Microinjection of acetazolamide into the fastigial nucleus augments respiratory output in the rat.

The rostral fastigial nucleus (FNr) of the cerebellum facilitates the respiratory response to hypercapnia. We hypothesized that some FNr sites are chemosensitive to focal tissue acidosis and contribute, at least partially, to respiratory modulation. Minute ventilation (VE) was recorded in 21 anesthetized and spontaneously breathing rats. Acetazolamide (AZ; 50 microM) was microinjected unilaterally into the FNr while an isocapnic condition was maintained throughout the experiment. AZ (1 or 20 nl) injection into the FNr significantly elevated VE (46.0 +/- 6.7%; P < 0.05), primarily via an increase in tidal volume (31.7 +/- 3.8%; P < 0.05), with little effect on arterial blood pressure. This augmented ventilatory response was initiated at 6.3 +/- 0.8 min and reached the peak at 19.7 +/- 4.1 min after AZ administration. The same dose of AZ delivered into the interposed and lateral cerebellar nuclei, or vehicle injection into the FNr, failed to elicit detectable cardiorespiratory responses. To determine whether the ventilatory response to AZ injection into the FNr resulted from an increase in respiratory central drive, the minute phrenic nerve activity (MPN) was recorded in seven paralyzed and ventilated rats. Similar to VE, MPN was increased by 38.9 +/- 8.9% (P < 0.05) after AZ administration. Our results suggest that elevation of CO2/H+ within the FNr facilitates respiratory output, supporting the presence of ventilatory chemoreception in rat FNr.

Fastigial nucleus-mediated respiratory responses depend on the medullary gigantocellular nucleus.

Electrical stimulation of the rostral fastigial nucleus (FNr) alters respiration via activation of local neurons. We hypothesized that this FNr-mediated respiratory response was dependent on the integrity of the nucleus gigantocellularis of the medulla (NGC). Electrical stimulation of the FNr in 15 anesthetized and tracheotomized spontaneously breathing rats significantly altered ventilation by 35.2 +/- 11.0% (P < 0.01) with the major effect being excitatory (78%). This respiratory response did not significantly differ from control after lesions of the NGC via bilateral microinjection of kainic or ibotenic acid (4.5 +/- 1.9%; P > 0.05) but persisted in sham controls. Eight other rats, in which horseradish peroxidase (HRP) solution was previously microinjected into the left NGC, served as nonstimulation controls or were exposed to either 15-min repeated electrical stimulation of the right FNr or hypercapnia for 90 min. Histochemical and immunocytochemical data showed that the right FNr contained clustered HRP-labeled neurons, most of which were double labeled with c-Fos immunoreactivity in both electrically and CO(2)-stimulated rats. We conclude that the NGC receives monosynaptic FNr inputs and is required for fully expressing FNr-mediated respiratory responses.

Modulation of respiratory motor output by cerebellar deep nuclei in the rat.

The present study was undertaken to determine what roles the various cerebellar deep nuclei (CDN) play in modulation of respiration, especially during chemical challenges. Experiments were carried out in 12 anesthetized, tracheotomized, paralyzed, and ventilated rats. The integrated phrenic nerve activity (integralPN) was recorded as an index of respiratory motor output. A stimulating electrode was sequentially placed into the fastigial nucleus (FN), the interposed nucleus, and the lateral nucleus. Only stimulation of the FN significantly altered respiration, primarily via increasing respiratory frequency associated with a pressor response. The evoked respiratory responses persisted after blocking the pressor response via pretreatment with phenoxybenzamine or use of transient stimulation (<2 s) but were abolished by microinjection of kainic acid into the FN. To test the involvement of FN neurons in respiratory chemoreflexes, ventilation with hypercapnic gases mixture and intravenous injection of sodium cyanide were applied before and after CDN lesions induced by kainic acid. CDN lesions did not significantly alter eupneic breathing, but FN lesions attenuated the respiratory response to hypercapnia and sodium cyanide. We conclude that, with respect to the CDN in the rat, FN neurons uniquely modulate respiration independent of cardiovascular effects and facilitate respiratory responses mediated by activation of CO(2) and O(2) receptors.

Role of the Bötzinger complex in fastigial nucleus-mediated respiratory responses.

We have reported that the phrenic neurogram (PN) is modulated by stimulation of the fastigial nucleus (FN) of the cerebellum. The present study was undertaken to search for brainstem site(s) involved in the FN efferent pathway to modulate phrenic nerve activities. Experiments were performed on 35 anesthetized, paralyzed, and ventilated cats, using the PN as the index of the respiratory motor output. Results showed that bilateral electrolytic lesions of the red nucleus (RN), the paramedian reticular nucleus (PRN), or the pontine respiratory group (PRG) had little effect on the ability of FN stimulation to modulate the respiratory output. However, the modulation was abolished by bilateral electrolytic lesions of the Bötzinger complex (BötC). Further studies showed that bilateral chemical inactivation of BötC neurons produced by topical microinjection of kainic acid or cobalt chloride failed to abolish the modulation. We concluded that fibers of passage, not synapses or cell bodies in the BötC, were involved in the modulatory effect of FN stimulation on the PN. The RN, PRN, and PRG appear not to be important in the neural circuitry responsible for the FN modulation of the phrenic activity.

Transient respiratory augmentation elicited by acute head-down tilt in the anesthetized cat.

Acute head-down tilt (AHDT, -30 degrees) in humans induces a transient ventilatory augmentation for 1-2 min accompanied by a high venous return. However, the mechanisms underlying this respiratory response remain obscure because of limitations of experiments carried out in human subjects. The present study was undertaken to determine whether AHDT-induced respiratory augmentation exists in the anesthetized, paralyzed, and ventilated cat and, if so, whether this response depends on 1) the cerebellum, 2) the carotid sinus (CS) and/or vagal afferents, and 3) elevation of central venous return. The integrated phrenic neurogram, arterial blood pressure, central venous pressure (CVP), and end-tidal PCO2 were recorded before, during, and after AHDT. The results showed that AHDT produced a transient ( approximately 2 min) enhancement of minute phrenic activity (approximately 30%) primarily via an increase in peak integrated phrenic neurogram amplitude associated with a remarkable elevation of CVP (approximately 3 min). Cerebellectomy, CS denervation, bilateral vagotomy, or clamping CVP did not affect the presence of the AHDT-induced minute phrenic activity response. These findings demonstrate that the anesthetized cat is a suitable model for investigating the mechanisms involved in AHDT-induced respiratory augmentation. Preliminary studies suggest that this response does not require the cerebellum, CS/vagal afferents, or an associated rise in central venous return.

Cerebellar modulation of cough motor pattern in cats.

Cerebellar modulation of cough motor pattern in cats. J. Appl. Physiol. 83(2): 391-397, 1997.-The cerebellum modulates respiratory muscle activity in part via its influence on the central respiratory pattern generator. Because coughing requires well-coordinated respiratory muscle activity, studies were conducted to determine whether the cerebellum influences the centrally generated cough motor pattern. Integrated phrenic and lumbar efferent neurograms (PN and LN, respectively) were monitored in decerebrated, paralyzed, and ventilated cats. Mechanical probing of the intrathoracic trachea was used to evoke fictive coughs; i.e., large increases in PN and LN amplitudes. Cerebellectomy resulted in a decrease in the number of coughs per trial (cough frequency) and LN peak amplitudes without any consistent change in PN peak amplitudes. Cerebellar nuclei [the rostral interposed nucleus (INr) and the rostral fastigial nucleus (FNr)] known to be involved in respiratory control were ablated to determine their potential role in the cough response. Control (eupneic) respiratory frequency was not affected by cerebellectomy or INr/FNr lesions. Cough frequency was depressed by lesion of the INr but not by ablation of the FNr. No significant changes in PN and LN amplitudes were observed after lesion of either the INr or FNr. These results suggest that the cerebellum, specifically the INr, is involved in modulation of the frequency of centrally generated coughing.

Involvement of the fastigial nuclei in vagally mediated respiratory responses.

Previous studies have demonstrated that the cerebellum, especially the fastigial nucleus (FN), is capable of modulating respiratory responses to chemical and mechanical stimuli. Because there is evidence to show projections from vagal afferents to the FN, the goal of this study was to determine the role of the FN in the respiratory reflexes elicited by activation of vagal afferents. Experiments were performed in anesthetized (chloralose), paralyzed, and artificially ventilated cats with an occipital exposure of the cerebellum. Administration of capsaicin (Cap; 5-10 micrograms/kg) via the right external jugular vein at the end of inspiration and application of lung inflation (LI; 10 cmH2O) during inspiration were carried out to stimulate nonmyelinated and myelinated vagal afferents, respectively. The phrenic neurogram was recorded as an index of the respiratory motor output. Control cardiorespiratory variables [expiratory duration (TE), arterial blood pressure] and their immediate responses to stimuli were compared before and after bilateral lesions of the FN. The results showed the following. 1) Cap injection and LI resulted in a dramatic increase in TE (apnea). 2) FN lesions did not significantly alter the control TE; however, the apneic duration induced by Cap injection was prolonged. 3) Neither FN lesions nor cerebellectomy affected the apneic duration that resulted from application of LI. 4) Cold blockade of the vagi (6-8 degrees C) eliminated the respiratory responses elicited by LI but not Cap injection; vagotomy abolished the responses to both stimuli. 5) FN lesions did not change the control ABP or its responses to either LI or Cap injection. It is concluded that the FN is involved in vagally mediated respiratory reflexes elicited by activation of nonmyelinated (C-fiber) vagal afferents.

Respiratory-related neurons of the fastigial nucleus in response to chemical and mechanical challenges.

Responses of cerebellar respiratory-related neurons (CRRNs) within the rostral fastigial nucleus and the phrenic neurogram to activation of respiratory mechano- and chemoreceptors were recorded in anesthetized, paralyzed, and ventilated cats. Respiratory challenges included the following: 1 ) cessation of the ventilator for a single breath at the end of inspiration (lung inflation) or at functional residual capacity, 2) cessation of the ventilator for multiple breaths, and 3) exposure to hypercapnia. Nineteen CRRNs having spontaneous activity during control conditions were characterized as either independent (basic, n = 14) or dependent (pump, n = 5) on the ventilator movement. Thirteen recruited CRRNs showed no respiratory-related activity until breathing was stressed. Burst durations of expiratory CRRNs were prolonged by sustained lung inflation but were inhibited when the volume was sustained at functional residual capacity; it was vice versa for inspiratory CRRNs. Multiple-breath cessation of the ventilator and hypercapnia significantly increased the firing rate and/or burst duration concomitant with changes noted in the phrenic neurogram. We conclude that CRRNs respond to respiratory inputs from CO2 chemo- and pulmonary mechanoreceptors in the absence of skeletal muscle contraction.

Fostering science education and science careers at the University of Kentucky.

The Outreach Center for Science and Health Career Opportunities opened at the University of Kentucky Medical Center in July 1993, to provide a central site of coordination for the university's science education activities designed to link those "doing science" at the medical center with students, teachers, and the general population throughout Kentucky. By providing an infrastructure for outreach programs and by being highly visible to the public, the center attracts extramural funding, allows tracking of the program's students, and facilitates the development of science education partnerships between the university of Kentucky communities. The rationale for establishing the center, methods of operation, and impact on the region's science literacy problem are discussed.

Medullary respiratory neuronal activity modulated by stimulation of the fastigial nucleus of the cerebellum.

The ability of the rostral fastigial nucleus (FNr) of the cerebellum to modulate medullary respiratory neuronal activity was examined in 17 anesthetized, paralyzed and ventilated cats. A bipolar stimulating electrode was positioned into the FNr and tungsten microelectrodes used to record units within the nucleus tractus solitarius (NTS), nucleus ambiguus (NA) and nucleus retroambigualis (NRA). Transient stimuli (< 150 microA, 5-200 Hz) were delivered during inspiration or expiration, and the effects noted on medullary neuronal activity and the phrenic neurogram. The results showed that FNr stimulation: (1) modulated inspiratory and expiratory neuronal (ramp-, early- and late-inspiratory and stage I and II expiratory) discharges recorded from the NTS, NA and NRA (n = 67, 14 and 28) when stimuli (> or = 20-50 Hz) were delivered during either the inspiratory or expiratory phases; (2) terminated the burst durations of inspiratory (77%) and expiratory (94%) neurons with stimulus-response latencies of 28.2 +/- 3.1 ms (inspiratory) and 29.4 +/- 3.6 ms (expiratory); (3) elicited changes in phrenic neurogram concomitant with the effects noted on medullary neuronal activities; (4) failed to change heart rate and arterial blood pressure; and (5) did not affect medullary neuronal and phrenic nerve activity following kainic acid injection into the FNr. We conclude that activation of the FNr (likely its cell bodies) can modulate the respiratory output via influences on medullary respiratory-related neurons. The primary cerebellar effect across all sub-types of respiratory neurons was early termination.

Hypoxic respiratory responses attenuated by ablation of the cerebellum or fastigial nuclei.

The general contribution of the cerebellum to hypoxic respiratory responses and the special role of the fastigial nucleus (FN) in the hypoxic respiratory reflex mediated via peripheral chemoreceptors were investigated in anesthetized and spontaneously breathing cats. Seven cats were exposed to isocapnic progressive hypoxia before and after cerebellectomy by decreasing the fractional concentration of end-tidal O2 (FETO2) from 15 +/- 0.3% to 7% while maintaining the pressure of end-tidal CO2 at a constant level of approximately 30 mmHg. Five additional cats inhaled five breaths of pure N2 (transient hypoxia) and received sodium cyanide (50 micrograms iv) before and after thermal lesions of the bilateral FN. The results showed that cerebellectomy or FN lesions failed to alter the respiratory variables (minute ventilation, tidal volume, respiratory frequency, and the peak of integrated diaphragm activity) during eupneic breathing. However, cerebellectomy significantly attenuated minute ventilation (FETO2 < or = 13%) and the peak of integrated diaphragm activity (FETO2 < or = 10%) compared with control. During progressive hypoxia, changes in respiratory frequency were noted earlier (FETO2 < or = 13%) than changes in tidal volume (FETO2 < or = 10%). Similarly, bilateral lesions of the FN resulted in a profound reduction in these respiratory responses to transient hypoxia and sodium cyanide. We conclude that the cerebellum can facilitate the respiratory response to hypoxia and that the FN is an important region in the modulation of the hypoxic respiratory responses, presumably via its effects on inputs from peripheral chemoreceptors.

Cerebellar modulation of ventilatory response to progressive hypercapnia.

The cerebellar contribution to the ventilatory response to progressive hypercapnia was examined in 18 anesthetized tracheotomized spontaneously breathing cats. The absolute values for minute ventilation (VE), tidal volume (VT), respiratory frequency (f), inspiratory duty cycle (TI/TT), and mean inspiratory flow (VT/TI) were measured. Progressive hypercapnia [35-65 Torr end-tidal PCO2 (PETCO2)] was induced using the rebreathing method. The respiratory variables at each level of PETCO2 and the slopes of ventilatory (VT and f) responses to hypercapnia were compared across the intact, decerebellate, and decerebellate-vagotomized preparations. In 12 cats, decerebellation preceded vagotomy, and in 6 cats the order of the surgical procedures was reversed. The results show that, compared with intact control, decerebellation had little effect on respiratory variables when PETCO2 was 30-35 Torr. However, during a hypercapneic challenge (40-65 Torr PETCO2), VE and the slope of the VE response were significantly reduced. Bilateral vagotomy increased VT and decreased f but failed to alter the ventilatory response in the PETCO2 range of 35-55 Torr. However, combination of decerebellation and vagotomy, regardless of the surgical order, severely blunted VE (35-65 Torr PETCO2) and the slopes of VE, VT and f responses. When decerebellation followed vagotomy, significant decreases in VT (absolute values and slopes) were noted with little further alteration in f response. We conclude that the cerebellum and its interaction with the vagus nerves play a facilitatory or disinhibitory role in the ventilatory responses to hypercapnia.

Cerebellar role in the load-compensating response of expiratory muscle.

The hypothesis that the cerebellum is involved in the load-compensating response of expiratory muscles to expiratory tracheal occlusion was tested in anesthetized cats. A continuous expiratory threshold load (ETL; 5 cmH2O) was applied to elicit consistent phasic baseline electromyographic activity in the transversus abdominis muscle (EMGab). Tracheal occlusion for single expirations (TOE) were applied, and the evoked responses were compared in the intact and decerebellate preparation. Cold blockade of the dorsal spinal column (C5-7) and bilateral vagal inactivation (cold blockade or transection) were employed to determine the role of afferents from the lung, airways, chest wall, and diaphragm in shaping the cerebellar involvement in the motor response. The results showed that 1) decerebellation increased the baseline amplitude of the integrated EMGab (fEMGab) activity (P < 0.05) with little change in expiratory duration, 2) TOE applied after decerebellation markedly increased the expiratory duration compared with the intact values (P < 0.05), with little effect on the peak fEMGab, 3) cooling the dorsal spinal columns (C5-7) did not significantly affect EMGab responses in the intact or decerebellate preparations, and 4) vagal inactivation in the intact or decerebellate preparation significantly eliminated the fEMGab responses to ETL and TOE. We conclude that the cerebellum is involved in the modulation of transversus abdominis activity during ETL and TOE. Vagal afferents provide the major sensory input for the cerebellar modulation of the expiratory loading response.

Respiratory load compensation. II. Role of the cerebellum.

Effects of inspiratory tracheal occlusion (TO) on respiratory duration (inspiratory and expiratory duration), ventilation, and the peak integrated diaphragm electromyographic (integral of EMGdi) response were tested in 16 anesthetized cats before and after decerebellation with and without vagal input. The same protocols were repeated in the decerebrate preparation. Decerebellation did not significantly affect the baseline or the loaded values [tracheal occlusion (TO)] for respiratory duration, tidal volume, or magnitude of the integral of EMGdi response. Vagal blockade eliminated the load-compensating responses in the intact and the decerebrate preparation. However, vagal blockade in concert with decerebellation resulted in a significant (P < 0.05) reversible inhibition of the peak integral of EMGdi response during inspiratory TO. This suggests that removal of vagal and cerebellar influences during loaded breathing unmasked inhibitory inputs to the respiratory pattern generator. With vagus intact, decerebellation before or after decerebration abolished the attenuation of the peak integral of EMGdi response to TO observed with decerebration alone. We conclude that the cerebellum does play a role in determining the pattern of the respiratory response to TO. This influence may be direct and/or indirect via interaction with information emanating from suprapontine, vagal, and nonvagal sources.

Respiratory load compensation. III. Role of spinal cord afferents.

In a previous study, we reported that inspiratory tracheal occlusion (TO) significantly inhibited the motor drive to the diaphragm in a decerebellated bilaterally vagotomized preparation (J. Appl. Physiol. 75:675-681, 1993). The hypothesis to be tested in the present study was that respiratory muscle afferents activated by inspiratory TO provided the inputs responsible for the observed inhibition. Adult cats were anesthetized, tracheotomized, and instrumented with diaphragm electromyographic (EMGdi) recording electrodes. The cerebellum, vagi, and dorsal spinal cord (C2-T2) were surgically exposed. Inspiratory TO was applied before and after cold blockade of the dorsal cord (C6) or dorsal root (C3-6) transection in the intact and decerebellated vagotomized cat. Respiratory timing (inspiratory and expiratory duration) was determined from the EMGdi record, and the peak integrated EMGdi (integral of EMGdi) response was used as an index of respiratory motor drive. Our results showed that 1) cold blockade at the dorsal C6 level in an intact preparation significantly increased the peak of the integral of EMGdi response to TO and was reversible upon rewarming; 2) as previously reported, decerebellation coupled with bilateral vagotomy significantly decreased the peak integral of EMGdi response to TO with no effect on timing; 3) cold blockade (-1 degree C) of the dorsal cord at C6 significantly attenuated this inhibition, and subsequent dorsal rhizotomy at C3-6 completely abolished this inhibition; and 4) decerebellation, cold blockade of the dorsal cord (C6), and dorsal rhizotomy (C3-6) did not significantly affect baseline values in bilaterally vagotomized cats.(ABSTRACT TRUNCATED AT 250 WORDS)

Experiences with a science hotline.

Scientific literacy of the population may be enhanced by outreach programs conducted by universities. One such program, the University of Kentucky Science Hotline, has been successful in attracting and answering many inquiries from students, teachers, and others. The authors describe the organization and management of this hotline. The operation is inexpensive and efficient, with 35 faculty and staff members in 21 departments responding to 515 calls during the first year of operation. Fifty-four outreach visits were arranged through the hotline. Other benefits have included a more positive public image of scientists and the creation of links between academic scientists and precollege teachers.

Respiratory load compensation. I. Role of the cerebrum.

This study examines the extent to which the cerebrum and other suprapontine structures modulate the respiratory response to added mechanical resistive loads to breathing. Nine adult cats were anesthetized with thiopental sodium, tracheotomized, and instrumented with diaphragm electromyographic (EMGdi) recording electrodes. Two levels of resistive loads and tracheal occlusion were applied at the onset of inspiration in random order before and after decerebration. The integrated signal of the EMGdi (integral of EMGdi) was used to detect changes in respiratory timing and as an index of respiratory motor drive. The results showed that, compared with intact cats, decerebration did not significantly change baseline values for peak integral of EMGdi, respiratory timing, systemic blood pressure, or arterial blood gases. Although the percent changes in the peak integral of EMGdi elicited by the added loads were still significantly greater than those elicited by unloaded control breaths after decerebration, the magnitude of the responses was significantly attenuated at all load levels compared with the intact preparation. It is concluded that the cerebrum and/or other suprapontine structures provide information that is facilitatory to the respiratory pattern generator with little effect on timing.

Effect of a single breath of cigarette smoke on slowly adapting receptors in canine lungs.

Inhalation of cigarette smoke has been shown to induce bronchoconstriction which should stimulate slowly adapting pulmonary stretch receptors (PSRs). To test this possibility, the activity of PSRs was recorded from fine afferent filaments of the vagus nerve before and after 120 ml of smoke generated from high-nicotine cigarettes was delivered into the lungs in a single breath in anesthetized, open-chest and artificially ventilated dogs. The base-line activity of PSRs did not change during the first two breaths following smoke delivery. However, PSR activity started to increase by the third breath (post-smoke), concomitant with an increase in tracheal (transpulmonary) pressure. Both the smoke-induced increase in tracheal pressure and the delayed effect on PSRs were prevented by a pretreatment with aerosolized isoproterenol, a bronchodilator, suggesting that the delayed response of PSRs to smoke was elicited by the change in bronchomotor tone. Although smoke evoked a delayed stimulation in the majority (61%) of the PSRs studied, it caused a mild delayed inhibition (24%) or had no effect (15%) in some of the receptors. The variable responses to smoke among PSRs are probably related to the smoke-induced heterogeneous changes of mechanical properties in the lungs and their different anatomic locations.

University of Kentucky science outreach program.

Institutions of higher learning and their faculty must make a significant commitment to participate in the revitalization of the science curriculum. An active science outreach program within colleges and universities can have a pronounced impact on science education at relatively little expense. This partnership requires time, energy, and the willingness to share one's dedication and enthusiasm for his/her vocation.