Synergistic decrease of spine density in HIV infected neuronal cells in the presence of nicotine. SK-N-MC cells were infected with HIV and/or treated with nicotine for 7 days. On the 5th day of HIV infection and/or nicotine treatment, vorinostat was added to the culture. a) Control SK-N-MC cells: High number of long spines on the dendritic length, high dendrite diameter, total dendrite area and spine area. b) Vorinostat treated Cells: Cells with the higher number of spines on a dendrite length similar to the control cells. c) Nicotine treated cells: Loss of spine on a dendrite length when compared to the control cells. d) Nicotine along with vorinostat: Restoration of spines on the dendrite length e) HIV infected cells: Loss of spines on the dendrite length, decreased dendrite diameter, dendrite and spine area was observed than the control neuronal cells. f) HIV infected cells in the presence of vorinostat: Recovery of spines on the dendrite length was observed. g) HIV infected cells in the presence of nicotine: Synergistic loss of number of spine on a dendrite length was observed when compare to the control or nicotine treated or HIV infected cells. h) HIV infected cells co-treated with nicotine in the presence of vorinostat: In the presence of vorinostat, spine density was restored when compare to the HIV + nicotine treated cells. (*, p ≤ 0.05; **, p ≤ 0.01; ***, p ≤ 0.001; ****, p ≤ 0.0001; NS-Not Significant).