RESUMO
This paper reports the occurrence of monosynaptic connections between dorsal root afferents and a distinct cell type-the giant neuron-deep in the dorsal horn of the turtle spinal cord. Light microscope studies combining Nissl stain and transganglionic HRP-labeling of the primary afferents have revealed the occurrence of axosomatic and axodendritic contacts between labeled boutons and giant neurons. The synaptic nature of these contacts has been confirmed by use of electron microscope procedures involving the partial three-dimensional reconstruction of identified giant neurons. Intracellular recording in spinal cord slices provided functional evidence indicating the monosynaptic connections between dorsal root afferents and giant neurons. The recorded neurons were morphologically identified by means of biocytin injection and with avidin conjugates. Electrical stimulation of the ipsilateral dorsal roots evoked synaptic responses with short, fixed latencies (1.6-5.6 ms), which remained unchanged at high frequencies (10 Hz). Excitatory polysynaptic potentials were also observed. By means of pharmacological procedures the short-latency response was dissected in two components: one insensitive to tetrodotoxin, the other abolished by the drug. The toxin-resistant component was presumed to be sustained by small-diameter C fibers. The synaptic response was mainly mediated by the glutamate-AMPA receptor subtype; however, a small component mediated by NMDA receptor was also present.
Assuntos
Neurônios Aferentes/citologia , Medula Espinal/citologia , Tartarugas/anatomia & histologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Vias Aferentes , Animais , Tamanho Celular/fisiologia , Potenciais Evocados/efeitos dos fármacos , Potenciais Evocados/fisiologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Peroxidase do Rábano Silvestre , Microscopia Eletrônica , Neurônios Aferentes/fisiologia , Neurônios Aferentes/ultraestrutura , Corpos de Nissl/ultraestrutura , Receptores de N-Metil-D-Aspartato/agonistas , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Raízes Nervosas Espinhais/citologia , Raízes Nervosas Espinhais/fisiologia , Tetrodotoxina/farmacologiaRESUMO
Observations were concentrated on the ultrastructure of perikarya and satellite cells of the otic ganglion of the adult rat. Characteristics of both cell types were morphologically analysed as well as their relationship. Quantitative data concerning the volumetric density were calculated for the following elements of the ganglion: glial cells together (28.5%), unmyelinated fibres (13.4%), myelinated fibres (2.7%), connective tissue (13.6%). This electron microscopic study is a sequence of our previous light microscopic study which determined neuronal densities (COSTA, MANDARIM-DE-LACERDA and BAUER, in press).