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Signal Transduction in the Brain

The brain is made up of over 50 billion neurons. Among these neurons, there is a lively exchange of information. Sensory input is received, cognitive and emotional processes are coordinated, impressions are stored and orders given. This requires highly complex information strategies and paths. At Jülich, researchers are investigating molecular structures and neurotransmitters that play crucial roles in this information network. Their aim is to understand the way a healthy brain works and use this insight for the early detection of pathological changes and development of treatments.

One technique used in their research is molecular imaging, which makes characteristic molecules and their function visible using methods such as positron emission tomography (PET), receptor autoradiography and in situ hybridization. The scientists at Jülich use this technique, for example, to study the function of neurotransmitters such as adenosine, serotonin and dopamine. The neurotransmitters play an essential role in signal transduction between neurons, since they transport information from cell to cell. One result of this research has been new insights on the origin of fatigue and the way caffeine works. This knowledge can help treat sleep disorders more effectively.

The point of contact for the neurotransmitters on the neurons are so-called transmitter receptors – complex protein molecules situated in the external sheath of the neurons. The transmitter receptors are a basic component of signal transduction in the central nervous system and for this reason, also play an important role in many neurological and psychiatric disorders. Their frequency and distribution can indicate the presence of diseases such as Parkinson's, multiple sclerosis, dementia or depression early on. With molecular imaging, the neuroscientists at Jülich are already on their way to discovering a marker for the early diagnosis of schizophrenia. Such a marker could be a sign of the disease even before clinical symptoms are apparent.

However, chemical processes and individual molecules are not the only factors influencing signal transmission. Transmitter receptors and neurotransmitters are in turn only parts of synapses, the contact sites of the neurons. A neuron can possess up to 15,000 synapses, all of them specialized, highly complex architectural masterpieces. Despite their common structural elements, synapses differ enormously. Their size and shape vary, as do the number, size and distribution of the active zones in which they release neurotransmitters, as well as the size and organization of the storage depots for neurotransmitters. The researchers at Jülich are using ultrathin slices of brain tissue to study structural, functional and molecular differences in these synapses and create virtual three-dimensional models with them.

So what happens with the signals inside a neuron? How do these cells process incoming signals and how do they pass them on? The way these circuits function is another topic of study for the Jülich scientists. Using animal models, they are gaining insight into the much more complexly structured human brain. To this end, they study both signal processing in individual neurons and the structure and function of neuron clusters, as well as their modulation and development.