The defecation reflex in rats: fundamental properties and the reflex center

While pharmacological and physiological studies in rats are now increasing, physiological properties of their defecation have been scarcely investigated. This study was performed to define the properties of defecation in decerebrate rats, with special reference to the pontine defecation reflex center, which has been postulated in dogs. Intraluminal pressure was recorded from the colon and rectum with balloon-pressure transducer method using balloons of 15-20 mm in length and 0.1-0.3 ml in volume. Distention of a balloon in the descending colon and rectum with an additional injection of 0.03-0.1 ml air induced propulsive contractions on the descending colon and rectum. The mean of threshold pressures to induce propulsive contraction was 17.0 +/- 5.8 mm Hg (mean+/-S.E.) in the proximal part and 18.3 +/- 3.3 mm Hg in the distal part of the descending colon, and 11.8 +/- 1.3 mm Hg in the rectum. The maximum amplitude of propulsive contractions was 55 mm Hg in the rectum, 47 mm Hg in the distal part of the descending colon and 38 mm Hg in the proximal part. Similar colorectal propulsive contractions were produced by gastric distention (5-10 ml, 20-30 mm Hg) and electrical stimulation of the anal canal. Contrarily, spontaneous contractions of the proximal colon were suppressed by rectal distention and anal-canal stimulation. These results suggest that the descending colon and rectum, but not the proximal colon, were innervated by the pelvic afferent and efferent fibers mediating the defecation reflex. Pontine transection at the cerebellar peduncle level abolished colorectal propulsive contractions induced by distention of the stomach, descending colon and rectum, and stimulation of the anal canal, although much smaller contractions were still induced after the pontine transection. These results suggest that the pontine defecation reflex center exists and works in rats, as in dogs.     

Age-dependent chemosensitive pontine inhibition of medullary respiratory rhythm generation in the isolated brainstem of the neonatal rat

Age-dependence and chemosensitivity of the pontine inhibitory effect on medullary respiratory rhythm generation were examined in the isolated brainstem-spinal cord of the neonatal rat. In early preparations (days 1-2), the increase in RR (Delta RR) induced by the pons resection was larger in 8% CO(2) (pH 7.2) than in 2% CO(2) (pH 7.8). That difference was not found in late preparations (days 3-4). Under a given pH, the Delta RR was larger in early preparations than in late preparations.     

Electrophysiological connections of the rat mediobasal hypothalamus with brain areas mediating adrenocortical responses

With the purpose of correlating neuroendocrine and neurophysiological data, the effects of stimulating brain areas which have been shown to be involved in the mediation of adrenocortical responses, i.e. pontine reticular formation (PRF), mammillary peduncle (MP), medial forebrain bundle (MFB), and the suprachiasmatic nucleus (SCN), were studied on unit activity in the mediobasal hypothalamus in the rat. About half of the units recorded responded significantly to one of these modalities by a change in the rate of firing, the MP producing mainly inhibition and SCN facilitation and changes also occurred in the post-stimulus histograms. There was a convergence of different modalities on the same hypothalamic unit. No changes occurred in the time-interval histograms. Stimulating the mediobasal hypothalamus activated synaptically units in the PRF, MP, and MFB but none of them were activated antidromically. The present data demonstrate electrophysiological connections between extrahypothalamic regions participating in adrenocortical regulation and the hypophysiotropic area of the hypothalamus.     

Prediction of outcomes for brainstem cavernous malformation

Objective

Brainstem cavernous malformation (CM) poses a challenge to neurosurgeons in terms of operability, postoperative complications and unpredictable outcomes. The present study was conducted to analyze the clinical parameters that might predict the outcomes and to summarize our center experience in treatment of brainstem CM.

Methods

A total 59 patients with radiological and histologically confirmed brainstem CM diagnosed between 2000 and 2012 were retrospectively reviewed. All but five patients were deemed amenable to surgical resection. Complete resection was attempted in all CM and was achieved in 58/59 patients. Modified Rankin scale (mRS) score dichotomized as mRS 0–2 (favorable outcome) or mRS 3–6 (unfavorable outcome) was employed for neurological status assessment. The association of various clinical parameters to the different brainstem location was evaluated. Predictors of the surgical outcomes were analyzed using the univariate and multivaraite regression statistics.

Results

Mean age of 32 female and 27 male patients was 34.3 years. The differences in size of cavernoma, conservative treatment and complications were significantly associated with various location of the CM in the brainstem. Clinical parameters including age at presentation (p = 0.029, OR = 0.061, CI = 0.009–0.414), favorable preoperative mRS (p = 0.004, OR = 0.058, CI = 0.009–0.343), pontine location of CM (p = 0.018, OR = 0.017, CI = 0.001–0.495), and early surgical treatment (p = 0.05, OR = 0.087, CI = 0.07–1.03) were independent predictors of favorable surgical outcomes. Mean long-term follow up of 42.9 months was available in 31/59 (52.5%). The mean size of CM was 22.5 mm; small size (<10 mm) at presentation was associated with favorable outcomes at long-term follow-up (univariate analysis, p = 0.041, adjusted R² = 0.471). Preoperative mRS (p = 0.039) and location of the CM (p = 0.034) in the brainstem were predictors of good surgical outcomes at long term follow-up.

Conclusion

Favorable surgical outcomes can be predicted in brainstem CM patients with early age at presentation, pontine location of the cavernoma, favorable preoperative mRS and those undergoing early surgery. The outcomes at long-term follow-up were associated with location of the CM in the brainstem, size of the CM and the preoperative mRS.     

Diffusion tensor imaging for anatomical localization of cranial nerves and cranial nerve nuclei in pontine lesions: Initial experiences with 3T-MRI

With continuous refinement of neurosurgical techniques and higher resolution in neuroimaging, the management of pontine lesions is constantly improving. Among pontine structures with vital functions that are at risk of being damaged by surgical manipulation, cranial nerves (CN) and cranial nerve nuclei (CNN) such as CN V, VI, and VII are critical. Pre-operative localization of the intrapontine course of CN and CNN should be beneficial for surgical outcomes. Our objective was to accurately localize CN and CNN in patients with intra-axial lesions in the pons using diffusion tensor imaging (DTI) and estimate its input in surgical planning for avoiding unintended loss of their function during surgery. DTI of the pons obtained pre-operatively on a 3 Tesla MR scanner was analyzed prospectively for the accurate localization of CN and CNN V, VI and VII in seven patients with intra-axial lesions in the pons. Anatomical sections in the pons were used to estimate abnormalities on color-coded fractional anisotropy maps. Imaging abnormalities were correlated with CN symptoms before and after surgery. The course of CN and the area of CNN were identified using DTI pre- and post-operatively. Clinical associations between post-operative improvements and the corresponding CN area of the pons were demonstrated. Our results suggest that pre- and post-operative DTI allows identification of key anatomical structures in the pons and enables estimation of their involvement by pathology. It may predict clinical outcome and help us to better understand the involvement of the intrinsic anatomy by pathological processes.     

桥脑出血的临床、CT与MRI

本文收集了经ＣＴ或ＭＲＩ证实的桥脑出血１９例，结合其ＣＴ及ＭＲＩ表现，对其临床表现进行分析，并比较ＣＴ及ＭＲＩ对桥脑出血的诊断价值。提出桥脑出血的预后与出血的部位及数量有关。桥脑出血各期ＭＲＩ均有阳性表现，且ＭＲＡ（磁共振血管成像）无创伤，可发现隐匿血管畸形，有助于桥脑出血病因诊断，故桥脑出血的最佳影像诊断方法为ＭＲＩ。     

The normal brain stem from infancy to old age

Our purpose was to develop a method of measuring the size of the brain stem by routine MRI and to determine brain stem dimensions in a normal population. We examined 174 subjects, aged 4 months to 86 years, with no known brain disease. Sagittal midline diameters of the mesencephalon, pons and medulla oblongata were measured on sagittal T1-weighted images, coronal diameters from axial T2-weighted images. The adult midsagittal diameter of the mesencephalon was reached at the age of 6 years, and decreased slightly after 45–50 years. Pontine dimensions increased until the age of 20 years and did not subsequently decrease. The midsagittal and midcoronal diameters of the medulla oblongata stopped increasing at the ages of 6 and 8 years, respectively. Minimal reduction in the midsagittal diameter occurs after 50 years. Normal ranges for each dimension were recorded. Knowledge of the normal variation in size of the brain stem can be helpful in the investigation of neurodegenerative diseases. The method described is rapid and needs no additional hard-or osoftware. An additonal finding was an increase in large vermian sulci in subjects over 50 years of age.     

Mode of neuronal migration of the pontine stream in fetal mice

Summary The migration of immature neurons in the pontomedullary subpial region was examined in fetal mice by light and electron microscopy. Immature pontine cells were observed forming a cell strand from the ventral aspect of the fourth ventricle to the pontine flexure during the period between the 14th and 17th day of gestation. These cells were elongated and oriented parallel to the direction of migration, and displayed features of immature neurons; they contained a high concentration of ribosomal rosettes and a few cisternae of rough endoplasmic reticula, as well as Golgi apparatus, mitochondria, microtubules and centrioles. Many of the neurons extended leading processes, and these contained longitudinally-arrayed microtubules. Filopodia extending from the processes were found beneath the pia mater. Relocating cells displayed contact relationships between themselves; in the caudal part of the stream, translocating neurons were apposed to each other and fibers of various diameters, and in the rostral area of the stream, many fibers were noted, and corresponded to leading processes of relocating neurons, to which other cell bodies had close contact. From the arrangement of the immature neurons and their processes, it can be inferred that developing fibers act as guidance substrates for the translocation of embryonic pontine neurons.     

Post-hypoxic frequency decline does not depend on α2-adrenergic receptors in the adult rat

The aim of this study was to determine whether post-hypoxic frequency decline (PHFD) requires central activation of α₂-adrenergic receptors. PHFD is defined as the undershoot in respiratory frequency that occurs immediately following brief hypoxic periods. Adult anesthetized, vagotomized rats were exposed to hypoxia (8% O₂, mean=45 s) before and after intracerebroventricular (i.c.v.) infusion of vehicle or α₂-antagonist. The efficacy of the i.c.v. antagonist was assessed by recording the response to intravenous injection of α₂-agonist before and after the infusion. We compared breathing frequencies before, during, and after hypoxia, both before and after treatments. The decline in breathing frequency after hypoxia was not prevented by the α₂-antagonists, RX 821002 or SK&F-86466. Guanabenz, an α₂-agonist, prolonged baseline expiration and potentiated PHFD. Prior treatment with SK&F-86466 blocked the agonist-evoked response which was also reversed by subsequent administration of SK&F-86466. We conclude that PHFD does not require the activation of α₂-adrenergic receptors, but that α₂-adrenergic receptors can modulate resting and post-hypoxic respiratory frequency.     

Efferent microvascular responses to electrical stimulation of the area postrema in rats

As part of its role to transduce blood-borne and afferent neural stimuli to the brain, the area postrema conducts efferent projections monosynaptically to individual nuclei of the medulla oblongata and pons. We hypothesized that electrical activation of the area postrema would mimic this transduction process and couple microvascular responses in efferent sites to local increases in tissue metabolism reported previously. We used quantitative autoradiographic techniques and image analysis to measure capillary transfer constants for [14C]alpha-aminoisobutyric acid (AIB, a small, neutral amino acid) and blood flow (iodo[14C]antipyrine) in individual brainstem structures of anesthetized rats. The area postrema was stimulated electrically by means of a monopolar microelectrode positioned stereotaxically 100 microns deep in the dorsocentral aspect of the organ. There were no significant effects of stimulation on [14C]AIB influx or blood flow in control hindbrain structures where postremal projections are sparse or absent--the spinal trigeminal nucleus, reticular formation, or cerebellar vermis. Stimulation of the area postrema produced equivalent increases in transcapillary influx of [14C]AIB and capillary blood flow in the nucleus of the solitary tract, dorsal motor nuclei of the vagus nerves, ventrolateral medullary C1 region, locus coeruleus, dorsal tegmental nuclei, and lateral parabrachial nuclei. Formation of ratios interrelating rates of [14C]AIB influx and blood flow with previously assessed values of tissue glucose metabolism indicated that these measures increased proportionately during postremal stimulation. Such proportional increases in capillary [14C]AIB transfer and blood flow during tissue activation by area postrema stimulation are consistent with interpretation that the increase in blood flow resulted from recruitment of unused surface area in the capillary networks of individual efferent nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)