Neural Plasticity

Review Article

Synaptic Plasticity, a Prominent Contributor to the Anxiety in Fragile X Syndrome

Table 1

Spine phenotypes in broad encephalic regions and at different periods. In the mouse model of FXS, spine density and morphology were altered in an age-, region-, and cell type-specific manner.


Brain areas		Methods	Spine phenotypes	Reference

Hippocampus	Development	P0 + 7 DIV or 21 DIV; fixed, Dil	Decreased density Normal length	[34]
		P0 + 16 DIV; fixed, FITC-phalloidin	High density Longer spines More immature and lacked synapse in puncta	[35]
		CA1 and CA3 E15/16 + 14 DIV or P7 Fixed and in vitro, GFP	Density not reported Longer spines at P7 More immature	[36]
		P6/7 + 4-5 DIV Fixed, cultured slices, two-photon, GFP	Normal density Length not reported	[37]
		CA1; 2-week-old; confocal imaging, fixed, Dil	Normal density Decreased spine length	[38]
	Adult	Dentate gyrus granule cells; juvenile-adult (P15–P60); fixed, Golgi, EM	Higher density Length NA More immature	[39]
		CA1; 3-month-old; fixed, Golgi	Higher density Length NA More immature	[40]
		CA1; 10/25-week-old; confocal imaging fixed, Dil	Normal density Longer spines	[38]

Amygdala	Adult	Basolateral amygdala; 3-month-old; fixed, Golgi	Higher density Longer spine More immature	[24, 40]

Cortex layer 2/3	Development	Barrel cortex; P7–P21; in vivo, two-photon, GFP	Normal density Normal length High turnover at P10–12 More immature spines	[23]
		Primary visual cortex; two-week-old; Golgi, fixed	Normal density Longer spines	[41]
		Prefrontal cortex; two-week-old; acute slice, two-photon	Normal density Longer spines	[13]
	Adult	Visual cortex; P35 (±1); Golgi, fixed	Higher density Length NA	[42]
		Temporal cortex Adult (two months) Golgi, fixed	Higher density Normal length (trend toward longer spines)	[43]
		Medial prefrontal cortex; adult (13 weeks); fixed, Golgi	Higher density Longer spines	[44]

Cortex layer 4	Development	Barrel cortex P7, P14; Golgi, fixed	Normal density	[45]

Cortex layer 5	Development	Barrel cortex P7–P21; fixed, two-photon, GFP	Normal density at P14 and P30; high density at P7 Longer at P7 and P14, then normal at P30	[19]
	Development	Barrel cortex P2 + 5 DIV; cultured slices, two-photon, GFP	Normal density Normal length Normal motility	[19]
	Adult	Visual cortex Adult Golgi, fixed	Higher density More immature	[46–48]
		Visual cortex Adult Golgi, fixed	Normal density Length NA More immature	[14]
		Barrel cortex Juvenile and adult Golgi, fixed	Normal density in juvenile (P25); higher in adults Normal length in juvenile; longer in adults More immature	[20]
		Occipital cortex Adult (60–90 days) Golgi, fixed	Higher density Longer spine More immature	[47]

Major drawbacks in comparing these different studies are caused not only by the use of different staining, quantification methods of spines, choice of tissue source, and hippocampal neurons cultured in in vivo or ex vivo brain tissue, but also by different mouse strains. Also, the classification of dendritic protrusions into different categories, such as mature and immature, differs between studies (some look at the presence versus absence of a head, other at the ratio between the width and the length of the protrusion, and also others, at the profile).
BDA, biotinylated dextran; DIV, days in vitro; EM, electron microscopy.
FITC, fluorescein isothiocyanate; Dil, diOlistic labelling.
GFP, green fluorescent protein; NA, not available.