Networks of inhibitory and excitatory commissural interneurons mediating crossed reticulospinal actions.

• Axonal projections and neurotransmitters used by commissural interneurons mediating crossed actions of reticulospinal neurons were investigated in adult cats. Eighteen interneurons, located in or close to lamina VIII in midlumbar segments, that were monosynaptically excited by reticulospinal tract fibres and projected to contralateral motor nuclei were labelled by intracellular injection of tetramethylrhodamine-dextran and Neurobiotin. The nine most completely labelled interneurons were analysed with combined confocal and light microscopy. None of the stem axons gave off ipsilateral axon collaterals. Seven cells had axon collaterals that arborized in the contralateral grey matter in the ventral horn of the same segments. Transmitters were identified by using antibodies raised against vesicular glutamate transporters 1 and 2, glutamic acid decarboxylase and the glycine transporter 2. The axons of two cells were immunoreactive for the glycine transporter 2 and hence were glycinergic. Three cells were immunoreactive for the vesicular glutamate transporter 2 and hence were glutamatergic. None of the axons displayed immunoreactivity for glutamic acid decarboxylase. Electron microscopy of two cells revealed direct synaptic connections with motoneurons and other neurons. Axonal swellings of one neuron formed synapses with profiles in motor nuclei whereas those of the other formed synapses with other structures, including cell bodies in lamina VII. The results show that this population of commissural interneurons includes both excitatory and inhibitory cells that may excite or inhibit contralateral motoneurons directly. They may also influence the activity of motoneurons indirectly by acting through interneurons located outside motor nuclei in the contralateral grey matter but are unlikely to have direct actions on interneurons in the ipsilateral grey matter.

Ämnesord

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

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

Nyckelord

Amino Acid Transport Systems

Neutral

metabolism

Animals

Axons

physiology

ultrastructure

Biotin

analogs & derivatives

metabolism

Carrier Proteins

metabolism

Cats

Electric Stimulation

Evoked Potentials

physiology

Excitatory Postsynaptic Potentials

physiology

Functional Laterality

Glutamate Decarboxylase

metabolism

Glycine Plasma Membrane Transport Proteins

Immunohistochemistry

Interneurons

physiology

ultrastructure

Membrane Transport Proteins

Microscopy

Confocal

Microscopy

Electron

Motor Neurons

physiology

ultrastructure

Nerve Net

anatomy & histology

physiology

Neural Inhibition

physiology

Reaction Time

Reticular Formation

cytology

physiology

Rhodamines

metabolism

Spinal Cord

cytology

physiology

Synapses

ultrastructure

Vesicular Glutamate Transport Protein 1

Vesicular Glutamate Transport Protein 2

Vesicular Transport Proteins

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