Ultrastructural evidence for a paucity of projections from the lumbosacral cord to the pontine micturition center or M‐region in the cat: A new concept for the organization of the micturition reflex with the periaqueductal gray as central relay

Abstract

Information concerning the rate of bladder filling is determined by receptors in the bladder wall and conveyed via afferent fibers in the pelvic nerve to sensory neurons in the lumbosacral cord. It was assumed that this information is relayed from the lumbosacral cord to a medial cell group in the dorsolateral pontine tegmentum, called the M-region, the pontine micturition center, or Barrington's nucleus. The M-region, in turn, projects via long descending pathways to the sacral parasympathetic motoneurons. In the present electron microscopic study, it was investigated in cats whether monosynaptic projections from lumbosacral neurons to the M-region indeed exist. Wheat-germ agglutinin-horseradish peroxidase injections were made into the lumbosacral cord. Many retrogradely labeled dendrites and somata were found in the M-region, but no labeled terminals were found on retrogradely labeled dendrites or somata. Only a small number of anterogradely labeled terminals, which were filled with mainly round vesicles, contacted unlabeled dendrites in the M-region. In contrast, many more anterogradely labeled terminals, which were filled with mainly round and, to a limited extent, dense core vesicles and with asymmetrical synapses, were found on dendrites in the lateral part of the periaqueductal gray (PAG). Previously (Blok and Holstege [1994] Neurosci. Lett. 166:93-96), it was demonstrated that the lateral part of the PAG contains neurons projecting to the M-region. A concept for the central organization of the micturition reflex is presented in which ascending projections from the lumbosacral cord convey information on bladder filling to the PAG.(ABSTRACT TRUNCATED AT 250 WORDS)

Bladder activation by selective stimulation of pudendal nerve afferents in the cat

“…That robust sustained bladder contractions could not be evoked in the acute SCT cat indicated this low frequency pudendo-vesicle reflex is associated with the Aδ afferent fiber mediated spino-bulbo-spinal micturition reflex (Barrington, 1931. In cats, this supraspinal micturition reflex loop involves an initial convergence of pudendal and pelvic afferents in the sacral spinal column (de Groat, 2006, Thor, et al, 1989, Ueyama, et al, 1987, an ascending projection to the pontine micturition center (Blok, et al, 1995), and a descending projection terminating in the sacral parasympathetic nucleus (SPN) (Holstege and Mouton, 2003). As a consequence of the loss of these connections, limited bladder responses are evoked by low frequency pudendal nerve trunk stimulation in the SCI cat and in persons with chronic SCI (Gustafson, et al, 2004.…”

Diverse Synaptic Terminals on Rat Stapedius Motoneurons

“…The brainstem was blocked, embedded in a gelatinalbumin mixture (0.5% and 27%, respectively), hardened with 2.3% glutaraldehyde, and sectioned at 80 μm thickness on a Vibratome in the transverse plane. Free-floating sections were processed to yield reaction product that is stable and electron dense for ultrastructural analysis (Blok et al 1995). Briefly, Vibratome sections were presoaked in a solution of tetramethylbenzidine and ammonium heptamolybdate (Olucha et al 1985) in 0.1 M phosphate buffer made hypertonic with dextrose.…”

Neural correlates of the emergence of consciousness of thirst

“…Functional neuroimaging has delineated the anterior cingulate as a major locus with regard to thirst (1,2). This region also plays a major role in hunger for air (3)(4)(5), hunger for food (6), micturition (7)(8)(9), and pain (10,11), as noted by Liotti et al (3) and Sewards and Sewards (12).…”