Sex differences in myelin-associated protein levels within and density of projections between the orbital frontal cortex and dorsal striatum of adult rats: Implications for inhibitory control

Abstract

Impulsive actions and decisions often lead to undesirable outcomes. Lesion and neuroimaging studies have revealed that the orbital frontal cortex (OFC) and dorsal striatum (dSTR) play key roles in inhibitory control. It has been proposed that greater OFC input into the dSTR reflects enhanced top-down cognitive control and less impulsive responding. We previously reported a sex difference in inhibitory control, such that female rats make fewer impulsive errors than do male rats. The goal of the present study was to investigate differences in the OFC and dSTR of young adult male and female rats. In Experiment 1, we measured levels of two myelin-associated proteins, myelin basic protein (MBP) and myelin proteolipid protein (PLP), in the OFC and dSTR. Western blot data revealed that females had significantly higher levels of both MBP and PLP in the OFC but similar levels in the dSTR as compared to males. In Experiment 2, we infused the anterograde tracer, biotinylated dextran amine (BDA), into the OFC and measured the density of BDA in the dSTR. BDA was visualized using histochemistry followed by light microscopy imaging and densitometry analysis. Density of BDA in the dSTR was significantly greater in females as compared to males indicating that the projections from the OFC to dSTR may be greater in females as compared to males. Our results suggest a potential neuroanatomical sex difference that may contribute to the reported differences in inhibitory control levels of male and female rats.

Adult age differences in subcortical myelin content are consistent with protracted myelination and unrelated to diffusion tensor imaging indices

“…Although in vivo literature on sex differences in white matter properties is very inconsistent (Salat, 2014), this finding is consistent with the reported higher levels of myelin associated proteins in female rodents (Bayless & Daniel, 2015) and may reflect greater g-ratio in men compared to women (Paus, et al, 2009). The g-ratio, the fraction of the axon radius within its membrane in the its radius including the myelin sheath, is a dimensionless index bracketed between 0 and 1, with values closer to 1 indicating thinner myelin sheathe relative to the axonal radius.…”

Pubertal hormones mediate sex differences in levels of myelin basic protein in the orbitofrontal cortex of adult rats

“…To test this hypothesis we conducted three experiments. In Experiment 1, we confirmed a previously observed sex difference (Bayless and Daniel 2015) in adult levels of myelin basic protein (MBP). In Experiment 2, we examined the role of adult circulating gonadal hormone exposure in mediating a sex difference in OFC MBP levels via activational hormone effects.…”

“…Results of research from our lab reveal a sex difference in levels of markers for connectivity within the OFC (Bayless and Daniel 2015). Specifically, adult female rats exhibit greater levels of myelin basic protein (MBP), an abundant protein involved in myelin structure (Boggs 2006), than males.…”

No Evidence for Sex Differences in the Electrophysiological Properties and Excitatory Synaptic Input onto Nucleus Accumbens Shell Medium Spiny Neurons

“…It remains unclear whether these sex differences in intrinsic electrophysiological properties persist into adulthood, although it is clear that cultured striatal neurons and adult dorsal striatal neurons and dopaminergic inputs are sensitive to the acute action of estradiol ( Mermelstein et al, 1996 ; Becker and Hu, 2008 ; Schultz et al, 2009 ; Grove-Strawser et al, 2010 ; Almey et al, 2015 ; Tozzi et al, 2015 ). Additionally, there is evidence suggesting increased excitatory projections into the dorsal striatum of adult females compared with males ( Bayless and Daniel, 2015 ), and estradiol modulation of striatal-mediated learning and memory processes ( Korol and Pisani, 2015 ).…”