Ultrasonic vocalizations by rat pups: The primary importance of ambient temperature and the thermal significance of contact comfort

AbstractEarly separation of preterm infants from their mothers has adverse, long-term neurodevelopmental consequences. We investigated the effects of daily maternal separation (MS) of rat pups from postnatal days 2–10 (PND2–10) on neurobehavioural responses to brief isolation at PND12 compared with pups receiving controlled handling without MS. Ultrasonic vocalizations (USV) were measured at PND12 during two, 3-minute isolations occurring immediately before and after a 3-minute maternal reunion. There were no significant differences in acoustic characteristics between MS and control animals in the first isolation. However, in the second isolation, MS pups produced a greater proportion of high (~60 kHz) vs low (~40 kHz) frequency calls. During this isolation, control pups made longer and louder low frequency calls compared to the first isolation, whereas MS pups did the opposite. Maternal behaviour of control and MS mothers modulated pup acoustic characteristics in opposite directions; higher maternal care was associated with more low frequency calls in control pups but more high frequency calls in MS pups. We hypothesize that MS results in USV emission patterns reflective of a greater stress response to isolation. This translational model can be used to identify mechanisms and interventions that may be exploited to overcome the negative, long-term effects of MS.

Download Full-text

Hering-Breuer reflex in conscious newborn rats: effects of changes in ambient temperature during hypoxia

Journal of Applied Physiology ◽

10.1152/jappl.1999.87.5.1656 ◽

1999 ◽

Vol 87 (5) ◽

pp. 1656-1661 ◽

Cited By ~ 15

Author(s):

Daniele Merazzi ◽

Jacopo P. Mortola

Keyword(s):

Oxygen Consumption ◽

Ambient Temperature ◽

Body Surface ◽

Neonatal Period ◽

Reflex Response ◽

Newborn Rats ◽

Lung Inflation ◽

Rat Pups ◽

Double Chamber

In a previous study in conscious normoxic newborn rats, we found that the strength of the Hering-Breuer reflex (HB reflex) was greater (188%) at high (36°C) than at low (24°C) ambient temperature (Ta; D. Merazzi and J. P. Mortola. Pediatr. Res. 45: 370–376, 1999). We now asked what the effect would be of changes in Ta during hypoxia. Rat pups at 3–4 days of age were studied in a double-chamber airflow plethysmograph. The HB reflex was induced by negative body surface pressures of 5 or 10 cmH2O and quantified from the inhibition of breathing during maintained lung inflation. Rats were first studied at Ta = 32°C in normoxia, followed by hypoxia (10% O2breathing). During hypoxia, oxygen consumption (V˙o 2) averaged 47%, and HB reflex 115%, of the corresponding normoxic values, confirming that in the newborn, differently from the adult, hypoxia does not decrease the strength of the HB reflex. As hypoxia was maintained, lowering Ta to 24°C or increasing it to 36°C, on average, had no significant effects onV˙o 2 and the HB reflex. However, with 5-cmH2O inflations, the HB reflex during the combined hypoxia and hyperthermia was significantly stronger than in normoxia. We conclude that in conscious newborn rats during normoxia the Ta sensitivity of the HB reflex is largely mediated by the effects of Ta on thermogenesis andV˙o 2; in hypoxia, because thermogenesis is depressed andV˙o 2 varies little with Ta, the HB reflex is Ta independent. The observation that the reflex response to lung inflations during hypoxic hyperthermia can be greater than in normoxia may be of importance in the pathophysiology of apneas during the neonatal period.

Download Full-text