Electron microscopic and immunocytochemical study of rapidly frozen, freeze-substituted neural lobes of rats

M. Tian, J. F. Reger, William Armstrong

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Abstract

Rapid freezing of freshly dissected or incubated neural lobes was explored as a means of obtaining ultrastructural preservation of the more natural state of this tissue. A quantitative assessment of the region of good fixation was made in order to determine the relative fractions occupied by axons, pituicytes and the extracellular space. The immunocytochemical distributions of neurophysins and the glycopeptide portion of the vasopressin precursor were evaluated using the immunogold technique in order to determine the relative numbers of oxytocin and vasopressin fibre types in the fixed region, and the subcellular localization of these antigens. The uncut surface of rat neural lobes was rapidly frozen against a highly polished copper plug and freeze-substituted in osmium-acetone either immediately after dissection (∼2 min), or after a 15 min incubation period in vitro in an oxygenated, balanced salt solution. Substituted neural lobes were prepared for either conventional electron microscopy, or for immunogold labelling of neurophysins and the glycopeptide precursor to vasopressin. Membranes, subcellular organelles and extracellular matrix were well preserved 10 μm deep to the contacted surface. The extracellular space accounted for ∼30% of the cross-sectional area of the neuropil and could be divided into two domains: an extended perivascular space (28-29% of total area); and a narrow(∼24 nm; ∼1% of total) space between closely apposed neurosecretory processes or between these processes and pituicytes. Pituicytes accounted for about 30% of the area and axons 20-25%. Pituicytes occupied close to 60% of the basal lamina at the neurohaemal contact zone, while axons occupied ∼20%. There were no differences between neural lobes frozen immediately after dissection and those incubated for 15 min in any of these measures, suggesting minimal fluid redistribution. Gold particles were specifically localized over large (100-200 nm) dense core vesicles, and less frequently over multivesicular bodies and lysosomes. No etching of the plastic or reduction of osmium was necessary to achieve labelling. Specific labelling of one set of terminals and axons (about 80%) was observed with the monoclonal antibody previously shown to be specific for oxytocin-neurophysin, while in neighbouring sections the remaining 20% of the processes were labelled with the antiserum to the vasopressin precursor, or with non-specific antibodies to neurophysins. In conclusion, ultrarapid freezing preserves a large extracellular space in the neural lobe and provides for high resolution morphological and immunocytochemical studies of neurohypophysial structure.

Original languageEnglish (US)
Pages (from-to)79-96
Number of pages18
JournalJournal of Neurocytology
Volume20
Issue number2
DOIs
StatePublished - Feb 1 1991

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Posterior Pituitary Gland
Neurophysins
Vasopressins
Electrons
Extracellular Space
Osmium
Axons
Glycopeptides
Oxytocin
Freezing
Dissection
Multivesicular Bodies
Neuropil
Presynaptic Terminals
Secretory Vesicles
Acetone
Lysosomes
Basement Membrane
Gold
Organelles

All Science Journal Classification (ASJC) codes

  • Anatomy
  • Neuroscience(all)
  • Histology
  • Cell Biology

Cite this

Electron microscopic and immunocytochemical study of rapidly frozen, freeze-substituted neural lobes of rats. / Tian, M.; Reger, J. F.; Armstrong, William.

In: Journal of Neurocytology, Vol. 20, No. 2, 01.02.1991, p. 79-96.

Research output: Contribution to journalArticle

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abstract = "Rapid freezing of freshly dissected or incubated neural lobes was explored as a means of obtaining ultrastructural preservation of the more natural state of this tissue. A quantitative assessment of the region of good fixation was made in order to determine the relative fractions occupied by axons, pituicytes and the extracellular space. The immunocytochemical distributions of neurophysins and the glycopeptide portion of the vasopressin precursor were evaluated using the immunogold technique in order to determine the relative numbers of oxytocin and vasopressin fibre types in the fixed region, and the subcellular localization of these antigens. The uncut surface of rat neural lobes was rapidly frozen against a highly polished copper plug and freeze-substituted in osmium-acetone either immediately after dissection (∼2 min), or after a 15 min incubation period in vitro in an oxygenated, balanced salt solution. Substituted neural lobes were prepared for either conventional electron microscopy, or for immunogold labelling of neurophysins and the glycopeptide precursor to vasopressin. Membranes, subcellular organelles and extracellular matrix were well preserved 10 μm deep to the contacted surface. The extracellular space accounted for ∼30{\%} of the cross-sectional area of the neuropil and could be divided into two domains: an extended perivascular space (28-29{\%} of total area); and a narrow(∼24 nm; ∼1{\%} of total) space between closely apposed neurosecretory processes or between these processes and pituicytes. Pituicytes accounted for about 30{\%} of the area and axons 20-25{\%}. Pituicytes occupied close to 60{\%} of the basal lamina at the neurohaemal contact zone, while axons occupied ∼20{\%}. There were no differences between neural lobes frozen immediately after dissection and those incubated for 15 min in any of these measures, suggesting minimal fluid redistribution. Gold particles were specifically localized over large (100-200 nm) dense core vesicles, and less frequently over multivesicular bodies and lysosomes. No etching of the plastic or reduction of osmium was necessary to achieve labelling. Specific labelling of one set of terminals and axons (about 80{\%}) was observed with the monoclonal antibody previously shown to be specific for oxytocin-neurophysin, while in neighbouring sections the remaining 20{\%} of the processes were labelled with the antiserum to the vasopressin precursor, or with non-specific antibodies to neurophysins. In conclusion, ultrarapid freezing preserves a large extracellular space in the neural lobe and provides for high resolution morphological and immunocytochemical studies of neurohypophysial structure.",
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