The intrinsic organization of the ventroposterolateral nucleus and related reticular thalamic nucleus of the rat: A double-labeling ultrastructural investigation with γ-aminobutyric acid immunogold staining and lectin-conjugated horseradish peroxidase

S. De Biasi, C. Frassoni, R. Spreafico

Research output: Contribution to journalArticle

Abstract

An electron-microscopic investigation of the synaptic organization of the rat's ventroposterolateral nucleus (VPL) and of a reticular thalamic nucleus (RTN) area related to somatosensory thalamic nucleus was performed. In a group of 11 rats, wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) was injected either in the first somatosensory area of cortex (SI) or in the dorsal column nuclei (DCN). The retrogradely and/or anterogradely transported enzyme was visualized using paraphenylenediamine-pyrocatechol (PPD-PC) as substrate. In a second series of six experiments, an immunocytochemical procedure using a specific anti-γ-aminobutyric acid (anti-GABA) was employed. Postembedding localization of GABA was performed for ultrastructural observation by means of the colloidal gold immunostaining procedure. Thin sections of recognized VPL and RTN areas from WGA:HRP-injected animals were further processed for immunocytochemistry in order to localize simultaneously, at the electron-microscopic level, the transported enzyme and GABA. The results obtained with this procedure demonstrated that HRP-labeled terminals from DCN contacted the soma and proximal dendrites of VPL neurons, while the terminals labeled after SI cortical injections were predominantly localized to the distal portion of the dentrites. The same cortical injection also determined the presence of labeled synaptic boutons contacting the soma, and both proximal and distal dendrites of RTN neurons. GABA-immunolabeled terminals were observed in VPL in a number larger than those observed with other methods, since not only typical F terminals were labeled but also terminals containing round and/or pleomorphic vesicles. GABA-ergic terminals contacted the soma and the proximal and distal dendrites of VPL neurons, while in RTN cells they made synaptic contact mainly with the soma and proximal dentrites. In the double-labeling experiments, terminals containing both HRP and specific immunogold GABA staining were never observed. The present data provide a direct demonstration of the presence of a strong inhibitory input from RTN upon VPL neurons and of the existence of autoinhibition within RTN neurons.

Original languageEnglish
Pages (from-to)187-203
Number of pages17
JournalSomatosensory Research
Volume5
Issue number3
Publication statusPublished - 1988

ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

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