A Pivotal Role of Lumbar Spinothalamic Cells in the Regulation of Ejaculation via Intraspinal Connections

Introduction.  A population of lumbar spinothalamic cells (LSt cells) has been demonstrated to play a pivotal role in ejaculatory behavior and comprise a critical component of the spinal ejaculation generator. LSt cells are hypothesized to regulate ejaculation via their projections to autonomic and motor neurons in the lumbosacral spinal cord. Aim.  The current study tested the hypothesis that ejaculatory reflexes are dependent on LSt cells via projections within the lumbosacral spinal cord. Methods.  Male rats received intraspinal injections of neurotoxin saporin conjugated to substance P analog, previously shown to selectively lesion LSt cells. Two weeks later, males were anesthetized and spinal cords were transected. Subsequently, males were subjected to ejaculatory reflex paradigms, including stimulation of the dorsal penile nerve (DPN), urethrogenital stimulation or administration of D3 agonist 7‐OH‐DPAT. Electromyographic recordings of the bulbocavernosus muscle (BCM) were analyzed for rhythmic bursting characteristic of the expulsion phase of ejaculation. In addition, a fourth commonly used paradigm for ejaculation and erections in unanesthetized, spinal‐intact male rats was utilized: the ex copula reflex paradigm. Main Outcome Measures.  LSt cell lesions were predicted to prevent rhythmic bursting of BCM following DPN, urethral, or pharmacological stimulation, and emissions in the ex copula paradigm. In contrast, LSt cell lesions were not expected to abolish erectile function as measured in the ex copula paradigm. Results.  LSt cell lesions prevented rhythmic contractions of the BCM induced by any of the ejaculatory reflex paradigms in spinalized rats. However, LSt cell lesions did not affect erectile function nor emissions determined in the ex copula reflex paradigm. Conclusions.  These data demonstrate that LSt cells are essential for ejaculatory, but not erectile reflexes, as previously reported for mating animals. Moreover, LSt cells mediate ejaculation via projections within the spinal cord, presumably to autonomic and motor neurons. Staudt MD, Truitt WA, McKenna KE, de Oliveira CVR, Lehman MN, and Coolen LM. A pivotal role of lumbar spinothalamic cells in the regulation of ejaculation via intraspinal connections. J Sex Med 2012;9:2256–2265.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93690/1/j.1743-6109.2011.02574.x.pd

Urinary Bladder Irritation Alters Efficacy of Vagal Stimulation on Rostral Medullary Neurons in Chronic T8 Spinalized Rats

ABSTRACT The presence of pelvic visceral inputs to neurons in the rostral medulla that are responsive to electrical stimulation of the abdominal branches of the vagus nerve (VAG-abd) was investigated in a complete chronic T8 spinal transection rat model. Using extracellular electrophysiological recordings from single medullary reticular formation (MRF) neurons, 371 neurons in 15 rats responsive to pinching the ear (search stimulus) were tested for somato-visceral and viscero-visceral convergent responses to stimulation of the following nerves/territories: VAG-abd, dorsal nerve of the penis, pelvic nerve, distention of urinary bladder and colon, penile stimulation, urethral infusion, and touch/pinch of the entire body surface. In addition to these mechanical and electrical stimuli, a chemical stimulus applied to the bladder was assessed as well. Of the total neurons examined, 205 were tested before and 166 tested beginning 20 min after application of a chemical irritant (2% acetic acid) to the urinary bladder (same rats used pre/post irritation). As with intact controls, many earresponsive MRF neurons responded to the electrical stimulation of VAG-abd. Although MRF neuron responses failed to be evoked with direct (mechanical and electrical nerve) pelvic visceral stimuli, acute chemical irritation of the urinary bladder produced a significant increase in the number of MRF neurons responsive to stimulation of VAG-abd. The results of this study indicate a central effect that potentially relates to some of the generalized below level pelvic visceral sensations that have been documented in patients with complete spinal cord injury

Spinal Cord Control of Ejaculatory Reflexes in Male Rats

Ejaculatory dysfunction impacts large numbers of men of all ages and around the world. In addition, a great majority of men with chronic spinal cord injury (SCI) experience ejaculatory dysfunction, which negatively impacts the quality of life of these individuals and their partners. SCI men emphasize the significance of regaining sexual function as their main goal. Currently, there is a marked absence of literature reporting the alterations to sexual function and ejaculation in particular in animal models of chronic SCI. In addition, there are many unanswered questions pertaining to the spinal cord control of ejaculation in healthy, intact men. It is known that ejaculation is controlled by a population of lumbar spinothalamic (LSt) cells in the lumbar spinal cord through their direct projections to preganglionic autonomic and motor neurons in the lumbosacral spinal cord. It is hypothesized that LSt cells control ejaculatory reflexes through the release of their neuropeptides galanin, cholecystokinin (CCK), gastrin-releasing peptide (GRP), and enkephalin onto receptors in autonomic and motor areas of the lumbosacral spinal cord. This hypothesis was tested in this thesis utilizing a paradigm in anesthetized and spinalized male rats, with stimulation of the sensory inputs via the dorsal penile nerve. Consistent with the hypothesis, mu and delta opioid receptor, galanin, CCK, and GRP receptor activation in LSt target areas in the lumbosacral spinal cord was demonstrated to be critical for ejaculatory reflexes. Next, the hypothesis that intrathecal infusions of the LSt neuropeptides can improve ejaculatory reflexes in male rats with chronic SCI was tested. Results indicated that intrathecal infusions of GRP and the mu opioid receptor agonist DAMGO improved ejaculatory reflexes in male rats with chronic contusion SCI. Finally, the hypothesis that the D3 receptor agonist 7-OH-DPAT will recover ejaculatory function in male rats with chronic spinal cord injury was tested. Indeed, systemic infusions of 7-OH-DPAT greatly improved ejaculatory reflexes in SCI males. Together, the studies in this thesis further clarified the mechanisms involved in the spinal cord control of ejaculation in male rats and represent an initial but pivotal first step towards the recovery of ejaculatory function after chronic spinal cord injury

An Exploration of the Control of Micturition Using a Novel in Situ Arterially Perfused Rat Preparation

Our goal was to develop and refine a decerebrate arterially perfused rat (DAPR) preparation that allows the complete bladder filling and voiding cycle to be investigated without some of the restrictions inherent with in vivo experimentation [e.g., ease and speed of set up (30 min), control over the extracellular milieu and free of anesthetic agents]. Both spontaneous (naturalistic bladder filling from ureters) and evoked (in response to intravesical infusion) voids were routinely and reproducibly observed which had similar pressure characteristics. The DAPR allows the simultaneous measurement of bladder intra-luminal pressure, external urinary sphincter–electromyogram (EUS–EMG), pelvic afferent nerve activity, pudendal motor activity, and permits excellent visualization of the entire lower urinary tract, during typical rat filling and voiding responses. The voiding responses were modulated or eliminated by interventions at a number of levels including at the afferent terminal fields (intravesical capsaicin sensitization–desensitization), autonomic (ganglion blockade with hexamethonium), and somatic motor (vecuronium block of the EUS) outflow and required intact brainstem/hindbrain-spinal coordination (as demonstrated by sequential hindbrain transections). Both innocuous (e.g., perineal stimulation) and nociceptive (tail/paw pinch) somatic stimuli elicited an increase in EUS–EMG indicating intact sensory feedback loops. Spontaneous non-micturition contractions were observed between fluid infusions at a frequency and amplitude of 1.4 ± 0.9 per minute and 1.4 ± 0.3 mmHg, respectively and their amplitude increased when autonomic control was compromised. In conclusion, the DAPR is a tractable and useful model for the study of neural bladder control showing intact afferent signaling, spinal and hindbrain co-ordination and efferent control over the lower urinary tract end organs and can be extended to study bladder pathologies and trial novel treatments

Chronic Contusion Spinal Cord Injury Impairs Ejaculatory Reflexes in Male Rats: Partial Recovery by Systemic Infusions of Dopamine D3 Receptor Agonist 7OHDPAT

Chronic spinal cord injury (SCI) causes major disruption of ejaculatory function in men. Ejaculation is a reflex and the spinal generator for ejaculatory reflexes in the rat has been located in the lumbosacral spinal cord. The effects of SCI on the rat spinal ejaculation generator and ejaculatory reflexes remain understudied. The first goal of the current study was to establish the effects of chronic SCI on the function of the spinal ejaculation generator. Male rats received a contusion injury of the spinal cord at spinal level T6?T7. Ejaculatory reflexes elicited by electrical stimulation of the dorsal penile nerve (DPN) were evaluated in injured and control rats at 4?6 weeks following SCI. SCI males demonstrated significant reductions in bursting of the bulbocavernosus muscle (BCM), an indicator for expulsion phase of ejaculation, and in seminal vesicle pressure (SVP) increases, an indicator for the emission phase of ejaculation, following DPN stimulation. Thus, contusion SCI resulted in long-term impairment of ejaculatory reflexes. The D3 agonist 7-hydroxy-2-(di-N-propylamino) tetralin (7OHDPAT) facilitates ejaculation in spinal cord intact rats, thus the second goal of the current study was to test whether subcutaneous infusions of 7OHDPAT can facilitate ejaculatory reflexes in rats with chronic SCI. Male rats received a contusion injury at T6?T7 and effects of systemic administration of 7OHDPAT (1?mg/kg) were tested 4?5 weeks following injury. Results showed that 7OHDPAT administration facilitated ejaculatory reflexes in SCI males with or without DPN stimulation, provided that supraspinal inputs to the lumbar cord were severed by transection just prior to evaluating the reflex. Thus, 7OHDPAT administration in SCI males was able to overcome the detrimental effects of SCI on ejaculatory reflexes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140172/1/neu.2015.4232.pd

Chronic contusion spinal cord injury impairs ejaculatory reflexes in male rats: Partial recovery by systemic infusions of dopamine D3 receptor agonist 7OHDPAT

Chronic spinal cord injury (SCI) causes major disruption of ejaculatory function in men. Ejaculation is a reflex and the spinal generator for ejaculatory reflexes in the rat has been located in the lumbosacral spinal cord. The effects of SCI on the rat spinal ejaculation generator and ejaculatory reflexes remain understudied. The first goal of the current study was to establish the effects of chronic SCI on the function of the spinal ejaculation generator. Male rats received a contusion injury of the spinal cord at spinal level T6-T7. Ejaculatory reflexes elicited by electrical stimulation of the dorsal penile nerve (DPN) were evaluated in injured and control rats at 4-6 weeks following SCI. SCI males demonstrated significant reductions in bursting of the bulbocavernosus muscle (BCM), an indicator for expulsion phase of ejaculation, and in seminal vesicle pressure (SVP) increases, an indicator for the emission phase of ejaculation, following DPN stimulation. Thus, contusion SCI resulted in long-term impairment of ejaculatory reflexes. The D3 agonist 7-hydroxy-2-(di-N-propylamino) tetralin (7OHDPAT) facilitates ejaculation in spinal cord intact rats, thus the second goal of the current study was to test whether subcutaneous infusions of 7OHDPAT can facilitate ejaculatory reflexes in rats with chronic SCI. Male rats received a contusion injury at T6-T7 and effects of systemic administration of 7OHDPAT (1 mg/kg) were tested 4-5 weeks following injury. Results showed that 7OHDPAT administration facilitated ejaculatory reflexes in SCI males with or without DPN stimulation, provided that supraspinal inputs to the lumbar cord were severed by transection just prior to evaluating the reflex. Thus, 7OHDPAT administration in SCI males was able to overcome the detrimental effects of SCI on ejaculatory reflexes

THE EFFECTS OF LONG-TERM SPINAL CORD INJURY ON THE URINARY BLADDER WALL TISSUE MECHANICS

Approximately 250,000 - 400,000 individuals in the United States have spinal cord injuries (SCI); urologic complications, including bladder dysfunction, are among the most common problems these patients encounter. Although extensive studies have been conducted on the effects of spinal cord injury on bladder function, the alterations in mechanical behavior and functional properties of the bladder wall tissue and the underlying mechanisms are not well understood. Using a rat model of SCI, it has been previously demonstrated that the bladder wall significantly remodeled in early stages after injury. The remodeling process included changes in mechanical properties, composition and structure of the bladder wall, and occurred as early as 10 days post-injury. Based on the previous findings, it was hypothesized that the altered mechanical environment of the urinary bladder following spinal cord injury was the key signal for the changes in the tissue functional properties. In order to test this hypothesis and gain a better understanding of relationship between function and structure of bladder wall following SCI, the present study combined different experimental methods (including mechanical testing, biochemical assays and histomorphometry) to investigate changes in mechanical properties, as well as alterations in composition and morphology of the bladder wall tissue at various time points up to 10 weeks after injury.Changes in mechanical compliance and material class found during the biomechanical analyses clearly indicated that the bladder wall continuously remodels after spinal cord injury beyond the time point previously tested. The results of histomorphometric study provided first evidence that bladder smooth muscle cells exhibited hypertrophy rather than hyperplasia, corroborated the previous mechanical anisotropy data, and provided the basis for development of structure-based constitutive models for urinary bladder wall tissue. Finally, the findings of biochemical study demonstrated that changes in extracellular matrix of bladder tissue played significant role in bladder functional behavior, and suggested that elastin/collagen ratio might be the key factor in determining the compliance of bladder wall

An investigation of the mechanism of sacral nerve stimulation in restoring voiding function.

Sacral nerve stimulation, or neuromodulation, has been shown to restore voiding in women with a specific type of urinary retention that is attributed to urethral sphincter overactivity. The therapy has gained popularity in this and other voiding dysfunctions, but its mechanism of action remains unexplained. This thesis explores the effects of neuromodulation on women with urinary retention. It incorporates a urodynamic study of the effect of neuromodulation on bladder and urethral (peripheral) function, a functional brain imaging PET (Positron Emission Tomography) study of cerebral (central) effects, and a review of the long-term efficacy of the technique. The urodynamics (including urethral pressure profilometry, cystometry, and sphincter electromyography) showed evidence of persistent urethral overactivity despite successful restoration of micturition. Together with the cystometric findings, this suggests that neuromodulation may facilitate voiding in this group by increasing detrusor contractility rather than by urethral relaxation. Review of the sacral nerve implants performed at this centre over several years reveals that approximately 75% continue to void at up to 5 years after surgery, while considering reasons for the loss of efficacy in other patients. The cerebral perception of bladder fullness was examined using PET scanning in a group of healthy female controls as well as women with retention treated by neuromodulation. The findings show that the brainstem activity which is present in healthy controls is not seen in retention patients until the neuromodulation is activated. The discussion addresses the respective roles of brainstem and cortical brain regions in the control of voiding function, and whether neuromodulation may 'normalize' cerebral activity. In conclusion, this thesis provides evidence, for the first time, of changes in brain activity following sacral neuromodulation in urinary retention, confirming that its effects may well be mediated by afferent innervation

Plasticity of neurons in mouse major pelvic ganglia in response to loos of physiological input in cases of nerve injury and spinal cord injury

Autonomic dysfunctions present significant effects on day to day functions of spinal cord-injured patients. Most people with spinal cord injury (SCI) reported a desire to recover autonomic functions such as bladder and sexual functions over regaining of locomotor functions. Lower urinary tract function is one of the autonomic functions that is impaired after SCI. Acute SCI results in areflexic bladder and complete urinary retention while patients with chronic SCI suffer from hyperreflexic bladder, incontinence and inefficient voiding. While extensive SCI research has been done locomotor recovery, relatively limited amount of research has been done on the underlying mechanisms of autonomic dysfunctions associated with SCI. The major pelvic ganglia (MPG) are peripheral ganglia that consist of postganglionic neurons that innervate the urogenital organs and are a part of the neural pathway that controls micturition. In mice, there is one MPG on each side of the animal. MPG receives cholinergic parasympathetic input from the preganglionic neurons in the sacral cord through pelvic nerve and sympathetic cholinergic inputs from those in the lumbosacral cord through the hypogastric nerve. Nicotinic cholinergic transmitter system is the major system involved in ganglionic synaptic transmission at the MPG neurons. The goal of this thesis is to understand the effects of neural injury on nicotinic cholinergic transmission at the postganglionic MPG neurons that innervate the urogenital organs. We are interested in the properties of MPG neurons in these injury states because these neurons are the final neurons in the autonomic pathway that directly innervate the target organs whose functions are compromised as results of these injuries. Before we could study the state of MPG neurons in injury conditions, we first needed to characterize the properties of these neurons in uninjured physiological state. By characterizing the normal cholinergic transmission in control mice, we are able to investigate the changes in the system after injury. Secondly, we sought to understand how MPG neurons respond to abrupt loss of all synaptic inputs. In these studies, we severed all the preganglionic neurons to MPG on one side of the animals leaving the other side intact. Finally, we studied the effects spinal cord injury on the synaptic transmission at the MPG. Spinal cord injury presumably presents altered forms of presynaptic inputs from the spinal cord to the MPG neurons due to hyperreflexic nature of the reflex pathway after SCI. We utilized molecular, electrophysiological, and pharmacological approaches using mouse models to answer our questions. In the first chapter of the thesis, I characterized the synaptic, passive, and firing properties of the MPG neurons in both male and female mice. I also characterized the nicotinic acetylcholine receptor subunits involved in cholinergic neurotransmission at the MPG. In the second chapter, I studied the effects of loss of direct inputs to the MPG neurons in both ipsilateral and contralateral intact ganglia in male mice. I performed unilateral decentralization of inputs to the MPG by severing pelvic and hypogastric nerves. In the third chapter, I studied the effects of spinal cord injury on properties of presynaptic inputs to the MPG as well as postganglionic properties, passive properties and firing properties of MPG neurons. In this injury model, I performed complete transections of the spinal cords between thoracic spinal segments (T10 and T11) in both male and female mice. All the mice had impaired bladder reflexes after spinal transection. Our results showed that decentralization and spinal cord injury effect the synaptic transmission at the MPG as well as the properties of the MPG neurons differently. These effects could be due to influences from both the nature of presynaptic input and the functional state of the target organ. We also observed different effects of spinal cord injury between MPG neurons of males and female. Understanding the mechanisms of changes at the neurotransmission at MPG neurons would be important in developing therapeutic measures for autonomic dysfunctions of the urogenital organs in nerve injury or in spinal cord injury.Includes bibliographical reference

The effect of spinal cord injury on vagal afferents.

Spinal cord injury (SCI) is a significant public health concern that leaves patients with a multitude of life-long disabilities. Major complications of SCI apart from paralysis, include deficits in bladder and bowel function. Lower urinary tract dysfunction continues to remain a top priority issue affecting quality of life for this population. The majority of visceral organs receive a dual sensory innervation from both spinal nerves as well as the vagus nerve. Following SCI, the vagus nerve is a potential pathway through which information from regions below the level of a spinal injury can travel directly to the brainstem, bypassing the spinal cord. The effect of SCI on the vagus nerve and the tissue it supplies has not been thoroughly examined. In order to advance bladder management after SCI, a thorough understanding of its neural control following chronic injury is needed to ultimately improve existing therapeutic options, as well as develop novel interventions that take advantage of this extraspinal route. The objective of this project was to describe the anatomical, neurochemical, and electrophysiological profiles of vagal innervation of the rat urinary bladder. Initially, the first study identified both single and double-labeled vagal afferents supplying the rat bladder and distal colon in the nodose ganglion (NG). The degree of neural innervation to the colon also was assessed, as a single axon that dichotomizes and innervates both organs can serve an important role for mediating both normal physiological and pathological reflexes. Following chronic SCI, we evaluated potential plasticity in subsets of NG neurons which contain projections that bypass the spinal cord from visceral organs, including those projections that specifically supply the bladder. Vagal sensory cell bodies displayed an increase in P2X3 expression and a decrease in IB4 binding, which also held true for many neurons innervating the bladder. Bladder-innervating neurons also displayed altered membrane electrophysiological properties, suggesting they are responsive to a chronic spinal injury. Even though SCI does not directly sever the vagus nerve, our results indicate vagal afferents, including those innervating the bladder, exhibit neurochemical plasticity post-injury that may have implications for visceral homeostatic mechanisms and nociceptive signaling