Preconceptual paternal environmental stimulation alters behavioural phenotypes and adaptive responses intergenerationally in Swiss mice

Highlights

• Environmental enrichment (EE) changed physiological, molecular and behavioural parameters in F₀ male breeders.

• F1 male offspring of EE fathers showed poor behavioural adaptive responses to the standard housing.

• F1 female offspring of EE fathers had lower relative adrenal weights.

• A short period of EE during adulthood in the male offspring of EE fathers negated their behavioural deficits.

Abstract

Experimental research has recently revealed that paternal environmental conditions can influence the offspring phenotype through epigenetic mechanisms. However, it is unclear whether these effects impact adaptive responses in the offspring. Environmental enrichment (EE) is a well-established paradigm that promotes neural plasticity. We investigated whether EE in male mice could modify behaviours that are highly relevant for determining adaptive fitness, i.e. spatial memory, attractiveness and social dominance, in the offspring of outbred mice. Male Swiss mice were housed in either EE or standard housing from post-weaning to adulthood before breeding for offspring. Their offspring were raised in standard housing until adulthood then assessed for behavioural, physiological and molecular parameters. F₀ male mice exposed to EE had lower body weight, higher adrenal, spleen and hippocampal weights, better novelty processing and spatial learning, greater hippocampal BDNF levels, and higher social dominance. Unexpectedly, their male offspring (F₁) showed spatial memory impairment, lowered social dominance and were less attractive to receptive females, compared to controls. These ethologically relevant measures suggest a maladaptive response in the male F₁ offspring. Interestingly, when separate cohorts of male F₁ offspring of standard housing or EE fathers were exposed to 8-day EE protocol during adulthood, differences in spatial memory and attractiveness to receptive females were no longer observed between them. These results provide evidence that the paternal environment can influence the offspring’s adaptiveness.

Introduction

In recent years there has been a growing interest in the influence of the paternal environment on behavioural and physiological phenotypes of the offspring [3,7,63]. Epidemiological studies have shown that paternal exposure to low food availability during childhood reduced cardiovascular disease mortality in the male offspring [22] and that men who started smoking before the age of 11 years had sons with comparatively higher body mass index [41].

In the past decade, rodent studies have provided evidence of paternal transgenerational influences on offspring health and behaviour. This has been reported in a range of paradigms, such as paternal high-fat diet [36], early-life trauma [14,17], adolescent and adult chronic stress [45], and adult glucocorticoid treatment [52]. A diversity of physiological and behavioural responses has been described inter and transgenerationally, such as higher goal-directed behaviours and improved behavioural flexibility [18], increased anxiety-like behaviours [52] and blunted HPA axis responsivity [46]. Most of the studies on the epigenetic mechanisms underlying these effects were performed in inbred mice, which are isogenic. Taken together, these studies strongly support the role of epigenetic mechanisms modulating phenotype inter and transgenerationally [9].

Few studies investigated the effects of positive environment modulation strategies across the generations. Environmental Enrichment (EE), a paradigm of cognitive and physical stimulation involving complex housing environments, is known for promoting beneficial behavioural and neurochemical outcomes, such as improved spatial memory [27], increased Brain-Derived Neurotrophic Factor (BDNF) levels in the hippocampus [38] and increased neural plasticity [59], as well as increased sociability and reduced anxiety-like behaviour [42] (for review, see [54]). Studies that investigated the impact of paternal environment on offspring performance have shown that paternal EE induced improvement in cognition and synaptic plasticity in the offspring [6].

Given that paternal environment can exert an influence on behavioural phenotypes across generations, we raised the question whether this phenotypic plasticity would be adaptive. Indeed, according to Mitra and Sapolsky [32], environmental manipulations can change innate behaviours towards adaptive responses. These authors showed that EE enhanced male attractiveness through elevated testosterone production, with increased display of risk-assessment behaviour, and argued that, from an ethological perspective, such phenotypic adaptations confer increased chances of survival and opportunities for mating [32]. Therefore, through this approach, adaptive fitness might also be assessed by analysing other innate behaviours, such as spatial memory, which can be related to successful spatial navigation in a complex environment, and social dominance, that is interpreted as the capability of defending territories [61]. To our knowledge, no other study has taken a similar approach to interpreting the effects of paternal EE in modulating phenotypes relevant to determine adaptive fitness in the offspring.

Moreover, most of inter and transgenerational studies have used inbred animals, known for low genetic heterogeneity. Therefore, showing that parental environmental effects can also modulate the offspring phenotype in outbred strain would increase the body of evidence supporting the relevance of paternal contribution in epigenetic inheritance.

Therefore, we hypothesised that the paternal exposure to EE would induce beneficial effects in behaviours that are highly important for determining adaptive fitness in the offspring of outbred mice, which have a more diverse genetic makeup. We assessed physiological and molecular measures (organ weights, plasma corticosterone and hippocampal BDNF levels) and behavioural responses, including spatial memory, attractiveness in the mate-choice test and social dominance in EE fathers and their offspring.