in one group of studies and decreased V(I) in a second group and the difference between the groups was significant (t = 9.16, P < 0.001). In one group of studies (n = 8), FA with 50 and 80% CO2 significantly increased (P < 0.05) Vi by 16 and 12%, respectively, and significantly increased (P < 0.05) heart rate by 13 and 9%, respectively. In contrast, in another group of studies (n = 6), FA with 25 and 50% CO2 significantly decreased (P < 0.05) Vi by 7 and 10%, respectively. In this group oxygen consumption was decreased during dialysis with 80% CO2. On the basis of histology, we estimate that the increased and decreased responses were associated with FA primarily in the rCFN and cCFN, respectively. We conclude that there are CO2/H+-sensitive neurons in the CFN that do not uniformly affect breathing. In addition, the significant changes in heart rate and oxygen consumption during FA indicate that the CFN can also influence non-respiratory-related control systems.

We investigated the ventilatory effects of the mu-opoiod agonist, DAMGO (1 nM, 500 nL), when injected into the pre-Botz C area of the intact, awake goat. DAMGO injected unilaterally or bilaterally into the pre-Botz C area via chronically implanted microtubules did not change pulmonary ventilation (VE), or respiratory rhythm and pattern during eupneic and hypoxic (PaO2 = 35 mmHg) breathing conditions (n = 4/4 goats), but did increase CO2 sensitivity (VE/PaCO2) (n = 4/4). This contrasts to the typical finding that opioid agonists administered globally depress breathing. Indeed, CO2 sensitivity decreased when DAMGO was injected into the raphe or parapyramidal area in a fifth goat. We also found that bilateral injection of DAMGO into the pre-Botz C periodically disrupts respiratory rhythm and pattern. In one goat breathing 5 and 7% CO2, periods of decreased inspiratory flow and frequency coincided with large, simultaneous diaphragm and abdominal muscle contractions that were 180° out of phase with flow. In a second goat breathing 5 and 7% CO2, periods of phasic abdominal muscle activity were twice the rate of the diaphragm activity. These data likely reflect the in vitro finding that DAMGO depresses inspiratory (I) neurons, disrupting the normal coupling between the pre-Botz C inspiratory rhythm generator and a rostrally located expiratory rhythm generator. Thus, our results not only provide in vivo evidence for the coupled oscillator concept, but also suggest that pre-Botz C I neurons can inhibit CO2 sensitivity. (Supported by NIH 25739 and the Veterans Administration)

We previously reported that in goats with chronically implanted stainless steel microtubules, microdialysis induced focal acidosis in the rostral CFN (rCFN) and caudal CFN (cCFN) increased and decreased pulmonary ventilation (VI), respectively. Here we report that injection of 10ul (n=8) ibotenic acid into the rCFN significantly (P < 0.05) increased both VI (36.1% ± 0.11) and breathing frequency (f) (42% ± 0.3) up to one hour after injection, with no significant effects on tidal volume (VT), mean arterial blood pressure (MABP) or heart rate (HR). 10ul (n=5) ibotenic acid injections into the cCFN did not significantly change VI, f, VT, MABP, or HR up to one hour after injection. However, in all goats, there were balance and posture deficits between 3 to 24 hours after injection. Histology indicated that in all goats portions of both the rCFN and cCFN were lesioned. These lesions did not significantly alter resting PaCO2, but decreased (P < 0.02) whole body CO2 sensitivity by 17%. In contrast, in two goats where the lesions were outside the CFN there was an average increase in the CO2 sensitivity of 52.5% ± 4.5. These data indicate that an intact CFN is an important determinant of CO2 sensitivity and that the rCFN and cCFN have both common and unique contributions to physiological functions. Supported by NIH HL-25739 and by the Department of Veterans Affairs.

The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is necessary for the hyperpnea to meet the gas exchange needs of submaximal exercise. Bilateral stainless steel microtubules were implanted in the cerebellum inside (n = 12) or outside (n = 2) the CFN for injection (0.5 to 10 microl) of the neurotoxin ibotenic acid. All goats had difficulty maintaining normal posture and walking for up to 1 mo after the implantation of the microtubules and again for hours or days after the neurotoxin was injected. Postmortem histology indicated there were 55% fewer living neurons (P < 0.001, n = 9, 3,720 +/- 553 vs. 1,670 +/- 192) in the CFN of the experimental goats compared with a control group of goats. As is typical for goats before implantation of the microtubules, the decrease in arterial Pco(2) from rest during mild and moderate treadmill exercise was 2.0 +/- 0.39 and 3.5 +/- 0.45 Torr, respectively. Implantation of the microtubules did not significantly change this exercise hyperventilation. However, neurotoxic lesioning with 10 mul ibotenic acid significantly (P < 0.05) attenuated the decrease in arterial Pco(2) by 1.3 and 2.8 Torr at the first and second workload, respectively. The modest attenuation of the exercise hypocapnia at both workloads in CFN-lesioned goats suggests that the CFN is part of the control system that enables the ventilatory response to meet the gas exchange requirements of submaximal exercise.

Controversies regarding the role of pontine nuclei in the control of breathing and paucity of studies during physiologic conditions have prompted us to chronically implant microtubules into the pons of 2 goats, one caudally (bilateral) and one rostrally (unilateral). Both goats recovered uneventfully and 3 weeks thereafter resting PaCO2 and CO2 sensitivity were near normal. However, both goats had abnormal post-inspiratory diaphragm activity following implantation. Injection of atropine (500nL, 5mM) during the day decreased CO2 sensitivity without altering resting PaCO2. Dialysis of atropine (50mM) at night disrupted activation patterns of respiratory muscles and depressed and destabilized breathing which was state independent. Injection of ibotenic acid during the day also acutely destabilized breathing and disrupted coordination of respiratory muscles, transiently altered PaCO2 and CO2 sensitivity, and chronically altered REM generating mechanisms at night. Subsequent histological analysis of the pons of both goats implicates the medial parabrachial nucleus in the caudally implanted goat and the pedunculopontine tegmental nucleus in the rostrally implanted goat. These findings suggest that chronically instrumented goats are a viable model to further elucidate the role of pontine nuclei in the control of breathing. Supported by NIH HL-25739 and by the Department of Veterans Affairs.

Our aim was to determine the effects of carotid body denervation (CBD) on the ventilatory responses to focal acidosis and ibotenic acid (IA) injections into the medullary raphe area of awake, adult goats. Multiple microtubules were chronically implanted into the midline raphe area nuclei either before or after CBD. For up to 15 days after bilateral CBD, arterial PCO2 (PaCO2) (13.3 +/- 1.9 Torr) was increased (P < 0.001), and CO2 sensitivity (-53.0 +/- 6.4%) was decreased (P <0.001). Thereafter, resting PaCO2 and CO2 sensitivity returned (P <0.01) toward control, but PaCO2 remained elevated (4.8 +/- 1.9 Torr) and CO2 sensitivity reduced (-24.7 +/- 6.0%) > or =40 days after CBD. Focal acidosis (FA) at multiple medullary raphe area sites 23-44 days post-CBD with 50 or 80% CO(2) increased inspiratory flow (Vi), tidal volume (Vt), metabolic rate (VO2), and heart rate (HR) (P <0.05). The effects of FA with 50% CO2 after CBD did not differ from intact goats. However, CBD attenuated (P <0.05) the increase in Vi, Vt, and HR with 80% CO2, but it had no effect on the increase in VO2. Rostral but not caudal raphe area IA injections increased Vi, BP, and HR (P < 0.05), and these responses were accentuated (P <0.001) after CBD. CO2 sensitivity was attenuated (-20%; P <0.05) <7 days after IA injection, but thereafter it returned to prelesion values in CBD goats. We conclude the following: 1) the attenuated response to FA after CBD provides further evidence that the carotid bodies provide a tonic facilitory input into respiratory control centers, 2) the plasticity after CBD is not due to increased raphe chemoreceptor sensitivity, and 3) the "error-sensing" function of the carotid body blunts the effect of strong stimulation of the raphe.

nucleus do not uniformly affect breathing of awake goats chemoreceptors in the cerebellar fastigial + /H 2 CO You might find this additional info useful... physiology, especially those papers emphasizing adaptive and integrative mechanisms. It is published 12 times a publishes original papers that deal with diverse area of research in applied

To gain insight into why there are chemoreceptors at widespread sites in the brain, mircrotubules were chronically implanted at two or three sites in the medullary raphe nuclei of adult goats (n = 7). After >2 wk, microdialysis (MD) probes were inserted into the microtubules to create focal acidosis (FA) in the awake state using mock cerebral spinal fluid (mCSF) equilibrated with 6.4% (pH = 7.3), 50% (pH = 6.5), or 80% CO(2) (pH = 6.3), where MD with 50 and 80% CO(2) reduces tissue pH by 0.1 and 0.18 pH unit, respectively. There were no changes in all measured variables with MD with 6.4% at single or multiple raphe sites (P > 0.05). During FA at single raphe sites, only 80% CO(2) elicited physiological changes as inspiratory flow was 16.9% above (P < 0.05) control. However, FA with 50 and 80% CO(2) at multiple sites increased (P < 0.05) inspiratory flow by 18.4 and 30.1%, respectively, where 80% CO(2) also increased (P < 0.05) tidal volume, heart rate, CO(2) production, and O(2) consumption. FA with 80% CO(2) at multiple raphe sites also led to hyperventilation (-2 mmHg), indicating that FA had effects on breathing independent of an increased metabolic rate. We believe these findings suggest that the large ventilatory response to a global respiratory brain acidosis reflects the cumulative effect of stimulation at widespread chemoreceptor sites rather than a large stimulation at a single site. Additionally, focal acidification of raphe chemoreceptors appears to activate an established thermogenic response needed to offset the increased heat loss associated with the CO(2) hyperpnea.

The major objective of this study was to gain insight into whether under physiological conditions medullary raphe area neurons influence breathing through CO2/H+ chemoreceptors and/or through a postulated, nonchemoreceptor modulatory influence. Microtubules were chronically implanted into the raphe of adult goats ( n = 13), and breathing at rest (awake and asleep), breathing during exercise, as well as CO2 sensitivity were assessed repeatedly before and after sequential injections of the neurotoxins saporin conjugated to substance P [SP-SAP; neurokinin-1 receptor (NK1R) specific] and ibotenic acid (IA; nonspecific glutamate receptor excitotoxin). In all goats, microtubule implantation alone resulted in altered breathing periods, manifested as central or obstructive apneas, and fractionated breathing. The frequency and characteristics of the altered breathing periods were not subsequently affected by injections of the neurotoxins ( P > 0.05). Three to seven days after SP-SAP or subsequent IA injection, CO2 sensitivity was reduced ( P < 0.05) by 23.8 and 26.8%, respectively, but CO2 sensitivity returned to preinjection control values >7 days postinjection. However, there was no hypoventilation at rest (awake, non-rapid eye movement sleep, or rapid eye movement sleep) or during exercise after these injections ( P > 0.05). The neurotoxin injections resulted in neuronal death greater than three times that with microtubule implantation alone and reduced ( P < 0.05) both tryptophan hydroxylase-expressing (36%) and NK1R-expressing (35%) neurons at the site of injection. We conclude that both NK1R- and glutamate receptor-expressing neurons in the medullary raphe nuclei influence CO2 sensitivity apparently through CO2/H-expressing chemoreception, but the altered breathing periods appear unrelated to CO2 chemoreception and thus are likely due to non-chemoreceptor-related neuromodulation of ventilatory control mechanisms.