Oxytocinergic inputs to the nucleus of the solitary tract and dorsal motor nucleus of the vagus in neonatal rats

BACKGROUND: Cetirizine is a H1 histamine antagonist which possesses anti-inflammatory properties through inhibition of leucocyte recruitment and activation, and reduction of ICAM-1 expression on mucosal epithelial cells. No studies have addressed the potential anti-inflammatory activities of cetirizine on skin keratinocytes. OBJECTIVES: Cetirizine and hydrocortisone were compared in their capacity to counteract human keratinocytes activation by IFNgamma. In particular, expression of immuno-modulatory membrane molecules and chemokine release have been examined. METHODS: Keratinocyte cultures established from normal skin of healthy donors were activated by IFNgamma (100-500 U/mL) in the absence or presence of cetirizine (10(-3)-10(3) microM) or hydrocortisone (10(-3)-10(2) microM), and tested for expression of ICAM-1, HLA-DR, MHC class I and CD40 as well as for release of RANTES, IL-8, macrophage chemotactic protein-1 (MCP-1) and granulocyte macrophage-colony stimulating factor (GM-CSF). RESULTS: Cetirizine at high concentrations (10(2)-10(3) microM) markedly inhibited IFNgamma-induced expression of membrane ICAM-1, HLA-DR and up-regulation of MHC class I, but had no effect on CD40 expression. In contrast, hydrocortisone (10(2) microM) enhanced IFNgamma-induced membrane ICAM-1, reduced expression of HLA-DR and did not alter expression of MHC class I and CD40. Consistently, high doses of cetirizine decreased, whereas hydrocortisone increased, soluble ICAM-1 levels in the supernatants of IFNgamma-treated keratinocytes. The inhibiting and stimulating effects of cetirizine and hydrocortisone, respectively, on ICAM-1 expression were confirmed at the mRNA level by Northern blot analysis. Finally, cetirizine, but not hydrocortisone, inhibited the release of MCP-1 and RANTES from IFNgamma-stimulated keratinocytes. In contrast, hydrocortisone, but not cetirizine, reduced GM-CSF and IL-8 release. CONCLUSIONS: The results indicate that cetirizine has the capacity to block the IFNgamma-induced activation of keratinocytes, and thus can exert important regulatory effects on TH1 cell-mediated immune responses in the skin. The high doses required for evidencing these activities suggest the potential benefits of a topical use of cetirizine.     

Impaired sexual response after lesions of the paraventricular nucleus of the hypothalamus in male rats

N-methyl-D-aspartic acid (NMDA) or radiofrequency (RF) lesions were made in the paraventricular nucleus of the hypothalamus (PVH) of male rats. The rats were tested for copulation, noncontact erection (NCE) evoked by remote cues from estrous females, and (after RF lesions) reflexive erection. NMDA, which destroyed parvocellular but spared magnocellular neurons, caused no deficits in copulation but caused longer NCE latencies and fewer NCEs. Rats with RF lesions had parvo- and magnocellular neuron damage; these males copulated to ejaculation, but they had lower intromission ratios and longer ejaculatory latencies. RF-lesioned rats also had longer NCE latencies, and a smaller proportion of males displayed reflexive erection. Results indicate that the PVH participates in mediating erectile function in copula and ex copula, and that the parvo- and magnocellular PVH neurons may have different roles in mediating erection.     

Intracerebroventricular CRF inhibits cold restraint-induced c-fos expression in the dorsal motor nucleus of the vagus and gastric erosions in rats

Acute exposure to cold-restraint induces vagal-dependent gastric erosions associated with activation of neurons in the dorsal motor nucleus of the vagus (DMN) in rats. The influence of intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF) (10 micrograms) on c-fos expression in the brain and gastric erosions induced by 3 h cold-restraint was investigated in conscious rats. In cold-restraint exposed rats, CRF injected i.c.v. inhibited gastric erosions and the number of Fos positive neurons in the DMN by 93 and 72%, respectively, while Fos labelling in the nucleus tractus solitarius (NTS) was increased by 5-fold compared with vehicle group. c-fos expression was also induced in the central amygdala by i.c.v. CRF, unlike the vehicle-injected group exposed to cold-restraint. c-fos expression induced by cold-restraint in the raphe pallidus (Rpa) and paraventricular nucleus of the hypothalamus was not altered by i.c.v. CRF. These data indicate that central CRF-induced gastric protection results from the inhibition of DMN neuronal activity enhanced by cold-restraint. CRF action on DMN neurons may be related to the increase in the NTS and central amygdala inputs leading to inhibition of DMN neurons rather than to the decrease in the excitatory input from the caudal raphe projections to the DMN.     

Vestibular nucleus projections to nucleus tractus solitarius and the dorsal motor nucleus of the vagus nerve: potential substrates for vestibulo-autonomic interactions

Autonomic effects of vestibular stimulation are important components of phenomena as diverse as acute vestibular dysfunction and motion sickness. However, the organization of neural circuits mediating these responses is poorly understood. This study presents evidence for direct vestibular nucleus projections to brain stem regions that mediate autonomic function. One group of albino rabbits received injections of Phaseolus vulgaris leucoagglutinin into the vestibular nuclei. The tracer was visualized immunocytochemically with standard techniques. Anterogradely labeled axons from the caudal medial vestibular nucleus (cMVN) and inferior vestibular nucleus (IVN) could be traced bilaterally to nucleus tractus solitarius (NTS). Fewer axons ended near the somata of neurons in the dorsal motor nucleus of the vagus nerve (DMX). A second group of rabbits received pressure or iontophoretic injections of cholera toxin B-HRP or Fluoro-Gold into a region including NTS and DMX. Retrogradely labeled neurons were observed bilaterally in the caudal half of cMVN and ipsilaterally in IVN. The labeled somata were small and they tended to occupy the center of cMVN in transverse sections. These previously unreported vestibular nucleus projections to NTS and DMX are a potential substrate for vestibular influences on autonomic function. In particular, they may contribute to both cardiovascular control during head movements (e.g., orthostatic reflexes) and autonomic manifestions of vestibular dysfunction, motion sickness and exposure to altered gravitational environments.     

Nitric oxide production is increased in the paraventricular nucleus of the hypothalamus of male rats during non-contact penile erections and copulation

Male rats put in the presence of a receptive female rat that they can see, hear and smell, but cannot touch, show penile erection episodes. These non-contact erections occur concomitantly with an increase in nitric oxide production in the paraventricular nucleus of the hypothalamus, as detected by the increase in the NO2- and NO3- concentration in the paraventricular dialysate obtained from these males by in vivo microdialysis. NO2- concentration increased from 0.81+/-0.12 to 2.51+/-0.43 microM and that of NO3- from 4.50+/-0.73 to 8.31+/-2.3 microM. The NO2- increase was prevented by the nitric oxide synthase inhibitor NG-nitro-L-arginine methylester (20 microg) given unilaterally in the paraventricular nucleus, which also prevented non-contact erections. In contrast, the nitric oxide scavenger haemoglobin (20 microg) prevented the NO2- increase, but not non-contact erections; while the guanylate cyclase inhibitor methylene blue (20 microg) was ineffective on either response. NO2-and NO3- concentration was also increased in the paraventricular dialysate of male rats during in copula penile erections, that is, when sexual activity was allowed with the receptive females. As found with non-contact erections, NG-nitro-L-arginine methylester prevented NO2- increase and impaired copulatory behaviour; haemoglobin prevented NO2- increase only; and methylene blue was ineffective on either response. The present results confirm that nitric oxide is a physiological mediator of penile erection at the level of the paraventricular nucleus of the hypothalamus.     

Oxytocin increases nitric oxide production in the paraventricular nucleus of the hypothalamus of male rats: correlation with penile erection and yawning

Dog collars made of PVC plastic impregnated with the pyrethroid insecticide deltamethrin at 40 mg/g were investigated for their protective efficacy against phlebotomine sandflies. Collared dogs were kept separately (two untreated control dogs lived together) in outdoor enclosures, each with a kennel, in the Cévennes, southern France. To measure sandfly mortality and anti-feeding effects due to the deltamethrin-impregnated collars worn continuously by the dogs for up to 8 months, each dog was periodically sedated and exposed for 2h to 150-200 laboratory-reared Phlebotomus perniciosus females (plus c. 25 males) inside a net (1.2 m square, 1.8 m high) indoors. After dogs were removed from the nets, allowed to recover and returned to their kennels, any dead sandflies were collected from inside the net and counted. Surviving flies were kept overnight, then scored according to whether they were still alive or dead, unfed or blood-fed. From tests 2, 3, 4, 13, 20, 26 and 34 weeks after the dogs began wearing collars, the overall numbers of blood-fed female sandflies recaptured were 75 from two dogs with collars, compared with 1911 from two collarless dogs. Thus, for every 100 flies which fed on collarless dogs, only 4 fed on collared dogs, i.e. the collars protected dogs from 96% of the bites and this activity was maintained for up to 34 weeks. During the same period, the percentage of recaptured female sandflies that had fed on collared dogs was 0-12% compared to 55-95% on collarless dogs. Immediately after dogs were taken out of the nets, 21-60% of flies confined with the collared dogs were found dead, compared to 0-12% with the controls. It is concluded that, at least in the Mediterranean subregion, this insecticidal collar would protect a dog from the majority of sandfly bites and retain a killing effect for a complete sandfly season. Moreover, it seems likely that the use of collars on all dogs in a focus of Leishmania infantum would reduce contact between sandfly vectors and canine reservoir hosts sufficiently to diminish the risk of infection for humans as well as dogs.     

Electrophysiological characterisation of tachykinin receptors in the rat nucleus of the solitary tract and dorsal motor nucleus of the vagus in vitro

1. Recent studies have shown antagonists at the NK1 subtype of receptor for tachykinins are antiemetics and suggested that this may result from blockade of tachykinin-mediated synaptic transmission at a central site in the emetic reflex. 2. We have used intracellular recording in vitro to study the pharmacology of tachykinins in the nucleus of the solitary tract (NST) and dorsal motor nucleus of the vagus (DMNV). 3. Neurones in the NST were depolarized by substance P (SP), the presumed endogenous ligand for the NK1 receptor and these effects were mimicked by the NK1 agonists, SP-O-methylester (SPOMe), GR73632 and septide; however, SP was nearly an order of magnitude less potent than the latter two agonists. 4. In the DMNV, SP and NK1 receptor agonists evoked similar depolarising responses but SP appeared to be more potent than in the NST and was closer in potency to the other agonists. 5. NK1-receptor antagonists blocked responses to septide and GR73632 in the NST but had little effect on responses to SP and SPOMe. In contrast, in the DMNV the NK1-receptor antagonists blocked responses to septide and GR73632 but also reduced responses to SP and SPOMe. 6. Neurokinin A (NKA) was almost equipotent with septide and GR73632 in depolarizing both NST and DMNV neurones but these effects were not mimicked by a specific NK2-receptor agonist. Responses to NKA were unaffected by an NK2-receptor antagonist; however, the depolarizing effects of NKA were blocked by NK1-receptor antagonists. 7. Neurones in both DMNV and NST were unaffected by the endogenous NK3-receptor ligand, neurokinin B and by a specific agonist for this site, senktide. 8. The results with NK1 receptor agonists and antagonists suggest that the septide-sensitive NK1 site is involved in the excitation of both NST and DMNV neurones. The 'classical' NK1 receptor may play more of a role in the DMNV and a third unknown site may be responsible for the depolarizing response to SP in the NST. The effects of NKA are best interpreted as an action at the septide-sensitive NK1 site. This raises the possibility that anti-emetic action of the NK1 antagonists may be due to blockade of NKA transmission at the septide-sensitive site.     

RU-486 blocks stress-induced enhancement of proenkephalin gene expression in the paraventricular nucleus of rat hypothalamus

The purpose of this study was to investigate the glucocorticoid (GC) mediated regulation of corticotropin-releasing hormone (CRH) and proenkephalin (PE) gene expressions in the paraventricular nucleus (PVN) of the hypothalamus during physical stress induced by a single intraperitoneal (i.p.) injection of hypertonic saline (9% NaCl). Previous intracerebroventricular (i.c.v.) administration of the type II glucocorticoid receptor (GR) antagonist RU-486 (20 ng/rat), increased the basal CRH mRNA levels in the PVN but had no effect on PE gene expression. Stress induced by injection of hypertonic saline increased both CRH and PE mRNA levels in PVN. Administration of RU-486 completely blocked the stress-induced increase of PE mRNA levels, but failed to alter the CRH mRNA levels in the PNV. These data suggests that, under these experimental conditions, endogenous GC are necessary for a normal PE response to hypertonic saline stress.     

Alterations in kappa opioid receptor mRNA levels in the paraventricular nucleus of the hypothalamus by stress and sex steroids

In this study, the levels of kappa opioid receptor (kOR) mRNA were determined using in situ hybridization following two types of stress (i.p. injection of hypertonic saline or novelty). In addition, we examined the possibility that estrogen or androgen would modify kOR mRNA. Gonadectomized male rats treated with estrogen or dihydrotestosterone were sacrificed 45 min after spending 15 min in a novel open field, or 60 min following hypertonic saline injection. Two-way ANOVA revealed that estrogen and novelty increased the levels of kOR mRNA in the ventral zone of the medial parvocellular part of the paraventricular nucleus (PVN), but not in the lateral parvocellular part of the PVN, claustrum, nucleus accumbens or the nucleus of the lateral olfactory tract. Furthermore, novelty increased kOR mRNA in gonadectomized (GDX) and GDX rats treated with dihydrotestosterone (DHTP), but not in sham-operated or estrogen-treated animals. Taken together, these data indicate that kOR mRNA levels are under estrogenic control and up-regulated in a stressor specific fashion.     

GABA receptors in the dorsal motor nucleus of the vagus influence feline lower esophageal sphincter and gastric function

Gamma-aminobutyric acid (GABA) antagonist (bicuculline methiodide, BIC; picrotoxin, PIC) or agonist (muscimol, MUS) microinjections were made into the dorsal motor nucleus of the vagus nerve (DMV), and effects on lower esophageal sphincter pressure (LESP), gastric motility, and gastric acid secretion were determined in chloralose-anesthetized cats. Right or left DMV sites were microinjected with BIC, PIC, MUS, or isotonic tonic saline (140 nl) through a glass micropipette having a tip diameter of 15-21 microns. Esophageal body, LESP, and gastric fundic pressures were measured manometrically. Circular smooth muscle contractions of the antrum and pylorus were recorded with strain-gauge force transducers. Gastric acid secretion was measured every 15 min through a gastric cannula and titrated to pH 7.0. DMV microinjection sites were verified histologically. Direct BIC microinjections (0.275 or 0.550 nmol) into the DMV primarily produced a decrease in LESP (71% of all sites tested), with mean LESP changing from 23.2 +/- 1.7 mmHg to 3.7 +/- 0.7 mmHg (p < 0.01). Tonic LESP increases and phasic LESP contractile activity occurred less frequently. BIC-induced LESP responses were abolished by vagotomy or by microinjections of MUS (0.5 to 10 nmol) into the DMV. Direct PIC microinjection (0.232 nmol) into the DMV produced a pattern of responses similar to those observed with BIC (which were also abolished by vagotomy or by MUS microinjections into the DMV). The antrum and pylorus were also responsive to DMV microinjections of both GABA antagonists. Microinjections of BIC or PIC into the DMV produced increases in gastric circular muscle activity that occurred less frequently than LESP effects, but also were eliminated by vagotomy. The high (0.550 nmol) dose of BIC increased gastric motility significantly more often than the low dose of BIC (p < 0.05). In addition, BIC (0.550 nmol) microinjections into the DMV increased gastric secretory volume (from 0.6 +/- 0.2 to 6.0 +/- 2.5 ml/15 min; p < 0.01) and total titratible acid (from 34.4 +/- 8.9 to 86.0 +/- 19.1 mEq/15 min; p < 0.01), and decreased gastric pH (from 4.63 +/- 0.44 to 3.50 +/- 0.49; p < 0.05). Vagotomy also eliminated the gastric secretory effects of DMV BIC. Direct microinjections of MUS into the DMV also blocked BIC- or PIC-induced changes in gastric motility and/or gastric acid secretion. Isotonic saline microinjected into the DMV did not increase basal or decrease stimulated gastric esophageal motility or gastric secretion. These data indicate that LESP, gastric motility, and gastric secretion are influenced by a tonic DMV inhibition mediated by GABAA receptor stimulation of the DMV. Because disinhibition of these receptors clearly activates the upper gut, future work should focus on identifying the nuclei providing this synaptic input to the DMV that might be involved in the functional regulation of upper gut motor and secretory function.     

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase activity in the paraventricular nucleus of the rat hypothalamus is modulated by estradiol

Leiomyomas represent 2% of gastric tumors. Commonly, gastric leiomyomas are clinically silent. Most often they become clinically apparent due to bleeding from ulceration of the overlying gastric mucosa. Surgical extirpation of the tumor is the standard treatment. Gastric leiomyomectomy was done routinely through open laparotomy until availability of laparoscopic equipment and techniques. Recently, there have been a few published reports regarding laparoscopic or laparoscopic-assisted removal of smooth muscle gastric tumors. There is little data, however, describing or discussing a laparoscopic approach to gastric leiomyomas located on the posterior gastric wall. We describe two different laparoscopic approaches to posterior wall gastric leiomyomas that we used in two patients. The postoperative recovery of both patients was remarkably quick and uneventful.     

Relationships between the morphology and function of gastric and intestinal distention-sensitive neurons in the dorsal motor nucleus of the vagus

The activity of vagal motor neurons is influenced by sensory information transmitted to the brainstem. In particular, there is evidence that distention of the stomach increases activity of motor neurons in the dorsal vagal motor nucleus, whereas distention of the duodenum, small intestine, and colon reduces neuron firing. In this study, we determined 1) the response of vagal motor neurons to distention of the stomach and duodenum and 2) whether the response properties were associated with specific morphological features. Using the single-cell recording and iontophoretic injection technique, we identified four groups of vagal motor neurons affected by gastric and/or duodenal distention. Group 1 neurons responded to either gastric or duodenal stimulation. Neurons in groups 2, 3, and 4 were affected by both gastric and duodenal distention. Group 2 neurons were excited by duodenal distention and were inhibited by gastric distention. Group 3 neurons were inhibited by duodenal distention and were excited by gastric distention. Most neurons belonged to group 4. Neurons in this group were inhibited by both gastric and duodenal distention. Our analyses revealed that the neurons affected by both stimuli had distinctive structural features. Neurons in group 2 had the largest somata, the most dendritic branches, and the greatest cell surface area. Neurons in group 3 were the smallest and had the shortest dendritic length. In addition, we were able to demonstrate that the neurons in group 4 had a smaller total dendritic length and a smaller cell volume than neurons in group 2 and had more dendritic branch segments than neurons in group 3. These results suggest that morphological features are associated with specific response properties of vagal motor neurons.     

Distributions of periventricular projections of the paraventricular nucleus to the median eminence and arcuate nucleus

Neuronal projections from the periventricular subnucleus of the hypothalamic paraventricular nucleus to the median eminence and the arcuate nucleus were investigated in the rat by the anterograde tract-tracer, Phaseolus vulgaris leucoagglutinin. The vast majority of labeled fibers coursed ventrally along the third ventricle and distributed in the external layer of the median eminence bilaterally, with ipsilateral predominance moving caudalwards. Periventricular fibers also terminated in the arcuate nucleus, but this innervation was exclusively ipsilateral.     

Serotonin stimulates corticotropin-releasing factor gene expression in the hypothalamic paraventricular nucleus of conscious rats

To examine the direct effects of serotonin (5-HT) on the release and synthesis of corticotropin-releasing factor (CRF) in the hypothalamic paraventricular nucleus (PVN), 5-HT was microinjected just onto the bilateral PVN of conscious rats. Plasma adrenocorticotropic hormone (ACTH) levels peaked at 30 min and returned to the basal levels in 90 min. Northern blot analysis revealed that the CRF messenger RNA (mRNA) level in the PVN as well as the proopiomelanocortin mRNA level in the anterior pituitary significantly increased 120 min after the 5-HT injections (50-250 nmol/side). Pretreatment with intracerebroventricular (i.c.v.) injection of pindobind 5-HT1A (5 nmol) or LY-278584 (500 nmol) completely abolished the 5-HT-induced ACTH response, whereas LY-53857 (100 nmol) was without effect. These results suggest that 5-HT stimulates CRF release, which has interactions with 5-HT1A and 5-HT3 receptors on CRF neurons in the PVN, and activates CRF synthesis in conscious rats.     

Effect of portal infusion of hypertonic saline on neurons in the dorsal motor nucleus of the vagus in the rat

Effects of hepatoportal osmo-receptive (or sodium-receptive) afferents on neurons within the dorsal motor nucleus of the vagus (DMV) were investigated electrophysiologically in urethane-chloralose anesthetized rats. Responses of 56 spontaneously active neurons to antidromic stimulation of the ventral trunk of the subdiaphragmatic vagus were recorded in the left DMV. Among them, 35 neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve (inhibitory neurons), except two neurons that were slightly excited. Effects of portal infusion of 3.6% NaCl were examined on 26 inhibitory neurons. Sixteen neurons increased their discharge rates and one neuron decreased its discharge rate in response to portal infusion of hypertonic saline. Thirty-five right DMV neurons responded to electrical stimulation of the dorsal trunk of the subdiaphragmatic vagus were inhibited by electrical stimulation of the hepatic branch of the vagus. Four neurons were excited by this stimulation. Relatively smaller number of neurons (5 out of 22 inhibitory neurons) increased their discharge rates in response to portal infusion of hypertonic saline. In conclusion, the response of DMV neuron observed in this experiment was characterized by increasing the frequency of spike discharges in response to portal infusion of hypertonic saline. However, these neurons were inhibited by electrical stimulation of the hepatic branch of the vagus nerve. These results suggest that the hepatoportal osmo-receptive afferents may be conveyed to the DMV via inhibitory synapses.     

Effects of hypothalamic paraventricular nucleus: electrical stimulation produce marked analgesia in rats

The effect of the electrical simulation induced analgesia (ESIA) on the hypothalamic paraventricular nucleus (PVN) was investigated by the paw pressure test, which was used to avoid any tissue damage to the paw of Wistar-SPF/VAF male rats. A stimulating electrode was chronically implanted in the parvocellular (PVN-prv) or magnocellular (PVN-mgn) divisions of the PVN. The ESIA was examined at least 10 days after surgery. The electrical stimulation of the PVN markedly showed analgesia (ESIA), but stimulation of most locations outside the PVN did not produce ESIA. Stimulation threshold for the ESIA was lower from PVN-prv than from PVN-mgn, but neither region was affected by naloxone administration (10 mg/kg, i.p.). These results indicate that the PVN is a part of the pain inhibitory system in the CNS, and show that PVN-ESIA might not be mediated either by opioids or by neuropeptides such as vasopressin.     

Muscimol suppression of the dorsal cochlear nucleus impairs frequency discrimination in rats

The cochlear nucleus is composed of three sub-nuclei: the dorsal (DCN), anteroventral (AVCN) and posteroventral cochlear nucleus (PVCN). In addition to connections between these sub-nuclei, each nucleus receives frequency specific tonotopically organised input from the cochlea. Evidence suggests that connections from the DCN to the AVCN are inhibitory and organised tonotopically but the functional significance of this pathway has yet to be elucidated. The possible role of this pathway in frequency discrimination using a T-maze behavioural paradigm and DCN suppression was examined. Five rats were trained on a two choice frequency discrimination task. Once frequency difference limens for 10-30% performance above chance were determined, rats had cannulae implanted bilaterally over the DCN. After recovery rats were tested on the behavioural task with nothing, saline and the GABA agonist muscimol injected into the DCN via the cannulae. Muscimol alone significantly reduced the rats ability to perform the task. This performance decrease was attributed to an inability to discriminate high frequency and not low frequency tones suggesting that place and not temporal coding of sound was compromised by DCN suppression. These results are consistent with the hypothesis that inhibitory drive from the DCN to AVCN may be crucial for the fine tuning of frequency information.     

Noradrenergic innervation of the hypothalamus of rhesus monkeys: distribution of dopamine-beta-hydroxylase immunoreactive fibers and quantitative analysis of varicosities in the paraventricular nucleus

The distribution of noradrenergic processes within the hypothalamus of rhesus monkeys (Macaca mulatta) was examined by immunohistochemistry with an antibody against dopamine-beta-hydroxylase. The results revealed that the pattern of dopamine-beta-hydroxylase immunoreactivity varied systematically throughout the rhesus monkey hypothalamus. Extremely high densities of dopamine-beta-hydroxylase-immunoreactive processes were observed in the paraventricular and supraoptic nuclei, while relatively lower levels were found in the arcuate and dorsomedial nuclei and in the medial preoptic, perifornical, and suprachiasmatic areas. Moderate levels of dopamine-beta-hydroxylase immunoreactivity were found throughout the lateral hypothalamic area and in the internal lamina of the median eminence. Very few immunoreactive processes were found in the ventromedial nucleus or in the mammillary complex. Other midline diencephalic structures were found to have high densities of dopamine-beta-hydroxylase immunoreactivity, including the paraventricular nucleus of the thalamus and a discrete subregion of nucleus reuniens, the magnocellular subfascicular nucleus. A moderate density of dopamine-beta-hydroxylase immunoreactive processes were found in the rhomboid nucleus and zona incerta whereas little dopamine-beta-hydroxylase immunoreactivity was found in the fields of Forel, nucleus reuniens, or subthalamic nucleus. The differential distribution of dopamine-beta-hydroxylase-immunoreactive processes may reflect a potential role of norepinephrine as a regulator of a variety of functions associated with the nuclei that are most heavily innervated, e.g., neuroendocrine release from the paraventricular and supraoptic nuclei, and gonadotropin release from the medial preoptic area and mediobasal hypothalamus. Additionally, quantitative analysis of dopamine-beta-hydroxylase-immunoreactive varicosities was performed on a laser scanning microscope in both magnocellular and parvicellular regions of the paraventricular nucleus of the hypothalamus. The methodology employed in this study allowed for the high resolution of immunoreactive profiles through the volume of tissue being analyzed, and was more accurate than conventional light microscopy in terms of varicosity quantification. Quantitatively, a significant difference in the density of dopamine-beta-hydroxylase-immunoreactive varicosities was found between magnocellular and parvicellular regions, suggesting that parvicellular neurons received a denser noradrenergic input. These differential patterns may reflect an important functional role for norepinephrine in the regulation of anterior pituitary secretion through the hypothalamic-pituitary-adrenal stress axis.