title: Low voltage-activated calcium and fast tetrodotoxin-resistant sodium currents define subtypes of cholinergic and noncholinergic neurons in rat basal forebrain.
abstract: Neurons of the basal forebrain (BF) possess unique combinations of voltage-gated membrane currents. Here, we describe subtypes of rat basal forebrain neurons based on patch-clamp analysis of low-voltage activated (LVA) calcium and tetrodotoxin-resistant (TTX-R) sodium currents combined with single-cell RT-PCR analysis. Neurons were identified by mRNA expression of choline acetyltransferase (ChAT+, cholinergic) and glutamate decarboxylase (GAD67, GABAergic). Four cell types were encountered: ChAT+, GAD+, ChAT+/GAD+ and ChAT-/GAD- cells. Both ChAT+ and ChAT+/GAD+ cells (71/75) displayed LVA currents and most (34/39) expressed mRNA for LVA Ca(2+) channel subunits. Ca(v)3.2 was detected in 31/34 cholinergic neurons and Ca(v)3.1 was expressed in 6/34 cells. Three cells expressed both subunits. No single neurons showed Ca(v)3.3 mRNA expression, although BF tissue expression was observed. In young rats (2-4 mo), ChAT+/GAD+ cells displayed larger LVA current densities compared to ChAT+ neurons, while these latter neurons displayed an age-related increase in current densities. Most (29/38) noncholinergic neurons (GAD+ and ChAT-/GAD-) possessed fast TTX-R sodium currents resembling those mediated by Na(+) channel subunit Na(v)1.5. This subunit was expressed predominately in noncholinergic neurons. No cholinergic cells (0/75) displayed fast TTX-R currents. The TTX-R currents were faster and larger in GAD+ neurons compared to ChAT-/GAD- neurons. The properties of ChAT+/GAD+ neurons resemble those of ChAT+ neurons, rather than of GAD+ neurons. These results suggest novel features of subtypes of cholinergic and noncholinergic neurons within the BF that may provide new insights for understanding normal BF function.
authors.affiliation: Department of Medical Pharmacology and Toxicology, College of Medicine, Texas A and M University System Health Science Center, 1114-TAMU, College Station, TX 77843-1114, USA.
authors.forename: Sun-Ho
authors.initials: SH
authors.lastname: Han
authors.forename: David
authors.initials: D
authors.lastname: Murchison
authors.forename: William H
authors.initials: WH
authors.lastname: Griffith
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D064032:Calbindin 2; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D002795:Choline O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D016548:Prosencephalon / Q000166:cytology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011916:Rats, Inbred F344; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D064030:S100 Calcium Binding Protein G / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology*
chemical_list: D064032:Calbindin 2; D015220:Calcium Channels; D012333:RNA, Messenger; D064030:S100 Calcium Binding Protein G; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D012964:Sodium; D002795:Choline O-Acetyltransferase; D005968:Glutamate Decarboxylase; D000109:Acetylcholine