ELSEVIER PII S0361-9230(96) 00220-1 BrainResearchBulletin, Vol.42, No. 2, pp. 105-110, 1997 Copyright© 1997Elsevier ScienceInc. Printedin the USA.All rightsreserved 0361-9230/97$17.00+ .00 Spectral Features of Central Pattern Generation in the In Vitro Brain Stem Spinal Cord Preparation of the Newborn Rat ARIEL TARASIUK .1 AND ANTHONY L. SICAI" *Department of Physiology, Faculty of Health Sciences, Ben Gurion University, Beer Sheva, 84105, Israel ?~Departmentof Medicine, Pulmonary and Critical Care Division, Long Island Jewish Medical Center, the Long Island Campus for the Albert Einstein College of Medicine, New Hyde Park, New York 11042, USA ABSTRACT: In the present investigation, brain stem spinal cord preparations of 0-4-day-old rats were used to determine whether inspiratory-related discharges were modulated by a central pattern generator either during baseline conditions or during conditions of increased chemical drive. Spectral analyses were carried out on pairs of nerve activities during superfusion with normal solutions (pH = 7.4) and during superfusion with acidic solutions (pH = 6.8-7.0). Autopower spectra of nerve dis- charges in normal pH solution revealed the presence of two peaks: one in the 2-6 Hz band and the other in the 20-39 Hz band. Peaks occurring over both frequency ranges were highly correlated as revealed by coherence spectral analysis. Acidic stimulation produced no systematic changes in spectral fea- tures, for example, shifting peaks to other frequency regions, or increasing the values of coherence. The 2-6 Hz peak is most likely due to the arrival of depolarizing inputs from the brain stem that generate a ramp of activity at recording sites. On the other hand, activity in the 20-39 Hz region represents the discharge frequency of inspiratory motoneurons. The fact that coherence is present in this latter band provides evidence for short-time scale (ms) synchronization of functionally and anatomically dis- tinct inspiratory motoneurons by a central pattern genera- tor. Copyright© 1997 ElsevierScience Inc. KEY WORDS: Brain stem spinal cord preparation, Central pat- tern generator, Coherence, Development. INTRODUCTION Power spectral analysis of inspiration-related motoneuron dis- charges in in vivo preparations has provided useful information about the characteristics of central pattern generator (CPG) af- ferents that synaptically modulate inspiratory premotor neurons [1-6,12,15]. Such inputs are thought to be necessary for syn- chronizing the discharges of functionally different and anatomi- cally disparate pools of inspiratory motoneurons. Further, the presence of such modulatory inputs is indicated by the presence of correlated frequencies in coherence spectra, for example, by coherent high-frequency (>50 Hz) oscillations (HFOs) in ma- ture mammals [1-5]. In developing mammals, the appearance of HFOs in inspiratory activities has been postulated as signaling the completion of developmental processes whereby modulation To whom requests for reprints should be addressed. by the adult-like CPG is established [13,14,17]. The absence of an HFO, however, does not necessarily mean that CPG modu- lation is not present. Rather, such modulation may be represented by periodicities located at other than HFO frequencies. In the developing swine model, for example, coherent frequencies have been demonstrated in the 20-50 Hz band, i.e., medium frequency oscillations (MFOs) [14,17]. As the in vitro brain stem and spinal cord preparation of new- born rats is an experimental system with spontaneous inspiratory activity [8,9,16,18-20], it offers an unanesthetized preparation suitable for studies of CPG modulation shortly after birth. An- other benefit of this preparation is that it could give information about the intrinsic frequency of the newborn CPG because all sources of respiration-related afferents have been eliminated, with the exception of chemoreceptors located near the ventral surface of the medulla. To test the hypothesis that inspiratory activities in this in vitro preparation are modulated by a CPG, power spectral analyses were performed on discharges of spinal motoneurons and, in a few cases, of cranial motoneurons. These experiments were carried out on activities during baseline con- ditions, i.e., superfusion with normal Krebs solution, and on ac- tivities under conditions of increased chemical drive, i.e., super- fusion with an acidic Krebs solution. This latter perturbation is included to determine whether CPG modulation required stimu- lation for its expression, or whether acidic stimulation produced an increase in the level of already present CPG modulation, which would be manifested as an increase in the value of coher- ence. METHODS This study was approved by the institutional animal use com- mittee. All experimental procedures are in compliance with Fed- eral and State regulations as well as the "Guide for the Use and Care of Laboratory Animals" approved by the council of the American Physiological Society. Surgical Preparation Fourteen newborn Sprague-Dawley rats (0-4 d old) were anesthetized with Halothane until flexion responses to noxious 105