Construction and implantation of a permanent cannula for making injections into the lateral ventricle of the rat brain

Antagonism by Taurine of Morphine Induced Growth Hormone Secretion

The intraperitoneal (IP) or intraventricular (IVT) administration of small amounts of taurine did not modify pentobarbital-induced sleep or pituitary hormone release. However, the drastic increment in plasma GH values induced by morphine administration was completely blocked by the IVT injection of the amino acid. Whether taurine plays a physiological role in the control ofGH secretion is highly speculative.

Simplified Surgical Placement and Stabilization Methods for Intracerebroventricular Cannulas in Rat Lateral Ventricles

Intracerebroventricular cannulation in rat models is an efficient tool for exploring the effects of substances directly injected into the CNS, bypassing the blood-brain barrier. Techniques for surgically securing the ICV cannula require a balance between ease of application and adequate stability. The authors tested several methods of lateral ventricle cannula stabilization, especially focusing on a comparison of cyanoacrylate gel to cranioplastic cement with an anchoring bone screw.

Open field is more sensitive than automated activity monitor in documenting ouabain-induced hyperlocomotion in the development of an animal model for bipolar illness

1. Intracerebroventricular (i.c.v.) administration of ouabain to rats induces motor hyper- and hypoactivity that have been hypothesized to model the mania and depression of bipolar illness, respectively. 2. The extent of ouabain-induced change in activity may vary according to the test environment. 3. To determine the degree of differential response to i.c.v. ouabain in the open field and automated activity monitors, the authors examined a large number of animals (n=40) in both environments. 4. I.c.v. ouabain produced a four-fold increase in open field activity versus i.c.v. artificial cerebrospinal fluid (aCSF) (mean +/- SD: 258.7 +/- 316.61 vs. 84.8 +/- 86.16 squares traversed) (t = 2.648, P = 0.011), but did not alter horizontal activity in automated activity monitors (8193.5 +/- 4902.52 vs. 7088.47 +/- 3046.85 beam interruptions) (t = 0.847, P = 0.4). This increase in activity persisted for at least one week (161.0 +/- 186.35 for i.c.v. ouabain vs. 46.1 +/- 47.46 for i.c.v. aCSF, P = 0.065). 5. Open field is superior to automated activity monitors in capturing ouabain-induced hyperlocomotion response.

Regulation of hypothalamic proopiomelanocortin by leptin in lean and obese rats

The mechanisms by which leptin influences energy homeostasis are not entirely understood. Several observations indicate that proopiomelanocortin (POMC) is involved in the regulation of food intake and may be a mediator of leptin action. To further study this interaction, a sensitive solution hybridization assay was used to compare the levels of POMC mRNA in the medial basal hypothalamus (MBH) of lean (+/+, +/fa(f)) and obese leptin receptor-deficient (fa(f)/fa(f)) rats. POMC peptide products were also measured by RIA in the same animals. Cytoplasmic POMC RNA levels were significantly reduced by 53% in obese rats as compared with lean controls: 0.30 +/- 0.04 vs. 0.64 +/- 0.07 pg/microgram total RNA (p < 0.02). Significant reductions in mean concentrations of hypothalamic POMC-derived peptides from the same dissections were detected in the obese rats vs. lean controls: alpha-MSH 1.77 +/- 0.07 vs. 2.34 +/- 0.10; beta-EP 4.06 +/- 0.24 vs. 5.86 +/- 0.36; gamma(3)-MSH 5.32 +/- 0. 20 vs. 6.52 +/- 0.12 ng/mg protein (p < 0.001). To determine whether leptin stimulates POMC gene transcription, the acute effect of an intracerebroventricular (i.c.v.) injection of leptin (5 microgram) on POMC primary transcript was quantified in the MBH of lean rats after a 16-hour fast. There was a significant 167% increase in mean POMC hnRNA levels 3 h after i.c.v. leptin injection (1.15 +/- 0.22 pg/MBH; p < 0.02), but not after 1 h (0.76 +/- 0.08 pg/MBH), compared to saline controls (0.69 +/- 0.08 pg/MBH). 4 h after the injection of leptin, POMC hnRNA was still increased, but to a lesser extent (140%), as compared with control animals (p = 0.006). These studies demonstrate for the first time in the leptin receptor-deficient rat that there is an associated decrease in POMC gene expression and peptide levels in the MBH. Furthermore, the acute increase in the levels of POMC primary transcript in non-obese rats after a single i.c.v. injection of leptin supports a role for leptin in the regulation of POMC gene transcription. Taken together, these studies provide further evidence that POMC is an important mediator of the effects of leptin on food intake and energy expenditure.

Brain lesions and delayed water maze learning deficits after intracerebroventricular spermine

The effects of spermine on the acquisition and retention of spatial learning in the Morris water maze were studied. Spermine 25 and 125 nmol i.c.v. did not alter the ability of rats to find a hidden platform in the water maze when administered before training over 5 days. However, the inhibitory effect of the benzodiazepine, diazepam (3 mg/kg i.p., 30 min prior to training), on path length to target was markedly potentiated by the higher dose of spermine, consistent with spermine acting as a functional antagonist at the NMDA receptor. This drug combination did not affect performance on visible platform trials. Administration of doses of 125 and 250 nmol (but not 62.5 nmol) of spermine i.c.v. in the week prior to training (daily for 5 days) dose-dependently inhibited subsequent learning of a platform position in the absence of drug. These higher doses of spermine produced neuronal loss and increased [3H]PK11195 binding indicating microglial activation predominantly in the hippocampus and to a lesser extent in the striatum, septum, thalamus and amygdala. Spermine 125 nmol i.c.v. (daily for 7 days) also abolished retention of a previously learned platform position when administered in an interval between training and retention testing. The inhibitory effects of spermine 125 nmol i.c.v. (daily for 7 days) on subsequent spatial learning were not antagonised by concomitant administration of 30 nmol dizocilpine. These results demonstrate that spermine produces a delayed neurotoxic effect in particular neuronal populations in the brain that selectively impair spatial learning and recall.

Persistent hyperactivity following a single intracerebroventricular dose of ouabain

Intracerebroventricular (i.c.v.) administration of ouabain has been shown to alter motor activity in the rat. It has been purported that this may model the behavioral abnormalities of human manic-depressive (bipolar) illness. Since manic-depression is a recurrent condition, we elected to investigate the effects of the multiple administration of i.c.v. ouabain. Male Sprague-Dawley rats were allowed to acclimate to the animal facility for 7-10 days after which time i.c.v. cannulae were placed. Animals received two i.c.v. injections of either ouabain (10[-3] M) or artificial cerebrospinal fluid (aCSF) 9 days apart, so that 6 rats received aCSF-aCSF, 6 received ouabain-aCSF, and 6 received ouabain-ouabain. Behavioral activity was evaluated in an open field (86 x 86 cm subdivided into sixteen 21.5 x 21.5-cm squares) for 20 min at baseline and immediately following each i.c.v. injection. After the last behavioral test, the animals were killed, and the brains were rapidly harvested and dissected over ice. Specific ouabain binding and sodium pump activity were determined. A single dose of ouabain produced a marked increase (297.0%, p = 0.002) in open field activity compared to both baseline behavior and to aCSF injected animals. The effects of ouabain appeared to last for 9 days. A second i.c.v. injection of either ouabain (136.5 +/- 60.4 SEM) or aCSF (108.0%, p < 0.01) had no effect on the activity level which was intermediate between the initial ouabain hyperactivity and the baseline level. Nine days after ouabain administration, hippocampal ouabain binding was increased relative to the control group (5477 +/- 485.7 vs. 3579 +/- 518.6, p < 0.05) and sodium pump activity was relatively lower (2293.8 +/- 265.5 vs. 3174.2 +/- 410.5, p < 0.05).

Lithium prevents ouabain-induced behavioral changes. Toward an animal model for manic depression

Both mania and bipolar depression have been associated with decrements in the activity of the sodium and potassium-activated adenosine triphosphatase (Na,K-ATPase) membrane pump. Although the role of this observation in the pathophysiology of bipolar illness is unclear, it has been proposed that this defect could be central to the pathogenesis of the illness. In an effort to test this hypothesis, the authors examined the efficacy of lithium pretreatment in attenuating behavioral changes secondary to acute administration of a single intracerebroventricular (i.c.v.) dose of the Na,K-ATPase-inhibiting compound, ouabain, in the Sprague-Dawley rat. Ouabain (10(-3)M) significantly decreased motor activity in automated activity monitors. Lithium pretreatment for 7 d totally prevented this effect. These preliminary data suggest that i.c.v. ouabain administration in the rat may prove to be a viable animal model for bipolar illness.

No evidence for involvement of angiotensin II in spatial learning in water maze in rats

There is increasing evidence suggesting angiotensin II (AII) may inhibit memory formation in a range of conditioned avoidance and habituation learning tasks in rodents. We were interested to determine if AII might also play an inhibitory role in spatial learning. Angiotensin-converting enzyme (ACE) inhibitors, which block the formation of AII from AI, improve acquisition and/or retention of basal performance inhibited by the muscarinic receptor antagonist, scopolamine, in conditioned avoidance and habituation tasks. In hooded Wistar rats, over 5 days of training in a water maze neither the ACE inhibitor, ceranapril 5 and 50 micrograms/kg/day, nor the ACE inhibitor, ramipril 2 and 10 mg/kg/day, altered the increase in path length produced by administration of scopolamine 0.75 mg/kg/day. In probe trails (without platform), on the last day of training, ceranapril 50 micrograms/kg produced a 35% further deterioration in performance in the scopolamine-treated rats (P < 0.02). Administration of the substrate, renin, that leads to AII formation, did not alter water maze performance over 5 days of training. The angiotensin receptor antagonist, losartan, has been shown to improve basal and scopolamine-impaired performance in a habituation task and reverse the inhibition in long-term potentiation produced by diazepam. However, neither losartan 10 and 30 mg/kg/day nor ramipril 2 and 10 mg/kg/day reversed diazepam-impaired (3 mg/kg/day) acquisition of the spatial memory task over 5 days of training. These studies suggest AII does not inhibit spatial learning in rats in the constant platform position water maze task nor does it mediate the inhibitory effects of scopolamine or diazepam in this task.

An animal model for mania: preliminary results

1. In human bipolar patients mania and bipolar depression are both characterized by decreased membrane Na,K-AtPase activity. Additionally, digoxin neurotoxicity in patients frequently presents with symptoms of mania or depression. 2. These findings suggest that central nervous system Na,K-ATPase inhibition may play a pathophysiologic role in bipolar illness. 3. The authors tested this hypothesis by administering intracerebroventricular (i.c.v.) ouabain to rats at sublethal doses. The authors then measured behavioral activity as total square crossings in an open field. 4. Motoric activity was significantly increased by i.c.v. administration of 5 microliters of ouabain at 10(-3) M. This preliminary study suggests that i.c.v. ouabain administration may provide a useful animal model of mania that is based on observed biochemical changes in humans.

Rapid alterations in cAMP accumulation in brain nuclei of rats following microinjections of vasoactive intestinal polypeptide (VIP) into the lateral ventricle

The in vivo effect of exogenous vasoactive intestinal polypeptide (VIP) on the accumulation of cAMP in 21 microdissected brain nuclei was investigated 3 and 7 min after intraventricular injections in rats. VIP elicited significant (up to 20-fold) increases in cAMP levels. This effect is region specific varying considerably among the brain regions investigated. VIP dramatically increased the cAMP content of the lateral septal nucleus, several hypothalamic nuclei, the habenula, the midbrain central gray and the locus coeruleus. Smaller increases were observed elsewhere including some VIP-rich brain areas such as the cerebral cortex and the hippocampus.

Procedure for assessing the behavioral effects of novel anti-parkinsonian drugs in normal and MPTP-treated marmosets following central microinfusions

Comparison between drug effects in MPTP- and non-MPTP-treated marmosets following intracerebroventricular (ICV) and intraputamen administration are given in the present report. Both side-effect profiles and the ability to reverse MPTP-induced hypokinesia were assessed using a variety of dopamine receptor agonists (quinpirole, PHNO, ADTN), cholinergic antagonists (scopolamine, secoverine, himbacine), a glutamate receptor antagonist (MK801) and a 5-HT receptor agonist (8-OH-DPAT). Our results show that direct infusion of agents into the putamen or via the ICV route can reverse parkinsonian-like symptoms in marmosets. Furthermore, chronic implantation of cannulae into the putamen or ventricles of nonhuman primates can be useful in assessing the therapeutic activity of agents that do not readily cross the blood-brain barrier.

Des-Leu angiotensin I: biosynthesis and drinking response

The crude rat and bovine synaptosomal lysate from brain can hydrolyze angiotensin I (AI) to des-Leu angiotensin I (AI-dL) and no further. This cytosolic enzyme has a specificity for angiotensin-related sequences, R-His-Pro-Phe-His-Leu and therefore named angiotensin-related carboxypeptidase (ARC). These studies led to the biosynthesis and purification of AI-dL in order to determine if it can provoke a drinking response. This nonapeptide is a potent dipsogen when injected into the cerebroventricles of rats. The drinking response probably requires a second hydrolysis to angiotensin II (AII) since both captopril and saralasin can inhibit this response.

A reliable, rapid and inexpensive method for producing and implanting chronic cannulae into brains of small animals

A new method for constructing and implanting cannulae into brains of small animals is described. This system allows drug microinjections to be performed on multiple occasions with little tissue damage, at a very low cost.

Effect of captopril on converting enzyme activity in chemically sympathectomized, spontaneously hypertensive rats

Effect of subacute angiotensin converting enzyme (ACE) blockade on the converting enzyme activity (ACE activity) in plasma, aorta, lung, kidney and whole brain was evaluated in chemically-sympathectomized (with 6-hydroxydopamine) normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) using captopril given peripherally via the intraperitoneal (i.p) route and centrally through intracerebroventricular (i.c.v.) administration. Daily i.p. injection of 25 mg/kg for 8 days reduced the blood pressure of both WKY rats and SHR, and the ACE activity in the aorta, lung and plasma of both WKY rats and SHR were correspondingly depressed. The brain ACE activity remained unaltered in both strain of rats. The ACE activity in the kidney of WKY was depressed, while that of SHR remained unchanged. These observations are independent of peripheral sympathectomy with 6-hydroxydopamine (6-OHDA). Daily central captopril administration at a dose of 2 mg/kg, i.c.v., for 8 days significantly reduced the blood pressure of SHR but not WKY rats, whereas the ACE activity of the whole brain of both WKY and SHR were depressed. Central sympathectomy with 6-OHDA did not alter these responses. It is concluded that captopril exerts its antihypertensive effect not only via reduction of the ACE activity in the plasma and lungs as reported earlier, but also that of other organs, principally the aorta, and that these effects are independent of the sympathetic nervous system.

Suppression of basal and stress-induced prolactin release and stimulation of luteinizing hormone secretion by alpha-melanocyte-stimulating hormone

alpha-MSH and beta-endorphin, both synthesized from a common precursor, have opposite behavioral actions. In order to determine if these peptides have opposite effects on pituitary function, basal LH secretion and basal and stress-induced prolactin release were studied in adult male rats after intraventricular injection of alpha-MSH. Each rat also received intraventricular saline in order to serve as its own control. 18 micrograms alpha-MSH stimulated plasma LH from 16.5 +/- 2.5 (SEM) ng/ml to a peak of 27.2 +/- 4.0 and 26.0 +/- 4.9 ng/ml at 5 and 10 min, and suppressed prolactin from 3.5 +/- 0.7 ng/ml to 1.3 +/- 0.1 and 1.2 +/- 0.1 ng/ml at 15 and 30 min. Intraventricular alpha-MSH also significantly blunted the prolactin rise associated with the stress of swimming. 10 and 20 min after the onset of swimming, prolactin levels in rats pretreated with alpha-MSH were significantly diminished: 7.4 +/- 1.5 and 6.5 +/- 2.0 ng/ml vs 23.8 +/- 3.6 and 15.2 +/- 2.8 after normal saline. Similarly, des-acetyl alpha-MSH which is the predominant form of alpha-MSH in the hypothalamus, diminished the stress-induced prolactin rise from 18.4 +/- 5.3 and 11.2 +/- 3.4 ng/ml at 10 and 20 min to 10.0 +/- 2.4 and 5.5 +/- 1.6 ng/ml. We conclude that centrally administered alpha-MSH stimulates LH and suppresses basal and stress-induced prolactin release in male rats. These actions are opposite to those previously shown for beta-endorphin and suggest that alpha-MSH may antagonize the effects of beta-endorphin on pituitary function.

Involvement of presynaptic dopamine receptors in the antihypertensive response to 2-NN-dimethylamino-5,6-dihydroxy-1,2,3,4,-tetrahydronaphthalene (M-7)

M-7, 1 and 3 mg kg-1 s.c., elicits an antihypertensive response and bradycardia in conscious spontaneously hypertensive rats (SHR) and causes inhibition of stimulation-evoked pressor response and tachycardia in pithed SHR. Metoclopramide (30 mg kg-1 i.p.), but not piperoxan (5 mg kg-1 i.p.), abolished the antihypertensive effect and inhibition of stimulation-evoked pressor responses produced by M-7 (1 mg kg-1 s.c.) in SHR. Conversely, piperoxan, but not metoclopramide, reduces the bradycardia and inhibition of stimulation-evoked tachycardia produced by M-7. Metoclopramide (30 mg kg-1 i.p.) did not affect the cardiovascular responses elicited by intracerebroventricular administration of either clonidine (1 microgram) of M-7 (3 micrograms). These results suggest that the antihypertensive effect of M-7 may be mediated by stimulation of presynaptic dopamine receptors on sympathetic nervous to the vasculature and is independent of the bradycardia, which is probably due to stimulation of presynaptic alpha 2-adrenoceptors on cardiac sympathetic nerve endings.

Role of midbrain raphe nuclei in stress-, pentobarbital-, beta-endorphin-, or TRH-induced changes in plasma PRL levels of adult male rats

Radiofrequency lesions of either the dorsal (LD) or the median (LM) raphe nuclei of male rat mesencephalon did not modify baseline levels of plasma prolactin (PRL). However, the PRL releasing effect of 30 min of immobilization stress was suppressed in LM rats and enhanced in LD rats. The PRL releasing effect of pentobarbital (PB, 50 mg/kg, IP) or of beta-endorphin (END, 15 micrograms/rat, intracerebroventricularly, ICV) also was enhanced in LD rats. TRH (10 micrograms/rat, ICV) administered concomitantly with either PB or END, antagonized the releasing effect of the former and enhanced the releasing effect of the latter in sham operated rats. Lesions of the raphe nuclei blocked the antagonizing effect of TRH, while the enhancing effect was heightened in LD rats. These results indicate that neurons originating in the raphe nuclei are not involved in the control of baseline plasma PRL levels. They indicate, furthermore, the existence of an inhibitory pathway originating in the dorsal raphe nucleus the suppression or activation of which is, at least partly, the mechanism of PB, END or TRH effects on PRL release. The PRL releasing effect of immobilization stress seems to be under a dual, mutually antagonistic control: activating through the median and inhibitory through the dorsal nucleus.

Acute changes in cyclic AMP levels of certain brain areas following intraventricular injection of renin in rats

Actions of the central angiotensin system on brain cAMP concentrations were studied after intraventricular injection of renin. Biosynthesis of endogenous brain angiotensin II was stimulated by 0.1 U renin and the blood pressure was elevated 40 min after the application. Stimulation of the brain angiotensin system affected cAMP metabolism in several brain areas, mostly expressed as decreased cAMP levels. Significant decreases in cAMP concentrations were found in the cerebral cortex, hippocampus, basal ganglia, various hypothalamic nuclei, substantia nigra, central grey matter and in the locus coeruleus. The unchanged cAMP levels in the nucleus of the solitary tract might indicate that intraventricular injection of renin induced an acute blood pressure elevation which is not associated with changes in the cAMP system in the primary baroreceptor area.

A comparison of the cardiovascular and sedative actions of the alpha-adrenoceptor agonists, FLA-136 and clonidine, in the rat

1 The cardiovascular and sedative effects of FLA-136 have been compared with those of clonidine after intracerebroventricular (i.c.v.) administration in the rat. The effects of both drugs on pre- and postsynaptic alpha-adrenoceptors in the periphery have been investigated after intravenous (i.v.) administration in the pithed rat.2 In the anaesthetized rat, i.c.v. FLA-136 and clonidine produced dose-related hypotension, FLA-136 having three to 30 times less activity than clonidine; both drugs caused concomitant bradycardia. In the conscious rat i.c.v. FLA-136 had less sedative potential than clonidine, in terms of overt sedation assessed visually.3 Yohimbine reduced the hypotension and bradycardia produced by i.c.v. FLA-136 and clonidine; prazosin and mianserin also antagonized the cardiovascular responses to clonidine, but not those to FLA-136.4 Chemical sympathectomy by 6-hydroxydopamine (6-OHDA) markedly reduced the cardiovascular effects of FLA-136 but only slightly reduced those of clonidine.5 Naloxone antagonized the cardiovascular responses to clonidine, but not FLA-136, suggesting a direct or indirect involvement of central opiate receptors in the responses induced by clonidine.6 Metiamide attenuated the cardiovascular responses to FLA-136 and clonidine, implying a direct or indirect involvement of central histamine (H(2))-receptors in such responses.7 FLA-136, unlike clonidine, did not stimulate peripheral pre- or postsynaptic alpha-adrenoceptors in the pithed rat.8 FLA-136 is a novel centrally-acting hypotensive compound which, unlike clonidine, selectively stimulates central alpha-autoreceptors (yohimbine-sensitive) in the rat; these autoreceptors may be different from peripheral pre- and postsynaptic alpha-adrenoceptors. The results suggest that clonidine lowers blood pressure by stimulation of two types of central postsynaptic alpha-adrenoceptors in the rat, one type being sensitive to yohimbine and the other to prazosin.

Bombesin-induced poikilothermy in rats

The effect of ambient temperature (Ta) on the rectal temperature (Tre) response to intraventricular injection of bombesin has been evaluated in conscious adult male rats. At Ta = 4 degrees C, bombesin (50 ng-1 microgram) caused a marked hypothermia which was dose-dependent both in terms of the magnitude and of the duration of the response. The bombesin-induced hypothermia was reduced at Ta = 24 degrees C, whereas at Ta = 31 or 33 degrees C, the peptide (1 microgram) failed to affect Tre.AtTa = 36 degrees C, bombesin 1-10 micrograms induced an elevation in Tre. The hyperthermia observed at high Ta could be reversed to hypothermia by transferring rats to cold. The analogs [d-Trp8]bombesin or [d-Leu13]bombesin, tested under the same conditions, failed to produce significant changes in Tre. These findings demonstrate that bombesin appears to act in the brain as a poikilothermic agent by disrupting thermoregulation at temperatures below or above thermoneutrality.

An easily constructed durable chronic intracerebral cannula system

A simple, inexpensive, and rugged intracerebral cannula system is described and construction details are provided for both guide and injection cannula assemblies. The guide cannula assembly is easily and quickly molded from dental acrylic cement and has a protective acrylic collar surrounding the end of the actual guide cannula. This system is believed to offer some advantage over current methodologies in terms of expense, durability and ease of construction and is well suited to use in rodents.

Central and peripheral effects of bradykinin and prostaglandin E2 on blood pressure in conscious rats

Bradykinin or prostaglandin E2 (PGE2), when injected intravenously, decreased blood pressure of conscious rats in a dose-dependent manner, while intracerebroventricular injections of bradykinin or PGE2 caused a dose-dependent increase in blood pressure. SQ 14,225, an inhibitor of angiotensin converting enzyme, potentiated the central pressor or peripheral depressor effect of bradykinin. Indomethacin, an inhibitor of prostaglandin synthesis, almost completely inhibited the central pressor effect of bradykinin when injected intraventricularly. Indomenthacin, when injected intravenously, failed to inhibit the peripheral depressor effect of bradykinin, whereas it significantly attenuated the peripheral depressor effect of bradykinin when the angiotensin converting enzyme was inhibited with SQ 14,225. These results suggest that the central pressor effect of bradykinin is mainly mediated by the synthesis of prostaglandins in the central nervous system, while only a small fraction of peripheral depressor effect of bradykinin is, at least in conscious rats, mediated by the synthesis of prostaglandins in the systemic circulation.

An opposing role for the adrenals in the hypotensive effects of propranolol in the spontaneously hypertensive rat

d,l-Propranolol (1 and 5 mg/kg s.c.) did not cause a fall in blood pressure and induced only a limited decrease in heart rate in conscious spontaneously) hypertensive rats (SHR). In contrast, after bilateral adrenalectomy, d,l-propranolol induced a rapid and profound decrease in blood pressure and heart rate. Decreases in heart rate and blood pressure in the individual animals were not correlated. The effects were mainly caused by l-propranolol but an additional effect of d-propranolol cannot be excluded. The decrease in blood pressure was not observed after removal of the adrenal medulla. Heart rate decreased only slightly in these animals. After treatment of adrenalectomized SHR with corticosterone (1 mg/kg b.w./h) the decrease in blood pressure due to d,l-propranolol was completely abolished. The fall in heart rate was diminished. Central injection of d,l-propranolol into the lateral brain ventricle of adrenalectomized SHR caused cardiovascular changes which were less pronounced than those following peripheral injection of comparable doses. The inhibitory effects of d,l-propranolol also occurred in adrenalectomized normotensive Wistar Kyoto rats. However, no significant changes in blood pressure and only a limited fall in heart rate were observed in adrenalectomized normotensive and renal hypertensive Wistar rats. It is concluded that the presence of the adrenal cortex, but not of the adrenal medulla prevents acute hypotension and bradycardia after propranolol in the conscious SHR.

Effects of intracerebroventricular administration of prostaglandins I2, E2, F2 alpha and indomethacin on blood pressure in the rat

The effects of intraventricularly administered prostaglandins I2 (PGI2), E2 (PGE2), F2alpha (PGF2 alpha) and indomethacin on systemic blood pressure were investigated in conscious rats. PGI2 (1.25--10 micrograms/kg) decreased blood pressure in a dose-related manner, whereas PGE2 (100--1000 mg/kg) dose-dependently increased blood pressure. Both PGF2 alpha (0.31--20 micrograms/kg) and indomethacin (0.625--40 micrograms/kg) had no effects on blood pressure. These results indicate that intraventricular injection of PGI2 or PGE2 can induce significant changes in blood pressure, while endogenous prostaglandins synthesized in the brain seem to play a minor role in direct regulation of systemic blood pressure in the rat.

Antidipsogenic effect of intracranial injections of substance P in rats

1. The effect on water intake of intracranial injections of Substance P was studied in the rat. 2. Substance P strongly inhibited drinking elicited by Angiotensin II, Carbachol water deprivation or sodium chloride load, in that order. 3. The peptide was particularly effective when water intake was induced by injections of Angiotensin II into the preoptic area. In these experiments, drinking was inhibited by doses of Substance P as low as 1 ng. 4. The results suggest that in the rat Substance P may play a role in the brain in the regulation of water intake, acting as a thirst inhibitor.

Cardiovascular responses to intraventricular adrenaline in spontaneous hypertensive rats

The effects of intracerebroventricular (i.c.v.) injections of adrenaline on the blood pressure and heart rate of spontaneous hypertensive (SH) rats have been investigated. Adrenaline induced dose-related falls in blood pressure and heart rate in both conscious and urethane anaesthetised rats. In conscious rats, the hypotension and metoprolol, but were unaffected by pretreatment with phentolamine, piperoxan, fluphenazine or methysergide. However, in urethane-anaesthetised rats, the hypotension and bradycardia induced by i.c.v. adrenaline was not significantly affected by i.c.v. pretreatment with propranolol or oxprenolol, while metoprolol significantly antagonised only the bradycardia. Piperoxan, fluphenazine and methysergide were also without effect. Pretreatment with mecamylamine (i.p.) abolished the cardiovascular depressor effects of i.c.v. adrenaline in both conscious and urethane anaesthetised SH rats. It is concluded that the cardiovascular depressor effects of i.c.v. adrenaline are mediated by central adrenoceptors in SH rats and that, in conscious rats, these depressor effects may be mediated by central beta-adrenoceptors rather than alpha-adrenoceptors.

Prostaglandins and sleep. Awaking effect of prostaglandins and sleep pattern of essential fatty acids deficient (EFAD) rats

The experiments were carried out to investigate the effects of prostaglandins (PGs) on the sleep pattern in the cat, and in normal and EFAD rats. The data indicate that the duration of slow wave sleep (SWS) was significantly longer in EFAD rats compared with the normal rats. However, no difference in the REM sleep was observed between the two groups. Intraventricular (i.vc. )administration of PGE1, PGE2 and PGF2alpha increased wakefulness without a significant alteration of REM sleep. PGE1 administered i.vc. did not alter the duration of SWS or REM sleep in the chronic cat, but induced ponto-geniculo-occipital (PGO) waves (spikes) which are the phasic phenomenon of REM sleep. The fact that previous administration of 5-hydroxytryptophane abolished the PGE1-induced PGO spiking, might indicate that this drug triggered the spikes mainly via the functional inhibition of the serotonergic system.

Antagonism of pentobarbital-induced hormonal changes by TRH in rats

In adult male rats, injection of TRH into a lateral ventricle of the brain 5 min prior to pentobarbital (PB) administration caused a significant dose-related inhibition of prolactin (PRL) release, in doses ranging from 500 to 5 ng. Among 8 TRH analogues devoid of thyrotropin-releasing activity, 6 were found to significantly suppress PB-induced PRL secretion at an intraventricular dose level of 10 microgram, and the 3 most effective in this respect were also able to counteract growth hormone (GH) release elicited by PB. The derivative [1,3'-DCM2]TRH was still potent enough to block PB-induced PRL secretion at an intraventricular dosage of 50 ng. The peptide ACTH 4--10 was ineffective, whereas another ACTH derivative H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH (Org 2766) reduced PRL release. TRH did not affect the increase of plasma PRL induced by acute stress. alpha-Methyl-p-tyrosine (alpha-MT) failed to influence the inhibiting effect of TRH on GH secretion but significantly reduced that on PRL release. p-Chlorophenylalanine (PCPA) completely blocked the antagonistic effect of TRH on all PB-induced hormonal changes, suggesting that serotoninergic mechanisms may be involved in the extra-pituitary effect of TRH.

Changes in rat hind limb vascular resistance following intracerebroventricular drug administration

The right hind limbs of rats (which had previously implanted intraventricular guide cannulae) were isolated from the systemic circulation, but with the nerves to the limb remaining intact, and perfused using a constant output blood pump. Using this preparation, changes in vascular resistance, blood pressure and heart rate were monitored following injection of noradrenaline, phentolamine and propranolol into the lateral cerebral ventricles (i.c.v.) of rats anaesthetised with alpha-chloralose. All three drugs lowered blood pressure. Noradrenaline administered i.c.v. induced a nervously mediated vasocilatation and an insignificant fall in heart rate whereas i.c.v. phentolamine administration was followed by a nervously mediated vasoconstriction in the isolated hind limb and a gradual rise in heart rate. After i.c.v. administration of propranolol there was no evidence of an immediate nervously mediated vasodilatation but heart rate fell significantly. Following i.c.v. phentolamine or propranolol vasodilatation did not occur in the hind limb until after the time taken for circulating blood ro reach the isolated vascular bed. The vasodilatatory and hypotensive responses to i.c.v. noradrenaline were not evident following prior i.c.v. injection of phentolamine. These results indicate the suitability of this preparation for investigations of central actions of other drugs.

Effects of schedules of reinforcement on brain catecholamine metabolism in the rat

Rats were trained on a fixed ratio 5 (FR 5) for 0.01 ml water reinforcer, a fixed ratio 20 (FR' 20) for 0.01 ml water reinforcer, a fixed ratio 20 (FR 20) for 0.04 ml water reinforcer, a variable time 15 sec (VT 15 sec) for 0.01 ml water reinforcer, a variable time 30 sec (VT 30 sec) for 0.01 ml water, variable time 60 sec (VT 60 sec) for 0.01 ml water, or a variable time 60 sec (VT 60 sec) for 0.10 ml water. In all these schedules, the rate of NE metabolism varied with the number of water presentations but not with the number of responses or the volume of water. The rate of metabolism of DA was increased over control values in rats on the VT schedules but no significant differences could be found in DA metabolism among the rats performing on the various VT schedules or receiving various volumes.

Effect of lofepramine and other antidepressants on the uptake of 5-hydroxytryptamine and noradrenaline into rat brain monoaminergic neurons

Lofepramine, (N-methyl-N-[4-chlorobenzoylmethyl]-3-[10,11-dihydro-5H-dibenz(b,f)-azepin-5-yl]-propylamine hydrochloride), is a new antidepressant with low toxicity and no peripheral anticholinergic activity. Its effect on 5-hydroxytryptamine (5-HT) and noradrenaline uptake into rat brain monoaminergic neurons was studied and compared with that of other antidepressants, particularly with that of imipramine and desipramine. Lofepramine inhibited both 5-HT and noradrenaline uptake into synaptosomal fractions in vitro but was 4 times more potent in inhibiting noradrenaline than 5-HT uptake, indicating the effect resembles that of desipramine. Noradrenaline uptake was also preferentially inhibited in synaptosomes from brain of rats treated previously with lofepramine or desipramine (i.p.). Pretreatment with SKF 525A (i.p.) did not diminish the effect of lofepramine, but rather potentiated it. Therefore it is suggested that the formation of desipramine is not necessary for lofepramine to exhibit, the effect on amine uptake in vivo. Both lofepramine and desipramine inhibited intraventricular noradrenaline uptake into synaptosomes without any effect on 5-HT uptake. These results suggest that lofepramine is qualitatively similar to desipramine with respect to preferential inhibition of noradrenaline uptake into central noradrenergic neurons.

A permanent plastic cannula for intraventricular injections into rat brain

The construction and use of a permanent, implanted plastic camnula for intraventricular injections in rat brain is described. The cannula can be used in either acute or chronic experiments.

Effect of intracerebroventricular 5,6-dihydroxytryptamine on blood pressure of spontaneously hypertensive rats

The effects of intracerebroventricular injections of 5,6-DHT on the development and maintenance of hypertension in spontaneously hypertensive rats has been investigated. 5,6-DHT, injected into 6 week old rats, retarded the development of hypertension for at least 6 weeks; this effect was not accompanied by inhibition of the pressor response produced by stimulation of the total peripheral sympathetic outflow. 5,6-DHT, injected into 14-15 week old rats with established hypertension, produced a short-lived fall in blood pressure. These findings suggest that central 5-HT neurones are involved in the development of hypertension in spontaneously hypertensive rats.

Prolonged effects of p-chlorophenylalanine on the blood pressure of conscious normotensive and DOCA/saline hypertensive rats

1. In deoxycorticosterone acetate (DOCA) saline hypertensive rats a single dose of p-chlorophenylalanine methylester (PCPAME) (400 mg/kg i.p.) produced a significant fall in blood pressure (20-43 mmHg) which lasted for at least 8 days and was accompanied by a parallel depletion of brain stem 5-hydroxytryptamine (5-ht) but not of noradrenaline (NA). 2. In normotensive rats single doses of PCPAME (200 and 400 mg/kg i.p.) produced a significant hypotension (15-20 mmHg) after a latent period of 5 days. An initial pressor response (12 mmHg) was observed at the higher dose level only on day 3. 3. The hypotensive response to PCPAME (200 mg/kg i.p.) in normotensive rats was not modified by pretreatment with 5,6-dihydroxytryptamine (5,6-DHT; 50 mug i.c.v.) or 6-hydroxydopa (6-ohda; 3 X 250 mug intracerebroventricularly). 4. It is concluded that the hypotensive response to PCPAME in normotensive rats in independent of brain stem depletion of 5-HT and is probably not mediated by the formation of a false transmitter substance acting via central noradrenergic inhibitory pathways. The mechanism involved in the antihypertensive response to PCPAME in DOVA/saline hypertensive rats has yet to be defined.