D2 receptor activation modulates NMDA receptor antagonist-enhanced high-frequency oscillations in the olfactory bulb of freely moving rats

Abstract

Rationale: NMDA receptor antagonists, used to model psychotic-like states and treat depression, enhance the power of high-frequency oscillations (HFO) in many mammalian brain regions. In rodents, the olfactory bulb (OB) is a particularly important site for generating this rhythm. OB projection neurons express D1 and D2 receptors (D1R and D2R) which interact with NMDA receptors.

Objectives: The aim of this study was to explore the effect of dopamine (DA) signalling in the OB on MK801-enhanced HFO.

Methods: Local field potentials from the OB and locomotor activity were recorded in adult male freely moving rats. MK801 was injected systemically or infused locally to the OB. The effects of D1R and D2R agonists (SKF38393, quinpirole) and antagonists (SCH23390, eticlopride), administered systemically or locally to the OB, were examined on MK801-enhanced HFO. Effects of the antipsychotics risperidone and aripiprazole were also examined.

Results: Local infusion of MK801 enhanced HFO power in the OB to levels similar to those observed after systemic injection. Neither systemic nor local blockade of D1R or D2R affected the MK801-enhanced HFO, despite reductions in hyperlocomotion. However, direct (systemic and local) D2R, but not D1R, stimulation caused a short-lasting reduction of MK801-enhanced HFO power and longer lasting reduction in frequency. Risperidone, but not aripiprazole, reduced MK801-enhanced HFO frequency.

Conclusions: These results suggest that NMDA receptor antagonist-enhanced HFO in the OB is generated predominantly independently of DA influence, however exogenous stimulation of D2R can modulate this rhythm. A second, but not third generation antipsychotic reduced HFO frequency.

Keywords: Antipsychotics; Dopamine agonist; Dopamine antagonist; Dopamine receptor; HFO; Local infusion; MK801; NMDA receptor antagonist; Olfactory bulb; Oscillations.

Fig. 1

Systemic and local blockade of NMDAR in the OB increase HFO power but differentially affect LMA. A Example spectrograms showing MK801-enhanced HFO after 0.15 mg/kg i.p. or (B) 4 μg/side local infusion. C Complete time-course showing the changes in power after systemic and local infusion of MK801 or saline (N = 7). 2-way ANOVA revealed a significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed a significant effect for saline inf. vs MK801 inf., p < 0.001 and saline inf. vs MK801 i.p., p < 0.01. There was no significant difference between MK801 inf. vs MK801 i.p. D Example raw and band-pass filtered (130–200 Hz) signals after 0.15 mg/kg MK801 i.p. injection or (E) 4 μg/side OB infusion of MK801 recorded in the OB. Note HFO are located in bursts in both cases. F Complete time-course showing the changes in frequency after MK801 i.p. injection (N = 7). 2-way ANOVA revealed a significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for saline vs MK801 inf. and saline vs MK801 i.p., p < 0.0001). There was no difference between MK801 inf. vs MK801 i.p. G Power spectra (60 s) before and after MK801 i.p. injection or (H) OB bilateral infusion of MK801 presenting a HFO peak around 160 Hz. I Complete time-course presenting LMA after MK801 i.p. injection, MK801 OB bilateral infusion and saline OB bilateral infusion (N = 7). 2-way ANOVA revealed a significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for saline vs MK801 i.p. and MK801 i.p. vs MK801 inf., p < 0.0001). There was no difference between saline vs MK801 inf. Scatter dot plot shows comparison between correlation of LMA and HFO power after MK801 injection and infusion. LMA showed a stronger correlation with HFO power following MK801 administered via injection (i.p.) compared to MK801 infusion (Pearson r value for MK801 i.p. = 0.46 ± 0.031, for MK801 inf. = −0.05 ± 0.062, paired t-test, p = 0.0004). ***p < 0.001

Fig. 2

Systemic stimulation of DA receptors reduces MK801-enhanced HFO frequency in the OB via a mechanism involving D2R. A Example spectrogram showing the effect of 2 mg/kg systemic apomorphine (APO) on MK801-enhanced HFO. B, C Complete time-courses presenting effects of 2 mg/kg amphetamine (AMPH) and APO on power and frequency of MK801-enhanced HFO in the OB (N = 7). For power, repeated measures 2-way ANOVA revealed no significant interaction. For frequency, repeated measures 2-way ANOVA revealed a significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for MK801 + saline vs MK801 + APO and MK801 + APO vs MK801 + AMPH, p < 0.0001 and no significant effect for MK801 + saline vs MK801 + AMPH. D Power spectra (60 s) showing HFO frequency peak after systemic injection of APO (black), AMPH (blue) and saline (grey). Note HFO frequency peak after APO is shifted to lower frequencies. E Example spectrogram showing the effect of 1 mg/kg systemic quinpirole (Q) on MK801-enhanced HFO. F, G Complete time-courses presenting effects of Q and 1 mg/kg SKF38393 (SKF) on power and frequency of MK801-enhanced HFO in the OB (N = 7). For power, repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 0.093). For frequency, repeated measures 2-way ANOVA revealed a significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for MK801 + Q vs MK801 + SKF, p < 0.01). H Power spectra (60 s) showing HFO frequency peak after systemic injection of Q (black) and SKF (blue). Note HFO frequency peak after Q is shifted to lower frequencies

Fig. 3

Local OB infusion of D1R & D2R agonists differentially affects MK801-enhanced HFO in the OB. A, B Spectrograms showing MK801-enhanced HFO after 5 µg/side D1R agonist SKF38393 (SKF) and 12.5 µg/side D2R agonist quinpirole (Q). C, D Complete time-courses presenting effect of 2.5 and 5 µg/side SKF (N = 7) on power and frequency of MK801-enhanced HFO. Repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 1.000 for power, p = 0.573 for frequency). E, F Complete time-courses presenting effect of 2.5 and 12.5 µg/side Q (N = 8) on power and frequency of MK801-enhanced HFO. The dashed lines represent 10-min. time bins before and after infusion of Q. G, H Bar charts showing power and frequency of MK801-enhanced HFO after 2.5 and 12.5 µg/side Q infusion for the 10-min. bins shown in E and F. Repeated measures 1-way ANOVA revealed no significant effect for SAL and Q 2.5 inf. (p < 0.05 for power and frequency) but a significant effect for Q 12.5 inf. (p = 0.0007 for power, p < 0.0001 for frequency); *p < 0.05, **p < 0.01, ***p < 0.001 (Bonferroni’s post hoc test)

Fig. 4

Local OB infusion of D1R & D2R antagonists does not affect MK801-enhanced HFO in the OB. A, B Spectrograms showing MK801-enhanced HFO after 6 µg/side D1R antagonist SCH23390 (SCH) and 12.5 µg/side D2R antagonist eticlopride (ETI). C, D Complete time-courses presenting effect of 1 and 6 µg/side SCH on power and frequency of MK801-enhanced HFO (N = 7). Repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 1.000 both for power and frequency). E, F Complete time-courses presenting effect of 2.5 and 12.5 µg/side ETI on power and frequency of MK801-enhanced HFO (N = 7). Repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 1.000 for power, p = 0.999 for frequency)

Fig. 5

Effect of systemic blockade of D1R and D2R and antipsychotics on HFO power, frequency and LMA. (A-C) Representative spectrograms illustrating the effects of systemic injection of 1 mg/kg eticlopride + 1 mg/kg SCH23390 (ETI + SCH), 3 mg/kg aripiprazole (ARI), and 3 mg/kg risperidone (RIS) on MK801-enhanced HFO. D Complete time-course presenting the effect of coadministration of ETI + SCH on MK801-enhanced power. Repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 0.362). E Complete time-course presenting the effect of coadministration of ETI + SCH on MK801-enhanced frequency. Repeated measures 2-way ANOVA revealed no significant time × group interaction (p = 0.732). F Complete time-course presenting the effect of coadministration of ETI + SCH on MK801-enhanced LMA. 2-way repeated measures ANOVA revealed a significant time × group interaction (p < 0.0001); Bonferroni’s post hoc test p < 0.0001. G Complete time-course presenting the effect of systemic ARI, RIS and vehicle dimethyl sulfoxide (VEH) on MK801-enhanced power. Repeated measures 2-way ANOVA revealed a significant effect of time × group interaction (p < 0.001). Bonferroni’s post hoc test revealed an effect for VEH vs RIS, p < 0.001 and ARI vs RIS, p < 0.05, but no difference for VEH vs ARI. H Complete time-course presenting the effect of systemic ARI, RIS and VEH on MK801-enhanced frequency. Repeated measures 2-way ANOVA revealed significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for VEH vs RIS, and ARI vs RIS, both p < 0.0001, but no significant difference for VEH vs ARI. (I) Complete time-course presenting the effect of systemic ARI, RIS and VEH on MK801-enhanced LMA. Repeated measures 2-way ANOVA revealed significant time × group interaction (p < 0.0001). Bonferroni’s post hoc test revealed an effect for VEH vs RIS, p < 0.001 and ARI vs RIS, p < 0.0001, but no difference for VEH vs ARI

Fig. 6

Potential mechanisms through which D2R activation in the OB could modulate MK801-enhanced HFO. Stimulation of D2R on olfactory sensory neuron (OSN) terminals and mitral cell (MC) apical dendrites reduces the excitability of MC. Effects on OSN (yellow): 1) D2R activation decreases cAMP levels, reducing PKA activity and weakening Ca²⁺ channel function, which lowers Ca²⁺ influx and glutamate (Glu) release from OSN terminals onto the apical dendrites of mitral cells; 2) D2R activation on OSN terminals enhances K⁺ efflux through GIRK channels, causing hyperpolarization and further suppressing Glu release. Effects on MC (blue): 1) D2R activation increases PKC-mediated phosphorylation of GABA-A receptors, enhancing Cl⁻ influx and hyperpolarizing mitral cell membranes; 2) Reduced cAMP levels lower PKA activity, decreasing Ca²⁺ influx and the excitability of mitral cells; 3) D2R activation also facilitates K⁺ efflux via GIRK channels, further hyperpolarizing MC. Legend: Ca²⁺ – calcium, cAMP – cyclic adenosine monophosphate, Cl⁻ – chloride, DA – dopamine, D2R – dopamine D2 receptor, EPL – external plexiform layer, GABA – gamma-aminobutyric acid, GC – granule cell, GCL – granule cell layer, GIRK – G-protein-coupled inwardly rectifying potassium channels, GL – glomerular layer, Glu – glutamate, GluR—glutamate receptor, INT – inhibitory interneuron, IPL – internal plexiform layer, K⁺ – potassium, LOT – lateral olfactory tract, MC – mitral cell, MCL – mitral cell layer, ONL – olfactory nerve layer, OSN – olfactory sensory neuron, PG – periglomerular cell, PKA – protein kinase A, PKC – protein kinase C. Black ellipses – speculated excitatory-inhibitory network generating HFO. Receptor images adapted from NIAID Visual & Medical Arts (2024): bioart.niaid.nih.gov/bioart/430 and bioart.niaid.nih.gov/bioart/439