Riemensperger, T. D. | Search bioRxiv

bioRxiv2026

foxQ2 marks fast-acting brain interneurons including a subset of dopaminergic neurons innervating mushroom bodies and central complex in the beetle Tribolium castaneum

The brain is one of the most complex animal organs and the development of the many different neuron types remains enigmatic. A set of brain-specific transcription factors is involved in brain patterning but their specific contributions mostly remain to be elucidated, including foxQ2II. This transcription factor is conserved in anterior neuroectodermal patterning of most animals while it has been lost from vertebrates. The contribution of foxQ2II-positive neurons to the adult brain has remained enigmatic. Here, we use our enhancer trap, immunostainings and our newly established beetle brainbow system to categorize Tc-foxQ2II-positive neurons into nine clusters with different projection patterns. All clusters contain neurons with the fast-activating neurotransmitters acetylcholine and glutamate while no Tc-foxQ2II positive neuron is GABA-ergic or serotonin-positive. Interestingly, we found that many dopaminergic neurons were Tc-foxQ2II positive and we homologize them with dopaminergic neurons of the PPL2c, PPM1 and PPL1 cluster described in the Drosophila brain. Our results show that Tc-foxQ2II marks subsets of fast-acting interneurons contributing to the higher order brain centers mushroom bodies and central complex. Taken together, our work expands the known functional range of foxQ2 genes from sensory and neurosecretory cell specification to interneurons involved in the function of higher order brain centers.

neuroscience↗

bioRxiv2024

Compromising tyrosine hydroxylase function establishes a delusion-like temporal profile of reinforcement by dopamine neurons in Drosophila

For a proper representation of the causal structure of the world, one must consider both evidence for and evidence against causality. To take punishment as an example, the causality of a stimulus is reasonable if the stimulus precedes punishment, whereas causality can be ruled out if the punishment occurred first. This is reflected in the associative principle of timing-dependent valence reversal: aversive memories are formed when a stimulus occurs before the punishment, whereas memories of appetitive valence are observed when a stimulus is presented upon its relieving termination. We map the temporal profile of punishment induced by optogenetic activation of the PPL1-01 neuron in the fly Drosophila melanogaster, and find that impairment of tyrosine hydroxylase function, either acutely by pharmacological methods or by cell-specific RNAi, i) enhances learning with a time gap between stimulus and PPL1-01 punishment (trace conditioning), ii) impairs learning when the stimulus immediately precedes PPL1-01 punishment (delay conditioning), and iii) prevents learning about a stimulus presented after PPL1-01 punishment has ceased (relief conditioning). This implies a delusion-like state in which causality is attributed to cues that do not merit it (better trace conditioning), whereas both credible evidence for and credible evidence against causality is not properly appreciated (worse delay and relief conditioning). Under conditions of low dopamine, we furthermore observe a compensatory role for serotonin that is pronounced in trace conditioning, weaker in delay conditioning, and absent in relief conditioning. We discuss a disturbed dopamine-serotonin balance as an endophenotype for the positive and cognitive symptoms in schizophrenia.

animal behavior and cognition↗