Department of Molecular Physiology

Our interests

Histology of the painsystem

The cornea of the mammalian eye is an interesting object for pain research. It is transparent, not vasculated, and can therefore easily be examined by microscopy. The cornea is also densely innervated by pain fibers which makes it a favourite object for pain research. In this cross section of the rat cornea, the pain fibers cannot be seen. The image shows the roughly 0.5 mm-thick stroma (green), a special kind of connective tissue which allows light to pass through. Several layers of corneal epithelium form the border between stroma and air (left), while a single layer of corneal endothelium (right) (Masson-Goldner stain).

Dorsal root ganglia contain several thousand cell bodies of somatosensory neurons. These somata belong to nociceptors as well as to sensory cells involved in the perception of non-painful stimuli (touch, temperature, etc). The smaller cell populations (diameter 10-30 µm) are mainly pain cells, larger cells (diameter 40 – 70 µm) belong to other sensory modalities. Axons are collected in bundles, like the one seen on the right of the image.

The sensory neurons of the dorsal root ganglia project a bifurcated axon to the synapse in the spinal cord and to the sensory endings in skin, joints, and organs. The cell bodies lie densely packed within the dorsal root ganglia, wrapped in a tough skin of connective tissue (the dura mater). Each individual cell body is completely covered by a single layer of satellite cells. These cells are non-neuronal, but there exact function is not yet understood. They may play a similar role like glia cells in the brain (Azan stain).

In a cross section of the spinal cord, the butterfly-shaped „grey matter“ contains most cell bodies and synaptic connections of the spinal-cord neurons. Afferent fibers from somatosensory neurons enter the grey substance via the dorsal roots and form synapses with spinal-cord neurons within the dorsal horn (top half of the butterfly). The ventral horn (bottom half) contains motoneurons which control skeletal muscles. Several large spinal-cord neurons are stained dark blue within the grey matter. The “white matter” consists mainly of myelinated axons that provide the communication between the spinal cord and the brain (Klüver-Barrera-Stain).