Behavioral effects of chronically elevated corticosterone in subregions of the medial prefrontal cortex

Behavioral comparison of the C57BL/6 inbred mouse strain and their CB6F1 siblings

A large portion of basic biomedical research studies are conducted using genetically defined, inbred mouse strains. The C57BL/6 mouse strain is the most widely used genetic background in current rodent research. The rationale for using inbred strains is that all individuals are genetically identical with minimal phenotypic variation, allowing for more statistically powerful analyses. F1 hybrids between two inbred strains are also genetically identical to one another but are heterozygous at every locus at which the parental strains differ rather than homozygous. Both theoretical and empirical evidence suggests that this heterozygosity in F1 hybrids allow for potentially greater resilience in response to the inevitable stresses of laboratory environments. The purpose of this study was to characterize the differences in commonly used tests of physical performance (forelimb grip strength and rotarod) and anxiety-like behavior between the F1 hybrids created from BALB/c females mated to C57BL/6 males (called CB6F1 mice) and one of its parental strains, C57BL/6. We used a natural cross-fostering breeding scheme to minimize maternal care effects and emphasize the effects of genetic differences. We found significant correlations between anxiety-like behavioral measures and physical performance measures which are not traditionally associated with anxiety-like behavior, and which differ between strains. Findings from this study should be taken into consideration when designing behavioral studies and choosing model organisms.

Post-weaning exposure to Sunset Yellow FCF induces behavioral impairment and structural changes in the adult rat medial prefrontal cortex: protective effects of Coenzyme Q10

Sunset Yellow FCF (E110) is a water soluble synthetic dye that has adverse neurobehavioral effects. Coenzyme Q10 (CoQ10) is known as a neuroprotective agent. The present study aimed to evaluate the effects of post-weaning exposure to Sunset Yellow FCF on behavioral and structural changes in the adult rat medial prefrontal cortex and the protective effects of CoQ10. The weanling rats were randomly divided into six groups: distilled water, CoQ10 (10 mg/kg/day), and low (2.5 mg/kg/day), and high (70 mg/kg/day) doses of Sunset Yellow FCF with or without CoQ10 consumption for six weeks. A battery of behavioral tests including open field and Morris water maze tests were done at the end of the 6th week, and then the animals' brains were removed for stereological methods. Our finding indicated that the high dose of Sunset Yellow FCF led to a reduced total volume of mPFC (15.16%), especially in the anterior cingulate cortex (ACC) region (21.96%), along with loss of neurons (32%) and glial cells (37%), which was associated with higher anxiety behavior and loss in spatial memory. However, CoQ10 prevented the neural loss and glial cells, improved anxiety like behaviors and memory impairment. On the other hand, the acceptable daily dose (low dose of Sunset Yellow FCF) did not show a discernible effect on the same parameters. This study showed that the CoQ10 can protect the alteration in mPFC structure and behavioral changes of the rats exposed to high dose of Sunset Yellow FCF.

Prefrontal Regulation of Threat-Elicited Behaviors: A Pathway to Translation

Regions of the prefrontal and cingulate cortices play important roles in the regulation of behaviors elicited by threat. Dissecting out their differential involvement will greatly increase our understanding of the varied etiology of symptoms of anxiety. I review evidence for altered activity within the major divisions of the prefrontal cortex, including orbitofrontal, ventrolateral, dorsolateral, and ventromedial sectors, along with the anterior cingulate cortex in patients with clinical anxiety. This review is integrated with a discussion of current knowledge about the causal role of these different prefrontal and cingulate regions in threat-elicited behaviors from experimental studies in rodents and monkeys. I highlight commonalities and inconsistencies between species and discuss the current state of our translational success in relating findings across species. Finally, I identify key issues that, if addressed, may improve that success in the future.

Maternal separation blunted spatial memory formation independent of peripheral and hippocampal insulin content in young adult male rats

This study explores the effects of maternal separation as a chronic early life stress (ELS) on pancreatic islets insulin content and secretion, and their potential relationship with the hippocampus insulin content and spatial memory in young adulthood. Male rat offspring were divided into two groups: stress (STR) and non-stress (non-STR) groups. The animals of the STR group were separated from their mothers during postnatal days (PND) 1 to 21. During the weaning time, that is, PND-0 to PND-21, the body weight and length of the pups were measured. Blood samples were collected on PND-1, 21, 29 and 34 and during young adulthood (53±2 days) to determine plasma corticosterone and insulin levels. The young adult animals were also tested for spatial memory. One day after the memory test, the animals were decapitated and their pancreases were removed to measure the islets insulin content and secretion. Finally, the animals' hippocampi were isolated to determine their insulin content and insulin receptor protein amounts. During the period of weaning, the body weight and length of pups belonging to the STR group were significantly lower as compared to those in the non-STR group. Maternal separation did not change the plasma levels of insulin but increased plasma corticosterone levels from PND-21 to young adulthood and also reduced the islets insulin content but did not affect insulin secretion and the hippocampus insulin content and insulin receptor protein amount. Although, at the end of the memory tests, rats of the STR group reached the escape box at almost the same time and distance and with the same errors as rats of the non-STR group, the distance traveled to reach the escape box showed a steep reduction in the non-STR group as compared to the STR group after the first trial. Moreover, as compared to the STR group, the non-STR group showed an increasing trend for direct strategy to find the escape box. The islets insulin content and secretion, and the plasma insulin concentration were not significantly correlated with the hippocampus insulin content. From the results of the present study, it appears that the main behavioral effect of the maternal separation stress in the spatial memory task was to impair the strategy used by the animals to reach the escape box. This may indicate that maternal separation stress affects brain regions other than the hippocampus. Moreover, due to the reduction of the body weight and length of offspring belonging to the STR group, it should be further considered that both maternal separation and early life malnutrition are directly (and mechanistically) linked to cognitive alterations later in life in ways that are not dependent on peripheral and hippocampal insulin content.

High dose Allura Red, rather than the ADI dose, induces structural and behavioral changes in the medial prefrontal cortex of rats and taurine can protect it

Allura Red is a food color that can lead to neurotoxicity. Taurine is an organic compound that can act as a neuroprotectant. This study aimed to assess the effects of Allura Red with or without taurine consumption on rats' medial Prefrontal Cortex (mPFC). The subjects were divided into six groups as follows: distilled water, taurine (200 mg/kg/day), and low (7 mg/kg/day = acceptable daily dose), and high (70 mg/kg/day) doses of Allura Red with or without taurine consumption for six weeks. The results of novel objects recognition and eight-arm radial maze tests indicated impairment of memory in the Allura Red groups. Subsequently, their brains were analyzed using stereological methods. Both doses of Allura Red caused an increase in working and reference memory errors during the acquisition and retention phases in comparison to the distilled water group (p < 0.01). Additionally, the high dose of Allura Red led to a reduction in the volume of mPFC (35%) and its subdivisions, number of neurons (59%) and glial cells (46%), length of dendrites, and number of spines (mushroom and thin) per dendritic length in comparison to the distilled water group (p < 0.05). The low dose group only showed a reduction in the number of glial cells. However, simultaneous treatment of rats with taurine plus Allura Red prevented the above-mentioned changes. The acceptable daily dose of Allura Red could bring about impairment in spatial learning and memory as well as in the number of glial cells. On the other hand, the high dose of Allura Red could impair learning, memory, and mPFC structure. Thus, taurine could act as a neuroprotectant.

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.