Dendritic Spine Density and Dynamics of Layer 5 Pyramidal Neurons of the Primary Motor Cortex Are Elevated With Aging.

It is well established that motor impairment often occurs alongside healthy aging, leading to problems with fine motor skills and coordination. Although previously thought to be caused by neuronal death accumulating across the lifespan, it is now believed that the source of this impairment instead stems from more subtle changes in neural connectivity. The dendritic spine is a prime target for exploration of this problem because it is the postsynaptic partner of most excitatory synapses received by the pyramidal neuron, a cortical cell that carries much of the information processing load in the cerebral cortex. We repeatedly imaged the same dendrites in young adult and aged mouse motor cortex over the course of 1 month to look for differences in the baseline state of the dendritic spine population. These experiments reveal increased dendritic spine density, without obvious changes in spine clustering, occurring at the aged dendrite. Additionally, aged dendrites exhibit elevated spine turnover and stabilization alongside decreased long-term spine survival. These results suggest that at baseline the aged motor cortex may exist in a perpetual state of relative instability and attempts at compensation. This phenotype of aging may provide clues for future targets of aging-related motor impairment remediation.

Cannabinoid system in the budgerigar brain.

Cannabinoid receptor density and cannabinoid receptor-mediated G protein stimulation were studied by autoradiographic techniques throughout the budgerigar (Melopsittacus undulatus) brain. The maximal CB(1) receptor density value (using [(3)H]CP55,940 as radioligand) was found in the molecular layer of the cerebellum (Mol), and high binding values were observed in the nucleus taeniae amygdalae (TnA), nucleus preopticus medialis, and nucleus pretectalis. The highest net-stimulated [(35)S]GTPgammaS binding values induced by the selective CB(1) receptor agonist WIN55,212-2 were observed in the nucleus paramedianus internus thalami, and high values of [(35)S]GTPgammaS binding were observed in the TnA, Mol, arcopallium dorsale and arcopallium intermedium. The distribution data suggest that in the budgerigar, as previously indicated in mammals, cannabinoid receptors may be related to the control of several brain functions in the motor system, memory, visual system, and reproductive behavior. The discrepancies between the cannabinoid receptor densities and the cannabinoid receptor-mediated stimulation found in several budgerigar brain nuclei support the hypothesis, previously described for mammals, of the existence of different G(i/o) protein populations able to associate with the cannabinoid receptors, depending on the brain structure, and could reflect the relative importance that cannabinoid transmission could exerts in each cerebral area.

Norepinephrine, epinephrine and MHPG levels in chick brain development.

In this study we determined the norepinephrine (NE), epinephrine and methoxy-hydroxy-phenyl-glycol (MHPG) levels in dissected chick telencephalon, diencephalon/mesencephalon and cerebellum in a number of stages from the late embryonic period (E16, E17, E18 and E19) and post-hatching period (P1, P2, P3, P4, P5, P15 and P30) using HPLC coupled with a coulometric detection system. A mobile phase which permits the detection of NE, epinephrine and MHPG simultaneously is also described. During development, NE levels increase dramatically after hatching in all brain structures studied and are not correlated in the same period with an increase in the MHPG/NE ratio. The values obtained for epinephrine and MHPG were significantly lower than the NE values in all the structures and stages studied. Our results support the notion of a specific role for NE during the first days after hatching.