Fraction of synapses contacted/covered by perisynaptic astrocyte processes acro…

Reported PAP-synapse coverage fractions vary from ~57% in hippocampal CA1 stratum radiatum (Ventura & Harris 1999) to ~80-90% in mouse motor/somatosensory cortex and higher values in rat cortex (Gavrilov 2018). Region and method differences (rat vs mouse; CA1 vs cortex; apposition vs leaflet contact) partially explain the spread, but the near-2x variation has direct consequences for models of glutamate spillover and synaptic isolation.

{
  "papers": [
    {
      "n": null,
      "doi": "10.1186/s12915-015-0176-7",
      "value": "81%",
      "method": "serial block-face scanning EM (SBEM)",
      "metric": "Fraction of dendritic spines contacted by perisynaptic astrocyte processes (PAP+)",
      "n_analyzed": null,
      "ci_or_error": null,
      "text_access": "fulltext",
      "n_definition": "dendritic spines scored for PAP contact",
      "scope_region": "mouse motor cortex, layer II",
      "study_system": "adult mouse motor cortex",
      "taxonomic_level": "spine-level EM reconstruction",
      "scope_population": "excitatory spines",
      "value_source_sentence": "Across all animals, ~81 % of spines were PAP + and ~19 % were PAP negative (PAP − ) (Fig. 5e ), consistent with findings in layer IV of the mouse barrel cortex, where only ~10 % of spines lack astrocytic coverage.",
      "experimental_conditions": "baseline (sleep/wake conditions)"
    },
    {
      "n": null,
      "doi": "10.3389/fncel.2018.00248",
      "value": "72.7%",
      "method": "serial section transmission EM, 3D reconstruction",
      "metric": "Fraction of dendritic thin spines with leaflet-contact astrocytic coverage",
      "n_analyzed": null,
      "ci_or_error": null,
      "text_access": "fulltext",
      "n_definition": "thin spines analyzed by 3D EM",
      "scope_region": "hippocampus CA1 stratum radiatum",
      "study_system": "rat hippocampus CA1 stratum radiatum",
      "taxonomic_level": "spine-level EM",
      "scope_population": "excitatory spine synapses",
      "value_source_sentence": "We found that both thin and mushroom dendritic spines are predominantly located within the area of the leaflets, but not in proximity to astrocytic branchlets (Figure 8A ). 72.7% of thin spines and 83.3% of mushroom spines were located within astrocytic leaflet area.",
      "experimental_conditions": "baseline"
    },
    {
      "n": null,
      "doi": "10.1155/2014/232105",
      "value": "90%",
      "method": "3D electron microscopy",
      "metric": "Fraction of spine synapses with PAP contact (reported from layer IV mouse somatosensory cortex)",
      "n_analyzed": null,
      "ci_or_error": null,
      "text_access": "fulltext",
      "n_definition": "synapses in 3D EM volumes",
      "scope_region": "mouse somatosensory cortex, layer IV",
      "study_system": "adult mouse somatosensory cortex",
      "taxonomic_level": "synapse-level EM",
      "scope_population": "excitatory spine synapses",
      "value_source_sentence": "In layer IV of adult mouse somatosensory cortex, 3D EM demonstrated high heterogeneity of synaptic coverage, with around 10% of spine synapses having no contact with PAPs, while the rest of the spines had an intermediate coverage (from 5% to 95% in surface apposition).",
      "experimental_conditions": "baseline"
    },
    {
      "n": null,
      "doi": "10.1523/jneurosci.19-16-06897.1999",
      "value": "57%",
      "method": "serial section EM, 3D reconstruction",
      "metric": "Fraction of hippocampal CA1 stratum radiatum synapses with astrocytic process apposition",
      "n_analyzed": null,
      "ci_or_error": "±11%",
      "text_access": "abstract_only",
      "n_definition": "synapses scored by serial EM",
      "scope_region": "rat hippocampus CA1 stratum radiatum",
      "study_system": "mature rat hippocampus (in vivo and slices)",
      "taxonomic_level": "synapse-level EM",
      "scope_population": "excitatory synapses",
      "value_source_sentence": "Only 57 +/- 11% of the synapses had astrocytic processes apposed to them.",
      "experimental_conditions": "baseline"
    }
  ],
  "comparison_id": "pap-synaptic-coverage-across-regions",
  "comparison_name": "Fraction of synapses contacted/covered by perisynaptic astrocyte processes across brain regions",
  "comparison_type": "cross-study conflict",
  "what_it_reveals": "Reported PAP-synapse coverage fractions vary from ~57% in hippocampal CA1 stratum radiatum (Ventura & Harris 1999) to ~80-90% in mouse motor/somatosensory cortex and higher values in rat cortex (Gavrilov 2018). Region and method differences (rat vs mouse; CA1 vs cortex; apposition vs leaflet contact) partially explain the spread, but the near-2x variation has direct consequences for models of glutamate spillover and synaptic isolation.",
  "homogeneity_check": {
    "caveats": [
      "Ventura & Harris 1999 measured rat hippocampus CA1 stratum radiatum, whereas Gavrilov 2018 and Bellesi 2015 measured mouse somatosensory/motor cortex — different regions and species",
      "Definitions differ: 'apposed to synapse' (Ventura 1999) vs 'PAP+ spine' (Bellesi 2015) vs 'within leaflet area' (Gavrilov 2018) — not identical measurements",
      "Bernardinelli 2014 and Popov 2021 cite review estimates rather than primary measurements in the quoted sentences"
    ],
    "n_definition_uniform": "false",
    "scope_region_uniform": "false",
    "taxonomic_level_uniform": "true",
    "scope_population_uniform": "true"
  },
  "suggested_plot_type": "forest plot"
}

[
  "paper:paper-6c1ee79fd5da",
  "paper:paper-79447c102381",
  "paper:paper-8cf019918a97",
  "paper:paper-9a7bb3c49d35"
]

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    "Local review repositories are read-only inputs.",
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  "source_commit_sha": "1a55da0634a3bc04e5688792ed12141ce271d28e",
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