The PPARα agonist fenofibrate attenuates disruption of dopamine function in a maternal immune activation rat model of schizophrenia

Abstract

Aims: Prenatal maternal immune activation (MIA) is associated with a risk to develop schizophrenia and affects dopamine systems in the ventral tegmental area (VTA), key region in the neurobiology of psychoses. Considering the well-described sex differences in schizophrenia, we investigated whether sex affects MIA impact on dopamine system and on schizophrenia-related behavioral phenotype. Furthermore, considering peroxisome proliferator-activated receptor-α (PPARα) expression in the CNS as well as its anti-inflammatory and neuroprotective properties, we tested if PPARα activation by prenatal treatment with a clinically available fibrate (fenofibrate) may mitigate MIA-related effects.

Methods: We induced MIA in rat dams with polyriboinosinic-polyribocytidylic acid (Poly I:C) and assessed prepulse inhibition and dopamine neuron activity in the VTA by means of electrophysiological recordings in male and female preweaned and adult offspring.

Results: Poly I:C-treated males displayed prepulse inhibition deficits, reduced number and firing rate of VTA dopamine neurons, and paired-pulse facilitation of inhibitory and excitatory synapses. Prenatal fenofibrate administration attenuated detrimental effects induced by MIA on both the schizophrenia-like behavioral phenotype and dopamine transmission in male offspring.

Conclusion: Our study confirms previous evidence that females are less susceptible to MIA and highlights PPARα as a potential target for treatments in schizophrenia.

Keywords: dopamine neurons; electrophysiology; maternal immune activation; peroxisome proliferator-activated receptor-alpha; schizophrenia; sex differences.

Figure 1

MIA impacts on VTA dopamine neuron activity in male but not female offspring. (A) Diagram representing the experimental protocol. Dams were fed with standard or 0.2% fenofibrate‐enriched diet from gestational day (GD) 8 to GD 18. At GD 15, a single iv injection of Poly I:C (4 mg/kg) or vehicle (sterile pyrogen‐free saline) was administered. Offspring underwent different experiments according to their postnatal age: patch‐clamp recordings were carried out between postnatal day (PND) 12‐20, prepulse inhibition of sensorimotor gating was tested at PND 60‐70, and in vivo electrophysiology experiments were performed at PND 70‐90. (B) Representative localization of recording sites of VTA putative dopamine neurons in vehicle (white dots for males and white squares for females) and Poly I:C (black dots for males and black squares for females) offspring, as verified by histological sections. RN, red nucleus; IP, interpeduncular nucleus, SN, substantia nigra pars reticulata. (C) Poly I:C offspring showed a reduced number of spontaneously active dopamine neurons. (D) Two‐way ANOVA yielded a significant interaction between sex and treatment for firing rate of dopamine cells. Hence, when compared with controls, the mean firing rate of VTA dopamine cells was decreased in males, as showed by the scatter plot. Burst duration (F) and mean spikes per burst (G) are impaired by MIA only in male offspring (two‐way ANOVA showed a significant interaction between sex and treatment). No significant difference was found for the percentage of spikes in burst (E) between sex or treatment. Superimposed colored diamonds show the averages for each individual rat. (H, I, J) Comparison of VTA dopamine cells from Poly I:C and controls in male and female offspring during preweaning age ex vivo. The graph shows individual firing rates of VTA dopamine neurons (H) recorded from male and female offspring from vehicle‐treated and Poly I:C‐treated dams. Each circle represents the mean firing rate of a 3‐min recording. Representative traces of action potential are displayed on top (calibration bars: 50 ms and 100 pA). No changes in paired‐pulse ratio (EPSC2/EPSC1) of AMPA EPSCs are observed between Poly I:C and vehicle female offspring (I), whereas a paired‐pulse facilitation is found in Poly I:C male rats as compared to controls. Representative traces of recordings from vehicle (top) and Poly I:C (bottom) rats are shown above graphs (calibration bars: 50 ms and 100 pA). Similarly, a paired‐pulse facilitation (IPSC2/IPSC1) has been observed in GABAA IPSCs of Poly I:C male offspring compared to vehicle rats, but not in females (J). Representative GABAA IPSCs from VTA dopamine neurons recorded in vehicle (top) and Poly I:C (bottom) rats are shown above graphs. N values are indicated in Table 1. Horizontal black lines represent means. Statistical analysis was conducted with two‐way ANOVA (sex and treatment as factors, see Table 1) and Sidak's multiple comparison test. Asterisks on graphs represent the results of the Sidak’s multiple comparison test: *P < 0.05, **P < 0.01, ***P < 0.001

Figure 2

Effect of sex and Poly I:C treatment on startle reflex parameters. In both sexes, startle amplitude (A), latency to peak (B), startle habituation (C), and PPI (D) were strongly affected by sex (two‐way ANOVA, see Table 1), but no significant effect of MIA was detected as a main factor, as evoked by exposure of dams to Poly I:C, nor interaction between sex and treatment. N values are indicated in Table 1. Horizontal black lines represent means. Statistical analysis was conducted with two‐way ANOVA (sex and treatment as factors, see Table 1). Prepulses are indicated by the intensity corresponding to decibels above background noise. AU, arbitrary units; % IBR, percent inter‐block ratio

Figure 3

Fenofibrate prevented several MIA‐induced alterations on VTA dopamine neuron activity in vivo and ex vivo and attenuated sensorimotor gating deficits induced by MIA in males. (A) Sample localization of recording sites in controls (white dots), fenofibrate (gray dots), and Poly I:C + fenofibrate (black dots) rats, as verified by histological sections. RN, red nucleus; IP, interpeduncular nucleus; SN, substantia nigra pars reticulata. Fenofibrate administration, per se ineffective, prevented the Poly I:C‐induced decrease in the number of spontaneously active VTA dopamine neurons (B) and in the average firing rate (C). Moreover, the graphs show the effect of fenofibrate on alterations in the percentage of spikes in burst (D), mean burst duration (E), and mean number of spikes in bursts (F) induced by prenatal fenofibrate. Superimposed colored diamonds show the averages for each individual rat. (G‐I) Scatter plots showing that fenofibrate partially prevents MIA‐induced detrimental effects in preweaned rats. (G) Effect of fenofibrate on the mean firing rate of dopamine cells recorded from vehicle‐treated and Poly I:C‐treated offspring from mothers fed with a control diet or fenofibrate. AMPA EPSCs (H), but not GABAA IPSCs (I), paired‐pulse facilitation, resulting by prenatal exposure to Poly I:C, is prevented by fenofibrate diet during pregnancy (calibration bars: 50 ms and 100 pA). (J) Fenofibrate prevents PPI impairment induced by Poly I:C. Prepulses are indicated by the intensity corresponding to decibels above background noise. Control groups are the same as in Figure 1 and are reported here to facilitate comparison. N values are indicated in Table 2. Horizontal black lines represent means. Statistical analysis was conducted with two‐way ANOVA (Poly I:C and fenofibrate treatments as factors, Table 2) and Sidak's multiple comparison test. Asterisks on graphs represent the result of the Sidak's multiple comparison test: *P < 0.05, **P < 0.01