Myron A. Hofer

Evidence that maternal ventral skin substances promote suckling in infant rats.

Abstract Washing a lactating rats ventral skin with acetone, alcohol and water markedly reduces the effectiveness with which her 2-week-old infants can initiate suckling on the anesthetized mother. Control experiments with detailed thermal and behavioral measures give evidence tending to rule out lowered skin temperature, altered thermal gradients, changed tactile characteristics of abdominal fur or nipples and aversion to remaining traces of the organic solvents as responsible for the infants failure to find and attach to nipples. The data suggest that some substance(s) on the skin of the mothers ventrum act as olfactory and/or gustatory cues for the infants orientation and attachment to nipples.

Effects of nasal ZnSO4 irrigation and olfactory bulbectomy on rat pups

Abstract Rat pups underwent bilateral olfactory bulbectomy (BOB) or irrigation of the nasal cavities with a 5% ZnSO 4 solution (Zn) at 2, 7, 11, or 13 days of age to determine whether the effects of these treatments are similar. Control pups were sham operated, handled only, or had their nasal cavities irrigated with saline. Both Zn and BOB pups lost weight, sometimes to the point of death, and exhibited deficiencies in attachment and suckling behavior compared to control animals. Histological investigation indicated degeneration in the olfactory epithelium and shrinkage of the glomerular layer of the olfactory bulb as a result of the nasal ZnSO 4 treatment. The vomeronasal organs of the Zn animals appeared to be intact. As a control for possible toxic effects of nasal ZnSO 4 irrigation, 12-day-old pups had their oral cavities irrigated with a 5% ZnSO 4 solution. Their weight gain and attachment and suckling behavior was like that of control pups.

Physiological Responses of Infant Rats to Separation from Their Mothers

Decreases of 40 percent in cardiac and respiratory rates occur during the first 12 to 16 hours after 2-week-old rat pups are separated from their mothers. These rates decrease without significant alteration in activity level and despite maintenance of body temperature, of nutrition by intubation, of an intact litter, and of the home cage nest.

The effects of brief maternal separations on behavior and heart rate of two week old rat pups

Abstract Behavioral and cardiac rate responses to a novel test box were recorded from rat pups separated from their mothers for 18 hr and from littermates allowed to remain with their mothers. If body temperatures of separated pups were maintained at nest levels, they showed increased numbers of rises, squares crossed and head raises but did not differ from their mothered littermates in self-grooming or elimination. If no temperature source was supplied, separated pups lost 3°C and showed generally reduced levels of behavior. Heart rates of separated pups decreased markedly during separation, regardless of whether body temperatures were maintained. The cardiac rate response of mothered pups to the test box was a transient slowing in the first two min. Both separated groups showed acceleratory responses to the test box. Those whose temperatures had been maintained had more prolonged cardiac acceleration which reached levels close to the range of their mothered littermates.

Lethal respiratory disturbance in neonatal rats after arterial chemoreceptor denervation

The role of afferent feedback from arterial chemoreceptors in the maintenance of rhythmic respiration during early development was studied by section of carotid sinus and aortic nerves of rat pups at different ages from 3 days to 3 weeks postnatally. This deafferentation produced a severe, episodic respiratory disturbance, limited to pups younger than 21 days and associated with mortality rates near 50% during the 2 weeks following surgery. These findings may have implications for the role of peripheral chemoreceptors in the periodic apneas of premature infants and in the Sudden Infant Death Syndrome.

Oxytocin reinstates maternal olfactory cues for nipple orientation and attachment in rat pups

Abstract Thoroughly washing the female rats ventrum with solvents results in a marked deficiency in nipple orientation and attachment by her 8-to-9-day old pups. However, if the thoroughly washed mother is injected with oxytocin, nipple attachment is reinstated even if the nipples are ligated. Thus some substance(s) other than milk excreted in the nipple area acts as an olfactory cue for pups.

Maternal separation affects infant rats' behavior *

Eighteen hour separations of 2 wk old Wistar rat pups from their mothers were found to increase levels of activity, elimination and self-grooming in a novel environment and to delay sleep onset. A control group supplied with nonlactating foster mothers suggested that whereas the sleep onset changes could have a nutritional mechanism, the waking behavioral effects of separation probably depended on deprivation of behavioral interaction with the mother.

Early Stages in the Organization of Cardiovascular Control

Abstract Our studies have revealed a number of unexpected characteristics of the immature cardiovascular system of the infant rat. Sympathetic and parasympathetic divisions of the autonomic system appear to have different timetables for the development of tonic and phasic activities. These different timetables of development result in unusual physiological organizations at particular stages in postnatal life. We have described some of the features of one of these: the infant rats cardiac rate responses in the second week after birth include a high resting rate, decreased rates in response to several (but not all) forms of activation, and two forms of phasic activity, a bradycardia and a tachycardia, that are related to naturally occurring behavioral states and have not been described in adults. The nature of this age-specific autonomic organization was explored further and found to be embedded in the infants relationship with its mother and in her role as a supplier of nutrient in particular. The mechanisms by which nutrient intake regulates autonomic cardiovascular control during this stage of life have been partially explored by analytic experiments and the results are described along with the possible adaptive value of this regulatory system.

Survival and recovery of physiologic functions after early maternal separation in rats

Fourteen-day-old rats separated from their mothers have greatly increased survival rates, if provided with a local heat source. Body weight, temperature, cardiac and respiratory rates declined for 3 days in all separated animals, and eye opening was delayed most in those separated at room temperature. In survivors, a second phase followed in which all measures rebounded to levels characteristic of normally mothered infants. Cardiac rate, having fallen 40 percent in the first days after separation, rose to levels higher than normally mothered infants at 21 and 30 days of age. Recovery was not clearly initiated by any singly system studied, although non-survivors showed greater weight and temperature loss and evidence of gross motor deficit during the separation response phase.

Cardiac Rate Regulated by Nutritional Factor in Young Rats

Milk fed by stomach tube to 2-week-old rats separated from their mothers without feeding for 16 hours transiently but fully reversed the decrease in cardiac rate which had occurred during separation. This effect was rapid in onset and was related to dosage; it was not dependent upon gastric distention, but did depend upon β-adrenergic transmission.