Preliminary evidence of neuropathology in nonhuman primates prenatally exposed to maternal immune activation

Abstract

Maternal infection during pregnancy increases the risk for neurodevelopmental disorders in offspring. Rodent models have played a critical role in establishing maternal immune activation (MIA) as a causal factor for altered brain and behavioral development in offspring. We recently extended these findings to a species more closely related to humans by demonstrating that rhesus monkeys (Macaca mulatta) prenatally exposed to MIA also develop abnormal behaviors. Here, for the first time, we present initial evidence of underlying brain pathology in this novel nonhuman primate MIA model. Pregnant rhesus monkeys were injected with a modified form of the viral mimic polyI:C (poly ICLC) or saline at the end of the first trimester. Brain tissue was collected from the offspring at 3.5 years and blocks of dorsolateral prefrontal cortex (BA46) were used to analyze neuronal dendritic morphology and spine density using the Golgi-Cox impregnation method. For each case, 10 layer III pyramidal cells were traced in their entirety, including all apical, oblique and basal dendrites, and their spines. We further analyzed somal size and apical dendrite trunk morphology in 30 cells per case over a 30 μm section located 100±10 μm from the soma. Compared to controls, apical dendrites of MIA-treated offspring were smaller in diameter and exhibited a greater number of oblique dendrites. These data provide the first evidence that prenatal exposure to MIA alters dendritic morphology in a nonhuman primate MIA model, which may have profound implications for revealing the underlying neuropathology of neurodevelopmental disorders related to maternal infection.

Keywords: Autism; IL-6; Neurodevelopment; Nonhuman primate; PolyIC; Pyramidal neuron morphology; Schizophrenia.

Figure 1

Neuroanatomy of dorsolateral prefrontal cortex. A) Lateral view of the left hemisphere indicating location of the coronal section depicted in B). B) Coronal section through DLPFC C) Approximate position of layer III pyramidal neuron soma measured along the dorsal limb of the principal sulcus (scale bar = 0.8mm).

Figure 2

A) Example of a Golgi impregnated layer III pyramidal neuron B) the same neuron with overlaid 3-D reconstruction of dendritic arbors from Neurolucida. Apical dendrite (yellow), basal dendrites (green, orange and red), axon (white) and spines (blue). Scale bar = 50μm

Figure 3

MIA treated animals exhibited more whole body stereotypies (i.e., pacing) compared to saline treated controls at 6 months of age. Each animal underwent 18 home cage observations (9 morning and 9 afternoon) comprising of six 10-second periods. Individual behaviors were scored using a one-zero sampling method corresponding to presence or absence of the behavior respectively (therefore the maximum score of any behavior over a single observation was 6). Scores were averaged across the 18 observations. (Control animals (all male – (blue)), MIA males (red), MIA female animals (pink), *P<0.05)

Figure 4

Diameter (μm) of apical dendrite shaft. MIA animals have thinner apical dendrites than control animals (A). Representative photomicrographs of control (B) and MIA (C) apical dendrites. (Control animals (all male – (blue)), MIA males (red), MIA female animals (pink)), scale bar = 5μm, *P<0.05)

Figure 5

Average number of oblique dendrites within the first 100μm of apical dendrite. MIA animals have a greater number of proximal dendrites compared to control animals. (Control animals (all male – (blue)), MIA males (red), MIA female animals (pink),* P<0.05)