A review of the neural control of micturition in dogs and cats: neuroanatomy, neurophysiology and neuroplasticity

Abstract

This article discusses the current knowledge on the role of the neurological structures, especially the cerebellum and the hypothalamus, and compares the information with human medicine. Micturition is a complex voluntary and involuntarily mechanism. Its physiological completion strictly depends on the hierarchical organisation of the central nervous system pathways in the peripheral nervous system. Although the role of the peripheral nervous system and subcortical areas, such as brainstem centres, are well established in veterinary medicine, the role of the cerebellum and hypothalamus have been poorly investigated and understood. Lower urinary tract dysfunction is often associated with neurological diseases that cause neurogenic bladder (NB). The neuroplasticity of the nervous system in the developmental changes of the mechanism of micturition during the prenatal and postnatal periods is also analysed.

Keywords: Canine; Feline; Humans; Micturition; Neurogenic bladder; Urination.

Fig. 1

a, b, and c storage, voiding, micturition. EUS: external urethral sphincter; IUS: internal urethral sphincter; SP: sacral parasympathetic; ON: Onuf’s nucleus; PMC: pontine micturition centre; PAG: periaqueductal grey nucleus; orange line: sensory information travelling along the pelvic nerve and hypogastric nerve and Spinobulbar tract. Turquoise line: afferent tract (reticulospinal tract). a Storage phase. Green dash line: relaxation. Red line: contraction. During the storage phase, A-delta-mechanoreceptors record bladder stretching, and the impulse travels along the hypogastric nerve and pelvic nerve. The efferent impulses run across the spinobulbar tract and reach PAG. PAG inhibits PMC and, through the reticulospinal tract, if the bladder isn’t entirely filled, the impulse reaches neuronal cells body of the hypogastric nerve, pelvic nerve and pudendal nerve to prevent urine leakage and guarantee continuing urine filling. In this manner, the bladder is relaxed while IUS and EUS continue to be contracted to avoid urine leakage. b Voiding phase. Green line: contraction. Red dash line: relaxation. During the voiding phase, A-delta mechanoreceptors register a stretch more significant than 15 ml/kg, and the efferent impulse travels along the spinobulbar tract reaching PAG. PAG excites PMC and L-region, running across the reticulospinal tract, through hypogastric and pelvic nerves inducing bladder contraction and IUS relation. Contemporary brainstem L-region sends information through the bulbospinal tract to the pudendal nerve through ON for EUS relaxation. c Micturition. Green line: contraction. Red dash line: relaxation. The urine voiding reflex is under the highest centre control (thalamus, insular and pre-frontal cortex) integrated by the hypothalamus and cerebellum. When PAG receives information about the fullness of the bladder, it sends information to the thalamus, insula and pre-frontal cortex. The integration with the pre-frontal cortex allows deciding if voiding (switch or not), depending on an appropriate site, learned behaviours. On the contrary, the pre-frontal cortex inhibits the switching, postponing the timing for voiding. The information is also integrated with the hypothalamus for meeting the needs to mark the territory, for example. The cerebellum receives information from pelvic and pudendal nerves, integrates information between the pre frontal cortex, hypothalamus and PAG and, bidirectionally, with PMC. Cerebellum modulates and coordinates micturition