Icv Infusion Research Articles

Role of angiotensin-(1-7) in the modulation of the baroreflex in renovascular hypertensive rats.

In this study, we evaluated the effect produced by lateral ventricle (intracerebroventricular, I.C.V.) infusion of the selective angiotensin (Ang)-(1-7) antagonist, D-Ala7-Ang-(1-7) (A-779), in the modulation of the baroreflex control of heart rate in two-kidney, one clip renovascular hypertensive rats (2K1C) treated with the angiotensin-converting enzyme (ACE) inhibitor enalapril. Twenty days after the surgery to produce renovascular hypertension, I.C.V. cannulas were implanted in the rats with blood pressure (BP) greater than 145 mm Hg (n=33) and in sham-operated rats (n=32). Five days later, the rats were treated with enalapril (10 mg x kg(-1) x d(-1); 6 days, in the drinking water) or vehicle (tap water). On the sixth day of treatment, direct continuous BP recording and measurement of reflex changes in heart rate elicited by phenylephrine were made in conscious rats before and at 1 hour of I.C.V. infusion of saline (8 microL/h) or A-779 (4 microg/h). To evaluate the degree of ACE blockade produced by enalapril treatment, the pressor effect of Ang I (50 ng, I.V., and 100 ng, I.C.V.) and plasma ACE activity was determined. As expected, enalapril treatment in 2K1C produced a significant fall in BP, significant attenuation in the pressor response of Ang I (I.V.), and a reduction in plasma ACE activity. In addition, enalapril treatment increased the baroreflex sensitivity (0.76+/-0.04 versus 0.43+/-0.04 ms/mm Hg in 2K1C untreated rats). I.C.V. infusion of A-779 reverted the improvement in baroreflex sensitivity produced by enalapril treatment in 2K1C (from 0.80+/-0.07 to 0.42+/-0.08 ms/mm Hg) and also attenuated the baroreflex sensitivity in untreated 2K1C (0.36+/-0.05 versus 0.48+/-0.06 ms/mm Hg) and untreated sham-operated rats (1.21+/-0.05 versus 0.78+/-0.17 ms/mm Hg). These results suggest that central endogenous Ang-(1-7) is involved at least in part in the improvement of baroreflex sensitivity observed in 2K1C after peripheral chronic ACE inhibition.

Hyperplastic Changes within the Leptomeninges of the Rat and Monkey in Response to Chronic Intracerebroventricular Infusion of Nerve Growth Factor

Recombinant human nerve growth factor (rhNGF) was delivered for up to 6 months by continuous intracerebroventricular (icv) infusion to CD (Sprague– Dawley derived) rats and cynomolgus monkeys. Rats (n=15/sex/group) received doses of 0 (vehicle), 6, 60, or 300 ng/day; monkeys (n=5/sex/group) received 0, 0.6, 6, or 60 μg/day of rhNGF. Animals tolerated icv infusion with no behavioral signs attributable to rhNGF. Body weight was transiently decreased in female rats at the highest dose. At the completion of dosing, histological examination in both species revealed an increase in the thickness of the leptomeninges along the ventral and lateral surfaces of the hindbrain and extending over the dorsal aspect of the spinal cord. The change was present to varying degrees at all doses of rhNGF and tended to be more severe at higher doses. At the light microscopic level, the leptomeninges contained layers of well-differentiated, spindle-shaped cells and a plexus of axonal fibers. Cells were immunoreactive for S-100 protein and were associated with an accumulation of Type IV collagen, suggesting Schwann cell origin. Electron microscopy revealed numerous fine caliber axons ensheathed by the presumptive Schwann cells, with myelination of individual axonal segments. These findings suggest that chronic icv delivery of rhNGF has stimulated axonal sprouting and secondary hyperplasia of Schwann or Schwann-like support cells within the pia-arachnoid.

Intracerebroventricular neuropeptide Y acutely influences glucose metabolism and insulin sensitivity in the rat.

Acute administration of neuropeptide Y(NPY) into the hypothalamus and third cerebral ventricle (ICV) increases respiratory quotient, reduces energy expenditure and increases circulating, insulin, glucagon and corticosterone. Therefore, it is likely that hypothalamic NPY has acute effects on the metabolism of fuels, such as glucose. To test this hypothesis, we determined if ICV infusion of NPY influences glucose metabolism and its sensitivity to insulin in conscious, unrestrained rats, not given access to food. Glucose turnover was 4.7+/-0.3 mg/min, 45-55 min after ICV NPY was administered at 3 microg/h vs 3.7+/-0.2 (P<0.05) for ICV saline. In a time course study, glucose turnover was significantly increased 30 min, and remained elevated at 50 min after starting a similar ICV NPY infusion. In neither study was plasma glucose, insulin, glucagon or corticosterone significantly affected by ICV NPY. During an hyperinsulinaemic euglycaemic clamp, the glucose infusion rate corrected for body weight and insulin concentration, M/I was 0.22+/-0.03 for NPY vs 0.36+/-0.05 mg min(-1) kg(-1) microU(-1) ml (P<0.05) for saline. NPY treatment prevented the decline in glucose production rate but did not influence the rise in glucose disposal rate resulting from hyperinsulinaemia. It was concluded that ICV NPY rapidly stimulates glucose turnover by a mechanism that does not depend on changes in insulin, glucagon or corticosterone secretion. Furthermore, ICV NPY decreased insulin sensitivity by reducing the effect of insulin on glucose production but not on whole body glucose disposal.

Microdialysis studies of the distribution of stavudine into the central nervous system in the freely-moving rat.

To study the extent and time course of distribution of stavudine (d4T) into the central nervous system (CNS) and to investigate the transport mechanisms of antiviral nucleosides in the CNS. Microdialysis with on-line HPLC analysis was used to measure drug concentrations in the brain extracellular fluid (ECF) and cerebrospinal fluid (CSF) in the freely-moving rat. The in vivo recovery of d4T and zidovudine (AZT) was estimated by retrodialysis, which was validated by the zero-net flux method. The CNS distribution of d4T was investigated during iv and intracerebroventricular (icv) infusion. In the subsequent studies, the effect of AZT on CNS distribution of d4T was examined. During iv infusion, d4T distributed rapidly into the CNS. Its brain ECF/plasma and CSF/plasma steady-state concentration ratios were 0.33 +/- 0.06 and 0.49 +/- 0.12, respectively (n = 15). During icv infusion, the steady-state d4T concentrations in the brain ECF were 23-fold higher than those during iv infusion, whereas its steady-state plasma levels were about the same for these two routes. Coadministration of AZT with d4T did not alter their respective brain distribution and systemic clearance at the concentrations examined. More importantly, the steady-state brain ECF/plasma and CSF/plasma concentration ratios of d4T were about 2-fold higher than those of AZT (0.15 +/- 0.04 and 0.25 +/- 0.08) determined in the same animals. d4T readily crosses the blood-brain barrier (BBB) and blood-CSF barrier. An active efflux transport system in the BBB and blood-CSF barrier may be involved in transporting d4T out of the CNS. Direct icv administration of d4T can be used to enhance its brain delivery. Moreover, d4T exhibits a more favorable penetration into the CNS than AZT and therefore may be useful in the treatment of AIDS dementia complex.

Chronic ICV Enterostatin Preferentially Reduced Fat Intake and Lowered Body Weight

Lin, L., J. Chen and D. A. York. Chronic ICV enterostatin preferentially reduced fat intake and lowered body weight. Peptides 18(5) 657–661, 1997.—The pancreatic peptide enterostatin will acutely reduce fat intake in rats provided a choice of diets. Chronic ICV infusions of enterostatin suppress the intake of high fat diet. However, the effects of chronic ICV enterostatin on diet choice has not previously been studied. To investigate this, enterostatin (0.5 μg/h) or artificial cerebrospinal fluid (CSF) was infused for 9 days into the lateral ventricle of rats adapted to a two-choice high-fat (HF) and low-fat (LF) diet regime. Enterostatin reduced intake of HF diet with the maximum depression at day 4, but there was no compensatory increase in LF intake. The body weight of enterostatin-infused rats declined. This was associated with a reduction in fat pad and liver weights compared to the CSF-infused control rats. Serum triglycerides and insulin were decreased and corticosterone was elevated in enterostatin-infused rats. The data show that enterostatin will chronically reduce fat intake and body weight and suggest that enterostatin may attenuate the appetite for fat.

The dipsogen angiotensin II does not stimulate ethanol intake in mice

Mice that were habituated to drinking ethanol solution and mice that had drunk water only (naive mice) were given an ICV infusion of angiotensin II (Ang II) at 2.9 ng/h for 8 days to determine the effect of chronic ethanol intake on the ingestive response to this potent dipsogen. Ang II infusion in alcohol-naive mice increased daily water intake from 3.7 ± 0.2 ml ( mean ± SE, n = 6) to 11.0 ± 1.5 ml on day 4 ( p < 0.001) and to 18.3 ± 2.6 ml on day 8 ( p < 0.001). In subsequent experiments, mice had access to 4% ethanol solution up to day 4 and then to water for 4 days during the Ang II infusion. Alcohol-naive mice did not increase daily fluid intake until the water was provided on day 5; intake increased to 17.5 ± 2.3 ml on day 8 ( p < 0.001, n = 7). Mice accustomed to drinking 4% ethanol (4.3 ± 0.3 ml/day) also did not increase intake until the water was provided; intake reached 22.9 ± 3.0 ml of water on day 8 ( p < 0.001, n = 7). Mice accustomed to drinking 10% ethanol behaved similarly ( n = 4). Thus, alcohol-naive or -habituated mice did not respond to this dipsogenic stimulus until water was available; the thirst for water was unimpaired. Preference-aversion tests showed that mice drank little or no 4% ethanol (or even 2% ethanol) when water was also available. Taste aversion, plus previous experience from ingestion of ethanol in habituated mice, may explain the rejection of ethanol to quench Ang II-induced thirst. Experimental results obtained using other aversive solutions, 3 mM quinine and 300 m M KCI, suggest that postingestional, metabolic effects of solutes may also contribute to such rejection.

Distribution of Radioiodinated Recombinant Human Nerve Growth Factor in Primate Brain Following Intracerebroventricular Infusion

The distribution of radioiodinated recombinant human nerve growth factor ([125I]rhNGF) was evaluated in adult cynomolgus monkeys following unilateral intracerebroventricular (icv) administration. Animals were cannulated into the right ventricle and recovered for 7 days. Monkeys were infused with 1.2 μg of [125I]rhNGF or [125I]rhNGF with a 140-fold excess of rhNGF. Twenty-four hours after infusion, animals were anesthetized and transcardially perfused with an aldehyde fixative. Coronal brain sections were processed for quantitative film autoradiography or for cholineacetyltransferase immunohistochemistry and then emulsion dipped. Specific radiolabel was distributed bilaterally and, with equal density, throughout the basal forebrain and was colocalized with choline acetyltransferase-positive neurons. Specific labeling was also present in the superficial ventral cortex. Nonspecific binding was observed surrounding the ventricles and lining blood vessels. These results demonstrate that unilateral icv infusion is an effective approach for delivering NGF to basal forebrain cholinergic neurons in primates and represents a viable drug delivery strategy for the therapeutic use of NGF in Alzheimer's Disease.

Vitamin B12 amplifies circadian phase shifts induced by a light pulse in rats.

Vitamin B12 (VB12) is a putative modulator of the human circadian clock, improving entrainability to the 24 h light-dark cycle. The present study was intended to elucidate the mechanism of VB12 action in an animal model. In male rats free-running under constant dim illumination, a single light pulse of 50-1000 lux for 20 min given at circadian time (CT) 20 induced a 0.28 to 1.08 h phase advance and at CT 14 induced a 0.54 to 2.10 h phase delay. A 3 h intracerebroventricular (icv) infusion of 30 nmol VB12 starting 2 h prior to a 20 min 200 lux light pulse significantly amplified phase shifts in comparison with saline-treated or untreated controls. The mean phase advance (1.13 h) was 1.8-fold greater than that of saline-infused controls, whereas the mean phase delay (2.28 h) was 2.9-fold greater. These values were comparable to the maximal phase shifts caused by 1000 lux light pulses in untreated rats. Since the same VB12 treatment alone had failed to induce a phase shift in a previous experiment, these results indicate that VB12 strongly enhanced light pulse-induced phase shifts and thus augmented the entrainability of the circadian clock to light.

Mineralocorticoids, salt and high blood pressure

Essential hypertensive patients often respond to treatments mitigating mineralocorticoid action, even though circulating levels of these steroids are within normal ranges. In addition to the kidney, mineralocorticoid or Type I receptors are found in the brain and vascular smooth muscle where they mediate effects associated with several forms of experimental hypertension. Studies in which discrete anatomic or functional areas of the brain have been ablated demonstrate that the periventricular areas of the hypothalamus and the central sympathetic and baroreceptor systems are crucial for the development of hypertension in the renoprival, DOCA salt, and Dahl salt-sensitive rat. Intracerebroventricular (icv) infusion of aldosterone in both rats and dogs at doses that do not raise serum levels above normal produce hypertension. The hypertension produced by systemic mineralocorticoid excess, adrenal regeneration, and icv or oral administration of glycyrrhetinic acid or carbenoxolone in genetically normotensive rats and by dietary salt in the Dahl salt-sensitive rat is inhibited by the icv infusion of a mineralocorticoid receptor antagonist or a Na + channel-selective amiloride analog. Recent data demonstrate the extraadrenal synthesis of steroids in aortic endothelial cells, smooth muscle cells and the brain. The role of the extraadrenal synthesis of steroids raises new avenues for research into the causes of hypertension.

Interactions of histaminergic and serotonergic neurons in the hypothalamic regulation of prolactin and ACTH secretion.

Serotonergic and histaminergic neuronal systems are both involved in mediation of the stress-induced release of the pituitary hormones prolactin (PRL) and ACTH. We investigated the possibility of an interaction between serotonin (5-HT) and histamine (HA) in regulation of PRL and ACTH secretion in conscious male rats. Animals were pretreated systemically with antagonists to 5-HT1, 5-HT2 or 5-HT3 receptors prior to intracerebroventricular (icv) administration of HA. The 5-HT1 + 2 receptor antagonist methysergide prevented and the 5-HT2 receptor antagonist LY 53857 attenuated the HA-induced PRL release while the 5-HT3 receptor antagonist ondansetron had no effect on this response. None of the three 5-HT receptor antagonists affected the ACTH response to HA. Specific blockade of HA synthesis by alpha-fluoromethylhistidine or blockade of postsynaptic HA receptors by icv infusion of the H1 receptor antagonist mepyramine or the H2 receptor antagonist cimetidine inhibited the PRL response to 5-HT or to the 5-HT precursor 5-hydroxytryptophan (5- HTP) given in combination with the 5-HT reuptake inhibitor fluoxetine (Flx). Blockade of the histaminergic system had no effect on the ACTH response to serotonergic stimulation. The H3 receptors are inhibitory HA receptors. Systemic pretreatment with the H3 receptor agonist R(alpha)methylhistamine, or the H3 receptor antagonist thioperamide had no effect on the hormone response to activation of the serotonergic system by 5-HTP plus Flx. We conclude that the serotonergic and histaminergic neuronal systems interact in their stimulation of PRL secretion, but not in their stimulation of ACTH secretion. This interaction involves serotonergic 5-HT1 and 5-HT2 receptors and histaminergic H1 and H2 receptors. Furthermore, the previously observed inhibitory effect of the H3 receptor agonist R(alpha)methylhistamine on stress-induced PRL and ACTH release seems not to be exerted by activation of presynaptic H3 receptors located on serotonergic neurons but rather on histaminergic neurons.

Downregulation of mu-opioid binding sites following chronic administration of neuropeptide FF (NPFF) and morphine.

The effect of continuous ICV infusion of NPFF (10 micrograms/microliter) and morphine (40 micrograms/microliter) on mu-opioid binding sites was examined in rats using the in vitro radiolabeled techniques of whole-brain homogenate receptor binding and quantitative autoradiography. Mu receptors were labeled with [3H][D-Ala2-MePhe4,Glyol5] enkephalin in the homogenate binding experiments and with [125I][D-Ala2-MePhe4,Gly-ol5]enkephalin in autoradiographic studies. In homogenate binding studies, chronic administration of NPFF or morphine significantly downregulated mu receptors by 20% and 44%, respectively. Quantitative autoradiographic experiments demonstrated downregulation of mu opioid receptors in specific brain nuclei for both NPFF- and morphine-treated animals. Within the striatum and several nuclei of the thalamus, the mu receptors of the NPFF- and morphine-treated animals were decreased by 20-30% and 38-73%, respectively. These results suggest that NPFF may modulate opioid-mediated responses in part by altering the density of mu-opioid receptors.

Chronic administration of neuropeptide Y into the lateral ventricle inhibits both the pituitary-testicular axis and growth hormone and insulin-like growth factor I secretion in intact adult male rats.

Neuropeptide Y (NPY) is known to be involved in the central regulation of appetite, sexual behavior, and reproductive function. Whereas central administration of NPY strongly stimulates feeding in satiated animals, diet restriction or other unfavorable metabolic situations, such as diabetes, produce enhanced NPY gene expression and NPY release in the hypothalamus. Numerous studies have indicated that acute central administration of NPY results in various actions on LH secretion in the rat, either stimulatory or inhibitory. We recently demonstrated that chronic infusion of NPY into the lateral ventricle of adult intact female rats profoundly inhibited both the gonadotropic and somatotropic axes, with disruption of estrous cyclicity. Furthermore, we showed that central chronic infusion of NPY delayed sexual maturation in female rats. To analyze the effects of the same type of chronic NPY treatment on the pituitary-testicular axis, 45-day-old Sprague-Dawley male rats were implanted with stainless steel cannulas in the right lateral ventricle. Ten days later, Alzet osmotic minipumps were filled with different NPY solutions, adjusted to deliver 6, 18, or 36 micrograms/day, connected to the intracerebroventricular (icv) cannula, and sc implanted dorsally. The effects of these treatments were evaluated over 7 days. In one case, rats were castrated 5 days after initiation of NPY treatment, and the effect of castration was evaluated 2 days later. Chronic icv infusion of NPY produced the expected dose-related increases in food intake from 33.0 +/- 0.9 (basal) to 53.4 +/- 3.3 g/day (18 micrograms NPY/day) and body weight gain (5.7 +/- 0.7 to 10.5 +/- 1.2 d/day). As in female rats, this orexigenic action of NPY resulted in a significant dose-related decrease in pituitary weight, from 12.4 +/- 0.7 to 9.9 +/- 0.4 mg. The 7-day NPY infusion produced highly significant decreases in seminal vesicle weight (853 +/- 77 to 230 +/- 31 mg) and testis weight (3.82 +/- 0.09 to 3.18 +/- 0.15 g; P = 0.003). Plasma levels of testosterone (231 +/- 71 to 48 +/- 13 ng/dl), LH (20.7 +/- 3.7 to 9.1 +/- 1.2 ng/ml), and FSH (282 +/- 17 to 190 +/- 18 ng/ml) were markedly decreased at the 18 micrograms/day dosage, as also demonstrated for the 36 micrograms/day dosage. None of these effects was observed if vehicle was infused into the lateral ventricle instead of the NPY solution. When bilateral orchidectomy was performed 5 days after initiation of the NPY infusion (18 micrograms/day), the immediate LH and FSH rises usually seen after castration were seriously blunted.(ABSTRACT TRUNCATED AT 400 WORDS)

Zidovudine Transport in the Rabbit Brain during Intravenous and Intracerebroventricular Infusion

The distribution of zidovudine (AZT) between plasma, brain extracellular fluid (ECF), and cerebrospinal fluid (CSF) was investigated in a crossover design study (n= 5) in unanesthetized rabbits. Drug was administered by intravenous (iv) and intracerebroventricular (icv) infusions at the same infusion rate (1.5 mg/h.kg). The concentrations of AZT in ECF and CSF were measured by HPLC with microdialysis sampling. Plasma concentrations of AZT were quantitated by HPLC. Following iv infusion, the ECF- and CSF-to-plasma concentration ratios at steady state (SS), were 0.19 ± 0.05 and 0.29 ± 0.06, respectively. These values were less than unity, indicating the existence of active transport processes for the transport of AZT from brain to plasma across the blood–brain barrier (BBB) or blood–CSF barrier (BCB). The transport processes were modeled by compartmental model analysis, and the results suggest that the transport efficiency of AZT across the BBB is asymmetric; that is, the efflux clearance was five times greater than the influx clearance. Similarly, the efflux clearance from CSF is three times larger than the influx clearance into CSF. The SS concentrations of AZT in brain ECF in the same animals that received an icv infusion of AZT in the crossover design study were approximately two orders of magnitude greater than those in animals following iv infusion at the same dosing rate. Nevertheless, the SS plasma concentrations of AZT were similar for both routes of administration (1.2 ± 0.19 and 1.2 ± 0.13 μg/mL for iv and icv routes, respectively), confirming that the brain is not an organ that exhibits first-pass metabolism under the present experimental conditions.

Behavior of sheep drinking ethanol solution

Sheep that were habituated to drinking 10% (vol/vol) ethanol solution instead of water were subjected to proven thirst stimuli to study the effect of chronic ethanol intake on brain mechanisms subserving thirst. Sheep that had not previously drunk 10% ethanol were also tested. All sheep were trained to press a pedal that delivered 50 ml/press of fluid (either 10% ethanol or water) into a drinking cup. In some experiments, fluids were presented in bins. All animals had access to only one fluid at a time. Five ethanol-drinking sheep appeared healthy and maintained body weight over 18 mo. They always preferred water to 10% ethanol. The intracerebroventricular (icv) infusion of angiotensin II (ANG II) at 3.8 micrograms/h for 2 h increased ethanol intake from 15 +/- 10 to 200 +/- 55 ml in the 1st h, but 2,850 +/- 320 ml of water was drunk in the 2nd h. The icv infusion of 500 mM NaCl had a similar effect. After fluid deprivation for 22 or 46 h, ethanol intake in 1 h of access was only 280 +/- 40 and 400 +/- 90 ml, respectively, and 24-h intake was not increased. Water-drinking sheep drank 1,300 +/- 195 ml of water in 1 h after 22-h water deprivation, and 24-h intake was 1.5 times normal. The icv infusion of ANG II in these sheep increased water intake in 1 h from 10 +/- 10 to 1,630 +/- 250 ml and intake of 10% ethanol to only 310 +/- 60 ml. In conclusion, sheep accept 10% ethanol as a substitute for water for daily drinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ICV infusion of CRF on blood pressure and adrenal steroids in rabbits

The effect of prolonged, 22 h long, intracerebroventricular (i.c.v.) infusion of corticotropin-releasing hormone (CRF) on plasma cortisol, corticosterone and electrolyte concentrations, mean arterial blood pressure (MAP) and heart rate (HR) were investigated in conscious rabbits. During i.c.v. infusion of CRF, 1 and 3 μ/h, at a rate of 17 μl/h, plasma cortisol and corticosterone concentrations rose to the level noted after ACTH stimulation in rabbits. Plasma [Na] did not change, but plasma [K] was reduced and plasma osmolality increased during the infusion of CRF, 3 μ/h. MAP and HR, recorded continuously during i.c.v. infusion of CRF, changed only with the higher dose of CRF: MAP was elevated during the first 5 h of infusion, and then returned to the control level. HR was lower than control at the end of the first hour of infusion and again between 9 and 15 h of infusion. The prolonged rise of CRF concentration in the brain induced a sustained rise in circulating adrenal steroid hormones. MAP did not increase to the level noted after bolus i.c.v. injection of CRF and the rise in MAP was not sustained.

A 5-day estradiol therapy, in amounts reproducing concentrations of the early-mid follicular phase, prevents the activation of the hypothalamo-pituitary-adrenal axis by interleukin-1 alpha in the ovariectomized rhesus monkey.

In a previous report, we have shown that intracerebroventricular (icv) administration of the cytokine interleukin-1 alpha (IL-1 alpha) in the ovariectomized (OVX) rhesus monkey results in the acute activation of the hypothalamo-pituitary-adrenal (HPA) axis and the inhibition of LH and FSH secretion. Here, we compare the cortisol response to IL-1 alpha administration in OVX monkeys and in OVX animals replaced with estradiol (E) to reproduce E concentrations typical of the early-mid follicular phase. Cortisol, LH and FSH were measured after an icv infusion of physiological saline or IL-1 alpha (2.1 or 4.2 micrograms/30 min) in both groups. E-containing capsules were implanted sc 5 days prior to the experiment. In OVX, E concentrations were < 5 pg/ml. Cortisol concentrations decreased throughout the afternoon after saline infusion (to 49.7 +/- 5.1% of baseline at 5 h; n = 7), but increased significantly after IL-1 alpha to 158.3 +/- 13.8% (n = 7). In OVXE, cortisol also declined after saline (to 76.4 +/- 16.2%; n = 5). There were 2 types of response to IL-1 alpha: in grp 1 (mean E: 18.0 +/- 0.7 pg/ml), the cortisol response was similar to that in OVX (160.8 +/- 17.0%; n = 5), while in grp 2 (E: 30.7 +/- 3.1 pg/ml), the cortisol response was absent (66.6 +/- 7.2% of baseline at 5 h; NS vs saline in OVXE; n = 7). The cortisol response to IL-1 alpha was restored in 2 monkeys when E was increased to > 100 pg/ml, confirming our previous observations.(ABSTRACT TRUNCATED AT 250 WORDS)

IGF feedback effects on growth hormone secretion in ewes: evidence for action at the pituitary but not the hypothalamic level

The putative negative feedback effects of IGF-I and IGF-II on GH secretion were tested by intracerebroventricular (icv) and intrapituitary administration to sheep. Over two consecutive days, serial jugular blood samples were taken at 10 min intervals for 6 h from ewes (n = 3/group) fitted with indwelling stainless steel cannulae into the lateral or third cerebral ventricles. The sheep were injected (icv) with either vehicle or purified ovine IGF-I (2, 4 or 8 micrograms). IGF-I injection had no effect on plasma GH secretion. Serial blood samples were taken from a second group of nine ewes in which ovine or recombinant human (rh) IGF-I was infused (2.5 micrograms/h for 2 h) into the third ventricle; once again, IGF-I failed to affect the episodic pattern of GH secretion. Three ewes fitted with indwelling stainless steel cannulae placed in the anterior pituitary gland were consecutively infused with either ovine or rhIGF-I (2.5 micrograms/h for 2 h) or vehicle. Plasma GH concentrations were suppressed in 3/3 sheep from 1-1.5 h after the commencement of infusion and GH levels remained low for the remainder of the sampling period. In another group of five ewes synergistic effects of IGF-I and IGF-II on GH secretion were tested by icv infusion of rhIGF-I, rhIGF-II, or rhIGF-I+rhIGF-II (5 micrograms/h for 2 h) or vehicle (sterile 10 mM HCl/saline). Each sheep received each treatment in a randomised design. Infusion (icv) of IGF-I and IGF-II alone or in combination failed to alter GH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic Site‐Dependent Effects of Neuropeptide Y on Gonadotropin‐Releasing Hormone Secretion in Rhesus Macaques

In rodents and rabbits, neuropeptide Y (NPY) has a bimodal effect on gonadotropin-releasing hormone (GnRH) secretion. Intracerebroventricular (icv) administration or direct infusion of NPY into the median eminence (ime) suppresses GnRH release in ovariectomized (OVX) animals, but stimulates GnRH release in intact or OVX animals treated with ovarian steroids. Specific ovarian steroid-dependent NPY effects are, however, not obvious in non-human primates. In OVX rhesus monkeys, icv administration of NPY has been shown to suppress luteinizing hormone (LH) secretion whereas ime infusion of NPY stimulates GnRH pulses. In such animals, estrogen replacement does not reverse the inhibitory NPY effect on LH release, although estrogen enhances the stimulatory NPY effect on GnRH secretion. These observations led us to speculate that the bimodal NPY effects in non-human primates may depend on either the site of NPY action or the nature of the steroid milieu. This study utilized the push-pull perfusion (PPP) technique to examine the effects of either ime or icv infusion of NPY on GnRH release in OVX monkeys treated with or without both ovarian steroids. Without exception, ime infusion of NPY increased GnRH concentrations in push-pull perfusates regardless of the steroid status of the animals. In contrast, GnRH levels were reduced during icv infusion of NPY in both untreated and estrogen/progesterone-treated, OVX monkeys. These results indicate that, unlike other mammalian species, in the rhesus monkey the stimulatory and inhibitory effects of NPY on GnRH release depend on the site of NPY infusion within the brain rather than the ovarian steroidal environment.

Modulation of glutaminergic inputs by osmotic challenge to the supraoptic nucleus of rat hypothalamus in vitro

It is widely accepted that calcium ions are critically important in both short- and/or long-lasting responses of neurons to a stimulus. We have shown previously that NMDA receptors play a role in dipsogenic responses and c-fos expression induced by intracerebroventricular (icv) infusion of angiotensin II (Ang II). Since NMDA receptors are known to be linked to receptor-operated calcium channels, this study determined whether voltage dependent calcium channels are also involved in Ang II-induced behavioural (drinking) and endocrine responses as well as c-fos expression. The antidipsogenic actions of three L-type calcium channel antagonists, nifedipine, diltiazem and verapamil on Ang II-induced drinking behaviour were studied. These bind to the dihydropyridine, phenylalkylamine and benzothiazepine sites respectively. Rats (Lister-hooded) pre-treated icv with either 25 or 100 μg nifedipine, followed by 25 pmol Ang II, drank significantly less water than controls during the first 15 min after infusion. However, rats pre-treated with icv 100 μg diltiazem or verapamil showed no change in Ang II-induced drinking behaviour. The antidipsogenic actions of N- and P-type calcium channel antagonists ω-conotoxin GVIA and ω-conotoxin MVIIC were also evaluated. Rats pre-treated with 5 pmol or 20 pmol ω-conotoxin GVIA did show a slight but not significant suppression of water intake, particularly after the higher dose. Rats pre-treated with ω-conotoxin MVIIC drank almost the same amount of water as those pre-treated with saline. Nifedipine was found to suppress both Ang II-induced corticosterone release and c-fos expression in the following areas: organum vasculosum of the lamina terminalis (OVLT), median preoptic nucleus (MNPO), hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). The results described in this paper provide evidence that calcium channels play important roles in the Ang II-induced behavioural and endocrine responses, and in the expression of the immediate-early gene c-fos. This suggests that an L-type calcium channel may participate both short- and longer-term neuronal actions of Ang II.

Stimulatory effects of interleukin-induced activation of the hypothalamo-pituitary-adrenal axis on gonadotropin secretion in ovariectomized monkeys replaced with estradiol.

In a previous report, we have shown that acute activation of the hypothalamo-pituitary-adrenal (HPA) axis by the cytokine interleukin-1 alpha (IL-1 alpha) in the ovariectomized (OVX) rhesus monkey results in an inhibition of LH secretion. Here, we study whether estradiol (E) replacement therapy, at a level that reproduces E concentrations typical of the late follicular phase, modifies the gonadotropin and cortisol responses to IL-1 alpha administration. For E replacement, two Silastic capsules containing E were implanted sc 5 days before the experiment. The serum E concentration increased from less than 5 in OVX to 103.0 +/- 5.2 pg/ml in OVX and E-replaced monkeys. The experimental protocols were carried out 24 h or more after the LH surge that had been induced by E. In Exp 1, the effects of an intracerebroventricular (icv) infusion of physiological saline (group 1) or IL-1 alpha (2.1 or 4.2 micrograms/30 min; group 2) on LH, FSH, and cortisol were compared. IL-1 alpha administration resulted in a progressive release of LH (to 159.0 +/- 8.3% of baseline at 5 h; P < 0.05, 3-5 h vs. saline). Cortisol decreased in group 1 (84.5 +/- 1.3% by 5 h), but increased after IL-1 alpha (147.3 +/- 12.6%; P < 0.05 vs. saline). In Exp 2, we determined whether the stimulatory effects of IL-1 alpha on LH result from the central activation of CRH release (group 3). Infusion of the CRH antagonist, D-Phe12, Nle21,38, CaMe,Leu37-CRF-(12-41) (240 or 360 micrograms/2 h) prevented the increase in LH seen after IL-1 alpha treatment (67.3 +/- 12.5% at 5 h, NS vs. saline). The CRH antagonist also prevented the increase in cortisol and progesterone induced by IL-1 alpha. In Exp 3, we tested whether the stimulatory effect of IL-1 alpha on LH secretion can be simulated by ACTH infusion (group 4). ACTH-(1-24) (10-micrograms bolus plus 50 micrograms/5 h, iv) induced a progressive increase in LH secretion (to 221.5 +/- 27.8% of baseline by 5 h; P < 0.05, 3-5 h vs. saline). ACTH also stimulated cortisol secretion (to 203.3 +/- 30.7% by 5 h). In Exp 4, we investigated the role of adrenal progesterone in the LH response observed in groups 2 and 4. This increase in LH did not occur after pretreatment with RU486, a progesterone antagonist (5 mg Mifepristone; 77 +/- 24.2% by 5 h; P = NS vs. saline), although the increases in cortisol and progesterone were not prevented.(ABSTRACT TRUNCATED AT 400 WORDS)