This image contains text and a line graph which show that exposure to nicotine has direct and indirect effects on dopamine release in the brain’s reward center, the nucleus accumbens. The text from the image follows:

Nicotine (Nic) directly stimulates (+) neurons in the ventral tegmental area (VTA) to release dopamine (DA) in the nucleus accumbens (NAc). Nic also stimulates release of glutamate (Glu), triggering additional DA release. VTA cells stimulate release of GABA to moderate DA’s effect.

Minutes later, Glu cells continue to stimulate DA release (++), but release of GABA becomes inhibited (-), resulting in sustained high dopamine levels in the NAc.

Relative activity percentage (unstimulated condition=100 percent):

• Glu relative activity at -2 minutes: 100 percent
• Glu relative activity at 0 minutes: 100 percent
• Glu relative activity at 2 minutes: 400 percent
• Glu relative activity at 4 minutes: 400 percent
• Glu relative activity at 6 minutes: approximately 270 percent
• Glu relative activity at 8 minutes: 200 percent
• Glu relative activity at 10 minutes: 200 percent
• GABA relative activity at -2 minutes: 100 percent
• GABA relative activity at 0 minutes: 100 percent
• GABA relative activity at 2 minutes: 300 percent
• GABA relative activity at 4 minutes: approximately 190 percent
• GABA relative activity at 6 minutes: approximately 25 percent
• GABA relative activity at 8 minutes: approximately 25 percent
• GABA relative activity at 10 minutes: approximately 25 percent

The increase in the VTA's glutamate-to-GABA ratio lasts for more than 1 hour after a single exposure to nicotine, prolonging and intensifying the drug’s pleasurable effects.