Prenatal allergic inflammation in rats confers sex-specific alterations to oxytocin and vasopressin innervation in social brain regions

Abstract

Prenatal exposure to inflammation via maternal infection, allergy, or autoimmunity increases one's risk for developing neurodevelopmental and psychiatric disorders. Many of these disorders are associated with altered social behavior, yet the mechanisms underlying inflammation-induced social impairment remain unknown. We previously found that a rat model of acute allergic maternal immune activation (MIA) produced deficits like those found in MIA-linked disorders, including impairments in juvenile social play behavior. The neuropeptides oxytocin (OT) and arginine vasopressin (AVP) regulate social behavior, including juvenile social play, across mammalian species. OT and AVP are also implicated in neuropsychiatric disorders characterized by social impairment, making them good candidate regulators of social deficits after MIA. We profiled how acute prenatal exposure to allergic MIA changed OT and AVP innervation in several brain regions important for social behavior in juvenile male and female rat offspring. We also assessed whether MIA altered additional behavioral phenotypes related to sociality and anxiety. We found that allergic MIA increased OT and AVP fiber immunoreactivity in the medial amygdala and had sex-specific effects in the nucleus accumbens, bed nucleus of the stria terminalis, and lateral hypothalamic area. We also found that MIA reduced ultrasonic vocalizations in neonates and increased the stereotypical nature of self-grooming behavior. Overall, these findings suggest that there may be sex-specific mechanisms underlying MIA-induced behavioral impairment and underscore OT and AVP as ideal candidates for future mechanistic studies.

Keywords: Allergy; Maternal immune activation; Oxytocin; Sex differences; Social behavior; Social play; Vasopressin.

Figure 1:

Experimental timeline. Vehicle and MIA offspring subjected to behavioral testing underwent isolation-induced ultrasonic vocalization testing on P6, self-grooming assessment on P30, and social preference testing on P67 or 68. Offspring employed for OT and AVP analyses were sacrificed on P28 and brains were collected and processed for OT and AVP immunohistochemistry.

Figure 2:

Maternal observation data. MIA did not affect maternal behavior as measured between P0-8. Dams spent most of the time either nursing pups or off the nest.

Figure 3:

MIA reduces neonatal ultrasonic vocalization behavior and increases stereotypical grooming behavior. A.) MIA offspring exhibited fewer isolation-induced ultrasonic vocalizations. B.) MIA increased the proportion of grooming transitions that fit stereotypical grooming syntax. C-D.) While no effect of sex or MIA was found on juvenile self-grooming bout microstructure, all rats primarily groomed one region in a given grooming bout, with the focus being on the paws and snout. E-H.) No other significant effects on grooming behavior were noted. I.) Females reared more during the grooming assessment compared to males. J-K.) MIA did not alter adult social preference behavior, but females exhibited more exploratory behavior in the chamber. M = male, F = female.

Figure 4:

MIA does not significantly alter OT or AVP neuron number. A.) Schematic of a coronal brain section highlighting the approximate location of the PVN with an example image of AVP+ cells. B-C.) No effects of sex or MIA on the PVN were documented. D.) Schematic of a coronal brain section highlighting the approximate location of the SON with an example image of AVP+ cells. E-F.) No effects of MIA were found on AVP or OT neurons in the SON. Males had significantly more OT neurons in the SON than females. G.) Schematic of coronal brain sections highlighting the anterior and posterior BNST with example images of OT+ cells. Boxes correspond to enlargements of images for visualization purposes. H-J.) MIA did not affect OT cell number in any BST subregion. Scale bars = 100μm (A. and D.) or 400μm (G.). The contrast on images was enhanced for visualization purposes.

Figure 5:

Lateral septum (LS) fiber analysis. A.) Schematic of a coronal section highlighting the LS with an example image of OT staining. B.) MIA did not significantly affect AVP in the LS. C.) MIA produced a non-significant reduction in OT in the LS, and males had more OT compared to females. D.) Representative images of OT staining. Scale bars = 75μm. Boxes correspond to enlargements of images. The contrast on images was enhanced for visualization purposes.

Figure 6:

Nucleus accumbens (NAc) fiber analysis. A.) Schematic of a coronal section highlighting the NAc core and shell, with example images of OT staining. B.) MIA produced a non-significant (p = 0.06) increase in AVP innervation in the shell, although a significant interaction reveals this was driven by males. Males also had more AVP compared to females. C.) Representative AVP staining in the shell. D-E.) MIA did not significantly affect OT innervation in the NAc, though males had significantly more OT in the shell compared to females. F.) Representative images of OT staining in the NAc shell. Scale bars = 75μm for shell, 50μm for core. Boxes correspond to enlargements of images and the contrast on images was enhanced for visualization purposes.

Figure 7:

Bed nucleus of the stria terminalis (BNST) fiber analysis. A.) Schematic of a coronal section of the BNST with an example image of OT staining in the anteromedial (AM) and medioventral (MV) subregions. B.) A significant interaction suggests MIA increases OT in medioventral BNST of males and decreases it in females. C-D.) MIA selectively increases AVP in the medioventral BNST in males, with representative images. E-F.) MIA reduced AVP in the anteromedial BNST in males, with representative images. G-H.) MIA reduced OT in the anteromedial BNST of females, with representative images. Scale bars = 75μm. Boxes correspond to enlargements of images, and the contrast on images was enhanced for visualization purposes.

Figure 8:

Lateral hypothalamic area (LHA) fiber analysis. A.) Schematic of a coronal section highlighting the lateral hypothalamic area. B.) MIA did not affect OT in the LHA. C-D.) MIA selectively reduced AVP in the LHA of males and males had more AVP than females (though p = 0.06), with representative images. Scale bars = 75μm.

Figure 9:

Medial amygdala fiber analysis. A.) Schematic of a coronal section with the medial amygdala highlighted. B-C.) MIA increased AVP in the MeA with representative images. D-E.) MIA increased OT in the MeA, with representative images. Scale bars = 75μm. Boxes correspond to enlargements of images. The contrast on images was enhanced for visualization purposes.