Anyone else attending the Catecholamines GRS/GRC in August? Can't wait to share some new data!

Want to thank all who helped bring this project to light! @anniely.bsky.social , @ampolter.bsky.social , @neuronroot.bsky.social and all those who aren't on Bluesky

Altogether, we conclude that the signaling patterns and behavioral functions of VTA dopamine neurons depend on whether they co-transmit glutamate or release dopamine alone. Distinct glu and DA subpops—and individual NTs in co-transmitting neurons—contribute differentially to motivated behaviors 21/n

Finally, Zachary Kilpatrick expanded a classic neural circuit model of temporal-difference learning to account for glu-DA neurons, as well as the individual contributions of glutamate and dopamine from glu-DA and DA-only neurons. The model recapitulated some of our key behavioral results. 20/n

…But blocking glutamate release did not cause gross motor deficits which might explain the differences, nor impair escape responses to a simulated predator. We concluded that blocking glutamate release impairs reward- and exploration-related vigor without affecting aversion-related vigor. 19/n

Blocking glutamate release did not impact the acquisition of reward learning or fear learning/extinction. But it slowed reward retrieval latency and enhanced reward extinction, and suppressed exploratory behavior in an open field… 18/n

Knocking down TH (to block DA synthesis) didn’t impact acquisition of reward learning. But mice had deficits when learning about less-rewarding (reward CS-, reward extinction) or aversive (shock CS+) associations. 17/n

We zoomed in on glu-DA co-transmitting neurons and identified distinct functional roles for glu release and DA release in motivated behaviors. Using recombinase-dependent shRNA vectors, we blocked molecules necessary for DA synthesis (in glu neurons) or vesicular glu release (in DA neurons) 16/n

Anatomically, we also observed (as others have before) that glu-DA neurons heavily innervate NAcc medial shell, with some innervation in medial core. DA-only neurons heavily innervate NAcc core with some innervation in ventral and lateral shell. 15/n

We used ChRmine & GRABDA to measure opto-elicited NAcc DA release from VTA glu-DA or DA-only terminals. Axonal stim in both subpops increased DA release. Glu-DA axons were more sensitive to longer pulse trains in phasic magnitude. DA-only were more sensitive to longer trains in tonic duration 14/n

In sum, glu-DA neurons were activated in both rewarding and aversive contexts, but DA-only neurons had bidirectional activity in reward vs aversion. Examining all DA neurons together obscures the dissociable activity of subpops. Glu-only neurons are distinct from previously studied VTA subpops. 13/n

Importantly, in the nonselective population of all dopamine neurons together, we saw intermediate results between glu-DA and DA-only subpops. This is best exemplified in RPE signaling as well as shock and shock-predictive cue signaling (see previous posts). 12/n

Differences in signaling dynamics were starker in an aversive context. Glu-DA and glu-only neurons were activated to shock and the shock-predictive cue—glu-DA neurons strongly so. When measuring the minimum GCaMP value, we saw that DA-only neurons were suppressed at shock and cue. 11/n

Considering both RPE signaling and behavior-dependent signaling during the non-predictive cue, it appears that DA-only neurons suppress their activity when the animal recognizes that reward is not forthcoming. This was not observed in glu-DA or glu-only neurons. 10/n

Interestingly, DA-only neurons responded to the neutral cue (CS-) depending on the mouse’s behavior. When the mouse correctly avoided the port, activity decreased at the cue. But when the mouse incorrectly entered the port, activity decreased at the time reward “would” have come on a CS+ trial. 9/n

When an expected reward was omitted (reward prediction error), sustained activity of glu-DA neurons prevented a suppression below baseline, while transient activity of DA-only and glu-only allowed RPE signaling. This is the first RPE signaling identified in a VTA glutamate subpopulation. 8/n

In Pavlovian reward, all subpops were activated at reward and reward-predictive cue. But glu-DA neurons exhibited sustained activation between cue and reward peaks, while DA-only and glu-only exhibited transient activation in which activity dropped toward baseline between cue and reward peaks. 7/n

In vivo, we found that these subpops are dissociable in GCaMP signaling dynamics related to rewarding and aversive cues and outcomes: 6/n

The incredible @ampolter.bsky.social and Kailyn Price demonstrated that these subpops are electrophysiologically distinct. Some highlights: a subset of glutamate-only neurons exhibited Ih and D2 sensitivity; glutamate-dopamine neurons largely lacked Ih. 5/n

Additionally, we used a subtractive genetic strategy to target (for the first time) neurons that do not release dopamine and do not release GABA, which in the VTA selects for neurons that release glutamate alone. Our cellular targeting strategy is summarized here. 4/n

Using INTRSECTional genetics, we isolated VTA populations that co-transmit dopamine and glutamate or release dopamine alone (without glutamate). We compared this to current standard, which is to examine all dopamine neurons together regardless of co-transmission. See next for a visual summary. 3/n

Despite well-known molecular heterogeneity in VTA dopamine neurons (esp. glutamate co-transmission), hypotheses of VTA dopamine function presume a homogenous influence on behavior. We examined the functional consequences of heterogeneity in VTA dopamine and glutamate subpopulations 2/n

Untangling dopamine and glutamate in the ventral tegmental area Ventral tegmental area (VTA) dopamine neurons are of great interest for their central roles in motivation, learning, and psychiatric disorders. While hypotheses of VTA dopamine neuron function posit a...

New preprint! We untangle glutamatergic and dopaminergic subpopulations in the ventral tegmental area. Long thread incoming, buckle up friends. 1/n

www.biorxiv.org/content/10.1...

Must watch speech by neuroscientist Kailyn Price at a HHS rally protesting funding cuts to science.

"Cutting indirect costs is like telling a football team to work with only the players.

No lights for the field, no physical therapists for the players, no water for the showers."

Honored to receive first place poster award at #wcbr2025! Thanks to all who stopped by. The poster (and my panel) explored divergent signaling dynamics in VTA dopamine subpopulations, as well as functional roles for glutamate and dopamine in co-transmitting VTA neurons. Stay tuned for more!