Ivy/Neurogliaform Interneurons Coordinate Activity in the Neurogenic Niche

Ivy/Neurogliaform Interneurons Coordinate Activity in the Neurogenic Niche Sean J. Markwardt, Cristina V. Dieni, Jacques I. Wadiche & Linda Overstreet-Wadiche Supplementary Methods. Animals We used hemizygous transgenic mice with green fluorescent protein expressed under control of the proopiomelanocortin promoter (POMC-EGFP) maintained in a C57BL/6J background 16,17. Paired recordings were performed in postnatal day (P)10-39 mice and unless noted, other experiments were performed in P30-60 mice. Some recordings from interneurons were done in NPY-YFP transgenic mice (Stock # 006417, Jackson Labs). All animal procedures followed the Guide for the Care and Use of Laboratory Animals, U.S. Public Health Service, and were approved by the University of Alabama at Birmingham Institutional Animal Care and Use Committee. Mice were anesthetized with isoflourane prior to removal of brain. Mice >P30 were perfused intracardially and slices were prepared as previously described 2 with the exception that 5 mm kynurenate was added to the cutting and perfusion solution. Electrophysiology Recordings were performed at 22 C in artificial CSF containing (in mm): 125 NaCl, 2.5 KCl, 1.25 NaH 2 PO 4, 2 CaCl 2, 1 MgCl 2, 25 NaHCO 3, and 25 glucose. Unless noted, postsynaptic patch pipettes were filled with the following (in mm): 90 K-gluconate, 45 KCl, 4 MgCl 2, 10 HEPES, 4 Mg-ATP, 0.3 Na-GTP, 7 phosphocreatine, and 0.1 EGTA, ph 7.3 and 305 mosm (4-6 MΩ). Presynaptic (interneuron) patch pipettes were filled

with a similar solution, but containing 120 K-gluconate and 15 KCl. Interneuron recordings in 4-AP were performed with the same internal solution, but without EGTA. GABAergic currents were isolated with NBQX (10 µm) and D-AP5 (25 µm) or DL-AP5 (50 µm), except in experiments shown in Fig. 2, S Fig. 6 & 7. Similar spontaneous activity in 4-AP was found in the presence of glutamate receptor antagonists (not shown). Experiments in Fig. 3 used a stimulating electrode placed in the molecular layer to evoke slow synaptic input to interneurons or mature cells. The gluconate-based intracellular solution containing 5 mm KCl was used for the experiments shown in Figs. 3a & b. Fig. 3c was performed at 32 C in the presence of CGP55845 (2 µm), using a CsCl based intracellular solution (129 mm) to maximize detection of sipscs. POMC-GFP cells were held at a potential of -80 mv. Series resistance was uncompensated (10-25 MΩ) and experiments were discarded if substantial changes (>20%) were observed. Voltages were not corrected for junction potentials. Currents and voltages were filtered at 2 khz and sampled at 10 khz (MultiClamp 700B; Molecular Devices). Chemicals were obtained from Sigma-Aldrich, Invitrogen, Tocris Bioscience, or Ascent Scientific. Iontophoresis/loose patch stimulation See Supplemental Figure 1. Data analysis The decay τ of upscs was calculated as the area from the peak to the tail of the synaptic current where the peak is normalized to 1. For latency measures, presynaptic action potentials were aligned by peak and upscs were normalized to peak amplitude. Latency

was defined as the time from the peak of the action potential to 20% of the peak of the upsc. 20-80% rise times and decay τs were fit with cumulative Gaussian distributions. Input resistance (R m ) was measured from the steady-state voltage in response to hyperpolarizing (-20 to -50 pa) current injections. The time constant (τ m ) was determined by fitting hyperpolarizing voltage responses with a single exponential. Membrane capacitance (C m ) was calculated according to C m = τ m /R m. Action potential amplitude was measured from threshold to the peak of the spike. The afterhyperpolarization (AHP) was measured from action potential threshold to the peak of the hyperpolarization. Spike and afterhyperpolarization properties were determined from the first spike in response to just suprathreshold current injection. Frequency was measured as the inverse of mean interspike intervals at threshold, or twice threshold, current injections. Adaptation ratio was calculated using the first interspike interval divided by the mean of the last two to three interspike intervals during a twice threshold current injections. Calculation of the cross-correlation between interneuron and NGC activity (Fig. 2d) was performed over a 3-4 min window using heavily decimated current traces in AxographX (Axograph Scientific, Sydney, Austalia). The polarity of PSCs in voltage clamped NGCs was reversed so that action potentials in interneurons were positively correlated with inward PSCs. Spontaneous IPSCs were detected using a template-matching protocol in AxoGraph 2 and analyzed in 100 ms bins relative to the onset of extracellular synaptic stimulation. The frequency of events was normalized to the average sipsc frequency 500 ms preceding the stimulus.

Interneuron parameters were compared using parametric ANOVA with Tukey post-hoc test when p < 0.05. Data are expressed as mean ± SEM and we used two-tailed paired or unpaired t tests to determine statistical significance at p < 0.05. Imaging Biocytin (0.2%) was included for morphological visualization after recording. Confocal images were taken of POMC-GFP and biocytin-filled interneurons in acute slices (350 µm) as described 2, using streptavidin-alexafluor 647 (Invitrogen). Anatomical reconstructions were made with Neurolucida (MicroBrightField, Inc). NPY/nNOS immunohistochemistry was performed in perfusion fixed sections (4% paraformaldehyde) from NPY-YFP transgenic mice, using anti-gfp (Invitrogen) and anti-nnos (AB5380; Chemicon) antibodies. nnos immunofluorescence was visualized using goat anti-rabbit IgG conjugated with AlexaFluor 568 (Invitrogen).

a 160 b Spike latency (ms) 120 80 40 0 interneuron; iontophoresis Iontophoresis interneuron; iontophoresis # spikes newborn granule cell 10 mv 100 ms 2 1 0 10 pa 250 ms c 10 d Spike latency (ms) 8 6 4 2 0 Loose Patch interneuron; loose patch interneuron; loose patch newborn granule cell 20 mv 10 ms # spikes 0 1 10 pa 50 ms S Fig 1

Supplemental Figure 1. Strategy for identifying presynaptic interneurons a, Borosilicate glass pipettes (80-100 MΩ) were filled with 500 mm glutamate (Glu; ph 8.6). A steady-state holding current (~10 na) was applied to prevent leakage from the pipette. Glu iontophoresis directly onto the soma (100-200 na, 1 2 ms, top cartoon) elicited single action potentials (APs) in the majority of trials (lower traces and pie chart). Due to the presence of NBQX and APV in the bath, Glu iontophoresis slightly away from the soma failed to generate APs. b, After patching a NGC (top), Glu iontophoresis was delivered to the soma of an interneuron while the NGC was monitored for synaptic current responses (bottom). If a response was deteted in the NGC, the iontophoresis pipette was removed and whole-cell recording was attempted. Typically 2 8 interneurons were tested for each NGC. Because of the long latency to fire using Glu iontophoresis (a), we used a loose patch stimulation protocol for most pairs (9/11). c, Current injection through loose seals (~6 15 MΩ; 200 na for 100 500 µs) on interneurons generated reliable single APs with short latency. d, Whole-cell recordings from NGCs were used to find synaptically coupled pairs during loose seal stimulation of multiple interneurons, in the same manner as Glu iontophoresis. NBQX and APV were included in the extracellular solution to isolate monosynaptic GABA A receptor-mediated currents.

a interneuron newborn cell b * * * loose patch 20 3.1 ± 0.1 ms 2 mv 10 pa 100 ms whole cell counts 10 2.5 ms 0 5 10 latency (ms) 0.5 mv 5 pa 25 ms c interneuron mature cell d 4 whole cell 2.6 ± 0.3 ms 2 whole cell 20 mv 10 pa 250 ms 2.5 ms 0 5 10 latency (ms) e interneuron mature cell f 10 20 mv 10 pa 250 ms whole cell 5 1.5 ± 0.1 ms whole cell * * * * 80 mv 20 pa 50 ms 2.5 ms 0 5 10 latency (ms) S Fig 2

Supplemental Figure 2. Comparison of synaptic latency in newborn and mature cells a, Evoked and spontaneous (asterisks) APs recorded from the presynaptic interneuron in loose patch mode and the postsynaptic response of a NGC. Evoked action potentials are truncated. Inset shows approximate location of the interneuron (black) and NGC (green) b, Spontaneous action potentials were aligned and the unitary responses normalized to measure latency (from cell in (a)). The average latency of PSCs in NGCs calculated from spontaneous action potentials in loose patch recordings from interneurons was 3.3 ± 0.3 ms (n = 3 pairs). c, Example of a delayed-spiking interneuron that generated slow uipscs in a mature granule cell (average 20-80% rise time = 3.5 ms). Similar to interneurons presynaptic to NGCs, this presynaptic interneuron had relatively broad action potentials (half-width, 1.8 ms) and relatively long uipsc latency (panel d). e, Example of an interneuron that generated fast (average rise time = 0.8 ms) uipscs in a mature granule cell. Expanded time scale is shown in bottom; APs (half-width 0.64 ms) marked with asterisks generated uipscs. Latency measures for this interneuron-mature cell pair is shown in (f).

a hilus GCL 5 pa 50 ms ML 20 mv 250 ms 100 µm 50 pa b 10 mv -60 mv 2.5 pa 250 ms 20 pa 50 ms S Fig 3

Supplemental Figure 3. Non-Ivy/NGs presynaptic to NGCs. a, Top, PSCs in a NGC following loose patch stimulation of a single interneuron. Black trace is average of 3 individual responses. Bottom, the firing pattern of the presynaptic interneuron suggests it is not an Ivy/NG. Right, reconstruction of this presynaptic interneuron. Arrowheads point to NGC (green) and presynaptic interneuron (red dendrites and gray axon). The interneuron had 4 primary aspinous dendrites, 3 of which were contained in the inner molecular layer and granule cell layer, the other extended into the hilus. The axon covered the granule cell layer and the inner molecular layer, with a less dense portion extending into the hilus. The mean interbouton distance was 7.1 µm, the total axon length was 15,750 µm, and the total dendrite length was 1,108 µm. The location of this NGC soma was atypically close to the inner molecular layer. b, Left, postsynaptic currents in a NGC in response to loose patch stimulation of an interneuron in the hilus. Right, firing pattern of this interneuron in response to increasing current injections. This cell had a long latency to first spike (~ 400 ms, not shown) but lacked the characteristic shape of the afterhyperpolarization and had a long membrane time constant and broad action potentials (~ 3 ms). Interneurons in (a) and (b) were excluded from further analysis.

3 pa 20 ms 30 mv 250 ms 2.5 ms 50 µm Supplemental Figure 4. Basket cells innervate mature granule cells. Left, reconstruction of a basket cell that was presynaptic to a mature cell. Dendrites are in red (length, 3,136 µm). The axon, in gray, was mostly contained within the granule cell layer and had a total length of 12,600 µm. Middle, presynaptic action potentials generated a fast uipsc. The interneuron firing pattern upon current injection is shown below (-100, 260, and 300 pa current injections). Right, the action potential half-width was 0.67 ms (black), compared to 1.4 ± 0.2 ms in interneurons presynaptic to newborn GCs (red; S Table 1; average of 60 action potentials from one presynaptic interneuron with a half-width of 1.9 ms).

Supplemental Figure 5. NPY+/nNOS+ interneurons in dentate gyrus Confocal images from the ventral (left) and middle (right) region of the dentate gyrus immunolabeled for neuropeptide Y (NPY-GPP, green) and neuronal nitric oxide synthase (nnos, red). Arrows indicate NPY+/nNOS+ colabled interneurons. Scale bars = 100 µm.

a newborn cell in juvenile mouse 4-AP picrotoxin 60 pa 2.5 min 60 pa 40 pa 10 s 500 ms b newborn cell in adult mouse 4-AP picrotoxin 200 pa 2.5 min 200 pa 10 s 200 pa 500 ms Supplemental Figure 6. 4-AP drives giant GABAergic currents in NGCs from juvenile and adult mice a, An example of 4-AP (100 μm) induced giant PSCs in a NGC from a juvenile mouse (< P30). Giant PSCs occurred at a frequency of ~ 0.04 Hz. All currents were blocked by the GABA A antagonist picrotoxin. Bottom insets show currents on expanded time scales. b, 4-AP generates the same pattern of GABA release in NGCs from adult mice 2. These results support the idea that the innervation pattern of NGCs is similar in juvenile and adult mice. Using nearphysiological intracellular [Cl - ], giant PSCs are associated with robust depolarization 2.

4 200 pa 20 pa 5 s 20 pa 1 s sipsc frequency (Hz) 3 2 1 0 p < 0.01 p > 0.05 control 4-AP 400 pa 30 pa giant IPSC freq. (Hz) (mature) 0.03 0.02 0.01 5 s 0 0 0.01 0.02 0.03 giant PSC freq. (Hz) (newborn) Supplemental Figure 7. 4-AP drives simultaneous giant GABAergic currents in NGC and mature cells a, Simultaneous recordings from a NGC and mature cell held at -30 mv. Under these recordings conditions GABAergic PSCs are outward and glutamatergic EPSCs are inward. Insets show currents on an expanded timescale. b, 4-AP (100 µm) increases the sipsc frequency in mature cells and triggers simultaneous giant GABAergic currents in NGC and mature cells (same cells as in a). c, The frequency of sipscs in mature cells increased significantly from 0.37 ± 0.1 in ACSF to 2.25 ± 0.04 Hz in 4-AP (n = 6, p < 0.01). The spsc frequency was not uniformly increased in NGCs (n = 6, p > 0.05), consistent with a lack of innervation by interneurons that generate the majority of sipscs in mature cells. d, Unlike sipscs, the frequency of giant currents induced by 4-AP was highly correlated in newborn-mature cell pairs (n = 6).

Molecular layer - + Granule cell layer - Hilus - Ivy/NG Supplemental Figure 8. Proposed innervation pattern of Ivy/NGs Ivy/NGs innervate NGCs (green), mature granule cells (white), and other interneurons (gray). This pattern of innervation predicts that GABAergic depolarization of NGCs by Ivy/NGs is accompanied by disinhibition of mature cells.

Supplemental Table 1. Intrinsic properties of interneurons presynaptic to NGCs Pairs n = 6 Putative Ivy/NG n = 12 Non-Ivy/NG n = 28 Input resistance (MΩ) 289 ± 24 * 354 ± 29 480 ± 37 Time constant (ms) 19.3 ± 3.1 * 21.6 ± 1.4 * 51.4 ± 5.4 Membrane capacitance (pf) 67.3 ± 7.7 * 63.2 ± 3.8 * 110.0 ± 7.1 Spike amplitude (mv) 43.2 ± 2.9 * 54.7 ± 3.0 * 72.8 ± 3.3 Spike half-width (ms) 1.8 ± 0.2 1.5 ± 0.2 1.7 ± 0.1 AHP amplitude (mv) 12.0 ± 1.2 16.1 ± 1.1 12.9 ± 1.2 AHP half-width (ms) 43.8 ± 16.7 32.5 ± 2.0 71.3 ± 14.3 Latency to 1 st spike (ms) 629 ± 120 * 443 ± 64 * 198 ± 34 Minimal frequency (Hz) 9.9 ± 2.2 8.6 ± 1.7 8.0 ± 1.2 Frequency at twice threshold (Hz) 20.9 ± 4.7^ 21.9 ± 2.2 18.4 ± 2.0 Adaptation ratio at twice threshold 0.76 ± 0.12^ 0.73 ± 0.07 0.61 ± 0.04 Putative Ivy/NG cells and non-ivy/ng cells were identified and grouped according to long spike latency following threshold current injection, characteristic afterhyperpolarization and morphology, when available. * indicates statistically significant difference (p < 0.05) from non- Ivy/NG cells. Not all protocols were completed, such that ^ n = 5; n = 11; n = 23.