Central neuronal circuit innervating the lordosis-producing muscles defined by transneuronal transport of pseudorabies virus.

The lordosis reflex is a hormone-dependent behavior displayed by female rats during mating. This study used the transneuronal tracer pseudorabies virus (PRV) to investigate the CNS network that controls the lumbar epaxial muscles that produce this posture. After PRV was injected into lumbar epaxial muscles, the time course analysis of CNS viral infection showed progressively more PRV-labeled neurons in higher brain structures after longer survival times. In particular, the medullary reticular formation, periaqueductal gray (PAG), and ventromedial nucleus of the hypothalamus (VMN) were sequentially labeled with PRV, which supports the proposed hierarchical network of lordosis control. Closer inspection of the PRV-immunoreactive neurons in the PAG revealed a marked preponderance of spheroid neurons, rather than fusiform or triangular morphologies. Furthermore, PRV-immunoreactive neurons were concentrated in the ventrolateral column, rather than the dorsal, dorsolateral, or lateral columns of the PAG. Localization of the PRV-labeled neurons in the VMN indicated that the majority were located in the ventrolateral subdivision, although some were also in other subdivisions of the VMN. As expected, labeled cells also were found in areas traditionally associated with sympathetic outflow to blood vessels and motor pathways, including the intermediolateral nucleus of the spinal cord, the paraventricular hypothalamic nucleus, the red nucleus, and the motor cortex. These results suggest that the various brain regions along the neuraxis previously implicated in the lordosis reflex are indeed serially connected.     

Transneuronal pathways to the vestibulocerebellum

The α-herpes virus (pseudorabies, PRV) was used to observe central nervous system (CNS) pathways associated with the vestibulocerebellar system. Retrograde transneuronal migration of α-herpes virions from specific lobules of the gerbil and rat vestibulo-cerebellar cortex was detected immunohistochemically. Using a time series analysis, progression of infection along polyneuronal cerebellar afferent pathways was examined. Pressure injections of >20 nanoliters of a 10⁸ plaque forming units (pfu) per ml solution of virus were sufficient to initiate an infectious locus which resulted in labeled neurons in the inferior olivary subnuclei, vestibular nuclei, and their afferent cell groups in a progressive temporal fashion and in growing complexity with increasing incubation time. We show that climbing fibers and some other cerebellar afferent fibers transported the virus retrogradely from the cerebellum within 24 hours. One to three days after cerebellar infection discrete cell groups were labeled and appropriate laterality within crossed projections was preserved. Subsequent nuclei labeled with PRV after infection of the flocculus/paraflocculus, or nodulus/uvula, included the following: vestibular (e.g., z) and inferior olivary nuclei (e.g., dorsal cap), accessory oculomotor (e.g., Darkschewitsch n.) and accessory optic related nuclei, (e.g., the nucleus of the optic tract, and the medial terminal nucleus); noradrenergic, raphe, and reticular cell groups (e.g., locus coeruleus, dorsal raphe, raphe pontis, and the lateral reticular tract); other vestibulocerebellum sites, the periaqueductal gray, substantia nigra, hippocampus, thalamus and hypothalamus, amygdala, septal nuclei, and the frontal, cingulate, entorhinal, perirhinal, and insular cortices. However, there were differences in the resulting labeling between infection in either region. Double-labeling experiments revealed that vestibular efferent neurons are located adjacent to, but are not included among, flocculus-projecting supragenual neurons. PRV transport from the vestibular labyrinth and cervical muscles also resulted in CNS infections. Virus propagation in situ provides specific connectivity information based on the functional transport across synapses. The findings support and extend anatomical data regarding vestibulo-olivo-cerebellar pathways. © 1996 Wiley-Liss, Inc.     

Percutaneous cholecystostomy: anatomic considerations

In 100 consecutive patients undergoing abdominal computed tomography, the anatomic relationships among the gallbladder fundus, liver, and right hemicolon were evaluated to assess the feasibility of direct transperitoneal versus percutaneous transhepatic cholecystostomy. In only 17% of patients was there no interposition of colon or liver between the skin and the gallbladder fundus. In 13% of patients the right hemicolon lay between the gallbladder fundus and skin. In the remaining 70% of patients, the gallbladder fundus was positioned posterior to the liver margin. Thus, in 83% of patients studied, percutaneous cholecystostomy would necessitate a transhepatic approach.     

Novel role for the pontine micturition center, Barrington's nucleus: evidence for coordination of colonic and forebrain activity

This report provides evidence for a novel role of Barrington's nucleus, considered the pontine micturition center, in regulation of colonic function. Barrington's activation elicited increases in colonic intraluminal pressure that were eliminated by scopolamine and intrathecal lidocaine, suggesting an impact of Barrington's neurons on colonic activity via projections to lumbosacral parasympathetic neurons. Consistent with this, Barrington's neurons were transsynaptically labeled from the distal colon by pseudorabies virus and several of these were also retrogradely labeled from the locus coeruleus, which projects extensively to the forebrain. Thus, Barrington's nucleus is strategically positioned to coordinate colonic and forebrain activity. Dysfunctions within this divergent system may underlie the frequent comorbidity of colonic and psychiatric symptoms.     

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 Barrington's 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-beta-galactosidase (PRV-beta-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 Barrington's nucleus, as well as a topographical arrangement whereby dorsal neurons were bladder-related and ventral neurons were colon-related. In rats injected with PRV-beta-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 Barrington's nucleus, suggesting that individual Barrington's nucleus neurons are synaptically linked to preganglionic parasympathetic neurons which independently innervate the colon or the bladder. In addition to these dual-labelled neurons, Barrington's 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 Barrington's 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.     

Thyrotropin-releasing hormone-immunoreactive projections to the dorsal motor nucleus and the nucleus of the solitary tract of the rat.

Thyrotropin-releasing hormone-immunoreactive nerve terminals heavily innervate the dorsal motor nucleus and nucleus of the solitary tract, whereas cell bodies containing thyrotropin-releasing hormone residue most densely in the hypothalamus and raphe nuclei. By using double-labeling techniques accomplished by retrograde transport of Fluoro-Gold following microinjection into the dorsal motor nucleus/nucleus of the solitary tract combined with immunohistochemistry for thyrotropin-releasing hormone, it was demonstrated that thyrotropin-releasing hormone-immunoreactive neurons projecting to the dorsal motor nucleus/nucleus of the solitary tract reside in the nucleus raphe pallidus, nucleus raphe obscurus, and the parapyramidal region of the ventral medulla, but not in the paraventricular nucleus of the hypothalamus. The parapyramidal region includes an area along the ventral surface of the caudal medulla, lateral to the pyramidal tract and inferior olivary nucleus and ventromedial to the lateral reticular nucleus. Varying the position of the Fluoro-Gold injection site revealed a rostral to caudal topographic organization of these raphe and parapyramidal projections.