Projections of medullary and pontine noradrenergic neurons to the horizontal limb of the nucleus of diagonal band in the rat

Involvement of Supraoptic Astrocytes in Basilar Artery Occlusion-Evoked Differential Activation of Vasopressin Neurons and Vasopressin Secretion in Rats

Vasopressin (VP) is a key factor in the development of brain injury in ischemic stroke. However, the regulation of VP secretion in basilar artery occlusion (BAO) remains unclear. To clarify the regulation of VP secretion in BAO and the underlying mechanisms, we performed this study in a rat model of BAO with (BC) or without common carotid artery occlusion (CCAO). The results showed that BAO and BC time-dependently increased neurological scores and that BC also increased water contents in the medulla at 2 h and in the pontine at 8 h. Moreover, plasma VP level increased significantly at BAO-8 h, CCAO and BC-2 h but not at BC-8 h; however, VP expressions increased in the supraoptic nucleus (SON) at BC-8 h. The neurological scores were highly correlated with pontine water contents and plasma VP levels. The number of phosphorylated extracellular signal-regulated protein kinase1/2-positive VP neurons increased significantly in the SON at BC-8 h. Similarly, the number of c-Fos-positive VP neurons increased significantly in the SON at BAO-8 h and BC-8 h. In addition, the length of glial fibrillary acidic protein (GFAP) filaments increased significantly in BC compared to BAO only. Aquaporin 4 (AQP4) puncta around VP neurons increased significantly at BC-8 h relative to BC-2 h, which had negative correlation with plasma VP levels. These findings indicate that BAO facilitates VP secretion and increases VP neuronal activity in the SON. The peripheral VP release is possibly under a negative feedback regulation of central VP neuronal activity through increasing GFAP and AQP4 expression in astrocytic processes.

Nicotine improved the olfactory impairment in MPTP-induced mouse model of Parkinson's disease

Olfactory impairment is an early feature of patients with Parkinson's disease (PD). Retrospective epidemiological studies reported lower scores on the University of Pennsylvania Smell Identification Test (UPSIT) in non-smokers than smokers with PD and showed an inverse correlation between susceptibility to PD and a person's history of smoking. But the mechanisms by which cigarettes affect olfaction in PD are not fully understood. So we investigated the effect of nicotine on the olfactory function in 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP)-treated mice. We observed that nicotine improved locomotor activity and protection against dopaminergic neuron loss in the midbrain in MPTP-treated mice. Compared to controls, MPTP-treated mice showed a deficit of odor discrimination and odor detection, which were alleviated by nicotine treatment. But no significant changes were found in olfactory memory in MPTP-treated mice. Moreover, we detected a marked decrease of Choline acetyltransferase (ChAT) expression in the olfactory bulb (OB) in MPTP-treated mice, which was also attenuated by nicotine administration. In addition, nicotine ameliorated the loss of cholinergic neurons and dopaminergic innervation in the horizontal limb of the diagonal band (HDB), which is the primary origin of cholinergic input to the OB. Our results suggested that nicotine could improve the olfactory impairment by protecting cholinergic systems in the OB of MPTP-treated mice. And nicotine protection of cholinergic systems in the OB is relevant to attenuating dopaminergic neuron loss in the midbrain and HDB.

Properties and opioid inhibition of mesolimbic dopamine neurons vary according to target location

The mesolimbic dopamine system, which mediates the rewarding properties of nearly all drugs of abuse, originates in the ventral tegmental area (VTA) and sends major projections to both the nucleus accumbens (NAc) and the basolateral amygdala (BLA). To address whether differences occur between neurons that project to these separate areas, retrograde microspheres were injected to either the BLA or the NAc of DBA/2J mice. Whole-cell recordings were made from labeled VTA dopamine neurons. We found that identified neurons that projected to the BLA and NAc originated within different quadrants of the VTA with neither group exhibiting large-amplitude h-currents. Neurons that projected to the NAc exhibited a greater outward current in response to the kappa-opioid agonist (5alpha,7alpha,8alpha)-(+)-N-methyl-N-[7-(pyrrolidinyl)-1-oxaspiro [4,5]dec-8-yl]-benzeneacetamide (U69593; 200 nM), whereas neurons that projected to the BLA exhibited greater inhibition to the mu/delta opioid agonist [Met5] enkephalin (ME; 3 microM). In addition, we found that the presynaptic inhibition of GABAergic transmission at both GABAA and GABAB receptors was differentially regulated by U69593 between the two groups. When dopamine IPSCs were examined, U69593 caused a greater inhibition in NAc- than BLA-projecting neurons. ME had no effect on either. Finally, the regulation of extracellular dopamine by dopamine uptake transporters was equal across the VTA. These results suggest that opioids differentially inhibit mesolimbic neurons depending on their target projections. Identifying the properties of projecting mesolimbic VTA dopamine neurons is crucial to understanding the action of drugs of abuse.

Neural connections between prosencephalic structures involved in vasopressin release

1. The diagonal band (DB) and the lateral septal area (LSA) are two prosencephalic structures, which were implicated in vasopressin release. 2. The present experiment was designed to investigate neural connections between the DB and the LSA and from these nuclei to the paraventricular (PVN) and supraoptic (SON) nuclei, which could be related to vasopressin release. 3. For the above purpose the bidirectional neuronal tracer biotinylated dextran amine (BDA) was injected into the DB or the LSA of male Wistar rats. Five days later the animals were sacrificed and brain slices were processed and analyzed to determine neuronal projections efferent from as well as afferent to these structures. 4. Neuronal staining was more prominent in regions ipsilateral to the BDA injection site. 5. After BDA injections into the DB, efferent projections from the DB were observed at the LSA, the PVN, the prefrontal cortex, the mediodorsal thalamic nucleus, and throughout the anterior hypothalamus, but not at the SON. At the PVN, labeled varicose fibers were observed at the magnocellular portion. The DB was found to receive a massive input from the LSA. More discrete projections to the DB were originated at the prefrontal cortex and from hypothalamic neurons outside the PVN and the SON. 6. After BDA injections into the ventral portion of the LSA, efferent projections from the LSA were intense at the DB and throughout the hypothalamus. Labeled fibers were observed at the structures surrounding the SON or the PVN but not within those nuclei. 7. The results indicate a massive neural output from the LSA to the DB and the existence of a direct neural connection from the DB to the PVN. No direct connections were observed between the LSA and the magnocellular nuclei (PVN and SON) or between the DB and the SON.

Autonomic brainstem nuclei are linked to the hippocampus

Vagal nerve stimulation has been reported to enhance memory in both rats and humans, and to be an effective treatment for epilepsy in some patients, but the underlying neuroanatomical substrate(s) responsible for these effects remains unknown. Since there is no direct anatomical projection from the nucleus tractus solitarius, the main vagal relay site of the brain, to the hippocampus, we tested whether a multisynaptic pathway exists. Pseudorabies virus, a pig herpesvirus that can be used as a retrograde transneuronal tracer, was injected into the ventral CA1 hippocampus of rats, and after 4 days, pseudorabies virus infected neurons were identified in the general visceral portion of the nucleus tractus solitarius, with the majority being localized in the A2 noradrenergic cell group. Other autonomic brainstem nuclei, including the parabrachial nucleus, locus coeruleus, A1 and A5 noradrenergic cell groups, and C1 adrenergic cell group, were labeled. In order to identify some of the potential relay sites of the nucleus tractus solitarius-->hippocampal pathway, immunotoxin lesions of the ventral CA1 region were made that selectively destroyed either the noradrenergic or cholinergic fibers. After 2 weeks' recovery, pseudorabies virus was injected in this same CA1 area, and 4 days later, the transneuronal labeling in the nucleus tractus solitarius was reduced by approximately 65%. These findings suggest that the noradrenergic neurons of the locus coeruleus and cholinergic neurons of the medial septum/diagonal band are likely to be relay sites for this pathway. Other potential linkages are discussed. In summary, this is the first anatomical report to show that the general visceral region of nucleus tractus solitarius is linked via multisynaptic relays to the hippocampus.

Hodological characterization of the septum in anuran amphibians: I. Afferent connections

On the basis of Nissl-stained sections, we subdivided the septum of the gray treefrog Hyla versicolor in the lateral, central, and medial septal complex. The afferent projections of the different septal nuclei were studied by combined retrograde and anterograde tracing with biotin ethylendiamine (Neurobiotin). The central and medial septal complex receives direct input from regions of the olfactory bulb and from all other limbic structures of the telencephalon (e.g., amygdalar regions, nucleus accumbens), whereas projections to the lateral septal complex are absent or less extensive. The medial pallium projects to all septal nuclei. In the diencephalon, the anterior thalamic nucleus provides the main ascending input to all subnuclei of the anuran septum, which can be interpreted as a limbic/associative pathway. The ventromedial thalamic nucleus projects to the medial and lateral septal complex and may thereby transmit multisensory information to the limbic system. Anterior preoptic nucleus, suprachiasmatic nucleus, and hypothalamic nuclei innervate the central and lateral septal complex. Only the nuclei of the central septal complex receive input from the brainstem. Noteworthy is the relatively strong projection from the nucleus raphe to the central septal complex, but not to the other septal nuclei.

Noradrenergic innervation of the developing and mature septal area of the rat

The noradrenergic innervation of the developing and mature septal area of the rat was examined with light and electron microscopic immunocytochemistry using an antibody against dopamine-beta-hydroxylase. At birth, a small number of relatively thick noradrenergic fibers were found to innervate the lateral septum (mainly its intermediate part) and the nuclei of the vertical and horizontal limbs of the diagonal band of Broca. By postnatal day 7, a substantial increase in their density was observed. At this age some labeled fibers left the medial forebrain bundle and invaded the nucleus of the horizontal limb of the diagonal band. These fibers then ran in a ventrodorsal direction and innervated the nucleus of the vertical limb before entering the medial septum. Immunoreactive fibers were finer and more varicose than at birth. In the subsequent 2 weeks, the density of labeled fibers in the septal area was further increased. By postnatal day 21, the distribution pattern and density of the noradrenergic innervation appeared similar to the adult. In the adult, noradrenergic fibers exhibited more varicosities than in younger rats. Electron microscopic analysis revealed a low proportion (peaked at P7) of noradrenergic varicosities engaged in synaptic contacts throughout development. The overwhelming majority of these synapses were symmetrical, predominantly with small or medium-sized dendrites. The present findings provide the morphological basis for the functional interactions between noradrenergic afferents and neuronal elements in the septal area. The low proportion of synaptic contacts found in this study suggests that noradrenaline may exert its action in the septal area mainly through transmission by diffusion (volume transmission), as has been suggested for other areas of the developing and adult brain.

Cytoarchitecture and efferent projections of the nucleus incertus of the rat

The nucleus incertus is located caudal to the dorsal raphe and medial to the dorsal tegmentum. It is composed of a pars compacta and a pars dissipata and contains acetylcholinesterase, glutamic acid decarboxylase, and cholecystokinin-positive somata. In the present study, anterograde tracer injections in the nucleus incertus resulted in terminal-like labeling in the perirhinal cortex and the dorsal endopyriform nucleus, the hippocampus, the medial septum diagonal band complex, lateral and triangular septum medial amygdala, the intralaminar thalamic nuclei, and the lateral habenula. The hypothalamus contained dense plexuses of fibers in the medial forebrain bundle that spread in nearly all nuclei. Labeling in the suprachiasmatic nucleus filled specifically the ventral half. In the midbrain, labeled fibers were observed in the interpeduncular nuclei, ventral tegmental area, periaqueductal gray, superior colliculus, pericentral inferior colliculus, pretectal area, the raphe nuclei, and the nucleus reticularis pontis oralis. Retrograde tracer injections were made in areas reached by anterogradely labeled fibers including the medial prefrontal cortex, hippocampus, amygdala, habenula, nucleus reuniens, superior colliculus, periaqueductal gray, and interpeduncular nuclei. All these injections gave rise to retrograde labeling in the nucleus incertus but not in the dorsal tegmental nucleus. These data led us to conclude that there is a system of ascending projections arising from the nucleus incertus to the median raphe, mammillary complex, hypothalamus, lateral habenula, nucleus reuniens, amygdala, entorhinal cortex, medial septum, and hippocampus. Many of the targets of the nucleus incertus were involved in arousal mechanisms including the synchronization and desynchronization of the theta rhythm.

Extracortical descending projections to the rat inferior colliculus

Feedback controlling is an important element in the sensory processing in the auditory system. It has been long recognized that the inferior colliculus (IC) sends direct ascending projections to the medial geniculate body (MGB), but receives feedback regulation from the auditory cortex. In the present study we probed the shorter extracortical projections to the IC, including the direct descending pathway from the MGB. In the rat, the fluorescence retrograde tracers Fluorogold, True Blue or Rhodamine latex microspheres were injected into the IC, and the auditory thalamus and surrounding regions were examined for fluorescent neurones. We did not find any retrograde labelling in the ventral division of the MGB. However, retrogradely labelled neurones were found in the medial and suprageniculate nuclei of the MGB. We also observed densely packed groups of fluorescent neurones in the peripeduncular nucleus and numerous labelled neurones in the nucleus of the brachium of the IC. The existence of a direct descending pathway to the IC from at least some auditory thalamic nuclei challenges the perception of the colliculo-thalamic relationship as one-way traffic and suggests more direct involvement of the auditory thalamus in the feedback regulation of the incoming acoustic signals.

Catecholaminergic innervation of the septum in the frog: a combined immunohistochemical and tract-tracing study

In the present study, we have investigated the distribution and the origin of the catecholaminergic innervation of the septal region in the frog Rana perezi. Immunohistochemistry for dopamine and two enzymes required for the synthesis of catecholamines, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) revealed a complex pattern of catecholaminergic (CA) innervation in the anuran septum. Dopaminergic fibers were primarily present in the dorsal portion of the lateral septum, whereas noradrenergic (DBH immunoreactive) fibers predominated in the medial septum/diagonal band complex. Catecholaminergic cell bodies were never observed within the septum. To determine the origin of this innervation, applications of dextran amines, both under in vivo and in vitro conditions, into the septum were combined with immunohistochemistry for TH. Results from these experiments demonstrated that four catecholaminergic cell groups project to the septum: (1) the group related to the zona incerta in the ventral thalamus, (2) the posterior tubercle/mesencephalic group, (3) the locus coeruleus, and (4) the nucleus of the solitary tract. While the two first groups provide dopaminergic innervation to the septum, the locus coeruleus provides the major noradrenergic projection. Noradrenergic fibers most likely arise also in the nucleus of the solitary tract. The results obtained in Rana perezi are readily comparable to those in mammals suggesting that the role of catecholamines in the septum is well conserved through phylogeny and that the CA innervation of the amphibian septum may be involved in functional circuits similar to those in mammals.

Increases in amino-cupric-silver staining of the supraoptic nucleus after sleep deprivation

Sleep deprived rats undergo a predictable sequence of physiological changes, including changes in skin condition, increased energy expenditure, and altered thermoregulation. Amino-cupric-silver staining was used to identify sleep deprivation related changes in the brain. A significant increase in staining was observed in the supraoptic nucleus (SON) of the hypothalamus of rats with high sleep loss (>45 h) vs. their yoked controls. Follow-up experiments showed that staining was not significantly different in rats sleep deprived for less than 45 h, suggesting that injurious sleep deprivation-related processes occur above a threshold quantity of sleep loss. These anatomical changes suggest that the effects of sleep deprivation may be related to protein metabolism in certain brain regions.

Role of the locus ceruleus in baroreceptor regulation of supraoptic vasopressin neurons in the rat

The goal of this study was to identify the source of baroreceptor-related noradrenergic innervation of the diagonal band of Broca (DBB). Male Sprague-Dawley rats underwent sinoaortic denervation (SAD, n = 13) or sham SAD surgery (n = 13). We examined Fos expression produced by baroreceptor activation and dopamine-beta-hydroxylase immunofluorescence in hindbrain regions that contain noradrenergic neurons. Baroreceptors were stimulated by increasing blood pressure >40 mmHg with phenylephrine (10 microgram. kg(-1). min(-1) iv) in sham SAD and SAD rats. Controls were infused with 0.9% saline. Only the locus ceruleus (LC) demonstrated a baroreceptor-dependent increase in Fos immunoreactivity in dopamine-beta-hydroxylase-positive neurons. In a second experiment, normal rats received rhodamine-labeled microsphere injections in the DBB (n = 12) before phenylephrine or vehicle infusion. In these experiments, only the LC consistently contained Fos-positive cells after phenylephrine infusion that were retrogradely labeled from the DBB. Finally, we lesioned the LC with ibotenic acid and obtained extracellular recordings from identified vasopressin neurons in the supraoptic nucleus. LC lesions significantly reduced the number of vasopressin neurons that were inhibited by acute baroreceptor stimulation. Together, these results suggest that noradrenergic neurons in the LC participate in the baroreflex activation of the DBB and may thus be important in the baroreflex inhibition of vasopressin-releasing neurons in the supraoptic nucleus.