GABAergic cell subtypes and their synaptic connections in rat frontal cortex

TLDR

The study used whole‑cell recordings and biocytin injections in vitro to characterize the physiological, morphological, and immunohistochemical properties of non‑pyramidal cells in the frontal cortex of young rats. Several GABAergic non‑pyramidal cell types were identified in rat frontal cortex, including parvalbumin fast‑spiking basket and chandelier cells, late‑spiking neurogliaform cells, and burst‑ or regular‑spiking cells, which correspond to distinct morphologies such as somatostatin‑positive Martinotti and VIP‑positive double‑bouquet cells, and each subtype formed GABAergic synapses onto specific cortical targets while overlapping in innervated domains.

Abstract

Physiological, morphological and immunohistochemical characteristics of non-pyramidal cells in frontal cortex of young rats were studied in vitro by whole-cell recording and biocytin injection. Several groups of GABAergic non-pyramidal cells were identified: (i) parvalbumin fast-spiking (FS) cells with low input resistances and spikes of short duration, including extended plexus (basket) cells and chandelier cells. These cells showed abrupt episodes of non-adapting repetitive discharges; (ii) late-spiking (LS) cells exhibiting slowly developing ramp depolarizations, including neurogliaform cells; (iii) the remaining groups contained both burst-spiking (BS) or regular-spiking (RS) non-pyramidal (NP) cells. BSNP cells exhibited bursting activity (two or more spikes on slow depolarizing humps) from hyperpolarized potentials. Both these physiological types corresponded to a range of morphologies: (i) somatostatin-containing Martinotti cells with ascending axonal arbors to layer I (some were also positive for calbindin D28k); (ii) VIP-containing double bouquet cells with descending axonal arbors as well as arcade cells (these included small cells immunoreactive for CCK or calretinin). Each subtype of cells made GABAergic synapses onto relatively specific portions of cortical cells, but similar domains were innervated by multiple classes of GABA cells.