Neuropsychopharmacology

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MDMA Induces EPSP–Spike Potentiation in Rat Ventral Hippocampus In Vitro Via Serotonin and Noradrenaline Release and Coactivation of 5-HT4 and bold italic beta 1 Receptors

Boris Mlinar, Simona Mascalchi, Raffaella Morini, Filippo Giachi and Renato Corradetti

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Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Figure 1.

Effects of N-methyl-3,4-methylenedioxyamphetamine (MDMA) on population responses. (a) Photomicrograph scheme shows the arrangement of the recording (R rad, R pyr) and stimulus (S) electrodes in the CA1 region of hippocampal slices. Dotted lines indicate position of a cut made to separate CA1 and CA3 regions. (b) Data traces recorded with electrodes positioned in the stratum pyramidale (R pyr, PS (population spikes); above) and in the distal part of stratum radiatum (R rad, fEPSP (field excitatory postsynaptic potential); below). Traces were averaged over 20 sweeps recorded immediately before (black lines) and 25–30 min after the beginning of perfusion with 10 muM MDMA (red lines). (c) Summary time–course plot (meanplusminusSD; n=9 from six animals) of MDMA (10 muM) effects on PSA (filled circles) and the fEPSP slope (open circles) recorded as shown above. (d) Scatter plot of effects of MDMA (10 muM, 30 min) on PSA and fEPSP slope for all 123 experiments. (e) Scatter plot shows the shift of PSL induced by MDMA (10 muM, 30 min) for all experiments.

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Figure 2.

Concentration-dependence of the increase in population spike amplitude (PSA) induced by N-methyl-3,4-methylenedioxyamphetamine (MDMA). (a) Summary time–courses of effects of indicated MDMA concentrations on PSA (meanplusminusSD; n=8, 13, 86, and 11, slices obtained from 6, 7, 47, and 7 animals, respectively). (b) Superimposed mean time–course of the indicated concentrations of MDMA showing faster PSA increase in response to the application of higher MDMA concentrations.

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Figure 3.

Reversibility and repeatability of the N-methyl-3,4-methylenedioxyamphetamine (MDMA) effect. (a) Summary time–course plot of effects on population spike amplitude (PSA) for experiments in which MDMA application was repeated following 2-h washout. Data points are rebinned over 1-min intervals for clarity. (b) Scatter plot shows responses to the second MDMA application relative to responses to the first application for single experiments. (c) Summary time–course plot of effects of MDMA application and the subsequent 1-h washout on the PSA. Data are expressed as the percent of the MDMA effect, normalized such that 0 and 100% correspond to mean PSA recorded over the last 20 min before MDMA application and over the last min of MDMA application. (d) Scatter plot shows reversal of ESPMDMA following the 1-h and 2-h washout in individual experiments. Data were normalized so that the reversal of 0 and 100% corresponds to average PSA values obtained during the last 1 min of MDMA application and during the last 20 min before the MDMA application, respectively.

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Figure 4.

N-methyl-3,4-methylenedioxyamphetamine (MDMA) increases population spike amplitude (PSA) by action on pyramidal neurons. (a) Superimposed data traces recorded in the stratum pyramidale showing the effect of MDMA application in continuous presence of the GABAA antagonist, bicuculline (10 muM). Traces were averaged over 20 sweeps recorded immediately before (black line) and 25–30 min after the beginning of perfusion with 10 muM MDMA (red line). Initial parts of the traces including the first PS of the burst are shown on the expanded scale in the inset. (b) Summary time–courses of effects of application of 10 muM MDMA on the population spike latency (PSL) (above) and PSA (below) in the continuous presence of 10 muM bicuculline (meanplusminusSD; n=22).

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Figure 5.

Antagonism of the N-methyl-3,4-methylenedioxyamphetamine (MDMA) effect by citalopram and nisoxetine. (a) Summary time–courses (meanplusminusSD) of the effect of MDMA application on population spike amplitude (PSA) in the presence of 1 muM citalopram (n=22, above), 200 nM nisoxetine (n=11, middle), and both 1 muM citalopram and 200 nM nisoxetine (n=10, bottom). (b) Bar graph shows the effect of 30-min application of 10 muM MDMA on the PSA in the control, in the presence of 1 muM citalopram, 200 nM nisoxetine, and both 1 muM citalopram and 200 nM nisoxetine. The error bars correspond to SD. n values are indicated. MDMA-induced PSA increase reached significance in control, in the presence of citalopram and nisoxetine (all three groups: pless than or equal to0.001, Wilcoxon test), but not in the presence of both citalopram and nisoxetine (p=0.11, Wilcoxon test). The groups are significantly different (p<0.0001, Kruskal–Wallis test). Dunn's multiple comparison post hoc analysis revealed significantly different effects of MDMA between citalopram and control groups (*** p<0.001), between citalopram+nisoxetine and control groups (*** p<0.001) and between nisoxetine and citalopram+nisoxetine groups (** p<0.01). Although Dunn's analysis revealed no significant difference between citalopram and citalopram+nisoxetine groups, the Mann–Whitney test showed a significant difference (## p<0.01).

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Figure 6.

p-Chlorophenylalanine (PCPA)-pretreatment reduces, but does not abolish the increase in population spike amplitude (PSA) induced by N-methyl-3,4-methylenedioxyamphetamine (MDMA). (a) Superimposed are summary time–courses (meanplusminusSD) of the effect of MDMA on PSA in slices obtained from PCPA-pretreated (open circles) and sham-operated (filled circles) rats. (b) Scatter plot shows the effect of PCPA and sham pretreatment on the increase in PSA induced by a 30-min application of 10 muM MDMA. MDMA significantly increased PSA in both groups (PCPA=20.0plusminus8.5%, n=11 from five animals; Sham=47.0plusminus20.3%, n=10 from five animals; Wilcoxon signed rank test, PCPA: p<0.001; Sham: p=0.002). The effect of MDMA is significantly different between the groups (Mann–Whitney test, p<0.001).

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Figure 7.

Receptor pharmacology of the N-methyl-3,4-methylenedioxyamphetamine (MDMA) response. (a) Bar chart shows the effect of the presence of single neurotransmitter receptor antagonists on the increase in population spike amplitude (PSA) induced by 10 muM MDMA. In the presence of 5-HT4 receptor antagonists, RS-23597-190 (10 muM) or SB-203186 (1 muM), or the beta 1 receptor antagonist, CGP-20712 (200 nM), the effect of a 30-min application of 10 mum MDMA was significantly reduced compared to the control group (Kruskal–Wallis test *** p<0.001; Dunn's multiple comparisons post hoc test, *** p<0.001; ** p<0.01), indicating that 5-HT4 and beta 1 receptors both mediate the MDMA action. The effect of MDMA did not significantly change in the presence of single 5-HT1A, 5-HT6, or 5-HT7 receptor antagonists, Way-100635 (50 nM), SB-258585 (200–500 nM), and SB-269970 (500 nM). n values are indicated. (b) Summary time–course (meanplusminusSD) of the MDMA effect on PSA in the presence of both 1 muM SB-203186 and 200 nM CGP-20712 reveals an inhibitory component of the MDMA effect (filled circles). This inhibitory effect was prevented in experiments in which Way-100635 (50–100 nM) was added to the antagonist mixture (open circles). (c) Superimposition of summary time–courses (meanplusminusSD) of the MDMA effect on PSA in the presence of indicated antagonist pairs shows excitatory components of the MDMA effect mediated by 5-HT4 receptors (filled squares) and by beta 1 receptors (open squares).

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Figure 8.

Persistence of ESPMDMA is only partially due to tonic activation of 5-HT4 and beta 1 receptors. (a) Time–course plot of a representative experiment in which reversal of N-methyl-3,4-methylenedioxyamphetamine (MDMA)-induced PSA increase was attempted by the addition of the 5-HT4 receptor antagonist, RS-23597-190 (10 muM). (b) Data traces from the above experiment. Traces were averaged over the last 20 sweeps recorded in control (left), in MDMA (middle) and in MDMA+RS-23597-190 (right). (c) Bar graph showing the reversal of MDMA-induced population spike amplitude (PSA) increase (meanplusminusSD) following 25 to 30-min addition of 5-HT4 and/or beta 1 receptor antagonists. In individual experiments, data were normalized so that 0 and 100% reversals correspond to average PSA values obtained during 25–30 min of MDMA application and during the last 5 min before MDMA application, respectively. n values are indicated. * p<0.05, ** p<0.01 (Wilcoxon test).

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