Rostral and caudal basolateral amygdala engage distinct circuits in the prelimbic and infralimbic prefrontal cortex

ILA (Infralimbic area) MBA:44 projects to BLA (Basolateral amygdalar nucleus) MBA:295 · Mouse

The same amygdala injections of retrograde cholera toxin B labelled cortico-amygdalar neurons in IL, found in both layer 2 and layer 5, as quantified by laminar distribution.

Fig. 2A; Fig. 2—figure supplement 1J

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

In awake mice, optical stimulation of rBLA with 20 Hz trains changed the firing of a substantial share of single units recorded with silicon probes in PL: about a fifth of units in layer 2 and a fifth in layer 5 responded, with activation dominating in layer 2 and suppression dominating in layer 5.

Fig. 4C,E,F; Fig. 4—figure supplements 1 and 2

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to ILA (Infralimbic area) MBA:44 · Mouse

In triplet recordings, train stimulation of cBLA fibres that reliably spiked IL layer 5 pyramidal tract neurons never produced action potentials in IL layer 5 or layer 2 cortico-amygdalar neurons (7 triplets, 4 animals), so cBLA does not functionally drive the reciprocal cortex-to-amygdala cells.

Fig. 5—figure supplement 1

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to ILA (Infralimbic area) MBA:44 · Mouse

Optical stimulation of cBLA axons evoked monosynaptic glutamatergic currents that were much larger in IL layer 5 pyramidal tract neurons than in any other recorded cell type, mapped to perisomatic and basal dendrites, and drove nearly every stimulus to spike (firing probability 0.98 ± 0.02, 7 pairs). Responses were also larger at IL L5 PT than at neighbouring IL L5 cortico-amygdalar neurons.

Fig. 2D, 2E–F; Fig. 3C,D,F; Fig. 2—figure supplement 1D–F

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 projects to PL (Prelimbic area) MBA:972 · Mouse

Anterograde virus injected at the rostral BLA coordinate produced labelled axons whose fluorescence peaked in layer 2 of PL (3 animals). A Cre-dependent version of the experiment, restricted to PL-projecting rBLA neurons, gave the same laminar profile.

Fig. 1D–F; Fig. 1—figure supplement 2A–E

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to ILA (Infralimbic area) MBA:44 · Mouse

Stimulating cBLA in awake mice mainly altered firing in IL layer 5, where 26.6 percent of single units responded and 17.7 percent were activated, with a much smaller effect in IL layer 2.

Fig. 4C,E,G; Fig. 4—figure supplements 1 and 2

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PL (Prelimbic area) MBA:972 projects to BLA (Basolateral amygdalar nucleus) MBA:295 · Mouse

Fluorescent cholera toxin B injected into the basolateral amygdala, and retrograde Cre virus injected there in other mice, labelled cortico-amygdalar neurons in PL, concentrated in layer 2 with a further group in layer 5.

Fig. 2A; Fig. 2—figure supplement 1J; Fig. 6A

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

Monosynaptic currents from cBLA axons onto PL layer 5 pyramidal tract neurons were essentially nil (under one percent of the IL L5 PT response), and even stimulation strong enough to make IL L5 PT neurons fire evoked no excitatory current in PL L5 PT neurons (9 pairs, 3 animals), only a trace of inhibition.

Fig. 2D; Fig. 5G–I

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 projects to PL (Prelimbic area) MBA:972 · Mouse

Retrograde AAV injected into PL labelled neurons throughout the basolateral amygdala, and these PL-projecting cells were concentrated in the rostral portion of the nucleus along the anterior–posterior gradient (583 ± 59 cells per animal, 3 animals). The same bias was seen when PL and IL were injected at matched anterior-posterior coordinates in separate mice.

Fig. 1A–C; Fig. 1—figure supplement 1

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

cBLA stimulation produced only few responsive units in PL in vivo: 2.6 percent of layer 2 units and 12.9 percent of layer 5 units changed firing, far below the effect in IL layer 5.

Fig. 4E,G; Fig. 4—figure supplements 1 and 2

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

When rBLA fibres were stimulated at intensities that made PL L2 CA neurons fire, PL L5 PT neurons showed large excitatory (-113 ± 24 pA) and inhibitory (508 ± 101 pA) currents, whereas subthreshold stimulation produced almost nothing (-9 ± 4 pA and 17 ± 5 pA; 8 pairs, 4 animals), indicating an indirect route through superficial layers.

Fig. 5A–C

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

Light activation of ChR2-expressing rBLA axons in slices evoked monosynaptic glutamatergic currents (isolated with TTX, 4-AP and raised Ca2+) that were far larger in PL layer 2 cortico-amygdalar neurons than in any other recorded projection neuron, and sCRACM showed the input lands on basal and perisomatic dendrites. In current clamp these inputs reliably drove action potentials (firing probability 0.88 ± 0.05, 8 pairs). Responses were also larger at PL L2 CA cells than neighbouring L2 cortico-cortical cells.

Fig. 2C, 2F; Fig. 3A,B,E; Fig. 2—figure supplement 1A–C

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

cBLA axon stimulation produced only very small monosynaptic excitatory currents in PL layer 2 cortico-amygdalar neurons (about six percent of the IL L5 PT amplitude; EPSC1 -31 ± 10 pA with trains), negligible inhibition, and never evoked action potentials in these cells (firing probability 0, 7 pairs).

Fig. 2D; Fig. 3C,D,F

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ILA (Infralimbic area) MBA:44 projects to PAG (Periaqueductal gray) MBA:795 · Mouse

The same periaqueductal gray injections also labelled layer 5 pyramidal tract neurons in IL, whose laminar distribution was quantified.

Fig. 2A; Fig. 2—figure supplement 1J

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 projects to ILA (Infralimbic area) MBA:44 · Mouse

Retrograde AAV placed in IL labelled amygdala neurons that were shifted toward the caudal end of the basolateral amygdala (694 ± 78 cells per animal, 3 animals), largely non-overlapping with the PL-projecting population (246 ± 30 dual-labelled cells).

Fig. 1A–C; Fig. 1—figure supplement 1

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PL (Prelimbic area) MBA:972 projects to PAG (Periaqueductal gray) MBA:795 · Mouse

Retrograde cholera toxin B injected into the periaqueductal gray labelled pyramidal tract neurons in layer 5 of PL, which were then targeted for recording.

Fig. 2A; Fig. 2—figure supplement 1J

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to ILA (Infralimbic area) MBA:44 · Mouse

rBLA fibre stimulation under TTX/4-AP produced small but detectable monosynaptic excitatory currents in IL layer 5 pyramidal tract neurons (about nine percent of the amplitude seen at PL L2 CA cells, 8 pairs), together with inhibitory currents of similar size to those in PL; because these responses did not depend on PL L2 firing the authors attribute them to a direct rBLA projection to IL L5.

Fig. 2C; Fig. 3A,B; Fig. 5D–F

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to PL (Prelimbic area) MBA:972 · Mouse

Subcellular mapping of rBLA axons under TTX/4-AP revealed no monosynaptic input to either the apical or the basal dendrites of PL layer 5 pyramidal tract neurons, and subthreshold stimulation of rBLA fibres evoked essentially no current in these cells; the authors conclude there is no direct rBLA to PL L5 PT connection.

Fig. 2F; Fig. 2—figure supplement 1I; Fig. 5A–C

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BLAa (Basolateral amygdalar nucleus, anterior part) MBA:303 functionally connects to ILA (Infralimbic area) MBA:44 · Mouse

rBLA stimulation in vivo modulated roughly a quarter of IL layer 5 single units (mostly suppression, 14 percent suppressed, 9.9 percent activated) and a smaller fraction of IL layer 2 units.

Fig. 4E,F; Fig. 4—figure supplements 1 and 2

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BLAp (Basolateral amygdalar nucleus, posterior part) MBA:311 projects to ILA (Infralimbic area) MBA:44 · Mouse

Anterograde virus injected at the caudal BLA coordinate labelled axons that were densest in layer 5 of IL, measured as normalized fluorescence from pia to white matter (3 animals), and the same profile was obtained when labelling only IL-projecting cBLA neurons.

Fig. 1D–F; Fig. 1—figure supplement 2F–J

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