Differential effects on naloxone on the release of neurohypophysial hormones in normotensive and spontaneously hypertensive rats

The hypothalamo-neurohypophysial system is altered in the spontaneously hypertensive rat (SHR). We hypothesized that an aberrant regulation of vasopressin (VP) and oxytocin (OT) release by endogenous opiod peptides alters this neuroendocrine system in the SHR. Concentrations of the neurohypophysial hormones in plasma and the pituitary were measured in 17-week-old SHRs and two strains of normotensive controls, Wistar Kyoto (WKY) and Sprague-Dawley rats. Animals were decapitated 20 min after s.c. injection of saline (1 ml/kg) or naloxone hydrochloride (1 or 10 mg/kg). In addition, neurohypophysial hormones excreted during the day (08.00–17.30 h) and night (17.30–08.00 h) were determined in urine from 16-week-old animals kept in metabolic cages for 5 days. VP at extrahypothalamic sites was also measured as [VP] in acid extracts of the subfornical organ area, hippocampal commissure-fornix and choriod plexus. Hormones were quantified by radioimmunoassay. The pituitary content, plasma concentration, and urinary excretion of OT were reduced (P < 0.05) in SHRs, whereas VP content was increased (P < 0.05) in the pituitary and plasma, but unchanged in urine, of hypertensive animals. In extrahypothalamic tissues, [VP] in the hippocampal commissure-fornix was increased in the SHR. Naloxone elevated (P < 0.05) the plasma concentration of OT in WKY animals and VP in SHRs. Neither [VP] nor [OT] in plasma was changed by naloxone in Sprague-Dawley rats. Pituitary stores of the neurohypophysial hormones were not altered by naloxone in either hypertensive or normotensive rats. In conclusion, endogenous opioid peptides tonically inhibit OT release in WKY rats, whereas VP releas is decreased by opioid peptides in SHRs, 16–17 weeks of age. The neuromodulatory role of opioid peptides in the release of neurohypophysial hormones appears to be altered in the SHR such that VP release is suppressed and OT release is augmented.     

Functional role of brain AT1 and AT2 receptors in the central angiotensin II pressor response

Intracerebroventricular (i.c.v.) angiotensin II (ANG II) increase vascular resistance and elicits a pressor response characterized by sympathetic nervous system activation (SNS component) and increased vasopressin (VP) secretion (VP component). This study examines the role of brain AT1 and AT2 ANG II receptors in mediating the pressor and renal hemodynamic effects of i.c.v. ANG II in conscious Sprague-Dawley rats. Mean arterial pressure, heart rate and renal vascular resistance responses to i.c.v. ANG II (100 ng in 5 μl) were determined 10 min after i.c.v. injection of either the AT1 receptor antagonist, DuP 753 (1.0, 2.5, 5.0, 10.0 μg), the AT2 receptor ligand, PD 123319 (3.5 × [10⁻⁶, 10⁻⁴, 10⁻², 10⁰ μg), or both. In control rats, i.c.v. DuP 753 prevented the pressor response and the increase in renal vascular resistance that occurred following i.c.v. ANG II in a dose-dependent manner (P < 0.05), while i.c.v. PD 123319 was without affect. When the VP- and SNS components were studied individually, by preventing the SNS component with intravenous (i.v.) chlorisondamine or the VP component with a V1 receptor antagonist (i.v.) similar results were obtained; DuP 753 prevented the SNS component and significantly reduced the VP component. These results indicate that both central ANG II pressor components are mediated primarily by brain AT1 receptors. However, doses of DuP 753 were more effective when combined with 3.5 μg of PD 123319 than when given alone (P < 0.05), suggesting that the pressor effects of i.c.v. ANG II may involve activation of multiple ANG II receptor subtypes.     

Intracerebroventricular neuropeptide Y increases gastric acid secretion by decreasing tonic adrenergic inhibition of acid in dogs

Neuropeptide Y (NPY) has been shown to increase basal gastric acid secretion in dogs. We examined the hypothesis that NPY might increase gastric acid secretion by interaction with central catecholaminergic control of acid secretion in dogs. Studies were performed in awake canines with gastric fistulas and cerebroventricular guides which allowed injection into the lateral cerebral ventricle. Intracerebroventricular (i.c.v.) injection of yohimbine (5 μg/kg) increased acid secretion compared to control (yohimbine: 9.1 ± 3.3mmol//h;control: 1.8 ± 1.0mmol/2h, P < 0.05), whereas prazosin and propranolol (both 5 μg/kg i.c.v.) had no effect, suggesting that there is tonic central α₂-adrenergic inhibition of acid secretion. NPY_13–36 significantly increased acid secretion compared to control (NPY_13–36 1000pmol/kg i.c.v.: 5.6 ± 1.9mmol/2h;control: 1.3 ± 0.8mmol/2h, P < 0.05), whereas [Leu³¹, Pro³⁴]-NPY had no effect, suggesting that the central effect of NPY is mediated at a Y₂, probably pre-synaptic receptor. Finally, i.c.v. desmethylimipramine (DMI) inhibited the acid response to i.c.v. NPY when injected before but not after NPY (i.c.v. DMI then i.c.v. NPY: control,15.2 ± 6.6mmol/2h;DMI, 3.5 ± 1.2mmol/2h, P< 0.05; i.c.v. NPY followed by i.c.v. DMI: control,8.9 ± 4.0mmol/2h;DMI, 9.9 ± 2.9mmol/2h, P > 0.05). This suggests that NPY acts by decreasing noradrenaline release. These findings are compatible with the hypothesis that i.c.v. NPY increases acid secretion by decreasing tonic central adrenergic inhibition of acid by decreasing release of noradrenaline at pre-synaptic level.     

Intracerebroventricular injection of choline increases plasma oxytocin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly (i.c.v.) injected choline on both basal and stimulated oxytocin release in conscious rats. I.c.v. injection of choline (50–150 μg) caused time- and dose-dependent increases in plasma oxytocin levels under normal conditions. The increase in plasma oxytocin levels in response to i.c.v. choline (150 μg) was greatly attenuated by the pretreatment of rats with atropine (10 μg; i.c.v.), muscarinic receptor antagonist. Mecamylamine (50 μg; i.c.v.), a nicotinic receptor antagonist, failed to suppress the effect of 150 μg choline on oxytocin levels. Pretreatment of rats with 20 μg of hemicholinium-3 (HC-3), a specific inhibitor of choline uptake into nerve terminals, greatly attenuated the increase in plasma oxytocin levels in response to i.c.v. choline injection. Osmotic stimuli induced by either oral administration of 1 ml hypertonic saline (3 M) following 24-h dehydration of rats (type 1) or an i.c.v. injection of hypertonic saline (1 M) (type 2) increased plasma oxytocin levels significantly, but hemorrhage did not alter basal oxytocin concentrations. The i.c.v. injection of choline (50, 150 μg) under these conditions caused an additional and significant increase in plasma oxytocin concentrations beyond that produced by choline in normal conditions. These data show that choline can increase plasma oxytocin concentrations through the stimulation of central cholinergic muscarinic receptors by presynaptic mechanisms and enhance the stimulated oxytocin release.     

Hypophysiotropic Role and Hypothalamic Gene Expression of Corticotropin-Releasing Factor and Vasopressin in Rats Injected with Interleukin-1β Systemically or into the Brain Ventricles

Intact adult male rats were injected intravenously (i.v., 400 ng/kg), intraperitoneally (i.p., 400 ng/kg) or intracerebroventricularly (i.c.v., 100 ng/kg) with interleukin-1β (IL-1β) or its vehicle. In comparison with vehicle-treated animals, IL-1β induced significant (P<0.01) increases in plasma ACTH levels measured 30 min later regardless of the route of cytokine administration. These changes were markedly blunted in rats administered specific antibodies directed against corticotropin-releasing factor (CRF). In contrast, vasopressin (VP) antibodies significantly blunted ACTH released by the i.c.v. injection of IL-1β, but only modestly altered the effect of the systemic injection of the cytokine. We then used semi-quantitative in situ hybridization analysis to measure changes in steady-state mRNA levels, as they might occur in response to these same doses of IL-1β. Following administration of the vehicle, measurement of gene expression in the paraventricular (PVN) portion of the hypothalamus indicated a measurable amount of hybridization signals for both CRF and VP. No detectable changes in either CRF or VP gene expression were observed in rats injected with IL-1β i.v. or i.p. 5 h earlier. In contrast, the i.c.v. administration of the cytokine significantly (P<0.01) increased both CRF and VP mRNA levels measured 5 h later. These results suggest that while endogenous CRF modulates the response of the corticotrophs to this cytokine regardless of the route of administration, the role of VP is more important in rats injected centrally than in those injected peripherally. The observation that at the dose tested and over the time-course studied, systemic injection of IL-1β failed to alter CRF or VP gene expression, supports our earlier hypothesis that blood-born IL-1β acts primarily at the level of nerve terminals in the median eminence.     

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1β (IL-1β) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1β (4 μg/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 μg/rat, i.c.v.) abrogated the effects of centrally administered IL-1β (30 ngn/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 μg/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1β (4 μg/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1β on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.     

Corticotropin-releasing factor and systemic capsaicin-sensitive afferents are involved in abdominal surgery-induced Fos expression in the paraventricular nucleus of the hypothalamus

We previously reported that abdominal surgery induces Fos expression in specific hypothalamic and medullary nuclei and also causes gastric stasis. The gastric ileus is reduced by systemic capsaicin and abolished by central injection of corticotropin-releasing factor (CRF) antagonist. We studied the influence of systemic capsaicin and intracerebroventricular (i.c.v.) injection of the CRF antagonist, α-helical CRF_9–41, on Fos expression in the brain 1 h after abdominal surgery in conscious rats using immunocytochemical detection. In control groups (vehicle s.c. or i.c.v.), abdominal surgery (laparotomy with cecal manipulation) performed under 7–8 min of enflurane anesthesia induced Fos staining in neurons of the spinal trigeminal, C1/A1 group, ventrolateral medulla, central amygdala, parabrachial nucleus, cuneate nucleus, nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and supraoptic nucleus (SON). Capsaicin (125 mg/kg s.c., 2 weeks before) or α-helical CRF_9–41 (50 μg i.c.v., before surgery) reduced the number of Fos-positive cells by 50% in the PVN while not modifying the number of Fos-labelled cells in the other nuclei. These results indicate that capsaicin-sensitive primary afferents and brain CRF receptors are part of the pathways and biochemical coding through which abdominal surgery activates PVN neurons 1 h post surgery.     

Cardiovascular effects of central administration of clonidine in conscious cats

The effects on arterial blood pressure and heart rate after an intracerebroventricular (i.c.v.) administration of clonidine were investigated using conscious normotensive cats. Injection of clonidine (5–10 μg; 5 μl; i.c.v.) elicited a decrease in mean arterial pressure (MAP) and heart rate (HR) in a dose-dependent manner. The highest dose of 10 μg of clonidine decreased MAP and HR by 39 ± 3 mmHg and 74 ± 5 b.p.m., respectively (n = 7). Pretreatment with yohimbine, the α₂-adrenoceptor antagonist (8 μg; 5 μl; i.c.v.) blocked the cardiovascular responses to a subsequent i.c.v. injection of 10 μg clonidine (n = 7). Furthermore, preadministration of cimetidine (100 μg; 5 μl; i.c.v.), the H₂ histamine receptor antagonist with imidazoline receptor activating properties, prevented the decreases in MAP and HR to a subsequent i.c.v. injection of 10 μg clonidine (n = 7). By contrast, pretreatment with the specific I₁ imidazoline receptor blocker, efaroxan (100–500 μg; 5 μl; i.c.v.), failed to inhibit the cardiovascular effects of an i.c.v. administration of 10 μg clonidine (n = 7). These results suggest that the effects of centrally administered clonidine on MAP and HR are probably not mediated through activation of the I₁ subtype of imidazoline receptors in conscious cats. However, the cardiovascular effects elicited by i.c.v. administration of clonidine appear to result from stimulation of central α₂-adrenergic or the H₂ histaminergic-like receptors.     

Long-lasting enhancement of synaptic excitability of CA1/subiculum neurons of the rat ventral hippocampus by vasopressin and vasopressin(4–8)

Vasopressin (VP) is axonally distributed in many brain structures, including the ventral hippocampus. Picogram quantities of VP injected into the hippocampus improve the passive avoidance response of rats, presumably by enhancing memory processes. Vasopressin is metabolized by the brain tissue into shorter peptides, such as [pGlu⁴r,Cyt⁶]VP(4–9[ and [pGIu⁴,Cyt⁶,]VP(4–8), which preserve the behavioral activity but lose the peripheral activities of the parent hormone. Using brain slices, we investigated whether VP or VP(4–8) affects excitatory postsynaptic potentials (EPSPs) and/or membrane responses to depolarization in neurons of the CA 1 /subiculum of the ventral hippocampus. The EPSPs were evoked by stimulating the stratum radiatum of the CAI field; the membrane responses were elicited by current injections. Exposure of slices for 15 min to 0.1 nM solution of these peptides resulted in an increase in the amplitude and slope of the EPSPs in 21 neurons (67%) tested. No consistent change in either the resting membrane potential or the input resistance of the neurons was observed. The peptide-induced increase in EPSPs reached a maximum 30–45 min after peptide application. In 14 of these neurons (66%), the peptide-induced increase in EPSPs remained throughout the entire 60–120 min washout period. In the remaining 7 neurons (33%), the initial increase in EPSPs amplitude was followed by a gradual decline to the pre-administration level. The increase in EPSP amplitude was often. but not always, associated with a decrease in the threshold and increase in the number of action potentials in response to depolarizing current injection. Suppression of GABA_A receptor-mediated inhibition and N-methyl-d-aspartate (NMDA) receptor-mediated excitation did not prevent the effects of VP and VP(4–8[ on the EPSP amplitude or the threshold for action potentials. The results demonstrate that 0.1 nM concentrations of these neuropeptides can elicit a long-lasting enhancement of the excitability of CA1/subiculum neurons of the ventral hippocampus to excitatory, glutamatergic synaptic input. This novel action of VP and its metabolite in the ventral hippocampus may be the physiological action, mediating the memory-enhancing effect of these peptides.     

Involvement of ACTH and MSH in active and passive avoidance behavior

Intracerebroventricular injection of antiserum to α-MSH induces a weak reduction of passive avoidance latencies after administration prior to retention testing. Administration of antiserum to ACTH 1–24 induces a more marked effect in this respect, whereas injection of a combination of these antisera results in the strongest reduction of passive avoidance retention. No effect of this treatment is observed when these antisera are injected immediately after the learning trial. In active avoidance behavior a facilitation of extinction of the response is observed after intra-cerebroventricular administration of the antisera prior to each extinction session. This effect is comparable with the one observed in passive avoidance behavior. From these data it is suggested that ACTH and α-MSH play an important role in processes related to the retrieval of information stored in the brain.     

Selective FSH-releasing activity of [D-Trp]GAP1–13: Comparison with gonadotropin-releasing abilities of analogs of GAP and natural LHRHs

We had previously shown that fragments of human gonadotropin-releasing hormone associated peptide (GAP) stimulated FSH and LH release in vivo. In particular, GAP₁₋₁₃ had a preferential FSH-releasing activity. To decrease enzymatic degradation, analogs of GAP_1–13 with D-amino acid substitutions were synthesized. The activities were tested in ovariectomized, estrogen-progesterone primed (OEP) rats and compared with those of GAP₁₋₁₃, mammalian (m), chicken II (eII), and lamprey (1) LHRH. The peptides were injected (IV) into conscious, OEP rats and blood samples were obtained via the jugular catheter. [D-Trp⁹]GAP_1–13 selectively stimulated FSH release at a dose of 1 μg. Multiple injections of this analog (10 μg every 30 min for 5 injections) induced a marked elevation of plasma FSH values which peaked (p < 0.001) after the third injection. By contrast, [D-Trp⁹]GAP_1–13 had no effect on LH and prolactin (PRL) release after either single or multiple injections. These doses of [DAla⁴] GAP_1–13 had no effect on the release of FSH, LH or PRL. Both human GAP_1–13 and its [D-Trp⁹] analog exerted a selective FSH-releasing effect at a dose of 10 μg, however, the [D-Trp⁹] analog was more potent than GAP_1–13 on FSH release. The potency of [D-Trp⁹]GAP_1–13 in releasing FSH was approximately that of mLHRH. Chicken II LHRH had slightly selective FSH-releasing activity with a potency that of mLHRH. Lamprey LHRH had a preferential LH-releasing activity and a potency 1000 times less than mLHRH. In conclusion, [D-Trp⁹]GAP_1–13 is a selective FSH-releasing peptide of potential clinical value.     

Cardiovascular effects elicited by central administration of physostigmine via M2 muscarinic receptors in conscious cats

The cardiovascular effects of an intracerebroventricular (i.c.v.) injection of physostigmine were studied using conscious cats. Physostigmine (5–25 μg: 5 μl) caused a dose-dependent increase in mean arterial pressure (MAP) and heart rate (HR). The highest dose (25 μg) increased MAP and HR by 32 ± 3 mmHg and 45 ± 5 beats/min, respectively (n = 5). Pre-administration of the muscarinic receptor antagonist, atropine (25 μg; i.c.v.) blocked the effects of physostigmine (25 μg; i.c.v.). Also, the pre-administration of the M₂ muscarinic antagonist, methoctramine (25 μg; i.c.v.), antagonized the cardiovascular effects of physostigmine without altering the baseline variables. However, the M₁ muscarinic antagonist, pirenzepine (100 μg; i.c.v.) did not alter baseline MAP or HR, and also failed to inhibit the cardiovascular responses to physostigmine. Similarly, the M₃ muscarinic blocker, 4-diphenyl-acetoxy-N-methylpiperidine methiodide (50 μg; i.c.v.), neither changed baseline cardiovascular variables nor blocked the effects of physostigmine. When the same cats were anesthetized with intravenous injection of sodium pentobarbital (25–30 mg/kg), physostigmine (25 μg; i.c.v.) evoked a decrease in MAP and HR of 13 ± 6 mmHg and 15 ± 6 bpm, respectively (n = 5). These results demonstrate that the increases in MAP and HR to the i.c.v. administration of physostigmine in conscious cats arepossibly mediated through stimulation of central M₂ muscarinic receptors. In addition, anesthesia reverses the effects elicited by the central administration of physostigmine to a decrease in MAP and HR.     

Stimulation of the rat mesolimbic dopaminergic system produces a pressor response which is mediated by dopamine D-1 and D-2 receptor activation and the release of vasopressin

Treatment with dopamine receptor agonists has been shown to induce centrally mediated effects on cardiovascular regulation. We have investigated the effect on blood pressure and heart rate of stimulating the release of endogenous dopamine in the brain from the mesolimbic/mesocortical (A10) dopaminergic system of conscious Sprague-Dawley rats. Stimulation of the region of origin of the A10 dopaminergic system, the ventral tegmental area (VTA), with local micro-injection of the substance P analogue DiMe-C7, produced a dose-dependent increase in blood pressure and heart rate. The injection of 10 nmol of DiMe-C7 produced a maximum increase in blood pressure of 15–20 mmHg at 10 min following administration and a maximum tachycardia of 70–80 B/min. Intravenous pretreatment with the dopamine D-1 receptor antagonist SCH 23390 (0.1 mg/kg) or the dopamine D-2 receptor antagonist raclopride (0.5 mg/kg) markedly inhibited the pressor response and revealed a bradycardia. Furthermore, the pressor response and tachycardia were completely blocked by pretreatment with the vasopressin V-1 receptor antagonist, Pmp¹,O-Me-Tyr²-[Arg⁸]vasopressin (10 μg/kg). Pretreatment with the ganglion blocker, pentolinium (10 mg/kg), had little effect on the blood pressure response, however it attenuated the tachycardia. Micro-injection of 10 nmol of DiMe-C7 into a region 2 mm dorsal to the VTA had little effect on blood pressure yet produced a marked bradycardia. The administration of DiMe-C7 into the region of origin of the nigrostriatal A9 dopaminergic system, the substantia nigra, produced a slight but significant increase in blood pressure with little effect on heart rate. Intracerebroventricular administration of DiMe-C7 also produced a pressor response with a more pronounced tachycardia. The blood pressure responses produced by intranigral or i.c.v. injection of DiMe-C7 were not inhibited by pretreating the rats with raclopride. These results suggest an involvement of the mesolimbic A10 dopaminergic system in the regulation of blood pressure and heart rate through the activation of dopamine D-1 and D-2 receptors and vasopressin release.     

Clonidine antagonism of angiotensin-related drinking: a central site of action

Administration of either isoproterenol (25 μg/kg, s.c.) or angiotensin II (200 μg/kg, s.c.) induces drinking in rats within 0.5–1 h. This drinking was inhibited by prior administration of the presynaptic α-adrenergic agonist clonidine (12 μg/kg, i.p.). Urine output was enhanced by clonidine in the angiotensin II-, but not the isoproterenol-treated group. Drinking in response to peripheral administration of either angiotensin II or isoproterenol was also inhibited by intracerebroventricular (i.v.t.) administration of clonidine (8 μ/kg). This dose of clonidine also enhanced the urine output after angiotensin II. Further, the drinking induced by i.v.t. administration of angiotensin II, at 4 but not 20 ng/kg was inhibited by peripheral administration of clonidine (12 μg/kg, i.p.). When clonidine was administered i.v.t. prior to i.v.t. injection of either angiotensin II (20 ng/kg) or carbachol (1.2 μg/kg), the drinking response to these dipsogens was attenuated. These results suggest that clonidine may act centrally to attenuate drinking at a site, possibly in the nucleus tractus solitarius, that may be considered a final common pathway for this response.     

Cardiovascular effects of neurotensin microinjections into the nucleus of the solitary tract

Neurotensin (NT) immunoreactivity and binding sites have been demonstrated to be extensively distributed throughout the caudal nucleus of the solitary tract (NTS). In this study, the cardiovascular effects of microinjecting the tridecapeptide neurotensin (NT) or its analogues NT 1–8 and [ -Trp¹¹]NT into NTS were investigated in the chloralose-anesthetized, paralyzed and artificially ventilated rat. Microinjection of NT (10 pmol) elicited decreases in arterial pressure (AP) (−34 ± 3 mm Hg) and heart rate (HR) (−28 ± 2 beats/min), whereas microinjection of equimolar amounts of the NT fragment NT 1–8 elicited a significantly smaller depressor response (−14 ± 3 mm Hg), but the bradycardic (−22 ± 4 beats/min) response was similar in magnitude to that elicited by NT. On the other hand, microinjection of [ -Trp¹¹]NT did not elicit cardiovascular responses from sites in NTS. In addition, the prior injection of [ -Trp¹¹]NT into cardiovascular responsive sites in the NTS did not significantly reduce the AP or HR response to NT. The depressor response elicited by NT was not affected by bilateral vagotomy but was abolished by either C1–C2 spinal cord transection or the i.v. administration of the nicotinic receptor blocker hexamethonium bromide. The cardiac slowing was partially attenuated by either bilateral vagotomy (−19 ± 2 beats/min, i.v. administration of atropine methyl bromide (−17 ± 4 beats/min), i.v. administration of hexamethonium bromide (−11 ± 4 beats/min) or by spinal cord transection (−12 ± 3 beats/min), and completely abolished after total autonomic blockade or by combined bilateral vagotomy and spinal cord transection. These data have demonstrated that within a restricted region of the caudal NTS NT activates neurons that contribute to vasodepressor responses as a result of sympatho-inhibition and to bradycardia responses as a result of vagal excitation and sympatho-inhibition. Furthermore, these data suggest that NT may act as a neurotransmitter or modulator in central cardiovascular reflex pathways.     

Conditioned place preference and locomotor activation produced by injection of psychostimulants into ventral pallidum

The ventral pallidum (VP) is often viewed as an output structure of the nucleus accumbens septi (NAS). However, VP, like NAS, receives a dopaminergic input from the ventral tegmental area. These experiments investigated some behavioral effects of microinjection into VP of drugs which enhance dopaminergic transmission. Injection of 25 μg dopamine or 5–10 μg amphetamine into VP produced hypermotility. In contrast, injection of 12.5–50 μg cocaine initially suppressed, then increased, activity. Injection of 100 μg cocaine only produced hypomotility in the 1-h period examined. The hypomotility following cocaine seemed to be a local anesthetic effect, because it was mimicked by 50–200 μg procaine. Procaine did not, however, produce subsequent hypermotility. Conditioned place preference (CPP) was produced by 10 μg amphetamine and 50 μg cocaine but not 100 μg procaine. We conclude that injection of cocaine into VP, unlike similar injections into NAS, produces CPP. These results support the idea of an involvement of dopamine in VP in reward and locomotor activation, independent of dopamine in NAS. The use of intracerebral injections of cocaine is complicated, however, by an apparent local anesthetic effect of the drug.     

Distribution of gastrin releasing peptide-bombesin-like immunostaining in rat brain

Several antisera were raised in rabbits against synthetic gastrin releasing peptide (1–27)(porcine)(GRP(1–27)) and GRP(1–16). In immunohistochemical staining experiments on frozen brain sections from rats, the antisera raised against GRP (1–27) also labeled substance P neurons. This substance P-like immunostaining was selectively blocked by incubation of the sections with GRP(1–27) antiserum in the presence of an excess concentration (50 μM) of synthetic substance P. A residual immunostaining was observed in sections stained with substance P absorbed GRP(1–27) antisera. This staining was blocked by addition of an excess concentration (10 μM) of synthetic GRP(1–27) or bombesin, but it was not blocked by a 10 μM concentration of GRP(1–16) or by a 100 μM concentration of vasoactive intestinal peptide, oxytocin, vasopressin, or by a further addition of 50 μM substance P. The antisera raised against GRP(1–16) did not label substance P neurons. The immunostaining produced by GRP(1–16) antisera was blocked by an excess (10 μM) concentration of GRP(1–16) or GRP(1–27). In the brainstem of normal rats both the substance P absorbed GRP(1–27) antisera and GRP(1–16) antisera labeled fibers in the ventral aspect of the medulla-pons region. In colchicine treated rats occasional cell bodies were seen in this ventral region. A group of cell bodies on the lateral border of the solitary nucleus was also visualized. Staining of 2.5 μm thick serial sections with substance P absorbed GRP(1–27) antisera and with GRP(1–16) antisera demonstrated that both antisera were labeling the same cells.In the forebrain of normal rats, the substance P absorbed GRP(1–27) antisera stained primarily axonal fibers and terminals in the suprachiasmatic nucleus. In colchicine treated rats the substance P absorbed GRP(1–27) antisera labeled cell bodies in the suprachiasmatic nucleus and in the parvocellular part of the paraventricular nucleus of hypothalamus. Unlike substance P absorbed GRP(1–27) antisera, antisera raised against GRP(1–16) produced only a faint immunostaining in these hypothalamic regions. These findings suggest that perhaps a differential processing of GRP-like peptides occurs in different brain regions or alternatively several forms of a GRP/bombesin-like peptide may exist.     

Role of IL-1α in central nervous system immunomodulation of glucoregulation

Hyperglycemia is a hallmark of the stress response, and has been largely attributed to elevated plasma levels of catabolic hormones. Recently, various cytokines have been shown to be endogenously produced within the brain and may represent an important component of the central regulation of this metabolic response. Therefore, the aim of the present study was to determine whether the intracerebroventricular (i.c.v.) injection of one such peptide, interleukin (IL)-1, can produce hormonal and metabolic alterations comparable to those observed under stress conditions. An i.c.v. cannula and vascular catheters were placed in rats prior to the experiment. Whole body glucose flux was assessed in overnight fasted conscious unrestrained rats using [3-³H]glucose. A mild hyperglycemia was elicited 20 min after the i.c.v. injection of IL-1α (human recombinant, 100 ng) that was not detected in control rats. Glucose levels gradually increased and were 26% higher than control values during the last hour of the 3 h experimental period. The hyperglycemia resulted from a 44% increase in the rate of hepatic glucose output (HGO), which preceded a propertional rise in peripheral glucose utilization. No increase in metabolic clearance rate was observed, suggesting that the increased glucose uptake was the result of mass action. The increased glucose flux was associated with a transient hyperinsulinemia (+95%), and sustained elevations in the arterial concentrations of glucagon (56%) and corticosterone (175%). In contrast, glucose flux was not altered by intravenous administration of the same dose of IL-1α, or i.c.v. injection of IL-1β, or heat-inactivated IL-1α. Indomethacin (5 mg/kg, i.v.) blocked the hyperglycemia and increased HGO induced by i.c.v. injection of prostaglandin E₂ (100 ng) produced comparable increases in glucose flux. These results indicate that IL-1α can act centrally to enhance whole body glucose metabolism, and that this response is probably mediated by prostaglandins.     

Elevation of plasma ACTH concentration in rabbits made febrile by systemic injection of bacterial endotoxin

This study was carried out to investigate the adrenocorticotrophic hormone (ACTH) response in rabbits made febrile by systemic injection of lipopolysaccharide (LPS,Salmonella typhosa endotoxin). Intravenous (i.v.) injection of LPS (0.1 μg/kg and 1.0 μg/kg) increased rectal temperature (biphasic fever) and the plasma concentration of ACTH (ACTH response) in a dose-related manner. These responses were suppressed by pretreatment with indomethacin (20 mg/kg, subcutaneously). Intracerebroventricular (i.c.v.) administration of indomethacin (400 μg) had no effect on the ACTH response to LPS, although it significantly suppressed febrile response. Small increases in plasma concentration of ACTH and significant fevers followed i.c.v. administration of prostaglandin E₂ (2 μg) or F_2α (2 μg). I.v. administration of corticotropin releasing factor (CRF) antagonist [α-helical CRF (9–41) (200 μg/kg)] partly suppressed the ACTH increased induced in plasma by i.v. LPS. These results suggest that prostagandins synthesized outside the blood-brain barrier play an important role in the ACTH response and that the mechanism for induction of the ACTH response is not exactly the same as that for the febrile response, although prostaglandins are involved in both responses.