Multiple Mechanisms Underlie Burst Firing In Mouse Ventral Tegmental Area Dopamine Neurons In Vitro

Dopamine neurons in ventral tegmental area (VTA) are associatedwith reward mechanisms and cognitive functions. And dopamine neuronsexhibit two common firing patterns: tonic spiking and bursting. Burst firingis linked with reward in behavioural studies and accumulates moredopamine (DA) in the synapses in cellular studies. Both apamin andNMDA evoke burst firing in dopamine neurons in vitro in rats. However,apamin-induced bursting was blocked by nifedipine. In contrast, NMDA-induced bursting was not blocked by nifedipine. These results show thatburst firing can be evoked in dopamine neurons via two differentmechanisms but not answer what type of synaptic input could serve totrigger apamin-induced burst firing. And at the same time, there are fewerstudies in firing patterns in mouse than in rats. Therefore, my studies focuson the electrophysiological properties of dopamine neurons in VTA inmouse and also try to study the multiple mechanisms underlie bursting. 1. There are two different firing activities in mouse VTA dopamineneurons in vitro. It is shown that 31% of the dopamine neurons were quiescent; 65%were regularly or irregularly spiking and 4% showed spontaneous bursting. 2. NMDA-induced bursting is not dependent on Ca2+. NMDA evoked bursting in 32% of the cells. And neither the bursting(n=5) nor the oscillations (n=3) underlying the bursting were blocked byvoltage-gated calcium channels antagonist. 3. Carbachol-induced bursting is mediated by L-type Ca2+channels. Carbachol induced bursting in 10% of the cells. And both the burstingand the oscillations underlying the bursting were blocked by calcium-freesolutions (n=3), voltage-gated calcium channels antagonist (n=3) and L-type Ca2+channels antagonist (n=3), but not by T-type Ca2+ channelsantagonist (n=3). These results show that there are also multiple mechanisms underlyingbursting in mouse in vitro: NMDA-induced bursting is not mediated byCa2+ while carbachol-induce bursting is mediated not only by Ca2+ but alsoby L-type calcium channels. Therefore, my study opens some new doors tothe study of mechanisms underlying burst firing.