There were quite a few interesting reports in the new issue of Nature Reviews Neuroscience.
A study pinpointed the neural circuitry behind social learning of avoidance in mice. Social learning means that the individual learns by observing a conspecific. In this study mice watched another mouse as it experienced a footshock after a sound cue. When these mice were placed in the same spot where the other one got shocked, they showed the freezing reaction in response to the sound cue, so they learned to associate the sound with the painful stimulus. The researchers showed that there are neurons in the anterior cingulate cortex projecting to a part of the amygdala, which become active when the mouse sees its conspecific in pain. Since the amygdala has an important role in the learning of negative outcomes, these anterior cingulate neurons were tought to convey the necessary information to it in this scenario. The hypothesis was supported by artificially influencing the activity of the anterior cingulate neurons.
Another study showed that endorphins and opiates have different subcellular effects in neurons. Opiates, like heroine and morphine, bind to opioid receptors of nerve cells to generate their effects. These receptors also bind endorphins, which are peptides synthesized by neurons. So to the opioid receptors, both opiates and endorphins are ligands. The researchers used ‘conformational biosensors’ to assess the ligand receptor interactions. These only bind to an opioid receptor which already binds one of its ligands and based due to its fluorescence, its location can be determined with certain microscopy methods. The results showed that opioid receptors binding endorphins are taken into the cell in little membrane-bound particles, while opiod receptors binding opiates are transferred quickly into the Golgi apparatus, a special subunit of the cell. It is not yet clear how this influences neural signalling.
Another study revealed that the molecular machinery of synapses, the focal points in the communication of neurons, are organized into transcellular units, which are closely aligned in the two cells connected by the synapse. This is another crucial detail required to understand neural signalling and the plasticity of the nervous system.
Finally, a study showed that a chemical generated by the body from the ingested food (a metabolite named tryptophan) regulates the immune cells of the brain. Dietary tryptophan triggers a complex regulatory mechanism which reduces inflammation in the brain of mice with experimental encephalitis. This may be relevant to the treatment of human diseases involving inflammation of the brain, like multiple sclerosis.
Source: NRN Vol. 19 Issue 7
Featured picture credit: King’s College London