[SYNAPTIC AND ELECTROTONIC CONTACTS ON THE PRIMARY AFFERENT AXONS OF THE SPINAL CORD IN THE LAMPREY LAMPETRA FLUVIATILIS].

Distribution of GABA and glycine immunoreactivity was studied in synapses on primary afferent axons of the spinal cord in the lamprey Lampetrafluviatilis by double labeling technique. Approximately 25 % of synapses on afferent axons revealed immunoreactivity to GABA and more than 70 % were im- munoreactive to both neurotransmitters. As in other vertebrates, axo-axonal contacts represented three-component synaptic complexes, the so-called triades, where the immunoreactive terminal was in sy- naptic contact both with the afferent axon and the dendrite contacting with this afferent.

[Gaba- and glycine-immunoreactive synapses in the spinal cord of the frog Rana temporaria].

Postembedding immunogold method was used to examine the distribution of gamma-aminobutyric acid- and glycine-immunoreactives synapses on the motoneurons and primary afferent axons in frog spinal cord. Analysis of all labeled boutons on dendrites and somata of motoneurons showed that 7% were labeled for GABA, 23% only for glycine and approximately 70% were immunoreactive for both GABA and glycine. These results confirm the predominant role of glycine in postsynaptic inhibition of motoneuronal activity.

[Immunoreactivity of the synapses on the primary afferent axons and sensory neurons of the spinal cord Lampetra fluviatilis].

The existence of GABA-like immunoreactivity in the synapses on the primary afferent axons and GABA- and glutamate immunoreactive synapses on the dorsal cell somatic membrane was shown using double postembedding immunogold cytochemistry. These morphological findings suggest that control of the sensory information in the lamprey spinal cord is realized by means of presynaptic inhibition through the synapses on the primary afferent axons as well as directly through the synapses on the somata of the sensory neurons.

Comparative study of spinal motoneuron axon collaterals.

Numerous spinal motoneurons in mammals possess recurrent axon collaterals included in a feedback loop for controlling motoneuron activity. For nonmammalian vertebrates, the data concerning the existence of collaterals and their intraspinal branching are fragmentary and contradictory. We focused on axonal branching of motoneurons in lampreys, frogs, turtles and young rats, using light microscopic analysis of HRP- or neurobiotin-labeled motoneurons.