CD38 in the nucleus accumbens and oxytocin are related to paternal behavior in mice

Abstract

Background: Mammalian sires participate in infant care. We previously demonstrated that sires of a strain of nonmonogamous laboratory mice initiate parental retrieval behavior in response to olfactory and auditory signals from the dam during isolation in a new environment. This behavior is rapidly lost in the absence of such signals when the sires are caged alone. The neural circuitry and hormones that control paternal behavior are not well-understood. CD38, a membrane glycoprotein, catalyzes synthesis of cyclic ADP-ribose and facilitates oxytocin (OT) secretion due to cyclic ADP-ribose-dependent increases in cytosolic free calcium concentrations in oxytocinergic neurons in the hypothalamus. In this paper, we studied CD38 in the nucleus accumbens (NAcc) and the role of OT on paternal pup retrieval behavior using CD38 knockout (CD38-/-) mice of the ICR strain.

Results: CD38-/- sires failed to retrieve when they were reunited with their pups after isolation together with the mate dams, but not with pup, in a novel cage for 10 min. CD38-/- sires treated with a single subcutaneous injection of OT exhibited recovery in the retrieval events when caged with CD38-/- dams treated with OT. We introduced human CD38 in the NAcc of CD38-/- sires using a lentiviral infection technique and examined the effects of local expression of CD38. Pairs of knockout dams treated with OT and sires expressing CD38 in the NAcc showed more retrieval (83% of wild-type sire levels). Complete recovery of retrieval was obtained in sires with the expression of CD38 in the NAcc in combination with OT administration. Other paternal behaviors, including pup grooming, crouching and huddling, were also more common in CD38-/- sires with CD38 expression in the NAcc compared with those in CD38-/- sires without CD38 expression in the NAcc.

Conclusions: CD38 in the NAcc and OT are critical in paternal behavior.

Figure 1

Latencies in retrieval, pup grooming, and crouching by sires. Times to the beginning of retrieval (left), grooming (center), and crouching (right) by sires in wild-type (blue) and CD38 knockout sires with (green) or without (red) re-expression of CD38 in the NAcc. Number of experiments is shown in parentheses. One-way ANOVA followed by Bonferroni’s post hoc test: F_2,66 = 36.81 (P = 0.0000) for retrieval, F_2,24 = 112.59 (P = 0.0000) for grooming and F_2,23 = 12.23 (P =0.0002) for crouching, respectively. ***P = 0.0000 (two-tailed t-test) between groups of CD38 knockout mice and wild-type or CD38 knockout with HCD38 re-expression.

Figure 2

Grooming and crouching by sires. Frequency of grooming (A) and duration of crouching (B) in wild-type (blue) and CD38 knockout sires with (green) or without (red) re-expression of CD38 in the NAcc. N = 10 males in each group. A One-way ANOVA was used followed by Bonferroni’s post hoc test: F_2,24 = 6.05 (P = 0.0075) for grooming and F_2,24 = 3.20 (P = 0.0584) for crouching. **P < 0.01 and *P < 0.05, two-tailed t-tests, respectively.

Figure 3

Representative fluorescence imaging of CD38 and DAPI in the NAcc. CD38^−/− sires were infected with either lenti-HA-HCD38 (A-C) or GFP (D-F). CD38 was stained using an anti-HA antibody. Images are enlarged in B and C or E and F as indicated by arrows. Scales are 100 μm (for A and D), 50 μm (for B and E) and 10 μm (for C and F), respectively. Aca: anterior commissure anterior; core: NAcc core; shell: NAcc shell.

Figure 4

Effect of CD38 re-expression in the NAcc on sucrose preference in wild-type and knockout mice. (A) Sucrose uptake ratio (preference) by CD38^+/+ (blue circles) and CD38^−/− (yellow circles) young adult (non-parental) males at the indicated concentrations of sucrose over water in the two-bottle test over 24 hours. N = 20 each out of a total of 320 males. A Two-way ANOVA was used: wild-type mice (F_5,124 = 12.97, P = 0.000), CD38^−/− mice (F_5,124 = 16.97, P = 0.0000) and their interaction with sucrose concentrations (F_5,124 = 3.80, P = 0.0006) were found to be significant factors. A two-tailed Student t-test was used to test significance of the difference between CD38^+/+ and CD38^−/− mice at 1%, ^#P < 0.002. (B) Sucrose preference tested with 1% sucrose in CD38^+/+ (blue) and CD38^−/− mice treated with (green) or without (red) OT and CD38^−/− mice expressing either GFP (yellow) or HCD38 (amber). N = 7 males in each group. A One-way ANOVA followed by Bonferroni’s post hoc test was performed: F_4,88 =11.00, P = 0.0000. A two-tailed Student t-test was performed: ^#P = 0.000, **P < 0.05.