Acute stress-induced neuronal plasticity in the corticoid complex of 15-day-old chick, Gallus domesticus

Unpredictable chronic mild stress shows neuronal remodeling in multipolar projection neurons of hippocampal complex in postnatal chicks

The hippocampal complex of birds is a narrow-curved strip of tissue that plays a crucial role in learning, memory, spatial navigation, and emotional and sexual behavior. This study was conducted to evaluate the effect of unpredictable chronic mild stress in multipolar neurons of 3-, 5-, 7-, and 9-week-old chick's hippocampal complex. This study revealed that chronic stress results in neuronal remodeling by causing alterations in dendritic field, axonal length, secondary branching, corrected spine number, and dendritic branching at 25, 50, 75, and 100 µm. Due to stress, the overall dendritic length was significantly retracted in 3-week-old chick, whereas no significant difference was observed in 5- and 7-week-old chick, but again it was significantly retracted in 9-week-old chick along with the axonal length. So, this study indicates that during initial days of stress exposure, the dendritic field shows retraction, but when the stress continues up to a certain level, the neurons undergo structural modifications so that chicks adapt and survive in stressful conditions. The repeated exposure to chronic stress for longer duration leads to the neuronal structural disruption by retraction in the dendritic length as well as axonal length. Another characteristic which leads to structural alterations is the dendritic spines which significantly decreased in all age groups of stressed chicks and eventually leads to less synaptic connections, disturbance in physiology, and neurology, which affects the learning, memory, and coping ability of an individual.

Neuronal plasticity in hippocampal neurons due to chronic mild stress and after stress removal in postnatal chicks

The avian dorsomedial surface of the cerebral hemisphere is occupied by the hippocampal complex (HCC), which plays an important role in learning, memory, cognitive functions, and regulating instinctive behavior patterns. The objective of the study was to evaluate the effect of chronic mild stress (CMS) in 4, 6, and 8 weeks and after chronic stress removal (CSR) in 6 and 8 weeks, on neuronal plasticity in HCC neurons of chicks through the Golgi-Cox technique. Further, behavioral study and open field test were conducted to test of exploration or of anxiety. The study revealed that the length of CMS and CSR groups shows a similar pattern as in nonstressed (NS) chicks, while weight shows nonsignificant decrease due to CMS as compared to NS and after CSR. The behavioral test depicts that the CMS group took more time to reach the food as compared to the NS and CSR groups. Due to CMS, the dendritic field of multipolar neurons shows significant decrease in 4 weeks, but in 6- and 8-week-old chicks, the multipolar, pyramidal, and stellate neurons depict significant decrease, whereas after CSR all neurons show significant increase in 8-week-old chicks. In 4- and 8-week-old chicks, all neurons depict significant decrease in their spine number, whereas in 6 weeks only multipolar neurons show significant decrease, but after CSR significant increase in 8-week-old chicks was observed. The study revealed that HCC shows continuous neuronal plasticity, which plays a significant role in normalizing and re-establishing the homeostasis in animals to survive.