Elsevier

Neuroscience

Volume 50, Issue 2, September 1992, Pages 355-370
Neuroscience

The regional, cellular and subcellular localization of GABAA/benzodiazepine receptors in the substantia nigra of the rat

https://doi.org/10.1016/0306-4522(92)90429-6Get rights and content

Abstract

The regional, cellular and subcellular distribution of GABAA/benzodiazepine receptors was investigated by light and electron microscopy in the rat substantia nigra. The regional distribution and density of GABAA/benzodiazepine receptor subtypes (Type I and II) was studied using quantitative receptor autoradiography following in vitro labelling of cryostat sections with tritiated ligands. This was followed by a detailed study of the cellular and subcellular distribution and localization of GABAA/benzodiazepine receptors by light and electron microscopy using immunohistochemical techniques with a monoclonal antibody (bd-17) to the β2.3, subunits of the GABAA/benzodiazepine receptor complex. Finally,in situ hybridization histochemistry using35S-labelled oligonucleotide probes was used to demonstrate the cellular distribution of mRNA for the α1 and α2 GABAA receptor subunits in the substantia nigra.

The results of the autoradiographic and immunohistochemical studies showed a close correspondence in the regional distribution of GABAA/benzodiazepine receptors in the substantia nigra. A moderate-to-high density of receptors was present throughout the full extent of the substantia nigra pars reticulata with a very low density of receptors in the substantia nigra pars compacta. Quantitative autoradiographic studies showed that: (i) the pars reticulata contained mainly central Type I receptors; (ii) the highest density of receptors was present in the caudal pars reticulata (200 ± 38fmol/mg) with successively lower densities of receptors in the middle (176 ± 31fmol/mg) and rostral (150 ± 26fmol/mg) levels of the pars reticulata; and (iii) the density of receptors in the pars reticulata was reduced by 34% following 6-hydroxydopamine-induced degeneration of dopaminergic pars compacta neurons. At the cellular level, GABAA/benzodiazepine receptor immunoreactivity was localized in a punctate fashion on dendrites and neuronal cell bodies in the pars reticulata. At the subcellular level, GABAA/benzodiazepine receptor immunoreactivity was associated with the pre- and postsynaptic membranes of axodendritic synaptic complexes along the length of small-to-large sized smooth dendrites in the pars reticulata. Two types of immunoreactive axodendritic synaptic complexes were identified: most (about 80%) immunopositive synapses showed equal staining of the pre- and postsynaptic membranes and were associated with small (<1.0 μm) axon terminals containing few mitochondria and small, round-to-pleomorphic vesicles in synaptic contact with small, peripheral dendrites; less frequently (about 20%) immunopositive synapses showed a marked immunoreactive thickening of the postsynaptic membrane and were associated with large (> 1.0 μm) axon terminals containing numerous mitochondria and mainly pleomorphic vesicles in synaptic contact with large mainstem dendrites. Finally, the in situ hybridization studies showed that cells in the pars reticulata, but not in the pars compacta, expressed mRNA for the α1 (but not for the α2) subunit of the GABAA receptor complex.

These results provide a detailed morphological characterization of the regional, cellular and subcellular distribution of GABAA/benzodiazepine receptors in the rat substantia nigra. These findings provide an anatomical basis for GABA-mediated synaptic inhibition in the substantia nigra.

References (56)

  • KuypersH.G.J.M. et al.

    Retrograde axonal transport of horseradish peroxidase in rat's forebrain

    Brain Res.

    (1974)
  • LüddensH. et al.

    Function and pharmacology of multiple GABAA receptor subunits

    Trends pharmac. Sci.

    (1991)
  • MenniniT. et al.

    Regional distribution of low-affinity GABA receptors coupled to benzodiazepine receptor subtypes in rat brain: an autoradiographic evaluation

    Eur. J. Pharmac.

    (1990)
  • MiyoshiR. et al.

    Autoradiographic studies on benzodiazepine receptor subtypes in the rat brain

    Jap. J. Pharmac.

    (1985)
  • MontaldoS. et al.

    Evidence for the presence of benzodiazepine receptor subclasses in different areas of the human brain

    Neurosci. Lett.

    (1984)
  • NautaH.J.W. et al.

    Afferents to the rat caudoputamen studied with horseradish peroxidase. An evaluation of a retrograde neuroanatomical research method

    Brain Res.

    (1974)
  • NitschC. et al.

    Immunocytochemical demonstration of GABAergic synaptic connections in rat substantia nigra after different lesions of the striatonigral projection

    Brain Res.

    (1988)
  • PersohnE. et al.

    In situ hybridization histochemistry reveals a diversity of GABAA receptor subunit mRNAs in neurons of the rat spinal cord and dorsal root ganglia

    Neuroscience

    (1991)
  • SmithY. et al.

    Neurons of the substantia nigra reticulata receive a dense GABA-containing input from the globus pallidus in the rat

    Brain Res.

    (1989)
  • SmithY. et al.

    Convergence of synaptic inputs from the striatum and the globus pallidus onto identified nigrocollicular cells in the rat: a double anterograde labelling study

    Neuroscience

    (1991)
  • StraughanD.W. et al.

    GABA and the nigrothalamic pathway

    Brain Res. Bull.

    (1980)
  • UnnerstallJ.R. et al.

    Quantitative receptor autoradiography using [3H]Ultrofilm: application to multiple benzodiazepine receptors

    J. Neurosci. Meth.

    (1982)
  • VerdoornT.A. et al.

    Functional properties of recombinant rat GABAA receptors depend upon subunit composition

    Neuron

    (1990)
  • VincentS.R. et al.

    The nigrotectal projection: a biochemical and ultrastructural characterization

    Brain Res.

    (1978)
  • WaldvogelH.J. et al.

    GABA, GABA receptors and benzodiazepine receptors in the human spinal cord: an autoradiographic and immunohistochemical study at the light and electron microscopic levels

    Neuroscience

    (1990)
  • WassefM. et al.

    Dopaminergic dendrites in the pars reticulata of the rat substantia nigra and their striatal input. Combined immunocytochemical localization of tyrosine hydroxylase and anterograde degeneration

    Neuroscience

    (1981)
  • WisdenW. et al.

    Distinct GABAA receptor α subunit mRNAs show differential patterns of expression in bovine brain

    Neuron

    (1988)
  • WisdenW. et al.

    Localization of GABAA receptor α subunit mRNAs in relation to receptor subtypes

    Molec. Brain Res.

    (1989)
  • Cited by (0)

    View full text