Proceedings of The Physiological Society

Ageing and Degeneration (Edinburgh, UK) (2015) Proc Physiol Soc 33, PC28

Poster Communications

The effects of ageing on the excitatory and inhibitory presynaptic inputs to the neurones controlling micturition and continence in mice

Y. Merican1, R. M. Ichiyama1, S. A. Deuchars1, J. Deuchars1

1. University of Leeds, Leeds, United Kingdom.

Incontinence or involuntary passing of urine remains a common and distressing problem in the elderly. Continence is influenced by the external urethral sphincter, but the urethral sphincter architecture and volume is unaltered in ageing (Russell et. al., 1996). We therefore hypothesised that there was a neural component contributing to reduced continence with age and examined the balance of excitatory and inhibitory influences on neurones involved in micturition. Ten wild-type mice C57BL6 female mice, age 3 month-old (n=5) and 24 month-old (n=5) were used. All mice were injected with Fluorogold i.p. to label motor and preganglionic neurones and 1 day later were anaesthetised with 80mg/kg pentobarbitone i.p, perfused with 4% paraformaldehyde and spinal cords subsequently sectioned at 50µm. Triple labelling immunofluorescence with vesicular glutamate transporter 2 (VGLUT2), glutamic acid decarboxylase (GAD67) and glycine transporter 2 (GlyT2) was conducted on sections from L6-S1 for the dorsolateral nucleus (DLN, mouse homolog to Onuf's nucleus, which controls the urethral sphincter) and parasympathetic neurones (influence bladder emptying), and segment L1 for the sympathetic neurones (which relax the bladder to allow filling). Immunoreactive close appositions on neuronal soma were identified and analysed by confocal microscopy (Chang & Martin,2009), with differences examined using a t-test and significance at p<0.05. In aged mice DL motoneurones had significantly fewer glutamatergic appositions (12.24 ± 0.70 bouton/100µm, n= 33 cells) compared to young (22.98 ± 1.13 bouton/100µm, n= 30 cells); increased apposing GABAergic boutons (aged 7.68 ± 0.70 bouton/100µm; young 4.42 ± 0.61 bouton/100µm) and increased glycinergic terminals (aged 8.42 ± 0.63 bouton/100µm; young (3.37 ± 0.76 bouton/100µm). For sympathetic neurones, aged mice had a decreased number of glutamatergic terminals (9.49 ± 0.64 bouton/100µm, n= 37 cells) compared to young (12.32 ± 6.67 bouton/100µm, n= 41 cells) but did not demonstrate any changes in both inhibitory inputs. Compared to young adults parasympathetic neurones of aged mice had a significantly increased number of glutamatergic terminals (aged 11.00 ± 1.07 bouton/100µm, n= 33 cells; young 6.88 ± 0.51 bouton/100µm, n= 31 cells) and increased number of GABAergic terminals (aged 7.22 ± 0.58 bouton/100µm; young 4.70 ± 0.65 bouton/100µm) but did not show any significant changes in the inhibitory GlyT2 inputs. The overall pattern in ageing suggests a net increase in the inhibitory effects on the DLN (suggesting a reduction in tone of the urethral sphincter) and sympathetic neurones (reducing the capacity of the bladder). The alteration of the synaptic excitatory-inhibitory balance on the neurones controlling micturition and continence may therefore contribute to the incontinence in the elderly.

Where applicable, experiments conform with Society ethical requirements