Involvement of metabotropic glutamate receptor 5 in pudendal inhibition of nociceptive bladder activity in cats

Abstract

This study used MTEP, a metabotropic glutamate receptor 5 (mGluR5) antagonist, to examine the role of mGluR5 in the neural control of the urinary bladder and in the inhibition of the micturition reflex by pudendal nerve stimulation (PNS). Experiments were conducted in 11 female cats under α-chloralose anaesthesia when the bladder was infused with either saline or 0.25% acetic acid (AA). AA irritated the bladder, induced bladder overactivity and significantly (P < 0.001) reduced bladder capacity to 14.9 ± 10.3% of the saline control capacity. MTEP (0.1-50 mg kg(-1), i.v.) significantly (P < 0.05) increased bladder capacity during saline distension but not during AA irritation. However, MTEP induced a transient inhibition of isovolumetric bladder contractions under both conditions. PNS (5 Hz), which was tested at the threshold (T) intensity for inducing a complete inhibition of isovolumetric bladder contractions and at an intensity of 3-4T, suppressed AA-induced bladder overactivity and significantly increased bladder capacity to 68.0 ± 31.3% at 1T (P < 0.05) and 98.5 ± 55.3% at 3-4T (P < 0.01) of the saline control capacity. MTEP dose dependently (0.1-50 mg kg(-1), i.v.) suppressed PNS inhibition of bladder overactivity at low intensity (1T) but not at high intensity (3-4T). During saline infusion PNS significantly (P < 0.05) increased bladder capacity to 167.7 ± 27.1% at 1T and 196.0 ± 37.4% at 3-4T. These inhibitory effects were not observed after MTEP (0.1-50 mg kg(-1), i.v.) which also increased bladder capacity. These results indicate that glutamic acid has a transmitter function in bladder and somato-bladder reflex mechanisms and raise the possibility that mGluR5 may be a target for pharmacological treatment of lower urinary tract disorders.

Figure 1. Intensity-dependent inhibitory effects of PNS on isovolumetric bladder contractions induced by distension of the bladder by 0.25% AA

Threshold intensity (T) for eliciting inhibition was 6 V. The black bars under the bladder pressure trace indicate stimulation duration. Stimulation: 5 Hz frequency, 0.2 ms pulse width.

Figure 2. Dose-dependent effect of MTEP on pudendal inhibition and micturition reflex during CMGs

A, control CMGs without MTEP during saline or 0.25% AA infusion with/without stimulation.B–D, the MTEP dosage marked on the left is for panelsB, CandD. The CMGs at increasing cumulative doses of MTEP were performed in sequence from left to right and from top to bottom in each panel.B, the AA CMGs without stimulation.C, the AA CMGs during 1Tstimulation.D, the AA CMGs during 4Tstimulation. The black bars under the pressure trace indicate stimulation duration. Stimulation: 5 Hz, 0.2 ms, inhibition thresholdT = 1.5 V. Short arrows indicate the start and stop of bladder infusion.

Figure 3. Summarized results of the effects of MTEP on the micturition reflex and on inhibition of the micturition reflex during PNS after irritation of the bladder with 0.25% AA

A, effect of 0.25% AA irritation and PNS inhibition on bladder capacity. *Significantly different from 0.25% AA data.B, dose-dependent effect of MTEP on bladder capacity with or without PNS during AA infusion. *Significantly different from the bladder capacity measured at 1Twithout MTEP treatment (i.e. at 1Tand 0 mg kg⁻¹). #Significantly different from the AA control data. Stimulation: 5 Hz, 0.2 ms.T, threshold intensity for inducing complete inhibition of isovolumetric rhythmic bladder contractions.n = 6 cats.

Figure 4. Transient inhibitory effect of MTEP on isovolumetric rhythmic bladder contractions during AA distension

A, recordings showing examples of complete inhibition of reflex bladder contractions during a short period after administration of MTEP (indicated by arrows).B, average duration of the complete inhibition increases with cumulative MTEP doses.n = 6 cats. Note: results inBexclude the data from tests where the MTEP-elicited transient inhibition was absent (i.e. duration = 0 min, see 3 mg kg⁻¹ dose inA). The number beside each data point indicates the number of animals that exhibited the transient inhibition.

Figure 5. Dose-dependent effect of MTEP on pudendal inhibition and micturition reflex during saline infusion CMGs

A–E, CMG traces with or without PNS at different dosage of MTEP. Stimulation: frequency 5 Hz, pulse width 0.2 ms, and inhibition thresholdT = 1.5 V. The black bars under bladder pressure traces mark the stimulation duration. Arrows indicate the start and stop of saline infusion.F, bladder capacity measured at different dosage of MTEP (n = 5 cats). *Significantly different from the bladder capacity measured during saline control before MTEP treatment (i.e. saline control at 0 mg kg⁻¹).

Figure 6. Transient inhibitory effect of MTEP on isovolumetric rhythmic bladder contractions during saline distension

After the MTEP is given (indicated by arrow) a complete inhibition of bladder contractions is observed in all cats at different doses. The inhibition lasted longer than the 10–15 min observation period (n = 5). In two cats the inhibition was monitored until contractions returned indicating a recovery period of about 30 min (see the second trace).

Figure 7

The possible locations (*) in the sacral spinal cord and brain stem of mGluR5s that participate in: (1) the spinobulbospinal and spinal micturition reflex pathways, and (2) the micturition inhibitory mechanism evoked by PNS. * also indicates possible sites of action of the mGluR5 antagonist.