Lactation diminishes lesion-induced permeability of tracers into the brain

Lactation attenuates pro-oxidant reactions in the maternal brain

Reactive oxygen species (ROS) are intimately linked to bioenergetics and redox biology, contributing to cellular functioning and physiological signaling, but also acting as toxic agents during oxidative stress. Hence, the balance between pro-oxidant reactions and the activity of antioxidant defenses sustains a basal oxidative status, controls the increase of redox signaling, and mediates potential pathological events during oxidative stress. Maternal experience, especially during nursing, requires high energetic demands and expenditure to ensure the well-being of the offspring. The mother must adapt from satisfying her own needs to additionally fulfilling those of her descendants. Oxidative stress has been proposed as one of the reproductive trade-off hallmarks. However, the oxidative shielding hypothesis has also been proposed in the context of reproduction. The reproductive experience induces a wide range of well-documented changes in the female brain, which potentially lead to protection against the enhanced oxidative activity. To date, the metabolic and cellular mechanisms that underlie lactation-induced neuroprotection against oxidants are unknown. The neuroendocrine changes in the brain of the lactating dam promote diminished propensity to excitotoxic brain injury and stress, as well as enhanced neuroprotection and plasticity. In addition to review studies on the oxidant balance due to motherhood, we included new data from our laboratory, addressing the importance of measuring pro-oxidant reactions in separated brain regions. The hippocampus of lactating rats exhibits lower levels of pro-oxidant reactions than that of virgin rats, supporting the oxidative shielding hypothesis in lactation.

Prolactin neuroprotective action against excitotoxic insult in the hippocampus of male mice

Prolactin (PRL) is known to exert neuroprotective effects against excitotoxic damage in the hippocampus of female rats, both in vitro and in vivo. It is still unknown whether this effect can be seen in the male hippocampus and intracellular signaling mediating such action. To assess this, adult male CD-1 mice were subjected to excitotoxic damage with kainic acid (KA; i.c.v.), after a) no manipulation (control group), b) treatment with saline, and c) treatment with PRL (8 μg of PRL/100 μl of saline s.c.). Treatments consisted of one daily injection of the mentioned dosage for seven consecutive days until the day of the excitotoxic lesion. Neurodegeneration (Fluoro-Jade C), neuronal survival (NeuN) and astrogliosis (GFAP) markers were identified with immunohistochemistry in the CA1, CA3 and CA4 areas of the dorsal hippocampus, as well as PRL-related protein levels by Western blot in the whole hippocampus 48 h after excitotoxicity. Anatomical measurements revealed a preferential protective effect of PRL against excitotoxic damage in the CA3 hippocampal subfield, with lower levels of cell death and neurodegeneration, compared to controls. In CA4, the results were not conclusive, and no damage was observed in CA1 after KA administration. PRL treatment provoked an upregulation of active Akt, a well-known cell survival pathway, after KA administration. PRL also caused downregulation of active MAPK, independently of the excitotoxic damage. The present results indicate a neuroprotective role for PRL preferentially located in the CA3 area of the hippocampus of male mice, possibly mediated by Akt-related survival mechanisms.

Fatherhood diminishes the hippocampal damaging action of excitotoxic lesioning in mice

Parental experience imposes neuroplasticity in the hippocampus of females and males. In lactating rat dams, the hippocampus is protected against excitotoxic damage by kainic acid lesioning, although it is still unknown whether paternity can provide such protection to male rodents. To evaluate the protective effects of fatherhood against excitotoxic lesions, we paired male mice with females and co-housed them until the day of parturition (PPD0), when we randomly assigned them to two groups: (i) the pregnancy group (males housed individually overnight and injected i.c.v. with 100 ng per 1 μL of kainic acid or vehicle on PPD1) and (ii) the sire group (males housed with the dam and pups until PPD8, when injected i.c.v. after evaluation of parental behaviour). Individually housed virgin adult male mice formed the control group. Markers of neurodegeneration (NeuN, Fluoro-Jade C) and astrogliosis (glial fibrillary acidic protein) were evaluated in fixed cerebral tissue containing the dorsal CA1, CA3 and CA4 hippocampal subfields. The CA1 subfield did not suffer damage in any of the experimental groups. The sire group exhibited less neurodegeneration and astrogliosis in the CA3 and CA4 subfields compared to their respective controls, independently of the expression of parental behaviour. Western blot analysis was conducted for prolactin (PRL), PRL receptor and related intracellular pathways. Monomeric PRL was lower in the hippocampus of sires in the first week postpartum with a parallel rise of a 48-kDa dimerised isoform compared to virgin controls. The long isoform of PRL receptor did not change, and signal transducer and activator of transcription 5 (STAT5) was not detected in the hippocampus. However, a sustained rise in pAkt, a signalling molecule that participates in cell survival, was observed in the sire group. These results indicate that the hippocampus of sires housed with the dam and pups is less sensitive to neurotoxic injury, which might not be primarily regulated by PRL-STAT5-modulated mechanisms.