Urological Sequelae to Acute Spinal Cord Injury in Pet Dogs: A Natural Disease Model of Neuropathic Bladder Dysfunction

Abstract

The authors review urologic dysfunction, including urine retention, incontinence, and recurrent and resistant urinary tract infection, in dogs as a sequela to acute spinal cord injury. Urologic sequelae to acute spinal cord injury (SCI) pose significant complications in human and canine patients impacting quality of life and long-term cost of treatment. Dogs with intervertebral disc extrusion may serve as a natural disease model of acute SCI for investigating translational interventions, both prophylactic and therapeutic, for urologic dysfunction in human SCI patients.

Keywords: dysuria; incontinence; intervertebral disc extrusion; urinary tract infection.

Figure 1.

Neurophysiology of normal urination. Normal urination is controlled by components of the central and peripheral nervous systems. The sympathetic nervous system facilitates urinary bladder filling via the hypogastric nerve from the L1-4 spinal cord segments. The hypogastric nerve causes contraction of the internal urethral sphincter via α1 receptors and relaxation of the bladder wall via β receptors in the detrusor muscle allowing the bladder to fill. The parasympathetic nervous system facilitates urinary bladder voiding via the pelvic nerve from the S1-3 spinal cord segments that synapses on cholinergic receptors in the detrusor muscle. The pudendal nerve is a somatic nerve that is under conscious control causing contraction of the external urethral sphincter. The pontine micturition center in the brainstem facilitates the filling and voiding phases. The pontine micturition center must signal the pelvic nerve in order to initiate voiding. If this signal is blocked, such as with an UMN spinal cord injury, voiding cannot be initiated. The cerebral cortex can consciously inhibit the pontine micturition center to allow for conscious voiding. However, cortical control is not necessary for voiding to occur. The urinary bladder spends the majority of time in the filling phase. There are stretch receptors in the detrusor muscle of the bladder wall. When the urinary bladder fills to a point that those stretch receptors reach threshold, afferent signals are relayed up the pelvic nerve and up the spinal cord afferent tracts to the pontine micturition center signaling the end of the filling phase. The pontine micturition center sends efferent signals down the spinal cord efferent tracts inhibiting the hypogastric nerve and facilitating the pelvic nerve. The internal urethral sphincter relaxes, the detrusor muscle contracts, and voiding is initiated. Reprinted, with permission, from Dewey CW, da Costa RC. Practical Guide to Canine and Feline Neurology. 3rd ed. Hoboken, NJ: Wiley-Blackwell; 2016.