Effect of Sarizotan, a 5-HT1a and D2-like receptor agonist, on respiration in three mouse models of Rett syndrome

Abstract

Disturbances in respiration are common and debilitating features of Rett syndrome (RTT). A previous study showed that the 5-HT1a receptor agonist (R)-(+)-8-hydroxy-dipropyl-2-aminotetralin hydrobromide (8-OH-DPAT) significantly reduced the incidence of apnea and the irregular breathing pattern in a mouse model of the disorder. 8-OH-DPAT, however, is not available for clinical practice. Sarizotan, a full 5-HT1a agonist and a dopamine D2-like agonist/partial agonist, has been used in clinical trials for the treatment of l-dopa-induced dyskinesia. The purpose of this study was to evaluate the effects of sarizotan on respiration and locomotion in mouse models of RTT. Studies were performed in Bird and Jaenisch strains of methyl-CpG-binding protein 2--deficient heterozygous female and Jaenisch strain Mecp2 null male mice and in knock-in heterozygous female mice of a common nonsense mutation (R168X). Respiratory pattern was determined with body plethysmography, and locomotion was determined with open-field recording. Sarizotan or vehicle was administered 20 minutes before a 30-minute recording of respiratory pattern or motor behavior. In separate studies, a crossover design was used to administer the drug for 7 and for 14 days. Sarizotan reduced the incidence of apnea in all three RTT mouse models to approximately 15% of their pretreatment levels. The irregular breathing pattern was corrected to that of wild-type littermates. When administered for 7 or 14 days, apnea decreased to 25 to 33% of the incidence seen with vehicle. This study indicates that the clinically approved drug sarizotan is an effective treatment for respiratory disorders in mouse models of RTT.

Figure 1.

Acute effect of sarizotan (5 mg/kg) on respiratory pattern in Mecp2-deficient heterozygous female mice. Data shown for individual mice (black lines = Mecp2^Jae/+ mice; gray lines = MeCP2^Bird/+ mice). (A) Number of apneas per hour. (B) Respiratory irregularity given as the variance in absolute (TTOTn − TTOTn + 1)/(TTOTn + 1). (C) Respiratory frequency in breaths per minute (bpm).

Figure 2.

Acute effect of sarizotan (10 mg/kg) on respiratory pattern in Mecp2^Jae/y null male mice. Data are shown for individual mice. (A) Number of apneas per hour. (B) Respiratory irregularity given as the variance in absolute (TTOTn − TTOTn + 1)/(TTOTn + 1). (C) Respiratory frequency in breaths per minute (bpm).

Figure 3.

Effect of 7-day treatment with sarizotan on respiration in Mecp2^Bird/+ female mice (n = 8). Thirty-minute monitoring of respiratory pattern with plethysmography was performed on the Days 3, 5, and 7 of vehicle or sarizotan administered in drinking water. (A) Incidence of apnea. (B) Irregularity score expressed as the variance. (C) Respiratory frequency. *P < 0.05 versus corresponding day receiving vehicle. **P < 0.01.

Figure 4.

Effect of 14-day treatment with sarizotan on respiration in Mecp2^R168X/+ mice (n = 8). Monitoring of respiratory pattern with plethysmography was performed at 0 minutes on Days 4, 7, 10, and 14 of vehicle or sarizotan administered in drinking water. (A) Incidence of apnea. (B) Irregularity score expressed as the variance. (C) Respiratory frequency. *P < 0.05 versus corresponding day receiving vehicle. **P < 0.01.

Figure 5.

Acute effect of sarizotan (5 mg/kg) on motor activity in Mecp2-deficient heterozygous and wild-type (WT) female mice. (A) Representative trace of locomotor activity in a Mecp2^−/+ mouse after receiving intraperitoneal injection of vehicle (left panel) and after sarizotan (right panel). (B) Total distance traveled in a 20 minute period. (C) Average velocity for all movements that exceed 10 mm/second⁻¹. (D) Percent time mouse spent in the centre square of the nine square grid. Total distance traveled was significantly decreased after sarizotan compared with after vehicle injections. *P < 0.0001 for WT; P = 0.0004 for Mecp2^−/+. Effects on velocity and time spent in center square were not significant. −/+, heterozygous Mecp2 deficient; sar, sarizotan; veh, vehicle.

Figure 6.

Effect of 13-day treatment with sarizotan on motor activity in Mecp2^R168/X mice (n = 8). (A) Representative trace of locomotor activity in a Mecp2^R168X/+ mouse on Day 13 of vehicle in drinking water (left panel) and on Day 13 of sarizotan (right panel). (B) Total distance traveled in a 20 minute period. (C) Average velocity for all movements that exceed 10 mm/second⁻¹. (D) Percent time mouse spent in the centre square of the nine square grid. *P = 0.031.

Figure 7.

Effect of serotonin 1a agonist injection unilateral into a Kölliker-Fuse nucleus. (A) Integrated nerve activity of central vagus (cVN) and phrenic (PN) nerves. The top two traces were made during baseline recording. The frequent phrenic apneas are characterized by prolonged cVN activity. The middle two traces were made after injection of (R)-(+)-8-hydroxy-dipropyl-2-aminotetralin hydrobromide (8-OH-DPAT) (60 nl, 500 μM) into a Kölliker-Fuse nucleus that had been identified by an earlier injection of glutamate. The bottom two traces were made after washout of dipropyl-2-aminotetralin. (B) Poincaré plots for periods that correspond to the adjacent traces.