Enduring cortical alterations after a single in-vivo treatment of HIV-1 Tat

Abstract

HIV-1 proteins, including the transactivator of transcription (Tat), are believed to be involved in HIV-associated neurocognitive disorders by disrupting Ca2+ homeostasis, which leads to progressive dysregulation, damage, or death of neurons in the brain. We have found previously that bath-applied Tat abnormally increased Ca2+ influx through overactivated, voltage-sensitive L-type Ca2+ channels in pyramidal neurons within the rat medial prefrontal cortex (mPFC). However, it is unknown whether the Tat-induced Ca2+ dysregulation was mediated by increased activity and/or the number of the L-channels. This study tested the hypothesis that transient/early exposure to Tat in vivo promoted enduring L-channel dysregulation in the mPFC without neuron loss. Accordingly, rats were administered a single intracerebroventricular injection of recombinant Tat (80 µg/20 µl; diluted by cerebrospinal fluids to pathophysiological concentrations) or vehicle. Rats were killed 14 days after injection for immunohistochemical assessments of the mPFC, motor cortex, caudate–putamen, and nucleus accumbens. Stereological estimates for positively stained cells indicated a significant increase in the number of cells expressing the pore-forming Cav1.2-α1c subunit of L-channels in the mPFC compared with other regions in Tat-treated or vehicle-treated rat brains. Optical density measurements showed a Tat-induced increase in glial fibrillary acidic protein expression, indicating astrogliosis in the cortical regions. There was no significant loss of neurons in any brain region investigated. These findings indicate that transient Tat exposure in vivo induced enduring L-channel dysregulation and astrogliosis in the mPFC without neuron loss. Such maladaptations may contribute toward dysregulated Ca2+ homeostasis and neuropathology in the PFC in the early stages of HIV infection.

HIV-1 Transgenic Rat Prefrontal Cortex Hyper-Excitability is Enhanced by Cocaine Self-Administration

“…High voltage-activated L-channel Ca v 1.2-α1c protein was overexpressed in the mPFC of Tg rats, both in the number of Ca v 1.2-ir PN and in the apparent level of expression within PN. Increased expression of Ca v 1.2-α1c also occurs in the mPFC of rats following intraventricular injections of HIV-1 Tat (Wayman et al, 2012). High voltageactivated L-channels are responsible for conducting large Ca 2+ currents into the neuron, and increasing the number and/or activity of these channels profoundly influences neuronal excitability.…”

“…Procedures for immunohistochemistry followed our published protocol (Wayman et al, 2012). To overview, chloral hydrate-anesthetized rats were perfused transcardially with ice-cold saline followed by 4% paraformaldehyde (pH 7.4).…”

“…Absence of primary antibody served as negative controls. Stereological estimates of Ca v1.2 -ir by a treatment-blind observer followed our published protocol (Wayman et al, 2012). In brief, the Stereo Investigator 2000 system (MBF Bioscience, Williston, VT) was used for unbiased stereological estimates per an optical fractionator procedure.…”

HIV-1-Tat excites cardiac parasympathetic neurons of nucleus ambiguus and triggers prolonged bradycardia in conscious rats

“…Five animals were used per each treatment group. In vivo studies evaluating Tat effects in the brain use Tat at a concentration of 3 or 4 g/l, which is Ͼ1,000 times higher than that commonly used in vitro (36,60). Similarly, microinjection in the rat nucleus ambiguus of higher concentrations of Tat (5-500 fmol/50 nl, i.e., 0.1-10 M) elicited the bradycardic responses.…”

“…Similarly, microinjection in the rat nucleus ambiguus of higher concentrations of Tat (5-500 fmol/50 nl, i.e., 0.1-10 M) elicited the bradycardic responses. The explanation may reside in the fact that Tat may be locally diluted upon microinjection (60) or that Tat is not only sensitive to oxidation, but also is particularly sticky, able to bind even to silanized glass surfaces (as in the syringe barrel and needle used in stereotaxic injections) (36).…”