Physiol Behav. 2017 May 1;173:144-155.

Alteration of neurotrophin and cytokine expression in lymphocytes as novel peripheral markers of spatial memory deficits induced by prenatal stress.

Pascuan CGb+, Di Rosso MEa+, Pivoz-Avedikian JEc, Wald MRa, Zorrilla Zubilete MAc,d, Genaro AMa,c*.

 

a Instituto de Investigaciones Biomédicas (BIOMED), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)—Universidad Católica Argentina (UCA), Av. Alicia Moreau de Justo 1600, Piso 3, 1107 Buenos Aires, Argentina.
b Instituto de Genética “Ewald A. Favret” (IGEAF), Centro de Investigación en Ciencias Veterinarias y Agronómicas (CICVYA), Nicolas Repetto y de los Reseros s/n, 1686, Hurlingham, Provincia de Buenos Aires, Argentina.
c Departamento de Farmacología, Facultad de Medicina, Universidad de Buenos Aires (UBA), Paraguay 2155, Piso 15, 1121 Buenos Aires, Argentina.
d Centro de Estudios Farmacológicos y Botánicos (CEFYBO), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad de Buenos Aires (UBA), Paraguay 2155, Piso 16, 1121 Buenos Aires, Argentina.

+Pascuan CG and Di Rosso ME contributed equally to this paper.

*Corresponding author at: Instituto de Investigaciones Biomédicas (BIOMED), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)—Universidad Católica Argentina (UCA), Av. Alicia Moreau de Justo 1600, Piso 3, 1107 Buenos Aires, Argentina. E-mail address: amgenaro@yahoo.com.ar (A.M. Genaro)

PMID: 28167147

 

Supplement:

Intrauterine experiences can profoundly affect the fetus and thus influence subsequent postnatal development. Research on both animals and humans is providing accumulating evidence that maternal psychosocial stress during pregnancy can have long-term effects on offspring development. The response to stress involves precise and fine interrelations between the hypothalamus–pituitary–adrenal axis (HPA), sympathetic–parasympathetic efferent pathways and chemical messengers (hormones, neurotransmitters, interleukins, neurotrophins) (1). When stress remains in time, dysregulation of these response system take place inducing severe consequences (1). Prenatal stress (PS) can result in stable long-term changes in central and peripheral stress response systems as well as influence the response to stress in adulthood (2). In particular, HPA dysregulation has been exhaustively studied and it has been the most commonly proposed mechanism related to behavior alterations (3). However, the participation of other factors involved in stress-related pathology, such as neurotrophins and cytokines (4), has not been exhaustively studied. Neurotrophins include secreted growth factors such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and NT4. It has been demonstrated that they have an important function in the formation and plasticity of neuronal networks (5). Moreover, it is now accepted that the immune system can signal the central nervous system through the action of cytokines (6). In addition, shifts in the relation Th1/Th2 cytokines have been implicated in many human illnesses including psychiatric disorders, such as autoimmune diseases, sleep disturbance, major depression and other disorders (7).

Taking into account these background, in these study we explored the impact of PS exposure on behavior and cognition in adult life as well as the impact of PS on chronic stress situations. As hippocampus is one of the main brain formations that participate in cognition, we analyzed the levels of neurotrophins and cytokines in this brain formation. Furthermore, we analyzed these changes in lymphocytes to propose these cells as peripheral markers of susceptibility to behavioral alterations. As there is a consensus about a differential response to PS for female and males, we performed a comparative study using both sexes.

To achieve these objectives pregnant mice were stressed by immobilization in a cylindrical tube (4 cm diameter, 10 cm long) for 2 h daily (from 10 AM to 12) from day 15 of pregnancy until delivery (days 20-21). Non-exposed control pregnant female were left undisturbed during their entire pregnancy. Offspring from control and stressed mothers were separated at postnatal day 21 and placed in an identical environment up to an age of 60 days. At this age, a group of mice of both prenatal conditions, subjected or not to PS, was exposed to chronic stress by immobilization (2h per day during 3 weeks). Thus, four groups of animals were established: mice that never were exposed to stress (offspring from unstressed females that were left undisturbed), mice from unstressed females that received chronic stress as adults, mice exposed only to PS and mice that received both PS and chronic stress as adults.

We observed that adult females exposed to PS had a spatial memory impairment that was major after chronic stress exposure. Thus, PS in females resulted in a deficit for recognizing objects in place. In addition, female exposed to PS showed a stronger impairment in object-in-place recognition and a poorer spontaneous alternation than control mice after chronic stress exposure. All these memories strongly depend on hippocampus integrity (8, 9). However, other task that are poorly dependent on hippocampus as object recognition without spatial cues were not affected (10). It appears that spatial memory, which strongly depends on hippocampus, is the main cognitive process affected by prenatal stress exposure. It is important to note that male subjected to PS did not present any memory impairment.

Concerning to molecular alterations, we found that spatial memory deficit was in parallel with increase in GR receptor, decrease of BNDF and Th1/Th2 alteration in hippocampus. The increase in glucocorticoid receptor mRNA expression and protein levels in hippocampus was found in both female and male. However, BNDF changes and decrease in INF-γ and increase in IL-4 was observed only in female. Interestingly these changes were observed in peripheral lymph nodes too.

The mechanisms underlying the link between PS and their behavioral consequences cannot be explained by a single pathway. Certainly, there are several central and peripheral pathways affected by PS with consequences that remain into adulthood. However, the most outstanding finding of the present investigation is that molecular alterations were found both in hippocampus and in peripheral lymphocytes. These results suggest that these cells could be peripheral markers of susceptibility to behavioral alterations. To confirm this proposal additional investigations are necessary, in particular to evaluate the potential helpfulness for the early treatment of the behavioral alterations associated with prenatal exposure to stress.

 

Figure 1: Schematics depicting the potential role of lymphocytes as peripheral markers of susceptibility to cognitive deficits induced by prenatal stress exposure.

 

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