Differential projections of excitatory and inhibitory dorsal horn interneurons relaying information from group II muscle afferents in the cat spinal cord.

• Dorsal horn interneurons with input from group II muscle spindle afferents are components of networks involved in motor control. Thirteen dorsal horn interneurons with monosynaptic group II input were characterized electrophysiologically and labeled intracellularly with Neurobiotin. Their axonal projections were traced, and neurotransmitter content was established by using immunocytochemistry. Two subpopulations were identified: five interneurons had axons that contained vesicular glutamate transporter 2 and hence were glutamatergic and excitatory. Terminals of the remaining eight interneurons were immunoreactive for the glycine transporter 2 or were apposed to gephyrin but did not contain the GABA-synthesizing enzyme glutamic acid decarboxylase and were therefore glycinergic and inhibitory. Excitatory cells were located mainly in the central region of lamina IV and had relatively small somata and restricted dendritic trees. In contrast, inhibitory interneurons were located more ventrally, in lamina V and had relatively larger somata and more extensive dendritic trees. Axonal projections of the two subpopulations differed considerably. Excitatory interneurons predominantly projected ipsilaterally, whereas most inhibitory interneurons projected both ipsilaterally and contralaterally. Three inhibitory axons formed contacts with large cholinergic cells in motor nuclei, thus revealing a novel direct coupling between inhibitory dorsal horn interneurons and motoneurons. The organization of the excitatory interneurons is consistent with current knowledge of reflex pathways to motoneurons, but the existence and connections of the inhibitory subpopulation could not be predicted from previous data. Our results indicate that these latter interneurons exercise widespread inhibitory control over a variety of cell types located on both sides of the spinal cord.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

Nyckelord

Afferent Pathways

physiology

Animals

Axons

chemistry

ultrastructure

Biotin

analogs & derivatives

analysis

Carrier Proteins

analysis

Cats

Fluorescent Dyes

analysis

Glutamate Decarboxylase

analysis

Glutamic Acid

physiology

Glycine

physiology

Glycine Plasma Membrane Transport Proteins

analysis

Interneurons

chemistry

classification

physiology

Membrane Proteins

analysis

Motor Neurons

physiology

Muscle

Skeletal

innervation

Nerve Endings

chemistry

ultrastructure

Nerve Tissue Proteins

analysis

Posterior Horn Cells

chemistry

physiology

Spinal Cord

anatomy & histology

cytology

physiology

Vesicular Glutamate Transport Protein 2

analysis

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)