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.     

Effects of perceived musical rhythm on respiratory pattern

The effects of rhythmic input on breath period (TT) under constant metabolic drive were assessed in 10 musically trained and 10 untrained subjects. They tapped to a metronome and then to four musical segments, each for 5 min. Ten of these subjects (5 from each group) also listened to the selections without tapping. TT, beat period (TB), and phase coupling (PC) were assessed during the last 20 breaths of each presentation. TT coefficient of variation decreased significantly (P less than 0.001) in all subjects (base line = 23%; listening = 15%; listening and tapping = 10%). Significant correlation between rhythm and TT, indicating relative entrainment, was found in half of the subjects (r greater than 0.45; P less than 0.01). Significant integer TT/TB ratio and PC, both indicating tight entrainment between rhythm and breathing, were observed in 12 subjects (though not consistently in each one). These data advance the following hypothesis: musical rhythm can be a zeitgeber (i.e., pacemaker), with its ability to entrain respiration dependent on the strength of its signal relative to spurious signals from the higher neural centers that introduce noise into the central pattern generator. Tapping reinforces the zeitgeber, increasing its signal-to-noise ratio and thereby promoting entrainment.     

Effects of vasopressin and prostaglandin synthesis inhibition on cyclic AMP accumulation in the dog renal inner medulla

The interaction of arginine vasopressin (AVP) and endogenous prostaglandins on cAMP production was investigated in the dog. Cyclic AMP content of dog inner medullary tissue slices exposed to different concentrations of AVP in the presence and absence of various prostaglandin synthesis inhibitors was determined. If the slices were incubated in isotonic media with 95% O2 and 5% CO2 gas phase, inhibition of prostaglandin synthesis decreased cAMP accumulation. A significant correlation was found between the decrements in cAMP content and basal cAMP levels. AVP-induced increments in cAMP accumulation was, however, unaffected by prostaglandin synthesis inhibitors. If incubation was performed in a hypertonic medium and at low O2 concentration, basal cAMP content was significantly reduced and it was not altered by inhibition of prostaglandin synthesis. The cAMP response to AVP was practically identical in the presence and absence of prostaglandin synthesis inhibitors. In conscious dogs AVP and indomethacin in itself had no effect on urinary cAMP excretion, but there was a significant decrease if the two compounds were combined. These results fail to lend support the hypothesis that endogenous prostaglandins modulate AVP-induced cAMP accumulation in the inner medulla.     

Inspiratory neuron activity in the ventrolateral medulla of the dog

The purpose of this study was to describe the distribution and activity pattern of respiratory neurons located in the ventrolateral medulla (VLM) of the dog. Spike activity of 129 respiratory neurons was recorded in 23 ketamine-anesthetized spontaneously breathing dogs. Pontamine blue dye was used to mark the location of each neuron. Most VLM neurons displaying respiratory related spike patterns were located in a column related closely to ambigual and retroambigual nuclei. Both inspiratory and expiratory neurons were present with inspiratory units being grouped more rostrally. The predominant inspiratory neuron firing pattern was "late" inspiratory, although eight "early" types were located. All expiratory firing patterns were the late expiratory variety. Each neuron burst pattern was characterized by determining burst duration (BD), spikes per burst (S/B), peak frequency (PF), time to peak frequency (TPF), rate of rise to peak frequency (PF/TPF), and mean frequency. CO2-induced minute ventilation increases were associated with decreases in BD and TPF and increases in PF, S/B, and PF/TPF. In 11 experiments the relative influences of vagotomy and tracheal occlusion on late inspiratory units were compared. Tracheal occlusion increased late inspiratory BD and S/B but did not alter PF/TPF. Vagotomy increased BD and S/B beyond those obtained by tracheal occlusion and, in some neurons, decreased the PF/TPF. We conclude that the location of respiratory units in the VLM of the dog is similar to that in other species, the discharge pattern of VLM respiratory units is similar to those in cat VLM, and vagotomy and tracheal occlusion affect discharge patterns differently.     

Control of respiratory pattern in conscious dog: effects of heat and CO2

We measured tidal volume (VT) and inspiratory (TI) and expiratory (TE) durations in five conscious tracheostomized dogs breathing air or 5% CO2 in air either at normal (20 degrees C) or elevated (30 degrees C) ambient temperatures. Respiratory frequency ranged between 16 and 333/min due to changes in both TI and TE. During panting TI exceeded TE. During air inhalation instantaneous ventilation (V) spontaneously ranged from 100 to 1,600 ml . kg-1 . min-1. Hypercapnia, heat stress, or both, increased this range of V by increasing maximum V, primarily due to increases in mean inspiratory flow. Under these conditions, changes in TI accounted for more of the spontaneous changes in breath duration. During inhalation of air and 5% CO2, a positive correlation between VT and TI was obtained for TI between 0.13 and 1.05 s; above 1.05 s VT decreased. Heat stress increased VT at a given TI. We suggest that either the decay rate or position of the inspiratory off-switch threshold curve (Clark and von Euler, J. Physiol. London 222: 267, 1972) varies in conscious dogs. Shifts in either the reset (onset) value or decay rate of the curve yield a positive correlation between VT and TI. This modification to the Clark-von Euler model implies that the primary effect of anesthesia on respiratory control is fixation of the inspiratory off-switch threshold curve.     

Intracellular recordings of respiratory neurons in the lateral medulla of piglets

Membrane potentials of respiratory neurons in the ventral respiratory group were recorded using intracellular techniques in the medulla of newborn piglets. Three types of neurons were demonstrated: inspiratory neurons with an augmenting pattern of spike activity during inspiration; postinspiratory neurons with a short decrementing firing pattern that started immediately after inspiration ended; and stage II expiratory neurons with an augmenting spiking pattern that began shortly after inspiratory termination and ended before onset of the next inspiration. When not firing, the membrane potential trajectories of each cell type revealed two complementary patterns of relative inhibition. This latter finding suggests arrival of inhibitory synaptic potentials during these periods. These findings suggest that the respiratory control mechanisms of the newborn piglet are organized in a three-phased manner similar to that of adult cats.