Does Early Environmental Complexity Influence Tyrosine Hydroxylase in the Chicken Hippocampus and “Prefrontal” Caudolateral Nidopallium?

Abstract

In adult chickens, the housing system influences hippocampal morphology and neurochemistry. However, no work has been done investigating the effects of the early life environment on chicken brain development. In the present study, we reared 67 commercial laying hens (Gallus gallus domesticus) in two environments that differed in the degree of complexity (aviary or cage system). These two groups were further divided into two age groups. At 20 weeks of age, 18 aviary-reared birds and 15 cage-reared birds were humanely euthanized and their brains dissected. At 24 weeks of age, a further 16 brains from aviary-reared birds and 18 brains from cage-reared birds were collected. These brains were prepared for immunohistochemical detection of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of dopamine, in the hippocampus and the caudolateral nidopallium (NCL). There were no differences between the treatment groups in TH staining intensity in the hippocampus or the NCL. In the medial hippocampus, the right hemisphere had higher TH staining intensity compared to the left hemisphere. The opposite was true for the NCL, with the left hemisphere being more strongly stained compared to the right hemisphere. The present study supports the notion that the hippocampus is functionally lateralized, and our findings add to the body of knowledge on adult neural plasticity of the avian brain.

Relationships Between Rearing Enrichments, Range Use, and an Environmental Stressor for Free-Range Laying Hen Welfare

“…It is possible that the structural enrichments during rearing resulted in neurological changes such as greater hemispheric flexibility that improved adaptive responses to their environments (43). Previous comparisons between cage-reared and aviary-reared hens showed functional lateralization in the hippocampus and caudolateral nidopallium but no differences between the rearing treatments, although all birds were in similar environments for the first 4 weeks of rearing (44). Campbell et al (45) found no differences in the telencephalon or hippocampal volume between enriched-reared and nonenriched-reared hens.…”

Spatial Cognition and Range Use in Free-Range Laying Hens

“…Adult laying hens (48 weeks of age) kept in different housing systems (battery cages, floor litter pens, and free-range) from 16 weeks onwards showed neuroanatomical differences, with free-range hens having larger cells in the dorsomedial hippocampus than caged but not floor-litter housed hens [ 11 ]. In contrast, neuroanatomical studies on a separate group of birds from the same adult environments showed no rearing-treatment impacts on the immunohistochemical detection of tyrosine hydroxylase in the hippocampus at 20 or 24 weeks of age [ 12 ]. Differences may have been detected in the current study if other measures were made such as dendritic length [ 34 ], neurogenesis [ 35 ], lateralisation, or immunohistochemical staining [ 12 ].…”

“…In contrast, neuroanatomical studies on a separate group of birds from the same adult environments showed no rearing-treatment impacts on the immunohistochemical detection of tyrosine hydroxylase in the hippocampus at 20 or 24 weeks of age [ 12 ]. Differences may have been detected in the current study if other measures were made such as dendritic length [ 34 ], neurogenesis [ 35 ], lateralisation, or immunohistochemical staining [ 12 ]. Alternatively, the enriched rearing treatment may not have been sufficient to have neurological impact.…”

“…These studies indicate spatial learning ability in laying hens can be experience-dependent and improved by environmental complexity during development. Different housing environments can also result in variation in hen brains such as in the hippocampus and nidopallium caudolaterale [ 11 ], but not in all cases, and thus may depend on extent of exposure to different housing environments and bird age [ 12 ]. The outdoor conditions in a free-range system are typically more dynamic compared to environmentally controlled indoor housing.…”

Study of environmental thermal variation in vineyards harvested by different curtain colors used as lateral closure

“…Although there is influence of the local climate the animals also generate heat. According to Cecchin (2016), the metabolism of growing chicken directly influences the temperature of the environment, supported by studies confirming the effect of chick age on avian temperature (FREITAS et al, 2017;TAHAMTANI et al, 2016). Nevertheless, for Freitas (2017), the greatest influence is on environmental factors, as evidenced by Mohammadalipour et al (2017) and Santos et al (2016).…”