Summary: A group of neurons in the forebrain release dopamine when activated by visual or tactile stimuli, a new study reports.
Source: University of Freiburg.
Regardless of whether we are sitting in a loud aeroplane or walking through a quiet forest clearing, how humans perceive their environment depends on the stimuli. This, in turn, affects our behaviour – sometimes consciously, sometimes subconsciously.
In their study of fish larvae, Dr. Wolfgang Driever and his team of neurobiologists at the University of Freiburg have discovered that a group of nerve cells in the forebrain release the neurotransmitter dopamine when activated by tactile or certain visual stimuli. These dopaminergic nerve cells send connections to almost all parts of the brain and spinal cord, thereby affecting the functions of many circuits. These new findings could play a role in the future treatment of such illnesses as restless leg syndrome, a condition in which patients have unpleasant sensations in their limbs during sleep.
The researchers have published their research results in the journal Current Biology.
For their research, the scientists studied the four-millimetre-long larvae of zebrafish, which are common aquarium fish. The scientists observed the activity of individual dopaminergic nerve cells within the brains of the larvae, which were alert and active, under a microscope. The researchers were able to make their activity visible using optogenetic calcium sensors, which emit light in active nerve cells. Until now, studies of the dopaminergic nerve cells in vertebrates have primarily focused on the midbrain, where the dopaminergic cells are involved in the control of locomotion and reward behaviour. These become functionally impaired in patients with Parkinson’s disease. The dopaminergic neurons of the forebrain, on the other hand, have been little researched until now because they are located deep in the brain and are therefore difficult to reach. In the forebrain, they are also connected to parts of the hypothalamus, which controls the switch in basic behaviour, such as fight or flight and rest or sleep.
The findings reveal that certain intense sensory stimuli may affect such basic behaviour through the activity of dopaminergic nerve cells. Because there are also connections between these nerve cells and the sensory organs, it is possible that dopaminergic nerve cells are involved in adjusting the sensitivity of sensory organs’ reactions to stimuli. This function could be useful for treating diseases. The properties of dopaminergic nerve cells in the forebrain could thus be used in the future to reduce the sensation of patients with restless legs syndrome and hence to supress the tingling in their extremities that occurs when sleeping.
Further research of these dopaminergic neurons is expected to help scientists understand how these diseases develop – and in general how humans adapt to quickly changing stimuli and sensations in their environments.
This research study was a collaboration with BIOSS Centre for Biological Signalling Studies, Cluster of Excellence at the University of Freiburg. Wolfgang Driever is a member of BIOSS and a professor at the Institute of Biology I at the University of Freiburg. Dr. Aristides Arrenberg is a researcher in Driever’s lab and a recipient of the post-doc grant Eliteprogramm für Postdoktoranden from the Baden-Württemberg Stiftung.
Source: Wolfgang Driever – University of Freiburg
Image Source: NeuroscienceNews.com image is credited to Research group Driever.
Original Research: Abstract for “The Descending Diencephalic Dopamine System Is Tuned to Sensory Stimuli” by Sebastian Reinig, Wolfgang Driever, and Aristides B. Arrenberg in Current Biology. Published online January 12 2017 doi:10.1016/j.cub.2016.11.059
The Descending Diencephalic Dopamine System Is Tuned to Sensory Stimuli
•Ventral diencephalic A11-type dopaminergic neurons are a “sensory” dopamine system
•A11-type subgroups selectively respond to mechanosensory or visual stimulation
•Mechanosensory-related A11 dopaminergic activity is tuned to stimulus intensity
•Hypothalamic dopaminergic groups show prolonged post-motor activity
The vertebrate diencephalic A11 system provides the sole dopaminergic innervation of hindbrain and spinal cord and has been implicated in modulation of locomotion and sensory processes. However, the exact contributions of sensory stimuli and motor behavior to A11 dopaminergic activity remain unclear. We recorded cellular calcium activity in four anatomically distinct posterior tubercular A11-type dopaminergic subgroups and two adjacent hypothalamic dopaminergic groups in GCaMP7a-transgenic, semi-restrained zebrafish larvae. Our analyses reveal the contributions of different sensory modalities and motor states to dopaminergic activity. Each posterior tubercular and hypothalamic subgroup showed distinct activity patterns, while activity was synchronous within individual subgroups. Caudal and dorsomedial hypothalamic dopaminergic neurons are activated following vigorous tail movements and stay active for about 10 s, revealing predominantly post-motor activity. In contrast, posterior tubercular dopaminergic neurons are predominantly sensory driven, with subgroups differentially responding to different tactile or visual sensory modalities. In the anterior subgroups, neuronal response magnitudes are tuned to tactile stimulus intensities, revealing features similar to sensory systems. We identify the lateral line system as source for this tactile tuning. In contrast, the posterior subgroup is responsive to distinct moving visual stimuli. Specifically, translational forward stimuli, which may indicate insufficient rheotaxis and drift, induce dopaminergic activity, but backward or rotational stimuli not. The activation of posterior tubercular dopaminergic neurons by sensory stimuli, and their projections onto peripheral mechanosensory systems, suggests a participation of A11-type neurons in the feedback regulation of sensory systems. Together with the adjacent hypothalamic neurons, they may serve to set basic behavioral states.
“The Descending Diencephalic Dopamine System Is Tuned to Sensory Stimuli” by Sebastian Reinig, Wolfgang Driever, and Aristides B. Arrenberg in Current Biology. Published online January 12 2017 doi:10.1016/j.cub.2016.11.059