The use of primary mammalian neurons derived from embryonic central nervous system tissue is limited by the fact that once terminally differentiated into mature neurons, the cells can no longer be propagated. Transformed neuronal-like cell lines can be used in vitro to overcome this limitation. However, several caveats exist when utilizing cells derived from malignant tumors. In this context, the popular SH-SY5Y neuroblastoma cell line and its use in in vitro systems is described. Originally derived from a metastatic bone tumor biopsy, SH-SY5Y (ATCC® CRL-2266™) cells are a subline of the parental line SK-N-SH (ATCC® HTB-11™). SK-N-SH were subcloned three times; first to SH-SY, then to SH-SY5, and finally to SH-SY5Y. SH-SY5Y were deposited to the ATCC® in 1970 by June L. Biedler. Three important characteristics of SH-SY5Y cells should be considered when using these cells in in vitro studies. First, cultures include both adherent and floating cells, both types of which are viable. Few studies address the biological significance of the adherent versus floating phenotypes, but most reported studies utilize adherent populations and discard the floating cells during media changes. Second, early studies by Biedler’s group indicated that the parental differentiated SK-N-SH cells contained two morphologically distinct phenotypes: neuroblast-like cells and epithelial-like cells (Ross et al., J Nat Cancer Inst 71:741–747, 1983). These two phenotypes may correspond to the “N” and “S” types described in later studies in SH-SY5Y by Encinas et al. (J Neurochem 75:991–1003, 2000). Cells with neuroblast-like morphology are positive for tyrosine hydroxylase (TH) and dopamine-β-hydroxylase characteristic of catecholaminergic neurons, whereas the epithelial-like counterpart cells lacked these enzymatic activities (Ross et al., J Nat Cancer Inst 71:741–747, 1983). Third, SH-SY5Y cells can be differentiated to a more mature neuron-like phenotype that is characterized by neuronal markers. There are several methods to differentiate SH-SY5Y cells and are mentioned below. Retinoic acid is the most commonly used means for differentiation and will be addressed in detail.

Approximately 40 million people worldwide are infected with human immunodeficiency virus (HIV). Despite HIV's known propensity to infect the CNS and cause neurological disease, HIV neurocognitive disorders remain under-recognized. Although combination antiretroviral therapy has improved the health of millions of those living with HIV, the penetration into the CNS of many such therapies is limited, and patients' quality of life continues to be diminished by milder, residual neurocognitive impairment. Synaptodendritic neuronal injury is emerging as an important mediator of such deficits in HIV. By carefully selecting specific antiretrovirals and supplementing them with neuroprotective agents, physicians might be able to facilitate innate CNS repair, promoting enhanced synaptodendritic plasticity, neural function and clinical neurological status.

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The risk for HIV infection attributable to methamphetamine (METH) use continues to increase. The combined effect of HIV and METH in the pathogenesis of HIV encephalitis (HIVE) is unclear, however. To better understand the neuropathology associated with HIV and METH use, the patterns of neurodegeneration were assessed in HIV-positive METH users and in HIV-positive non-METH users. Patients in the study met criteria for inclusion and received neuromedical and postmortem neuropathologic examinations. Immunocytochemical and polymerase chain reaction analyses were performed to determine brain HIV levels and to exclude the presence of other viruses. METH-using patients with HIVE showed significantly lower gp41 scores and less severe forms of encephalitis but a higher frequency of ischemic events, a more pronounced loss of synaptophysin immunoreactivity, and a more severe microglial reaction than HIVE non-METH users. Furthermore, in METH-using patients with HIVE, extensive loss of calbindin (CB)-immunoreactive interneurons displaying phylopodial neuritic processes suggestive of aberrant sprouting was observed. Taken together, these studies indicate that the combined effects of METH and HIV selectively damage CB immunoreactive nonpyramidal neurons. In combination, METH and HIV may increase neuronal cell injury and death, thereby enhancing brain metabolic disturbances observed in clinical populations of HIV-positive METH abusers.