Regional Differences of Serotonin‐Mediated Synaptic Plasticity in the Chicken Spinal Cord With Development and Aging

Abstract

Previous studies in our laboratory /3,17/ have demonstrated that serotonin (5-HT) appears to have a trophic-like effect in enhancing synapse formation and maintenance in both the developing and the adult central nervous system. In the present study, we focused on age-related changes in the density of the axosomatic and axodendritic synapses and the number of 5-HT-positive fibers in the chicken spinal cord, with special reference to differences between the ventral (laminae VII and IX) and the dorsal (lamina I) horn. At 1 week posthatching (PIW), a transient overproduction of synapses and 5-HT-immunoreactive fibers occurred in lamina IX; all parameters had returned to their initial levels by 1 month post-hatching (PIM). The density of synapses further decreased by about 40% between P6M and P2Y (2 years posthatching). Although the magnitude of the transient increase in lamina VII was less than that in lamina IX, the changing pattern of the synapses and the 5-HT-positive fibers was similar in both regions. In the ventral horn, thin 5-HT-positive fibers were most prominent at P1W and then decreased with development; thin 5-HT-positive fibers were still found at P6M but had almost disappeared by P2Y. By contrast, at P2Y the density of the synapses and the 5-HT-positive fibers in the dorsal horn was even higher than that of younger animals.Reduction of 5-HT levels in P2Y-old chickens by p-chlorophenylalanine (pCPA) administration decreased the synaptic density in lamina I but not in lamina IX. The results of this study demonstrate that 5-HT-mediated synaptic plasticity is markedly different in the ventral and dorsal horns of the aged chicken. In the ventral horn, synaptic plasticity reached a maximum at about P1W, remained stable in the young-adult period, and then finally disappeared in the aged chicken. Conversely, the results suggest that in the dorsal horn, 5-HT fibers continue to mediate the trophic influence on synaptic plasticity even in the old chicken.

Exogenous dehydroisoandrosterone sulfate reverses the dendritic changes of the central neurons in aging male rats

“…It would appear therefore that dendritic change is a common feature affecting most central neurons such as pyramidal neurons in the medial prefrontal cortex (Grill and Riddle, 2002), motor cortices (Nakamura et al, 1985) and hippocampus (Luine et al, 2011), cerebellar Purkinje neurons (Zhang et al, 2010) and retinal ganglion cells (Samuel et al, 2011). It is suggested that regression in dendritic arbor and loss of dendritic spines on layer III, layer V primary somatosensory cortical neurons or hippocampal CA1 pyramidal neurons as observed in this study in aging rats may reflect different degrees of degenerative changes that might be induced by regional changes in trophic support (Chen et al, 1997) or in neuronal activity (Grill and Riddle, 2002). In the clinic, such dendritic arbor regression and reduction in dendritic spine density of cortical pyramidal neurons may contribute to behavioral dysfunctions as observed in aging including cognitive loss, anxiety, fatigue, poor concentration and memory, and confusion.…”

Communication breakdown: The impact of ageing on synapse structure

“…In both the rat (monoaminergic innervation − 3 versus 24 months; Ranson et al, 2003) and chicken (serotonin-mediated innervation – up to 2 years; Chen et al, 1997), innervation decreases with age in the ventral horn, yet it is retained or even increases during ageing in other areas, such as for 5-HT positive fibers in the dorsal horn of the chicken. Comparison of axosomatic and axodendritic synaptic density from hatching to 2 years in lamina I of the dorsal horn and lamina IX of the ventral horn shows opposite changes in synaptic density, with an increase in I and a decrease in IX (e.g., for the latter, axodendritic density changes from ~24 to ~13 synapses per 200 square micrometers).…”

Maternal administration of thalidomide or valproic acid causes abnormal serotonergic neurons in the offspring: implication for pathogenesis of autism

“…Coronal serial sections were cut at a thickness of 40 m on a freezing microtome, and every third section was used for 5-HT immunohistochemistry staining. The free-floating sections were pretreated overnight with 0.3% triton X-100/0.01 M PBS, then were blocked by 5% normal goat serum (NGS, Invitrogen, Carlsbad, CA, USA), prior to an incubation with anti-5-HT antiserum (at 1:10,000 dilution for 4 h at 37 • C,) (Chen et al, 1997). Biotinated anti-rabbit antibody (Vector Laboratories, Burlingame, CA, USA) was used as the secondary antibody, at 1:400 dilution for 1 h, followed by a Vecstastain ABC kit (Vector Laboratories).…”