Paule Poulin

Subcellular localization and characterization of vasopressin binding sites in the ventral septal area, lateral septum, and hippocampus of the rat brain.

[Arg8]‐Vasopressin (AVP) has been shown to exert characteristic central physiological actions in the ventral septal area of the rat brain. This study reports the characterization of receptors for AVP in synaptic plasma membranes prepared from the ventral septal area, the lateral septum, and the hippocampus. Binding of [3H]AVP was temperature and time dependent, linearly related to protein concentration, saturable, and specific. Scatchard plot analysis suggested the presence of a population of binding sites in the three brain areas with dissociation constants and maximal binding capacities, respectively, of 1.06 ± 0.39 nM and 24.0 ± 7.01 fmol/mg of protein (mean ± SEM; n = 3) for the ventral septal area, 0.92 ± 0.13 nM and 47.0 ± 4.96 fmol/mg of protein (n = 3) for the lateral septum, and 0.91 ± 0.14 nM and 25 ± 5.02 fmol/mg of protein (n = 3) for the hippocampus. In all three brain regions, the rank order of potencies of several vasopressin analogs, unrelated peptides, and other compounds for competitive displacement of ligand indicated a receptor with properties resembling those of the V1‐like receptor for AVP. These data document the presence of a high‐affinity, V1‐like vasopressin receptor in the rat ventral septal area for which the pharmacological properties are similar to those previously reported in physiological studies.

The role of vasopressin as an antipyretic in the ventral septal area and its possible involvement in convulsive disorders

Perfusion of the peptide, arginine vasopressin (AVP), within the ventral septal area (VSA) of the brain of a number of species reduces fever but not normal body temperature. This antipyretic response appears to be mediated by AVP receptors of the V1 subtype. Lesions of the VSA with kainic acid are associated with prolonged and enhanced fevers in rats. A role for endogenous AVP in fever suppression within the VSA comes from several types of experiments: (1) AVP release within the VSA is inversely correlated to fever height; (2) AVP antagonists or antiserum injected into the VSA prolong fever; (3) animals lacking endogenous AVP in the VSA (Brattleboro rat, long-term castrated rat) develop enhanced fevers. Electrical stimulation of the AVP-containing cell bodies of the bed nucleus of the stria terminalis (BST) orthodromically inhibits VSA neurons and also suppresses fever; the latter effect can be abolished with application of a V1 antagonist to the VSA. Iontophoretic studies indicate that AVP inhibits glutamate-stimulated activity of thermoresponsive and other VSA neurons. AVP can also act in the VSA to cause severe motor disturbances; this action is receptor mediated and increases in severity upon sequential exposure to AVP. Because sites of action of the antipyretic and convulsive action of AVP are similar, and because animals lacking brain AVP display reduced convulsive activity, it is possible that AVP, released during fever, could be involved in the genesis of convulsive activity.

Vasopressin-induced motor effects: Localization of a sensitive site in the amygdala

Arginine vasopressin (AVP) induces motor effects when administered into the cerebral ventricles, the ventral septal area (VSA), or the vestibular cerebellum of the rat brain. Because AVP-like immunoreactivity and AVP-binding sites exist in the central medial amygdala (cmeA), and because the amygdala can be kindled to produce motor effects, we hypothesized that the amygdala might play a role in AVP-induced motor effects. This hypothesis was tested by observing motor behavior in response to injection of AVP into the central medial region of the amygdala. Our results demonstrate that an initial injection of AVP into the cmeA caused minor motor effects, including immobility, prostration and ataxia, whereas a similar injection, given 24 h later, caused severe motor effects including barrel rotations and myoclonic/myotonic-like convulsive behavior. A potential receptor basis for the AVP-induced motor and sensitization effects in the cmeA was investigated using AVP analogues. A V1 antagonist, d(CH2)5Tyr(Me)AVP, blocked both the motor and sensitization effects produced by cmeA AVP injection. A V2 receptor agonist, DDAVP, did not affect motor activity upon cmeA injection, but did, however, sensitize animals to subsequent cmeA AVP injection. These results suggest that the cmeA is a sensitive site for AVP-induced motor effects and that these motor effects are sensitized by prior exposure to AVP. While the motor effects observed after cmeA AVP injection are mediated via AVP receptors that resemble the V1 type, the sensitization effect may be mediated via multiple receptor systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic localization of binding sites for vasoactive intestinal peptide (VIP) in bovine cerebral arteries

A substantial body of published evidence indicates that vasoactive intestinal peptide (VIP) may function as a vasodilatory neurotransmitter to cerebral blood vessels via a specific VIP receptor. In the present study in vitro autoradiography utilizing monoiodinated [125I-Tyr10]-VIP demonstrated VIP binding sites in the medial layer of bovine anterior, middle, and posterior cerebral arteries. This observation is consistent with the VIP receptor being localized in vascular smooth muscle components.

Oxytocin Pretreatment Enhances Arginine Vasopressin-lnduced Motor Disturbances and Arginine Vasopressin-lnduced Phosphoinositol Hydrolysis in Rat Septum: A Cross-Sensitization Phenomenon

The recent observation that the central oxytocin (OT) receptor has high affinity for both OT and arginine vasopressin (AVP) raises the possibility that it may be involved in some of the central actions of AVP. Repeated intracerebroventricular (icv) injections of AVP in rats evoke an unusual sensitization phenomenon in that a first exposure to the peptide enhances the sensitivity (sensitization) of the brain to a second exposure. This report investigates the possibility that the OT receptor may be involved in the mediation of the phenomenon of sensitization, using OT, a specific OT receptor agonist, [Thr4, Gly7]OT, and a specific OT receptor antagonist, d(CH2)5, [Tyr(Me)2, Thr4, Tyr‐NH29]OVT (compound 6; cpd 6), as well as a V1 AVP receptor antagonist, d(CH2)5Tyr(Me)AVP. Peptides were injected icv in conscious, adult male Sprague‐Dawley rats. The data showed that: 1) a first icv AVP injection (10 pmol/5μl) enhanced the sensitivity of the rat brain to the motor response of a second AVP injection (10 pmol/5 μl) given 24 h later; 2) injection of d(CH2)5Tyr(Me)AVP (100 pmol/5 μl icv) but not cpd 6, (100 pmol/5 μl icv) 2 min prior to the first AVP injection, blocked AVP‐induced sensitization; 3) a first injection of OT or [Thr4, Gly7]OT (10 pmol/5 μl) enhanced the sensitivity of the brain to the motor actions of a subsequent AVP injection given 24 h later; 4) the magnitude of this cross‐sensitization induced by OT pretreatment varied with dose and appeared to be ten times more potent than the sensitization induced by a first AVP injection; 5) injection of cpd 6 (100 pmol/5 μl) but not d(CH2)5Tyr(Me)AVP (100 pmol/5 μl icv) 2 min prior to the first OT injection (1 pmol/5 μl) blocked the cross‐sensitization induced by OT; 6) an injection of OT (100 to 1,000 pmol/5 μl) or [Thr4, Gly7]OT (10 pmol/5 μl) in rats that had been cross‐sensitized with OT or [Thr4, Gly7]OT pretreatment did not evoke enhanced motor responses; 7) OT injected 2 min prior to the second AVP injection in AVP‐sensitized rats did not block the enhanced AVP‐induced motor responses; 8) AVP‐induced [3H]inositol monophosphate accumulation in septal slices was also enhanced in rats cross‐sensitized by OT pretreatment.

Arginine vasopressin-induced sensitization in brain: facilitated inositol phosphate production without changes in receptor number

Arginine vasopressin (AVP) has been shown to have a unique sensitization effect whereby repeated injection of AVP into a lateral cerebral ventricle or a mediobasal region of the rat forebrain below the lateral septum and including the anterior hypothalamus referred to as the ventral septal area, causes enhanced motor responses to the ligand. To elucidate possible neuronal mechanisms responsible for AVP sensitization, 1) we determined the dose and the time required for the development and expression of AVP sensitization, and 2) we tested the hypotheses that AVP sensitization may result in a) alteration of septal AVP V1 receptor affinity or number, and/or b) alteration of septal AVP V1 receptor signal transduction (phosphatidylinositol hydrolysis) mechanisms. Our behavioral data show that the magnitude of AVP sensitization varies with dose and time, and the effect is dependent on the time interval between injections, in that an initial intracerebroventricular AVP injection enhances the sensitivity of the animals to the motor effects of similar AVP injections given 6 h to 6 days later but not to injections given hourly or weekly. No changes in septal AVP binding site density and affinity, as measured by [3H]AVP binding to septal synaptic plasma membrane, were found in sensitized animals; [3H]inositol monophosphate stimulation in response to AVP in septal slices, however, was found to be significantly enhanced. This enhanced [3>H]inositol monophosphate stimulation appears specific to a V1‐type receptor because it was significantly reduced in the presence of the V1 receptor antagonist, d(CH2)5Tyr(Me)AVP, and was not found using oxytocin or the V2 receptor agonist, DDAVP. Our results therefore indicate that receptor binding, while critical to peptide neurotransmitter action, is not the sole factor for determining responsiveness. Rather, an appropriate schedule of AVP administration, which may cause changes in postreceptor effector system(s) such as inositol phosphate hydrolysis, appears most important.

[3H]Arginine vasopressin binding to rat brain: a homogenate and autoradiographic study

Arginine-vasopressin (AVP) has been implicated as a putative central neurotransmitter or neuromodulator in some brain functions. This study demonstrates binding of [3H]AVP to rat brain homogenates that is pH and temperature dependent, is saturable (Kd = 0.77 nM, Bmax = 0.374 pmol/mg) and reversible. A number of AVP analogues competitively displaced the [3H]AVP binding, indicating that central AVP binding sites may have a resemblance to the peripheral (V1) AVP vasopressor receptor. Homogenate binding occurred predominantly in the microsomal fraction (P3) of the hypothalamus while in the hippocampus and septum binding was predominantly in the synaptosomal fraction (P2). Autoradiographic methods showed displaceable [3H]AVP binding in the lateral septum, amygdala, supraoptic, paraventricular and suprachiasmatic nuclei of the hypothalamus supporting the results of homogenate binding in preparations of these regions.

Vasopressie-induced sensitization: involvement of neurohypophyseal peptide receptors

Rats pretreated with an intracerebroventricular (i.c.v.) injection of 10 pmol of vasopressin or vasopressin analogs, including deamino-D-vasopressin, [pGlu4,Cyt6]vasopressin, [pGlu-Asn-Cys(Cys)]Pro-Leu-Gly-NH2, des-Gly-NH9(2)-vasopressin, Pro-Leu-Gly-NH2, Pro-Arg-Gly-NH2, became markedly hyper-responsive to the motor effects, 24 h later, to a subsequent challenge dose of vasopressin, but not vasopressin-related peptides. A vasopressin V1 receptor antagonist, [d(CH2)1(5),Tyr(Me)2]vasopressin, but not the vasopressin V2 receptor antagonist, [d(CH2)1(5),Tyr(Et)2,Val4]vasopressin, or a more selective vasopressin V2 receptor antagonist, [d(CH2)1(5),D-Ile2,Ile4]vasopressin, or the oxytocin receptor antagonist, [d(CH2)1(5),Tyr(Me)2,Thr4,Orn8,Tyr-NH9(2)]vasotocin ([d(CH2)1(5),Tyr(Me)2,Thr4,Tyr-NH9(2)]OVT), blocked vasopressin and vasopressin analog-induced sensitization. Furthermore, both vasopressin V2 receptor antagonists were found to sensitize the brain to a subsequent vasopressin injection. This vasopressin V2 receptor antagonist-induced sensitization was also blocked by the vasopressin V1 receptor antagonist. Next, we wanted to determine if this sensitization process could involve the release of endogenous vasopressin in the brain as reflected in an amplification of vasopressin mRNA expression. However pretreatment of rats with an i.c.v. vasopressin injection was not associated with an increase in vasopressin mRNA expression in the bed nucleus of the stria terminalis, medial amygdala or the paraventricular nucleus of the hypothalamus when measured 0, 1, 3, 7, 12, or 24 h after the first vasopressin injection. As many vasopressin analogs can induce sensitization, we suggest that a novel type of receptor may be involved in the sensitization process.

The Evidence Decision Support Program Within the Surgery Strategic Clinical Network of Alberta Health Services in Canada

The Surgery Strategic Clinical Network (SSCN) within Alberta Health Services (AHS) has implemented an “Evidence Decision Support Program (EDSP)” to help identify, prioritize, evaluate, and recommend new technologies for possible introduction into the health-care system, with specific focus on the hospital setting. The EDSP does not conduct health technology assessment (HTA) reports, but rather provides a model to make evidence-informed decision about whether and under what conditions innovations should be adopted. The Program consists of a standing multidisciplinary committee (consisting of scientists, clinicians, nurse managers, and administrators) and uses standardized forms and processes to gather both context-free and context-sensitive evidence on new technologies being considered. The objective is to review the evidence in context and use external professional expertise, when required, to make recommendations to the Surgical Executive Committee for subsequent decision. The goal is to ensure patients receive optimal treatment while safety, training/credentialing, resources, and other organizational issues are considered. Unlike traditional large-scale HTA organizations, the EDSP collects and integrates local data with published HTA reports. This helps to ensure better applicability of HTA report recommendations to meet local needs. The scope of the Program’s impact is varied and may include impact on hospital/operating room budgets, clinical practices, patient outcomes monitoring, training, and credentialing. The EDSP continues to evolve as stakeholder engagement and input with respect to practical issues of implementing recommendations for adoption of new technology are recognized.