Microinjection of the Tachykinin Neuropeptide K into the Ventromedial Hypothalamus Disrupts the Hormonal Onset of Maternal Behavior in Female Rats

Abstract

The medial amygdala exerts an inhibition of maternal behavior in virgin rats, but neither the site to which it projects to exert this effect nor the neurotransmitter used in such a pathway is known. There is also evidence that the ventromedial nucleus of the hypothalamus exerts an inhibition of maternal behavior, and the medial amygdala projects to this nucleus, suggesting that it may receive a projection from the medial amygdala which is inhibitory for maternal behavior. Tachykinin injection into the hypothalamus inhibits reproductive behavior in male rats, and there is a tachykininergic projection from the medial amygdala to the ventromedial hypothalamus. Consequently, the present study was conducted to evaluate the hypothesis that the tachykinin neuropeptide K can inhibit maternal behavior after injection into the ventromedial hypothalamus. Female rats were primed to be maternal by pregnancy termination and estrogen injection. Four doses of the peptide (279 pmol, 186 pmol, 116 pmol, and 66 pmol) were bilaterally injected into the ventromedial hypothalamus, and all were effective in delaying the onset of maternal behavior. Evidence that neuropeptide K disrupts maternal behavior in animals that have already begun to be maternal is also presented. Site specificity of neuropeptide K's effect to within the region of the ventromedial hypothalamus was supported, as injection into the mediodorsal thalamus was without effect. Some possibly relevant neuroendocrine effects are addressed, as well as the possibility that tachykinins may act within the ventromedial hypothalamus to promote virgin female rats' fear of pup odors.

Psychological and neurobiological mechanisms underlying the decline of maternal behavior

“…Neurotoxic lesions of DMH and VMH can also advance the onset of maternal behavior in primigravid rats (first-time pregnant rats) (Mann and Babb, 2004). Applications of various doses of neuropeptide K (NPK) into the VMH are found to be inhibitory to the occurrence of maternal behavior (Sheehan and Numan, 1997). The inhibitory effect of the VMH on maternal behavior might be related to its role in mediating avoidance, aggressive and defensive behaviors (Wang et al, 2015).…”

Neuroendocrinology and Neurochemistry of Maternal Motivation and Behavior

“…In support, nonmaternal female rats show elevated Fos expression in the anterior hypothalamus and ventromedial nucleus in response to pups whereas maternal females do not (Sheehan et al, 2000). Other than the requirement for ovarian hormones to be present, little is known about the neurochemistry underlying the inhibition of maternal behavior by the mediobasal hypothalamus, with the exception that neuropeptide K infused into the VMH can inhibit the behavior (Sheehan and Numan, 1997). Evidence that these mediobasal hypothalamic areas receive an input from the MeA to inhibit maternal behavior is provided by the finding that MeA lesions reduce Fos expression in these sites of nonmaternal females after exposure to pups (Sheehan et al, 2001).…”

“…CCK can act as an opioid antagonist and when infused into the POA, it blocks the impairments in maternal behavior after POA injection of morphine (Mann et al, 1995). The tachykinin, neuropeptide K, delays the display of maternal behavior in pregnancy-terminated, estradiol-treated female rats when infused into VMH (Sheehan and Numan, 1997), which so far, is the only neurochemical known to act in the VMH to impede this behavior.…”

Histone deacetylase inhibitor treatment promotes spontaneous caregiving behaviour in non‐aggressive virgin male mice

“…Although plasticity within this circuit contributes to the maintenance of caregiving behaviour across the postpartum period long after hormonal stimulation has waned, caregiving behaviour likely depends on changes in both antisocial and pro‐social neural systems . For example, the onset of mothering in rats also coincides with a reduction in the ability of infants to activate fear/defensive neural systems and experimentally induced reactivation of this system can turn mothering off . Thus, the occurrence of caregiving behaviour may depend on both a pup‐induced activation of the maternal circuit and an inhibition of a competing fear/escape/attack neural system …”

“…18,19 For example, the onset of mothering in rats also coincides with a reduction in the ability of infants to activate fear/defensive neural systems 11 and experimentally induced reactivation of this system can turn mothering off. 20 Thus, the occurrence of caregiving behaviour may depend on both a pup-induced activation of the maternal circuit and an inhibition of a competing fear/escape/attack neural system. 19 The transition from pup avoidance to pup approach in female rats is typically uni-directional, although male mice can revert back to an aggressive state under certain circumstances.…”