Fig. 2.

Secretagogin⁺ neurons of the olfactory tract synaptically integrate into the olfactory circuitry. (A) Secretagogin⁺ bipolar shell cells populate the margins of the human olfactory tract. (B) Secretagogin⁺ cells are predominantly bipolar, except a subset of multipolar calretinin (CR)⁻/PSA-NCAM⁻ shell cells at locations proximal to the trigone. Somatodendritic afferents are in green. (C) The percentage of secretagogin⁺/CR⁺ and secretagogin⁺/PSA-NCAM⁺ neurons declines toward the distal olfactory tract. **P < 0.01. (D and D₁) Dendritic (arrowheads), but not somatic MAP-2, immunoreactivity was seen in secretagogin⁺ neurons. (E–H) Synaptobrevin⁺ (E–E₂), synaptophysin⁺ (F and F₁), or GAD65/67⁺ (G and G₁) profiles (arrowheads) on secretagogin⁺ somata and dendrites. (H–K) Similar to the human olfactory tract, SNAP25⁺ (H), synaptobrevin-2⁺ (I), VGLUT1⁺ (J and J₁), or GAD65/67⁺ (K–K₂) boutons contact secretagogin⁺ somata or processes in the mouse lemur olfactory tract. Note that postsynaptic GABA_ARα1 subunits (31) appose GAD65/67⁺ afferents (K₂). (L) Markers of cellular identity and afferent synapses on secretagogin⁺ neurons (n.d., nondetectable due to e.g., epitope mismatch). [Scale bars: 10 μm (B), 3 μm (D, E₂, F, G, and G₁), 2 μm (D₁, F₁, H, I, I₁, J, K, K₁, and K₂), and 1 μm (E and E₁).]