Influence of electric stimulation of the region of the area postrema/nucleus of the solitary tract on unit activity in the anterior raphe and the cortical electroencephalogram of the rat

The human nucleus of the solitary tract: visceral pathways revealed with an "in vitro" postmortem tracing method

Visceral relay neurons in the nucleus of the solitary tract (NTS) regulate behavior and autonomic reflex functions. NTS projections have been extensively characterized in animal studies but not in humans. For the first time, NTS fiber trajectories in the human medulla oblongata were revealed with an "in vitro" postmortem tracing method. Local intramedullary pathways were labeled by direct pressure injections of free horseradish peroxidase centered on the medial subnucleus at a level adjacent to true obex. Labeled elements were resolved by peroxidase histochemistry as a dark brown intracellular reaction product. A prominent transtegmental system of axons emerged from the NTS injection sites and entered the intermediate reticular zone, a region corresponding to an autonomic reflex center in other mammals. A medial system of axons arched across the dorsomedial reticular formation toward the dorsal medullary raphe and projected ventrally toward the nucleus gigantocellularis. A small lateral fiber trajectory coursed towards the dorsomedial zone of spinal trigeminal nucleus caudalis. Presumptive terminals appeared as dustings of fine punctate processes within the NTS, dorsomotor nucleus and reticular formation. NTS projections in humans resemble those identified in other mammals including primates. Axonal tracing studies predict that visceral impulses in humans may transmit over evolutionarily conserved pathways involved in autonomic feedback control and stress adaptation.

The area postrema of newborn swine is activated by hypercapnia: relevance to sudden infant death syndrome?

This study was performed to investigate a role of the neonatal area postrema (AP) in the chemoreceptor response to hypercapnia which is defective in sudden infant death syndrome (SIDS). AP responses to CO2 inhalation were monitored in 1 to 5 week old piglets by mapping neurons that were induced to express the c-fos gene product, Fos--a marker of functional activation. Interpretive confounds were minimized by controlling for hypoxia, the effects of surgical procedures and ambient environmental stressors on neuronal activity (c-fos expression). The AP demonstrated a powerful and reproducible response in neonatal swine breathing 10% CO2 for 1 h. Intensely immunolabeled nuclei were detected throughout the longitudinal extent of the circumventricular organ, and were especially heavily concentrated at rostral levels proximal to obex. Quantitative analysis verified statistically significant increases in numbers of cells that were induced to express Fos-like immunoreactivity (FLI) in the AP of CO2- stimulated piglets as compared to control groups. No detectable age-related differences were observed in AP response patterns. Conclusions. The AP responds to hypercapnic stress in the newborn piglet. A mature circumventricular organ response in the neonate may be crucial in defending against common environmental stressors, such as nicotine exposure--an emetic agent acting via the AP and a major risk factor in SIDS. Hence, a defect of the AP or its network may underlie a loss of state-dependent controls over cardiopulmonary reflex function in SIDS.

Visceral afferent pathways to the thalamus and olfactory tubercle: behavioral implications

The goal of this study was to support the hypothesis that visceral signals may integrate and influence behavior by way of direct pathways from the nucleus tractus solitarii (NTS) to the olfactory tubercle and the midline/intralaminar thalamus. An anterograde tracer, biotinylated dextran amine (BDA) was iontophoresed bilaterally into the caudal NTS to optimize terminal labeling. NTS-cortical projections traversed both limbs of the diagonal bands providing heavy innervation, and terminated lightly within layer 3 of the olfactory tubercle. NTS-thalamic projections terminated within anterior and, as previously shown, posterior divisions of nucleus paraventricularis thalami and avoided the adjoining mediodorsal thalamic nucleus. Heretofore unrecognized projections were traced to the parafascicular and reuniens thalamic nuclei, and the peripeduncular nucleus. Control experiments identified the nucleus gracilis as the principal source of ascending projections to ventroposterior lateral, posterior and intralaminar thalamic nuclei. Our data corroborate the supposition that olfactory signals may integrate with visceral stimuli in the striatal compartment of olfactory tubercle. NTS projections encompass thalamic nuclei that project topographically to the prefrontal cortex, hippocampus and ventral (limbic) striatum, regions activated by visceral stimulation. Structural data support the idea that compartments of the non-discriminative thalamus may contribute to perception and behavioral responses to visceral stimulation.

Quantification of hippocampal noradrenaline and zinc changes after selective cell destruction

Deafferentation of septo-hippocampal projections results in sprouting of sympathetic noradrenergic (NA) fibers into the hippocampus. To determine whether dentate granule cells are necessary for the initiation and/or direction of this sprouting, both NA intensity and zinc density were microspectrophotometrically quantified at 10 or 30 days after selective neurotoxin lesions of either granule cells or CA3 pyramidal cells, and electrolytic lesions of medial septum. Groups with elevated zinc density at 10 days also had significantly higher NA levels at 30 days. Destruction of granule cells eliminated the rise in zinc and prevented the NA increase. The zinc increase may be related to a nerve growth factor-like protein responsible for the initiation of sympathetic sprouting.

Mapping of regions in the caudal brain stem that produce stimulus-bound synchronization in the cortical EEG

This study was aimed at filling the lacunae in our knowledge regarding the localization of the regions in the caudal brain stem that bring about cortical EEG synchronization on electrical stimulation and characteristic features of synchronized waves elicited from those regions. Studies were conducted on 40 encéphale isolé cats. Stimulation of ventromedial regions of the caudal brain stem, with low frequency, elicited stimulus-bound synchronized waves in the cortex which were more prominent ispsilaterally. On the other hand, low-frequency stimulation of dorsal and lateral areas produced synchronized waves which were either equally prominent on both sides, or more prominent on the contralateral side. The loci in the brain stem that produce synchronization were very specific. The induced synchronized waves showed amplitude modulation and did not outlast the train of stimuli. The results are further confirmation of the role of caudal brain stem structures in cortical EEG synchronization. They also provide information regarding the nature of cortical synchronization elicited from these brain stem structures.