David K. Sundberg

Extracellular oxytocin in the paraventricular nucleus: hyperosmotic stimulation by in vivo microdialysis.

The effect of central osmotic stimulation on oxytocin (OT) secretion from the paraventricular nucleus (PVN) was examined using a newly developed in vivo microdialysis technique. A dialysis probe was inserted into the PVN region and microdialysis was performed in conscious animals. Hyperosmotic solutions were delivered via the dialysis probe, and perfusate and blood samples were collected. OT was consistently detected in the PVN dialysate. Hyperosmotic sodium chloride (1 M) produced a significant increase in dialysate and plasma OT, whereas D-mannitol (2 M) had no effect. These results suggest that (1) in vivo microdialysis may provide a useful technique for the evaluation of neuropeptide secretion from specific brain regions and (2) there are sodium-sensitive cells in the PVN region which respond to increases in extracellular sodium, resulting in an increase in central and peripheral oxytocin secretion.

Central and systemic oxytocin release : a study of the paraventricular nucleus by in vivo microdialysis

The mechanisms controlling central and systemic oxytocin (OT) release were examined using in vivo microdialysis of the paraventricular (PVN) region. Dialysate and plasma samples were collected from conscious male rats and stimuli were administered via the dialysate fluid. Characterization studies showed that microdialysis was a viable technique for the study of peptide secretion in the conscious animal. OT was consistently detected in the PVN dialysate and a partially purified extract crossreacted in parallel fashion with the synthetic peptide. In vitro studies showed that peptide recovery was positively correlated with the pore size of the dialysis membrane and that there was an inverse relationship between flow rate and recovery. Hypertonic saline administered centrally caused an increase in dialysate and plasma oxytocin while the intravenous injection affected only plasma oxytocin. The excitatory amino acid, glutamate (0.05-0.5 M), caused an increase in plasma, but not dialysate oxytocin, while depolarization with potassium chloride (0.05-0.15 M) had no significant effects. Histological examination showed that the dialysis probe was located in the rostral, lateral PVN. Our results show that in vivo microdialysis provides a method for the delivery of drugs into specific brain regions as well as a useful technique for the evaluation of in vivo neuropeptide release.

Excitotoxin paraventricular nucleus lesions: stress and endocrine reactivity and oxytocin mRNA levels

Electrolytic lesion of the paraventricular nucleus (PVN) of the hypothalamus blocks the tachycardia response to stress. The current study examined the effects of chemical lesion of PVN parvocellular neurons on the cardiovascular and endocrine responses to stress and on the content of hypothalamic oxytocin (OT) mRNA levels. Acute footshock stress increased heart rate in both ibotenic acid lesion and control groups of animals; however, the tachycardia was significantly lower in animals with a PVN lesion than the controls. Lesion of the PVN also attenuated the increase in plasma OT induced by stress, 4-fold in the lesion group versus 20-fold for the controls. There was not a generalized decrease in hormonal responsiveness since the OT response to an osmotic challenge was exaggerated in the lesion group. There was no difference between the groups in the arterial pressure and vasopressin responses to acute stress. Neurotoxin lesions of the PVN also resulted in significant depletions of VP and OT in all levels of the spinal cord and decreased OT levels in the dorsal brainstem. Ibotenic acid lesions of the PVN resulted in no significant changes in OT mRNA in the PVN, SON and PP. In addition, the 48-h dehydration resulted in a significant increase in plasma OT and OT mRNA in the PVN. These data indicate that the parvocellular neurons of the PVN play a role in integration of cardiovascular and endocrine responses to both stressful and osmotic stimuli and provide further evidence that parvocellular OT and VP neurons project to the brainstem and spinal cord.

Mammalian aging: Theoretical implications of changes in brain and endocrine systems during mid- and late-life in rats

Abstract Endocrine theories of aging have historically focused on altered peripheral or central regulatory mechanisms and, more recently, on the possibility that hormones may modulate the rate of brain aging itself. However, few systematic tests of such hypotheses have been conducted—partly due, perhaps, to a lack of clear criteria for putative endocrine mechanisms of aging. Simple criteria proposed here include: universality and similarity of fundamental patterns among mammals and detectable alterations early in mature life. Data are reviewed which indicate a possible role for elevated adrenocorticoid activity in aging of the mammalian brain. Additionally, recent data are summarized which show that, as early as mid-life in aging rats, widespread alterations occur in hypothalamic peptides and catecholamines and in peripheral endocrine systems. The pattern of these changes suggests that central and peripheral changes are linked. These findings are consistent with the view that early alterations in neural-endocrine processes may play a role in mammalian aging. Moreover, they provide possible insights into the specific nature of relevant alterations.

Central neural peptides and catecholamines in spontaneous and DOCA/salt hypertension

Hypothalamic and neurophypophyseal levels of catecholamines and peptides were measured in spontaneous and deoxycorticosterone (DOCA)/salt hypertension. Catecholamines, norepinephrine, epinephrine and dopamine were measured by electrochemical detection while the peptides, vasopressin, oxytocin, luteinizing hormone-releasing hormone (LHRH), the enkephalins and somatostatin (SRIF) were measured by radioimmunoassay. Blood pressure was significantly elevated in both groups as compared to their controls. Marked changes in central neural peptides were observed in the SHR, while no differences were seen in DOCA/salt hypertension. Hypothalamic vasopressin, oxytocin, LHRH and SRIF were significantly decreased. In the posterior pituitary, enkephalins were increased twofold in the SHR. With regard to catecholamines, there was no change in hypothalamic content. However, a dramatic decrease in neurohypophyseal dopamine was observed in SHR. Plasma levels of vasopressin were significantly elevated in both types of hypertension while oxytocin was increased only in the DOCA/salt model. These result show that (1) a wide spectrum of neuroendocrine changes are associated with genetic hypertension, (2) there are CNS differences between DOCA/salt and spontaneous hypertension, and (3) central aminergic changes may be involved in th neuroendocrine alterations seen in the SHR.

Distribution and development of proenkephalin-like immunoreactivity in the Lumbar spinal cord of the chicken

Met5-enkephalin- (Met-ENK), Leu5-enkephalin-, Met5-enkephalin-Arg6-Phe7-, metorphamide- and BAM 22P-like peptides could be detected in the lumbar spinal cord of the chicken by immunocytochemistry and/or high performance liquid chromatography. However, a peptide identical to Met5-enkephalin-Arg6-Gly7-Leu8 could not be detected in the lumbar spinal cord of the chicken using an antiserum that was capable of detecting the octapeptide in mammalian tissues. Nerve fiber- and terminal-like processes containing proenkephalin-derived peptides were concentrated in the superficial laminae of the dorsal horn and along the midline rostral to the central canal. A lesser concentration of processes containing proenkephalin-derived peptides occurred in the medial and lateral motor columns of the ventral horn. The level of total radioimmunoassayable Met-ENK in the lumbar spinal cord of the chicken embryo increased more than 1000-fold between day 4.5 and day 18. A schedule of curare administration that had previously been shown to prevent naturally occurring somatic motoneuron death in the chicken lumbar spinal cord resulted in a two-fold increase in total radioimmunoassayable Met-ENK in the lumbar spinal cord.

Plasma catecholamine levels in patients transported by helicopter for acute myocardial infarction and unstable angina pectoris

Fourteen patients with either acute myocardial infarction or unstable angina pectoris were transported by helicopter air ambulance to North Carolina Baptist Hospital during a 1-month period. Six patients had preflight and inflight plasma epinephrine and norepinephrine levels determined. All 14 patients were monitored for ventricular arrhythmias. The mean inflight plasma epinephrine level was significantly higher than the mean preflight level (3455 v 841 pg/mL, P less than .005). There was also a trend toward higher inflight norepinephrine levels; however, this increase was not statistically significant. No patient had a monitored ventricular arrhythmia. These findings suggest that helicopter transport of cardiac patients may be associated with significant patient stress, as reflected by high inflight catecholamine levels. Further study with a larger population of patients is needed to determine whether or not an increased incidence of inflight ventricular arrhythmias is associated with these catecholamine changes.

Sinoaortic denervation alters the molecular and endocrine responses to salt loading.

Neuroanatomical and physiological evidence indicates that baroreceptors influence hypothalamic vasopressin (VP) and oxytocin (OT) neurons. We evaluated the effects of sinoaortic denervation (SAD) on the molecular and endocrine response to salt loading. Sham-operated or SAD rats were given a 2% NaCl solution to drink for 72 h. A group with limited salt water intake was included as a second control because the denervated rats consumed less salt than the controls. Plasma VP, OT and osmolality and posterior pituitary peptide content were measured. Brains were processed for evaluation of VP and OT mRNA expression using in situ hybridization with computer quantitation. Salt loading produced equivalent increases in plasma VP and OT in the control and SAD groups, however, there was a greater depletion of posterior pituitary peptides in the denervated animals. Salt loading produced significant decreases in pituitary VP and OT in the SAD animals, 69.8 +/- 8.4% and 68.3 +/- 4.0%, respectively. In the control groups, there was no decrease in VP content and a decrease in OT only in the control ad lib group. The peptide mRNA response to salt loading was also altered in the denervated rats. There was a significant increase in the area and intensity of the labeling for OT mRNA in the PVN in the SAD salt group. The control salt rats showed an increase in the SON and the salt-limited group showed no changes. For VP mRNA, the only change noted was in the SON of the salt-loaded SAD animals. These results show that chronic denervation of arterial baroreceptors augments the hypothalamic VP and OT response to salt loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of Radioactivity in the Eyes of Rats after Injection of Iodinated Prolactin

The present study involves the intracardial injection of iodinated ovine prolactin into albino rats and the autoradiographic demonstration of patterns of isotopic incorporation into ocular tissues, including the retina, choroid coat and ciliary body. Control procedures include the utilization of competitive hormonal binding, a comparison of the radioactive pattern in eyes after the injection of iodinated beef serum albumen and an autoradiographic evaluation of the thyroid glands of all groups. The competitive uptake of iodinated prolactin into ocular tissues also was examined by liquid scintillation spectrometry. In normal rats, radioactivity was localized over the cells of the choroid coat and ciliary body of all groups receiving iodinated prolactin. The inner segments of the photoreceptors were radioactive in rats at 15 min after injection, but were unlabeled at only 5 min after injection.The present study involves the intracardial injection of iodinated ovine prolactin into albino rats and the autoradiographic demonstration of patterns of isotopic incorporation into ocular tissues, including the retina, choroid coat and ciliary body. Control procedures include the utilization of competitive hormonal binding, a comparison of the radioactive pattern in eyes after the injection of iodinated beef serum albumen and an autoradiographic evaluation of the thyroid glands of all groups. The competitive uptake of iodinated prolactin into ocular tissues also was examined by liquid scintillation spectrometry. In normal rats, radioactivity was localized over the cells of the choroid coat and ciliary body of all groups receiving iodinated prolactin. The inner segments of the photoreceptors were radioactive in rats at 15 min after injection, but were unlabeled at only 5 min after injection.

Catecholamine biosynthesis and vasopressin and oxytocin secretion in the spontaneously hypertensive rat: An in vitro study of localized brain regions

The in vitro synthesis of catecholamines and the secretion of vasopressin (AVP) and oxytocin (OT) was measured in localized regions of the hypothalamo-neurohypophyseal system in the spontaneously hypertensive rat (SHR). The posterior pituitary (PP), median eminence (ME) and supraoptic (SON) and paraventricular (PVN) nuclear regions were incubated in vitro in media containing 3H-tyrosine. Media and tissue levels of AVP and OT were measured as well as norepinephrine and dopamine content and biosynthesis. There were no differences in peptide release in either the PP, ME or SON. However, there was a marked increase in peptide release from the PVN of the SHR. Media AVP levels were 0.3 pg/ml/micrograms protein in the WKY as compared to 2.1 pg/ml/micrograms protein in the SHR. OT release was increased 2 fold, from 0.85 to 1.7 pg/ml/micrograms protein. PVN content of both AVP and OT was significantly lower in the SHR. ME and SON peptide levels were not changed, while neurohypophyseal AVP levels were increased in the SHR. With regard to the catecholamines appreciable norepinephrine synthesis was measured in the PVN and SON while there was little 3H-norepinephrine in the ME or PP. In the hypertensive rat, there was an increase in norepinephrine synthesis in the PVN with no change in the SON. These results provide further support for fundamental changes in the catecholaminergic and peptidergic systems of the hypothalamo-neurohypophyseal axis of the SHR.