Pharmacological manipulations illustrate the contributions of the sympathetic and parasympathetic branches of the autonomic nervous system.

<p>(<b>A</b>) Atenolol (8 mg/kg, i.p.) blocked the pup-induced heart rate increase, with main effects of time and treatment. * indicates the effect of treatment, such that the saline treatment produced a higher heart rate than the atenolol treatment. (<b>B</b>) Atropine (4 mg/kg, i.p.) delayed initial approach to the pup. * indicates p<0.05.</p

The cardiovascular response to a pup does not readily habituate.

<p>(<b>A</b>) Heart rate during interaction with a pup did not differ during repeated pup exposures (1st three bars) or during prolonged pup exposure (4th bar) (p>0.05). Time was collapsed across the 10 minutes of each condition (baseline, divided cage, united with pup) to yield a main effect of condition on heart rate (<b>B</b>), no effect on activity (<b>C</b>) and a trend towards an effect on RSA (<b>D</b>) (p>0.05). * indicates p<0.05 in comparison to both other conditions.</p

Respiratory sinus arrhythmia (RSA) is maintained and heart rate increased during alloparental behavior which is not explained by locomotor activity.

<p>(<b>A</b>) Heart rate during exposure to social (pup, female) and non-social (dowel) stimuli yielded main effects of stimulus and time, with the pup condition generally highest. (<b>B</b>) The correlation between heart rate and RSA during exposure was highest in the pup condition. (<b>C</b>) There were no effects on RSA other than a main effect of time. (<b>D</b>) Locomotor activity yielded main effects of stimulus and time as well as an interaction between stimulus and time. * indicates the effect of stimulus, such that both the dowel and female stimuli were significantly different than the pup condition (p<0.05), # difference significant only between the female and pup groups (p<0.05).</p

c-Fos activity is higher in brainstem autonomic nuclei related to parasympathetic function (A).

<p>Mean c-Fos optical density (+/− SEM) in the dorsal motor nucleus of the vagus (DMX), nucleus ambiguus (NA), nucleus tractus solitarius (NTS), and rostral ventrolateral medulla (RVLM) following exposure to either a dowel (gray) or pup (blue). † indicates p<0.1 * indicates p<0.05. Representative photomicrographs at 4× magnification (<b>B</b>).</p