Effects of hypoglossal and facial nerve injuries on milk‐suckling

Abstract

Functional roles of the perioral anatomical structures involved in breastfeeding were examined in newborn rat pups in which the hypoglossal (XII) and facial (VII) nerves had been resected at the neonatal stage. The XII nerve controls tongue movement and is comprised of two functionally distinct branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction. Newborn rat pups with bilateral resection of either of the XII nerve components (main trunk: XII-trunk; medial branch: XII-med; lateral branch: XII-lat) failed to suckle milk and did not survive. Unilateral XII nerve-resected neonates showed different milk-suckling capabilities, which thus resulted in differences in survival rate (XII-trunk: 38%; XII-med: 24%; XII-lat: 92%) and postnatal growth during the postnatal 3 weeks until P21. Unilateral and bilateral resections of the VII nerve innervating the buccolabial musculature produced lowered suckling capabilities and retarded postnatal growth, although all pups showed 100% survival. The results indicate a crucial role of the tongue, especially of protruding muscular elements innervated by the XII-med nerve, in breastfeeding. The results also indicate differential effects of the VII and XII nerve components on suckling capability, survival, and postnatal growth of newborn rat pups.

Neural plasticity of neonatal hypoglossal nerve for effective suckling

“…It seems surprising that only 1 or 2 days are needed for axonal sprouting. Early onset of nerve reinnervation is of considerable significance for survival of neonatal pups, because the XII nerve‐injured pups without milk intake died 2–3 (P3–P4) days after nerve injury (Fujita et al, 2006; Fukuyama et al, 2006). At the later stages, advances in axonal sprouting between P4 and P7 corresponded well with the timing of marked increments in milk intake in pups with unilateral XII‐trunk (P4, 30% of the control value; P7, 52%) or XII‐med (P4, 36%; P7, 71%) nerve injury (Fujita et al, 2006).…”

“…Before starting the experiments on P1 pups, we observed the dam's maternal behavior (Jirik‐Babb et al, 1984; Yeo and Keverne, 1986; Kinsley et al, 1994) and the pup's gastric milk. If the dam did not show maternal behavior and the pups did not contain milk in their stomachs, the animals were excluded from the experiments as described in our previous reports (Fukushima et al, 2006; Fujita et al, 2006; Fukuyama et al, 2006). A total of 49 newborn pups from six pregnant dams were used in the present study.…”

“…Newborn mammals cannot survive without effective suckling. We reported recently the essential roles of the tongue in suckling in hypoglossal (XII) nerve‐injured newborn rats (Fujita et al, 2006; Fukuyama et al, 2006). The XII nerve controls tongue movements and has two functionally different nerve branches: the medial branch related to protrusion of the tongue and the lateral branch related to its retraction (Lowe, 1978; Dobbins and Feldman, 1995; Fuller et al, 1999; Mu and Sanders, 1999; McClung and Goldberg, 2000).…”

“…Some of the pups with unilateral XII‐trunk or XII‐med nerve injury were unsuccessful in suckling milk and died, whereas others in the same experimental groups gradually acquired suckling capability and survived. The surviving pups with unilateral XII‐trunk or XII‐med nerve injury on P1 showed marked increases in milk intake between P4 and P7, strongly suggesting adaptive tongue movements for effective suckling (Fujita et al, 2006).…”

Wired for eating: how is an active feeding circuitry established in the postnatal brain?

“…In newborn rats, resection of the XII nerve results in the death due to a failure to suckle milk [24]. How are these motor nuclei controlled at birth?…”