2-methoxyestradiol inhibits differentiation and is cytotoxic to osteoclasts.

2-Methoxyestradiol (2-ME), a naturally occurring metabolite of 17beta-estradiol, is highly cytotoxic to a wide range of tumor cells but is harmless to most normal cells. However, 2-ME prevented bone loss in ovariectomized rats, suggesting it inhibits bone resorption. These studies were performed to determine the direct effects of 2-ME on cultured osteoclasts. 2-ME (2 microM) reduced osteoclast number by more than 95% and induced apoptosis in three cultured osteoclast model systems (RAW 264.7 cells cultured with RANKL, marrow cells co-cultured with stromal support cells, and spleen cells cultured without support cells in media supplemented with RANKL and macrophage colony stimulating factor (M-CSF)). The 2-ME-mediated effect was ligand specific; 2-hydroxyestradiol (2-OHE), the immediate precursor to 2-ME, exhibited less cytotoxicity; and 2-methoxyestrone (2-MEOE1) the estrone analog of 2-ME, was not cytotoxic. Co-treatment with ICI 182,780 did not antagonize 2-ME, suggesting that the cytotoxicity was not estrogen receptor-dependent. 2-ME-induced cell death in RAW 264.7 cells coincided with an increase in gene expression of cytokines implicated in inhibition of differentiation and induction of apoptosis. In addition, the 2-ME-mediated decrease in cell survival was partially inhibited by anti-lymphotoxin(LT)beta antibodies, suggesting that 2-ME-dependent effects involve LTbeta. These results suggest that 2-ME could be useful for treating skeletal diseases in which bone resorption is increased, such as postmenopausal osteoporosis and cancer metastasis to bone.

Cocaine self-administration alters the morphology of dendrites and dendritic spines in the nucleus accumbens and neocortex.

We studied the influence of cocaine use on the structure of neurons in brain regions that contribute to its rewarding effects by allowing rats to self-administer cocaine (0.33 mg/infusion) for 1 h a day for 1 month. Control animals were left undisturbed or allowed to work for food for the same period of time. After an additional 1 month drug-free period the brains were processed for Golgi-Cox staining. In rats that self-administered cocaine, but not rats that worked for food, there was a significant increase in dendritic branching and in the density of dendritic spines on medium spiny neurons in the shell of the nucleus accumbens and on pyramidal cells in the prefrontal and parietal (but not occipital) cortex. There was also a 2.6-fold increase in the incidence of spines with multiple heads (branched spines) on medium spiny neurons. Finally, in the prefrontal cortex some of the apical dendrites of pyramidal cells appeared misshaped, having large bulbous structures on their terminal tips. We speculate that cocaine self-administration experience alters patterns of synaptic connectivity within limbocortical circuitry that is thought to contribute to cocaine's incentive motivational effects and may have neuropathological effects in frontal areas involved in decision making and judgment. Together, these two classes of drug-induced neuroadaptations may contribute to the development of addiction.

Immunosuppression prevents neuronal atrophy in lupus-prone mice: evidence for brain damage induced by autoimmune disease?

An early onset of systemic, lupus-like disease in MRL-lpr mice is accompanied by deterioration in their behavioral performance and atrophy of pyramidal neurons in the parietal cortex and the hippocampal CA1 area. Using the immunosuppressive drug cyclophosphamide (CY) to attenuate the disease, we have tested the hypothesis that the autoimmune/inflammatory process is responsible for changes in brain morphology. A modified Golgi impregnation method revealed that, in comparison to saline-treated controls, immunosuppressive treatment with CY (100 mg/kg/week i.p. over 8 weeks) increased dendritic branching and spine numerical density in the CA1 region of MRL-lpr mice and MRL +/+ mice, which develop less severe manifestations of the disease. More interestingly, CY selectively prevented the atrophy and aberrant morphology of pyramidal neurons in the parietal cortex of MRL-lpr mice. The neuropathological measures (in particular reduced dendritic spine density) significantly correlated with increased serum levels of antinuclear antibodies and splenomegaly. The present results support the hypothesis that chronic autoimmune disease induces functionally important changes in neuronal morphology, and provide an empirical basis for understanding the behavioral dysfunction in systemic lupus erythematosus and autoimmune phenomena reported in some forms of mental illness.

Cortical plasticity and the development of behavior after early frontal cortical injury.

It has been known for over 100 years that frontal lobe injury in children is often associated with considerably more functional recovery than after similar injury in adulthood. Systematic study of frontal cortical injury in laboratory animals has shown that this recovery is tightly tied to developmental age: There is a brief window of time during cortical development during which the brain is able to compensate. Simply being young is not sufficient because injury prior to this critical period leads to miserable behavioral outcomes. For humans, the least favorable time for cortical injury is likely at the end of the gestational period, perhaps including the 1st month or so of life whereas the most favorable time is around 1 to 2 years of age. In addition to age, the extent of behavioral recovery is influenced by age at assessment, the nature of the behavioral assessment, sex, and lesion size. Anatomical studies have shown that functional recovery following early cortical injury is correlated with a reorganization of remaining cortical circuitry, including increased dendritic arborization and increased spine density. Recovery, and the compensatory anatomical changes, can also be potentiated by application of different treatments including behavioral therapy, trophic factors, and neuromodulators. Finally, there is preliminary evidence in laboratory animals to suggest that it may be possible to induce neural regeneration in the injured brain and that the regenerated brain functions to support functional recovery.

Progressive atrophy of pyramidal neuron dendrites in autoimmune MRL-lpr mice.

The autoimmune-prone MRL-lpr substrain of mice develop an autoimmunity-associated behavioral syndrome (AABS) which resembles in many respects the behavior of animals exposed to chronic stress. The present study examined whether these mice show changes in the morphology of neuronal dendrites, as found in animals exposed to chronic stress. A modified Golgi-Cox procedure was used to visualize the dendrites of pyramidal neurons in the parietal cortex and in the CA1 hippocampal field of 5-week and 14-week old MRL-lpr mice and MRL + / + controls. Reduced dendritic branching and length, and an up to 20% loss of dendritic spines were observed in parietal and hippocampal pyramidal neurons of MRL-lpr mice at both ages. In the parietal cortex, there was an age-dependent potentiation in the reduction of basilar, but not apical, dendrite branching and length, as well as in the loss of spines on basilar segments. Loss of spines in the hippocampus followed an age-related course for apical but not basilar dendrites. Moreover, compared to age-matched controls, brain weight was smaller in MRL-lpr mice at 14 but not 5 weeks of age. Considering that dendritic atrophy becomes more extensive when autoimmune disease is florid in MRL-lpr mice, it is proposed that immune/inflammatory factor(s) produce dendritic loss. Reduced dendritic complexity may represent, at least in part, a structural basis for the altered behavioral profile of MRL-lpr mice.

Possible regeneration of rat medial frontal cortex following neonatal frontal lesions.

The experiments described here show that the cavity left by midline frontal cortex removals at 10 days of age (P10) fills in with neural tissue. Similar changes are not found at earlier and later ages. This neuronal filling is blocked by prior pretreatment by administration of Bromodeoxyuridine (BrdU) on embryonic day 13. Administration of BrdU following the P10 lesion does not interfere with regrowth. Subsequent immunohistochemical staining for BrdU demonstrates the regrown area to be composed of newly generated cells. which include pyramidal and nonpyramidal neurons. Injections of a retrograde tracer into the striatum or posterior parietal cortex shows that the new neurons have connections similar to those of undamaged brains. The regrowth of this tissue is correlated with recovery of function in a test of forelimb use. Thus, the mammalian brain, during some privileged postnatal stages of growth. is capable of extensive reorganization that includes regeneration of lost neurons. These results are discussed in relation to the proximity of the lesion to the stem cells in the lateral ventricle and their postnatal migrational activities.

Age, experience and the changing brain.

In this review, various aspects of how environmental experience effects the structure of the cortex at different times in the age of the animal are summarized. The interactions of brain injury and sex on the age-dependent plastic changes in the cortex are also considered. Finally, we have attempted to reach some general conclusions that describe the effects of age, experience, sex, and injury on the cortex.

Nerve growth factor stimulates growth of cortical pyramidal neurons in young adult rats.

The cytoarchitectonics of pyramidal neurons in the cerebral cortex of non-lesioned rats can be re-modeled by i.c.v. infusions of nerve growth factor (NGF). 4 months after the application of NGF, the pyramidal neurons in layers III and V of the motor cortex and layer V of the anterior cingulate cortex were analyzed and compared with pyramidal neurons from vehicle-treated rats. NGF-treated brains showed: (1) significant increase in dendritic branching in the basilar fields of the layer V, but not layer III, neurons; and (2) a significant increase in spine density in the terminal, but not proximal, dendritic branches. These findings indicated that, besides its known effects on forebrain cholinergic neurons, NGF produces a very generalized synaptic re-modeling involving the cells responsible for the major output of the cerebral cortex in the intact adult brain.

Does dendritic growth underly recovery from neonatal occipital lesions in rats.

Rats were given lesions of visual cortex on postnatal day 4 or 10, or in adulthood. Ninety days later they were trained on a horizontal-vertical stripes discrimination task and a visual-spatial navigation task. None of the operated rats acquired the tasks. The brains were processed for Golgi-Cox staining and dendritic arborization was quantified in the layer III pyramidal cells in somatosensory cortex. Relative to normal control brains, the neurons of the day 4 and adult operates showed a reduction in dendritic branching, whereas the neurons of the day 10 operates had a significant increase in dendritic arborization. This arborization may be related to enhanced somatosensory function but does not support recovery of visually-guided behavior.