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selective estrogen receptor modulators ( serms ) either synthetic or natural , such as phytoestrogens , are candidates for the treatment or the prevention of cognitive and affective disorders in men and women [ 15 ] .
several studies have shown that some synthetic serms , such as tamoxifen , raloxifene , or bazedoxifene [ 629 ] , some nonfeminizing estrogens [ 3034 ] , and some natural serms , such as genistein [ 35 , 36 ] , are neuroprotective in vitro and in vivo .
the neuroprotective effects of serms are associated with a decrease in the activation of microglia and astroglia and a reduction in brain inflammation [ 3743 ] .
in addition , some serms have shown to induce neuritic outgrowth in vitro [ 44 , 45 ] , suggesting that these molecules may also affect synaptic connectivity in vivo .
indeed , ers are involved in the regulation of dendritic spines in the hippocampus of female animals in vivo [ 4651 ] , where tamoxifen regulates synaptophysin expression .
serms are also able to regulate cholinergic , serotonergic , and dopaminergic neurotransmission in female animals [ 5356 ]
. however , the effects of serms on synaptic connectivity in males have not been adequately explored .
nevertheless , previous studies have shown that serms such as raloxifene and tamoxifen are able to counteract hippocampus - dependent cognitive deficits caused by androgen deprivation in male rats .
in addition , raloxifene reduces working memory deficits in male rats after traumatic brain injury . to further characterize the mechanisms of action of serms in the male brain ,
we have assessed in this study the effects of tamoxifen and raloxifene on the number and geometry of dendritic spines in ca1 pyramidal neurons of the rat hippocampus .
sprague - dawley adult male rats were maintained under regular 12  h light - dark cycles ( lights on : 07:0019:00  h ) and controlled environmental humidity ( 4550% ) and temperature ( 22  2c ) .
all the experimental procedures were conducted to minimize pain or discomfort in the animals and performed in accordance with the nih guide for care and use of laboratory animals ( nih publications no .
protocols were approved by our institutional animal care committee .    at the age of three months , animals were injected with raloxifene ( 1  mg / kg ; n = 6 ) , tamoxifen ( 1  mg / kg ; n = 6 ) , or vehicle ( 20  mg / ml dmso diluted 3% in saline solution ; n = 6 ) .
animals were anesthetized with 30  mg / kg intramuscular ketamine and 50  mg / kg i.p .
then , animals were perfused intracardially with 100  ml of a washing phosphate - buffered solution ( ph 7.4 ; 0.01  m ) containing 1000  iu / l of sodium heparin and 1  g / l of procaine hydrochloride . then
, 200  ml of a fixing phosphate - buffered 4% formaldehyde solution was perfused .
each brain remained for at least 48  h in 100  ml of a fresh fixing solution .
the bilateral dorsal hippocampi were dissected out and impregnated using a modification of the golgi method .
spine numerical density and the proportion of thin , mushroom , stubby , wide , branched , and double spines [ 5961 ] were assessed in ca1 pyramidal neurons .
spines were counted in one 50  m segment per cell , located in the middle of one of the secondary dendrites that protrude from the apical dendrite ( figure 1 ) .
the total number of spines counted was 5,796 in the animals treated with vehicle : 9,295 in the animals treated with raloxifene and 9,180 in the animals treated with tamoxifen .
the one - way anova and tukey post hoc test were used for statistical comparisons of data from spine numerical density .
in addition , one - way anova and bonferroni correction post hoc test were used for statistical comparisons of the proportion of the different types of spines .
the n used for statistical analysis was the number of animals ( n = 6 , per experimental group ) .
raloxifene and tamoxifen increased significantly the total numerical density of dendritic spines compared to control animals ( table 1 ) .
both serms increased the numerical density of mushroom , stubby , and wide spines ( table 1 ) .
in addition , raloxifene increased the numerical density of thin spines ( table 1 ) .
numerical density of mushroom spines was greater in tamoxifen - treated rats than in raloxifene - treated animals .
in contrast , thin and wide spines were less numerous in the tamoxifen group than in raloxifene - treated animals ( table 1 ) .
furthermore , raloxifene increased the proportion of stubby and wide spines and did not significantly affect the proportion of mushroom , branched and double spines ( table 2 ) .
as observed for raloxifene , the proportion of thin spines was also reduced in the animals treated with tamoxifen .
in contrast , mushroom and stubby spines were seen in greater proportion in animals treated with tamoxifen than in control animals .
tamoxifen had no significant effects in the proportion of wide , branched , and double spines ( table 2 ) .
the animals treated with tamoxifen showed a higher proportion of mushroom spines than those treated with raloxifene ( table 2 ) .
our present findings indicate that some serms , such as raloxifene and tamoxifen , affect the number of dendritic spines in male rats
. this action of serms may affect the processing of novel information used in memory formation .
in addition to increase the numerical density of spines , raloxifene and tamoxifen also affected spine geometry .
dendritic spine morphology affects the diffusion and compartmentalization of membrane - associated proteins   and the expression of ampa receptors [ 6467 ] .
in particular , the length of the spine neck seems to be a key regulator of spinodendritic ca2 + signaling [ 6872 ] and of the transmission of membrane potentials . in consequence ,
the geometry of dendritic spines may influence the processing of synaptic impulses [ 7479 ] .
our findings suggest , therefore , that raloxifene and tamoxifen , decreasing the proportion of thin dendritic spines , may influence the processing of information by hippocampal pyramidal neurons .
in addition , the action of raloxifene and tamoxifen presents some differences that may have functional significance .
thus , the animals treated with tamoxifen had an increased numerical density and proportion of mushroom spines compared to animals treated with raloxifene .
mushroom spines may be involved in the management of previously acquired information since they have larger postsynaptic densities   and express higher levels of ampa receptors [ 6467 ] .
therefore , the synapses on mushroom spines are functionally stronger   and it has been suggested that these spines would sustain memory storage [ 78 , 81 , 82 ] .  
the induction of plastic changes in dendritic spines by raloxifene and tamoxifen may be linked with the precognitive effects of these molecules in male rats [ 20 , 57 ] .
however , the possible impact of raloxifene and tamoxifen on cognitive decline in men remains to be adequately explored , in particular in association with neurodegenerative diseases .
for instance , both serms increase the levels of luteinizing hormone ( lh ) in men   and it has been proposed that elevated levels of lh may contribute to alzheimer 's disease pathogenesis .
indeed , leuprolide acetate , a gnrh agonist that lower serum levels of lh , has been shown to improve cognitive performance and decrease amyloid- deposition in a mouse transgenic model of alzheimer 's disease .
the findings of this study indicate that raloxifene and tamoxifen , two serms currently used in clinical treatments , promote an increase in the numerical density of dendritic spines and changes in spine geometry in the hippocampus of male rats .
these findings , together with the regulation exerted by tamoxifen and raloxifene on hippocampus - dependent cognitive function in male rats , suggest that serms may influence the processing of information by male hippocampal pyramidal neurons by affecting the number and shape of dendritic spines .
some selective estrogen receptor modulators , such as raloxifene and tamoxifen , are neuroprotective and reduce brain inflammation in several experimental models of neurodegeneration . in addition , raloxifene and tamoxifen counteract cognitive deficits caused by gonadal hormone deprivation in male rats . in this study 
 , we have explored whether raloxifene and tamoxifen may regulate the number and geometry of dendritic spines in ca1 pyramidal neurons of the rat hippocampus . 
 young adult male rats were injected with raloxifene ( 1  mg / kg ) , tamoxifen ( 1  mg / kg ) , or vehicle and killed 24  h after the injection . 
 animals treated with raloxifene or tamoxifen showed an increased numerical density of dendritic spines in ca1 pyramidal neurons compared to animals treated with vehicle . 
 raloxifene and tamoxifen had also specific effects in the morphology of spines . 
 these findings suggest that raloxifene and tamoxifen may influence the processing of information by hippocampal pyramidal neurons by affecting the number and shape of dendritic spines .