The autonomic nervous system, which is
the part of the nervous system beyond conscious control, plays an
important role in the release of insulin from beta cells in the
endocrine part of the pancreas.
The process by which this occurs has
been a mystery, since it is difficult to give detailed study to such
an inaccessible organ. However, researchers at Karolinska Institutet
in Sweden have now managed to graft beta cells into the eyes of mice
in order to study them in a living organism over a prolonged period
of time. As a result, the group and a team of colleagues from the
University of Miami have gained detailed knowledge of how the
autonomic nervous system regulates beta-cell insulin secretion.
For this study, a technique of
transplanting beta cells to the anterior chamber of the mouse eye
was used. This technique was previously developed by Professor Per-Olof
Berggren's group at Karolinska Institutet. In the anterior chamber
of the eye the beta cells receive a supply not only of blood
vessels, but also of nerves from the sympathetic and parasympathetic
system, which constitute the autonomic nervous system. Put simply,
the sympathetic nervous system can be said to prepare us for flight;
one way it does this is to boost our energy by reducing insulin
release and increasing glycogen, and consequently blood glucose.
The parasympathetic nervous system operates in the reverse direction
when we are at rest.
Now, the teams from Karolinska
Institutet and the University of Miami have shown for the first time
how the autonomic nervous system controls the beta cells and
influences the regulation of blood glucose in living animals.
Using fluorescent markers for different
types of nerves in combination with advanced microscopy, the
researchers were able to probe the animals' eyes to study in detail
the contact between the nerves and the beta cells.
When the pupil contracted on exposure to light, the animals' blood
glucose levels plummeted as a direct result of the stimulation of
the parasympathetic nervous system.
Conversely, when the pupil dilated in darkness and activated the
sympathetic nervous system, their blood glucose levels rose. They
also managed to influence the animals' blood glucose levels by
inhibiting or stimulating each set of nerves with different
substances applied directly into the eye.
"We now understand the fundamentals of
how insulin secretion works and is affected by the autonomic nervous
system," says Per-Olof Berggren. "The next step is to see if it
works in the same way in people with diabetes or if there are
defects in the signalling relevant to the disease pathogenesis."
For more information
'Noninvasive in vivo model demonstrating the effects of autonomic
innervation on pancreatic islet function', Rayner Rodriguez-Diaz,
Stephan Speier, Ruth Damaris Molano, Alexander Formoso, Itai Gans,
Midhat H. Abdulreda, Over Cabrera, Judith Molina, Alberto Fachado,
Camillo Ricordi, Ingo Leibiger, Antonello Pileggi, Per-Olof Berggren
and Alejandro Caicedo, Proceedings of the National Academy of
Sciences (PNAS), Online Early Edition 10-14 December 2012.
http://www.pnas.org/content/109/52/21456.abstract
Karolinska Institutet
(MDN) |
