Unilateral vagotomy alters astrocyte and microglial morphology in the nucleus tractus solitarii of the rat

The nucleus tractus solitarii (nTS) is the initial site of integration of sensory information from the cardiorespiratory system and contributes to reflex responses to hypoxia. Afferent fibers of the bilateral vagus nerves carry input from the heart, lungs, and other organs to the nTS where it is processed and modulated. Vagal afferents and nTS neurons are integrally associated with astrocytes and microglia which contribute to neuronal activity and influence cardiorespiratory control. We hypothesized that vagotomy would alter glial morphology and cardiorespiratory responses to hypoxia. Unilateral vagotomy (or sham surgery) was performed in rats. Prior to and seven days after surgery, baseline and hypoxic cardiorespiratory responses were monitored in conscious and anesthetized animals. The brainstem was sectioned and caudal, mid-area postrema (mid-AP), and rostral sections of the nTS were prepared for immunohistochemistry. Vagotomy increased immunoreactivity (-IR) of astrocytic glial fibrillary acidic protein (GFAP), specifically at mid-AP in the nTS. Similar results were found in the dorsal motor nucleus of the vagus (DMX). Vagotomy did not alter nTS astrocyte number, yet increased astrocyte branching and altered morphology. Additionally, vagotomy both increased nTS microglia number and produced morphologic changes indicative of activation. Cardiorespiratory baseline parameters and hypoxic responses remained largely unchanged, but vagotomized animals displayed fewer augmented breaths (sighs) in response to hypoxia. Altogether, vagotomy alters nTS glial morphology, indicative of functional changes in astrocytes and microglia that may affect cardiorespiratory function in health and disease.

Cholinergic regulation along the pulmonary arterial tree of the South American rattlesnake: vascular reactivity, muscarinic receptors, and vagal innervation

Vascular tone in the reptilian pulmonary vasculature is primarily under cholinergic, muscarinic control exerted via the vagus nerve. This control has been ascribed to a sphincter located at the arterial outflow, but we speculated whether the vascular control in the pulmonary artery is more widespread, such that responses to acetylcholine and electrical stimulation, as well as the expression of muscarinic receptors, are prevalent along its length. Working on the South American rattlesnake ( Crotalus durissus), we studied four different portions of the pulmonary artery (truncus, proximal, distal, and branches). Acetylcholine elicited robust vasoconstriction in the proximal, distal, and branch portions, but the truncus vasodilated. Electrical field stimulation (EFS) caused contractions in all segments, an effect partially blocked by atropine. We identified all five subtypes of muscarinic receptors (M1–M5). The expression of the M1 receptor was largest in the distal end and branches of the pulmonary artery, whereas expression of the muscarinic M3 receptor was markedly larger in the truncus of the pulmonary artery. Application of the neural tracer 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindo-carbocyanine perchlorate (DiI) revealed widespread innervation along the whole pulmonary artery, and retrograde transport of the same tracer indicated two separate locations in the brainstem providing vagal innervation of the pulmonary artery, the medial dorsal motor nucleus of the vagus and a ventro-lateral location, possibly constituting a nucleus ambiguus. These results revealed parasympathetic innervation of a large portion of the pulmonary artery, which is responsible for regulation of vascular conductance in C. durissus, and implied its integration with cardiorespiratory control.

Cerebellar heterotopia of infancy in sudden infant death syndrome: an observational neuropathological study of four cases

Sudden infant death syndrome (SIDS) is the sudden unexpected death of an infant < 1 year of age that remains unexplained after comprehensive workup including complete autopsy and investigation of the circumstances of death. The triple risk hypothesis posits that SIDS results as a combination of both intrinsic and extrinsic factors on the background of a predisposing vulnerability. Neuropathological examination in the past has focussed mainly on the brainstem as the major player in respiratory control, where subtle findings have been linked to the chain of events leading to death in SIDS. The cerebellum has received less attention, probably due to an assumed negligible role in central cardiorespiratory control. We report four cases of SIDS in which neuropathological investigation revealed cerebellar heterotopia of infancy, a distinct malformation of the cerebellum, and discuss the potential impact of this condition on the aetiology and pathogenesis of SIDS.

IMMUNOHISTOCHEMICAL IDENTIFICATION AND DISTRIBUTION OF GLUTAMATERGIC NMDA AND mGlu1 RECEPTORS IN THE PONTINE INTERTRIGEMINAL REGION IN RATS

Local glutamate simulation of intertrigeminal region (ITR) in the lateral pons evoked immediate cardiovascular and respiratory effects proposing its role in central cardiorespiratory control. Since pharmacological studies provided only functional evidence for the existence of glutamate receptors in the ITR and thereby specifying putative neurochemical substrate involved in this control, here we employed immunohistochemistry to examine expression and distribution of NMDA and mGlu1 receptors in this structure. Thirty adult male Sprague-Dawley rats were perfuse-fixed, their brains frozen and cut into sequential series of 20 µm thick sections through the ITR. Immunohistochemistry was performed using polyclonal antibodies against NMDA-NR1, NMDA-NR2A and mGlu1 receptors. Labeled neurons in the ITR were analyzed using light microscope and computerized image analysis system for quantification of relative immunoreactivity as the mean of integrated optical density (IOD), and counting the immunopositive cells. Light microscopic analyses demonstrated NMDA-NR1-immunoreactivity mainly localized in the neuronal cell bodies with sparse distribution on primary dendrites, while NMDA-NR2A-immunoreactivity was basically somatically distributed. The mGlu1-immunoreactivity was moderate and observed both in neuronal bodies and primary dendrites or extracellular matrix suggesting somatodendritic localization. Quantitative analyses of IOD showed very strong expression of NMDA-NR1, weak of NMDA-NR2A and strong-to-moderate expression of mGluR1, with differences in immunostaining signal distribution over rostro-caudal span of the ITR. Counting of immunopositive cells followed similar expression profile. Our data directly confirm the presence of glutamatergic NMDA and mGlu1 receptors in the ITR apparently involved in signaling pathways by which this region modulates cardiorespiratory functions such as blood pressure, heart rate and breathing.

Maternal dyslipidemia during pregnancy and lactation increases blood pressure and disrupts cardiorespiratory and glucose hemostasis in female rat offspring

Hypertension and metabolic disorders evidenced in adults who have been exposed to nutritional insults during early life may be sex-dependent. We evaluated if blood pressure (BP), cardiorespiratory control, and metabolic parameters are affected in female offspring (FO) from dams fed a dyslipidaemic diet during pregnancy and lactation. FO was obtained from dams who received control (CTL) or dyslipidaemic diets during pregnancy and lactation. The effects of a maternal dyslipidaemic diet on BP, cardiorespiratory control, and biochemical parameters were assessed at 30 and 90 days of age. The experimental protocol based on a dyslipidaemic diet intervention was effective in developing maternal dyslipidemia. At 30 days of age, the FO from dyslipidaemic dams displayed disordered respiratory pattern, enhanced ventilatory response to hypercapnia (P < 0.05), and increased serum levels of total cholesterol and triglycerides (P < 0.05) when compared with CTL female offspring. At 90 days of age, FO from dyslipidaemic dams had augmented BP (P < 0.05), exacerbated cardiorespiratory responses to hypercapnia (P < 0.05), enhanced pressor responses to peripheral chemoreflex activation (P < 0.05), impaired baroreflex (P < 0.05), and larger delta variations in arterial pressure after ganglionic blockade (P < 0.05). Furthermore, during oral glucose and insulin tolerance tests, FO from dyslipidaemic dams exhibited altered glucose tolerance and insulin sensitivity (P < 0.05) when compared with FO from CTL dams. Altered breathing linked to enhanced central and peripheral chemosensitivity, impaired baroreflex, and augmented sympathetic tone may be predisposing factors for increased BP and metabolic disorders in female offspring from dyslipidaemic dams.