Ž . Developmental Brain Research 114 1999 217–227 Research report Substance P and central respiratory activity: a comparative in vitro study on foetal and newborn rat Krzysztof Ptak a,b , Eric Di Pasquale a , Roger Monteau a, ) a Laboratoire de Neurobiologie des Fonctions VegetatiÕes, ESA CNRS 6034, Faculte des Sciences de St. Jerome, 13397 Marseille Cedex 20, France ´´ ´ ´ˆ b Zaklad Fizjologii Zwierzat, Uniwersytet Jagiellonski, Krakow, Poland Accepted 9 March 1999 Abstract Ž . Ž . Experiments were performed in vitro on foetal embryonic days 18 to 21, E18–21 and newborn rat postnatal days 0 to 3, P0–3 brainstem spinal cord preparations to analyse the perinatal developmental changes in the effects induced by substance P. Superfusion of Ž . the preparations with SP-containing artificial cerebrospinal fluid aCSF induced significant increase in the respiratory frequency of Ž y9 . y7 newborn rats 10 M , whereas concentration up to 10 M induced no change in foetal preparations. A whole cell patch clamp approach was used to record intracellularly from phrenic motoneurones. In newborn or E20–21 foetal rats SP-containing aCSF depolarised the phrenic motoneurones, increased their input resistance, reduced the rheobase current and shifted the frequency–intensity curves upward. In E18 foetal rats, no change was evoked by SP. A peptidase inhibitor mixture was used to block the enzymatic degradation of endogenous SP. This mixture was ineffective in changing the respiratory frequency in newborn and foetal preparations. In newborn rat phrenic motoneurones, the peptidase inhibitor mixture induced changes similar to those caused by SP but no change was Ž. induced in foetal rats. These results indicate that SP may modulate i the activity of the respiratory rhythm generator in newborn but not Ž. in foetal rats, and ii the activity of phrenic motoneurones at E20, E21 and in newborn rats but not at E18. Results obtained using the peptidase inhibitor mixture suggest that endogenous SP is probably not involved in the control of the respiratory rhythm in the prenatal period, but may influence the activity of the phrenic motoneurones after birth. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Substance P; Respiratory rhythm; Phrenic motoneuron; Whole cell recording; In vitro; Newborn and fetal rat 1. Introduction Ž . Ž The location of substance P SP containing nerves i.e., 9th and 10th cranial nerves connected to arterial barocep- w x. tors and chemoceptors 16,24,29 and of SP receptors in the brainstem supports a possible role of this peptide in regulating the respiratory function. The intraventricular injection of SP or its microinjection in the nucleus of the wx tractus solitarius increases the respiratory frequency 8 and microiontophoretic application of SP exerts an excita- w x tory effect on medullary respiratory neurones 41 . Several results have suggested that SP may play an important role during the perinatal period. Higher concentrations of SP than those present in adults are to be found in the medulla w x of rabbit pups and human babies 2,52 . Marked perinatal changes in the level of SP expression in the nucleus tractus solitarius occur at birth suggesting a possible role for the ) Corresponding author. Fax: q33-4-91-28-88-85; E-mail: roger.monteau@neurosciences.u-3mrs.fr w x peptide in regulating the onset of breathing 44 . Further- more, the expression of the mRNA encoding for the Ž . neurokinin-1 NK receptor undergoes marked postnatal 1 changes in the rat brain supporting a possible role associ- w x ated with development of the central nervous system 49 . The in vitro brainstem spinal cord of the newborn rat responds to application of exogenous SP with an enhance- w x ment of the respiratory frequency 31,53 . NK and NK 1 3 receptors mediate the stimulant action of exogenous w x tachykinins 31 but the application of receptor antagonists does not alter the basal respiratory activity in this prepara- w x tion 31,53 suggesting that endogenous SP is not involved in the control of the basal respiratory activity. Results obtained on the in vitro brainstem spinal cord of the newborn rat suggest that SP exerts facilitatory effects on the inspiratory motor output at the spinal level by w x acting on the phrenic motoneurones 31 . This result is consistent with previous observations indicating that termi- nals containing SP and SP receptors are present within the w x phrenic nucleus 19,21,35 . In mammals, the respiratory 0165-3806r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0165-3806 99 00044-9