Richard R. Miselis

The efferent projections of the subfornical organ of the rat: A circumventricular organ within a neural network subserving water balance

The efferent projections of the subfornical organ (SFO) of rats were traced using the autoradiographic method of following anterograde transport of labelled proteins through axons. The efferents of the SFO go to two different areas. The first is the anteroventral third ventricular area of the preoptic region and the second is the hypothalamus particularly the neurosecretory, magnocellular nuclei. Specifically, the apparent terminal fields in the first area are in the nucleus medianus of the medial preoptic area (NM), the organum vasculosum of the lamina terminalis (OVLT), and the anterior periventricular area (PeV). Many efferent fibers to this area emerge from the rostral SFO, pass anteriorly over the anterior commissure in the midline and either descend along the anterior border of the NM or enter the PeV dorsally just beneath the anterior commissure. The apparent terminal fields within the hypothalamus are in the anterior and tuberal supraoptic nuclei (SONa and SONt), the paraventricular nucleus (PVN) including its rostral accessory cluster, the nucleus circularis (NC), the dorsal perifornical area (PFd), and in both the lateral preoptic area and lateral hypothalamus adjacent to the SON. Many efferent fibers to the hypothalamus emerge from the rostral SFO and enter the columns of the fornix, diverge with the ventral stria medullari to disperse medially and laterally over the columns of the fornix and along their dorsal border at the anterior dorsal level of the columns trajectory through the hypothalamus. These findings are discussed in terms of the SFOs role within a neural network mediating water balance behaviorally and physiologically.

Vasopressin secretion: osmotic and hormonal regulation by the lamina terminalis.

The lamina terminalis, located in the anterior wall of the third ventricle, is comprised of the subfornical organ, median preoptic nucleus (MnPO) and organum vasculosum of the lamina terminalis (OVLT). The subfornical organ and OVLT are two of the brains circumventricular organs that lack the blood–brain barrier, and are therefore exposed to the ionic and hormonal environment of the systemic circulation. Previous investigations in sheep and rats show that this region of the brain has a crucial role in osmoregulatory vasopressin secretion and thirst. The effects of lesions of the lamina terminalis, studies of immediate–early gene expression and electrophysiological data show that all three regions of the lamina terminalis are involved in osmoregulation. There is considerable evidence that physiological osmoreceptors subserving vasopressin release are located in the dorsal cap region of the OVLT and possibly also around the periphery of the subfornical organ and in the MnPO. The circulating peptide hormones angiotensin II and relaxin also have access to peptide specific receptors (AT1 and LGR7 receptors, respectively) in the subfornical organ and OVLT, and both angiotensin II and relaxin act on the subfornical organ to stimulate water drinking in the rat. Studies that combined neuroanatomical tracing and detection of c‐fos expression in response to angiotensin II or relaxin suggest that both of these circulating peptides act on neurones within the dorsal cap of the OVLT and the periphery of the subfornical organ to stimulate vasopressin release.

Central nervous system neurons labelled following the injection of pseudorabies virus into the rat urinary bladder

Pseudorabies virus was injected into the wall of the urinary bladder and, following incubation times of 2, 3 and 4 days, central nervous tissue was processed immunohistochemically for the presence of virus. Longer incubation times resulted in more extensive spread of the virus. Infected neurons were initially found in the spinal cord (mainly lumbosacral) and, after longer survival times, in raphe nuclei, reticular area, pontine micturition center, locus coeruleus, red nucleus, hypothalamus, preoptic, and cortical areas. These data define a multisynaptic circuit of neurons whose ultimate output influences urinary bladder function.

Pontine regulation of pelvic viscera: pharmacological target for pelvic visceral dysfunctions

The pathophysiology and pharmacological targets of disorders of the bladder and colon have focused predominantly on the periphery. However, these viscera are regulated by the CNS, which, in turn, must integrate their functions with compatible behaviours. This review focuses on the role of the pontine micturition centre, Barringtons nucleus, as a key to this integration. Through its efferent network this pontine centre links parasympathetic preganglionic neurones with forebrain-projecting nuclei, providing an anatomical substrate for coregulation of pelvic visceral and forebrain activity. Disorders characterized by multiple pelvic visceral symptoms and comorbidity with psychiatric disorders (for example functional bowel disorders) might have their roots in dysfunctions of this circuit, which could provide a novel target for pharmacological treatment.

Polydipsia and abolition of angiotensin-induced drinking after transections of subfornical organ efferent projections in the rat

Rats with transections of subfornical organ (SFO) efferent projections failed to drink to intravenous angiotensin-II (AII) but responded to intracellular dehydration and water deprivation and suppressed drinking when food deprived. However, the transected rats were polydipsic and polyuric. Thus SFO efferent projections mediate AII-induced drinking and may be involved in the regulation of body fluid balance.

The central organization of the vagus nerve innervating the colon of the rat

BACKGROUND The extent to which the vagus nerve innervates the colon remains controversial. METHODS In 29 rats the tracer cholera toxin-horseradish peroxidase was injected into the cecum, the ascending, transverse, or descending colon or the rectum. For comparison, control injections were made into the stomach. RESULTS For all areas of colon except the rectum, brainstem motoneuronal labeling was limited to the lateral third of the dorsal motor nucleus of the vagus nerve bilaterally. In contrast, gastric injections resulted in motoneuronal labeling limited to the medial portions of the nucleus. The number of labeled motoneurons was greatest following injection of the cecum, and it significantly decreased for the more distal areas of the colon. Colonic motoneuron dendrites projected into the nucleus of the solitary tract and within the dorsal motor nucleus of the vagus nerve. Sensory afferent terminal labeling was limited to the commissural and medial subnuclei of the nucleus of the solitary tract. For the rectum, sensory and motor labeling was limited to the spinal cord. CONCLUSIONS The distribution of labeling within the vagal complex indicates that all regions of the colon, except the rectum, are innervated by the celiac and accessory celiac branches of the vagus nerve.

Brain stem localization of rodent esophageal premotor neurons revealed by transneuronal passage of pseudorabies virus

BACKGROUND/AIMS Brain stem premotor neurons control swallowing through contacts with both afferent neurons and motoneurons. The location and connectivity of premotor neurons innervating the esophagus was determined using pseudorabies virus. METHODS In 30 rats, viral injections were made into either the cervical or subdiaphragmatic esophagus, cricothyroid muscle, or stomach. After a 48-62-hour survival, brain sections were processed immunocytochemically for the virus. RESULTS Neuronal labeling was limited to the compact formation of the nucleus ambiguus for survivals of 48-54 hours. At 57-62-hour survivals, virus-labeled second-order neurons (premotor neurons) were localized to the central subnucleus of nucleus of the solitary tract. Injections in the cricothyroid muscle and stomach resulted in distinct patterns of motoneuronal labeling in the nucleus ambiguus and dorsal motor nucleus and premotor neuronal labeling in the nucleus of the solitary tract. CONCLUSIONS Virus-labeled premotor neurons in the nucleus of the solitary tract occurred as a result of retrograde transport of the virus from the nucleus ambiguus because no viral antigen was present in the tractus solitarius. The esophagus is controlled by a central circuit whereby esophageal vagal afferents terminate on premotor neurons in the central subnucleus that in turn innervate esophageal motoneurons in the nucleus ambiguus.

Transneuronal labeling from the rat distal colon: anatomic evidence for regulation of distal colon function by a pontine corticotropin-releasing factor system.

Neural circuits that are positioned to regulate rat distal colon function were identified by immunohistochemical detection of pseudorabies virus (PRV) and corticotropin‐releasing factor (CRF). The distribution of PRV‐immunoreactive neurons was examined in spinal cord and brain at increasing times (72–118 hours) after distal colon injection. At 72–80 hours, PRV‐labeling was confined to the spinal cord, in the parasympathetic preganglionic column in the lumbosacral spinal cord and in the intermediolateral column of the thoracic spinal cord. At longer survival times (88 hours), PRV‐immunolabeled neurons in the lumbosacral spinal cord were also distributed in superficial layers of the dorsal horn, the dorsal commissure, and around the central canal. Trans‐synaptic labeling was identified in the medullary raphe nuclei, parapyramidal region, A5, Barringtons nucleus, A7, and the dorsal cap of the paraventricular nucleus of the hypothalamus after longer survival times (88–91 hours). Substantial labeling of the locus coeruleus, periaqueductal gray and forebrain regions occurred at later survival times (≥96 hours). In dual‐labeled sections, CRF terminal labeling surrounded PRV‐labeled neurons in the parasympathetic preganglionic column of the lumbosacral spinal cord. Additionally, many neurons in Barringtons nucleus, but not other CRF‐containing nuclei, were double labeled for CRF and PRV. These results, taken with previous studies, support a convergence in transneuronal labeling from different pelvic viscera that may be related to coordination of overall pelvic visceral functions. Importantly, they provide an anatomic substrate for an impact of CRF from Barringtons nucleus in normal and pathophysiological functions of the distal colon. J. Comp. Neurol. 417:399–414, 2000.

The organization of vagal innervation of rat pancreas using cholera toxin—horseradish peroxidase conjugate

The present study was initiated to address the current controversy concerning the parasympathetic innervation of the pancreas, using a more sensitive tracer. The location of retrogradely labeled neurons within the dorsal motor nucleus of the vagus (DMV) was examined 48 h following injections of cholera toxin-horseradish peroxidase (CT-HRP) into designated areas of the rat pancreas. The brainstem and spinal cord were searched for any additional labeled neurons located outside of the DMV. Separate groups of animals were used for control injections into the adipose tissue of the greater omentum, the spleen, abdominal musculature, and the diaphragm. In addition, CT-HRP was dripped over the surfaces of the abdominal viscera in another group of animals. These control cases were designed to indicate whether diffusion of the neural tracer away from injection sites had occurred and had resulted in labeling of neurons which did not innervate the injected areas. Following injection of CT-HRP into the right lobe of the pancreas, labeled neurons were found primarily within the medial region of the left DMV. Injection of CT-HRP into the left lobe of the pancreas resulted in retrogradely labeled neurons predominantly within the medial region of the right DMV. Following injections into the entire pancreas, neural labeling was seen bilaterally within the DMV and was concentrated within the medial regions, with a slightly higher degree of labeling within the right DMV. No labeled neurons were seen within the nucleus ambiguus or other areas of the brainstem or spinal cord following pancreatic injections. Furthermore, no afferent labeling within the nucleus of the solitary tract (NTS) was observed, although a very small number of neurons within the nodose ganglia were labeled. The dendrites of backfilled DMV neurons could be seen extending across the midline to the contralateral DMV as well as dorsally into certain subnuclei of the NTS, and to the borders of the area postrema and the fourth ventricle. These results indicate that both the motor and sensory innervation of the rat pancreas are more restricted than has been previously suggested.

Central representation of bladder and colon revealed by dual transsynaptic tracing in the rat: substrates for pelvic visceral coordination.

The neurocircuitry underlying regulation of bladder and distal colon function by Barringtons nucleus (the pontine micturition centre) was investigated in rats by identifying neurons which were transsynaptically labelled from these viscera, with pseudorabies virus (PRV) or genetically modified forms of PRV [PRV–β‐galactosidase (PRV‐β‐Gal) and PRV–green fluorescent protein (PRV‐GFP)]. PRV injection into the bladder or the colon of separate rats suggested an overlap in the distribution of bladder‐ and colon‐related neurons in Barringtons nucleus, as well as a topographical arrangement whereby dorsal neurons were bladder‐related and ventral neurons were colon‐related. In rats injected with PRV‐β‐Gal into one viscera and PRV‐GFP into another, neurons in the major pelvic ganglion and lumbosacral spinal cord were primarily single‐labelled at relatively early survival times. With longer survival times many double‐labelled neurons (>70%) appeared in Barringtons nucleus, suggesting that individual Barringtons nucleus neurons are synaptically linked to preganglionic parasympathetic neurons which independently innervate the colon or the bladder. In addition to these dual‐labelled neurons, Barringtons nucleus neurons which were single‐labelled from either viscera were observed and these exhibited a viscerotopic organization consistent with the single‐labelling studies. Together, these findings suggest the existence of three neuronal populations in Barringtons nucleus, one which is synaptically linked to both the bladder and the colon and the other two populations which are specifically linked to either viscera. These anatomical substrates may underlie the central coordination of bladder and colon function and play a role in disorders characterized by a coexistence of bladder and colonic symptoms.