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Multi-modal interrogation of instinctive behaviours and intrahypothalamic connectivity

Periodic Reporting for period 1 - DRIVOME (Multi-modal interrogation of instinctive behaviours and intrahypothalamic connectivity)

Reporting period: 2016-03-01 to 2018-02-28

Experiments dating back to the 1920's demonstrated that manipulating a deep brain structure called the hypothalamus can dramatically affect basic mammalian instincts like hunger and aggression. Building on these findings with improved tools, recent work has uncovered hypothalamic neuronal populations that can drive fundamental mammalian behaviours: feeding, sex and aggression, sleep/wakefulness and parental behaviours. These neuronal cell types are located very close to each other and are likely to interact in a specific manner giving rise to organized behavioural outputs (e.g. coordinated wakefulness and sexual drive).
Classical work in ethology has outlined hypotheses for e.g. how reciprocal inhibition between neuronal populations generating opposing behaviours may guide the organization of fundamental mammalian behaviours into the coherent, adaptive, context-relevant displays evident throughout the animal kingdom. Modern techniques including opsins, genetically encoded calcium indicators (GECIs), transgenic mice, and multi-photon imaging of deep brain structures, are now ripe for comprehensive cell-type specific probing of the hypothalamic networks in charge of fundamental drives and possibly emotions. Despite the above mentioned advances, major fundamental questions about neuronal communication in hypothalamus are still open while the microcircuitry in the neocortex has been studied for over a century. Given my background in studying neurons in the neocortex and hypothalamus, we employed a comparative approach considering the differences between these two brain structures as an entry point to this project. Since the hypothalamus contains intermingled neurons that directly control various (and some of them mutually exclusive) behaviours, connectivity between neighboring cells could be highly specific, e.g. involving reciprocal inhibition between cell types promoting exclusive behaviours. This can be assayed by patch clamp in multiple transgenic slices where we can utilize the genetic handles on these cell types.
We focused on the lateral hypothalamus, a relatively large hypothalamic subfield which controls arousal, feeding, metabolism and motivation. We used transgenic mice to label two non-overlapping neuronal populations at a time with different coloured fluorescent proteins and then used patch clamp electrophysiology to probe their synaptic connectivity. We repeated the procedure to assess pairwise connectivity between orexin, melanin-concentrating hormone, gamma-amino butyric acid, and glutamate containing neurons in the lateral hypothalamus. We found that the lateral hypothalamus is connected extremely sparsely. Repeating this approach in the neocortex showed the characteristic densely connected cortical microcircuit, assuring us that the method is reliable.
The primary result indicates that the rapid synaptic communication utilized by the neocortex is mostly missing from the lateral hypothalamus. This raises the question of how do these neurons communicate to each other via other means, if at all. We are probing this further by recording the activity dynamics in these neurons in awake behaving animals to see if there are repeatable activity patterns to gain further insight into how the neurons coordinate behavioural states.