Subpial and stellate cells: Two populations of interneurons in turtle visual cortex

Abstract

Turtle visual cortex has three layers and receives direct input from the dorsolateral geniculate complex of the thalamus. The outer layer 1 contains several populations of interneurons, but their physiological properties have not been characterized. This study used intracellular recording methods followed by filling with Neurobiotin to characterize the morphology and physiology of two populations of layer 1 interneurons. Subpial cells have somata positioned in the outer third of layer 1 and dendrites confined within the band of geniculate afferents that runs from lateral to medial across visual cortex. Their dendrites are composed of a sequence of many beads or varicosities separated by intervaricose segments. They have membrane time constants of tau(o) = 45.5 +/- 5.2 ms and electrotonic lengths of 1.1 +/- 0.2. Subpial cells show spike rate adaptation in response to intracellular current pulses. Stellate cells have somata located in the inner two-thirds of layer 1 and, less frequently, in layers 2 and 3. Their dendrites extend in a stellate configuration across the cortex. They are smooth or sparsely spiny, but never bear distinct varicosities. They have membrane time constants of tau(o) = 155.1 +/- 12 ms and electrotonic lengths of 3.8 +/- 0.5. They show little spike rate adaptation in response to intracellular current pulses. The positions of the two populations of cells in visual cortex and their physiological properties suggest that subpial cells may participate in a feedforward inhibitory pathway to pyramidal cells, whereas stellate cells are involved in feedback inhibition to pyramidal cells.

Micro-, Meso- and Macro-Dynamics of the Brain

“…Similarly, different populations of inhibitory interneurons in turtle DCx subserve mainly feed-forward (subpial cells; Mancilla et al 1998) or feedback (Mancilla et al 1998;Connors and Kriegstein 1986) inhibition. Axonal reconstructions of DCx interneurons (Colombe et al 2004) and immunocytochemical labeling (Reiner 1991(Reiner , 1993 suggest the existence of morphologically and physiologically identifiable classes of inhibitory interneurons. It remains to be shown that those groupings also share functional similarities with those in PCx.…”

Comparison of visually evoked local field potentials in isolated turtle brain: Patterned versus blank stimulation

“…After being surgically removed from the cranium and bathed in oxygenated artificial cerebrospinal fluid, an intact turtle brain (with eyes attached) can display essentially normal electrophysiological activity in response to visual stimulation (Kriegstein, 1987;Fan et al, 1993). This isolated turtle eye-brain preparation has been extensively used in electrophysiology (Kriegstein, 1987;Fan et al, 1993;Mancilla et al, 1998;Colombe et al, 2004) and optical imaging (Senseman, 1996;Prechtl et al, 1997;Senseman, 1999) in the study of visual function since 1980s.…”

Two Cortical Circuits Control Propagating Waves in Visual Cortex

“…This is presumably because the density of geniculate synapses on lateral pyramidal cells in the rostral cortex is much higher than the density of geniculate synapses on medial or lateral pyramidal cells in the caudal cortex. Subpial cells have their somata and dendrites embedded in the fascicle of geniculate afferents that courses across the cortex (Colombe et al, 2004). Stellate cells have dendrites that extend into the band of geniculate afferents.…”