Increases in heart rate and blood pressure produced by injections of dermorphin into discrete hypothalamic sites

Galanin in the brain: chemoarchitectonics and brain cartography--a historical review

We present a review of galanin in the brain from a historical perspective of the development of "chemoarchitectonics" and "brain cartography" accomplished in the Histopharmacology Section at the National Institutes of Health. It was the mapping of potential brain neuroregulators that served as a springboard of ideas from which behavioral studies emanate. The integration of the known localization of neurotransmitter/neuromodulatory nerves ("chemoarchitectonic maps") and receptor binding sites with biochemical data derived from brain micropunches coupled with behavioral analysis at the level of discrete brain allows one to define the anatomical circuits which support behavioral changes and which ultimately will improve our understanding of mental disorders.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Effect of dermorphin on thermoregulation in rats at selected ambient temperatures

Intraperitoneal administration of dermorphin caused dose-dependent changes in rats core temperature and tail skin temperature (indicative of compensatory thermoregulatory vasoreactions in rats). The character of these changes depended strongly on the environmental temperature at which the inversion of the dermorphin-induced thermoregulatory effect was observed. In the cold environment (4-7 degrees C) dermorphin caused a significant, stable, dose-dependent hypothermia. In the thermoneutral environment (27-28 degrees C) dermorphin also caused hypothermia, but this effect was less pronounced. In the hot environment (31-32 degrees C) dermorphin caused hyperthermia. Dermorphin-induced changes in tail skin temperature indicate that dermorphin suppresses the thermoregulatory peripheral compensatory vasomotor reactions. Pretreatment with naloxone attenuated dermorphin-induced effects on core temperature and partially enhanced vasomotor effects of dermorphin. The data obtained indicate that dermorphin affects the core temperature regulation via mu-opiate receptors, whereas vasomotor effects of the peptide are probably mediated via naloxone-insensitive receptors.

Evidence for differential opioid μ1- and μ2-receptor-mediated regulation of heart rate in the conscious rat

The possibility that mu-opioid-induced tachycardia and bradycardia could be mediated by different subtypes of the mu-receptor was studied in conscious Sprague-Dawley rats. The selective mu-receptor agonist dermorphin and its analog, TAPS (Tyr-D-Arg-Phe-sarcosine), a putative mu 1-receptor agonist, were given centrally. Tyr-D-Arg-Phe-sarcosine increased the heart rate, the response being inversely correlated to the dose (an increase of 71 +/- 22, 49 +/- 14 and 30 +/- 17 beats/min at doses of 0.3, 3 and 30 pmol, respectively). Dermorphin induced less clear changes in heart rate (maximum increase of 39 +/- 14 beats/min at the dose of 1 pmol). After treatment with the mu 1-selective antagonist naloxonazine (NAZ), TAPS 30 pmol and dermorphin 1 pmol decreased heart rate by -22 +/- 10 and -24 +/- 7 bpm, respectively. The bradycardiac effect of larger doses of dermorphin was potentiated by NAZ (from -25 +/- 8 to -97 +/- 22 bpm) but abolished by the non-selective antagonist naloxone. These data suggest that the high affinity mu 1-opioid receptors mediate tachycardic responses and mu 2-receptors mediate bradycardic responses.

Cardiovascular actions of intrahypothalamic injections of atrial natriuretic peptide

Accumulating evidence implicates atrial natriuretic polypeptide (ANP) as a neurotransmitter in brain. The presence and distribution of ANP, its high affinity binding sites, and the messenger RNA of its precursor have been described in the central nervous system. However, the function(s) of ANP in specific brain areas is largely unknown. We have now determined the cardiovascular effects elicited by microinjection of atriopeptin-III (ANP-III) in hypothalamic and preoptic areas in rats. ANP-III (40 pmol) increased heart rate when injected into the anteromedial preoptic nucleus (AMPO), the medial preoptic area (MPA), the periventricular area, and in two regions of the dorsal hypothalamus. Other nuclei within the hypothalamus were unresponsive. The tachycardic effects elicited by AMPO-MPA injection of ANP-III were abolished by adrenalectomy. These data indicate that ANP-III acts at discrete sites to elicit tachycardia and the mechanism of action for at least one brain site appears to be through central pathways which selectively activate the adrenal gland.

Atrial natriuretic peptide in the central nervous system of the rat

1. Studies of the presence of atrial natriuretic peptide immunoreactivity and receptor binding sites in the central nervous system have revealed unusual sites of interest. 2. As a result, numerous studies have appeared that indicate that brain atrial natriuretic peptide is implicated in the regulation of blood pressure, fluid and sodium balance, cerebral blood flow, brain microcirculation, blood-brain barrier function, and cerebrospinal fluid production. 3. Alteration of the atrial natriuretic peptide system in the brain could have important implications in hypertensive disease and disorders of water balance in the central nervous system.

Opioid peptides in pituitary gland, brain regions and peripheral tissues of spontaneously hypertensive and Wistar-Kyoto normotensive rats

The concentrations of beta-endorphin (beta-END), dynorphin (DYN) and methionine-enkephalin (MEK) in pituitary, brain regions, heart, kidney and adrenal of 8 week old male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats were determined by radioimmunoassay and compared. The brain regions examined were hypothalamus, striatum, pons + medulla, midbrain and cortex. The concentration of beta-END in pituitary of SHR rats was 49% higher than those of WKY rats. The concentration of beta-END in the striatum of SHR rats was 71% lower as compared to WKY rats. The concentration of beta-END in the heart, adrenals and kidney of SHR rats was significantly lower (92, 48 and 57%, respectively), than those of WKY rat tissues. The concentration of DYN in pituitary, striatum and heart were lower by 38, 55 and 46%, respectively, in SHR compared to WKY rats, but in hypothalamus it was greater (33%) than in WKY rats. The concentration of DYN in other brain areas and in kidney and adrenal did not differ. The tissues of SHR and WKY rats which showed significant difference in the concentration of MEK were pituitary, pons + medulla, cerebral cortex and adrenals. The concentration of MEK was greater in SHR rats with pons + medulla, cortex and adrenals showing 33, 40, 268% higher levels, respectively, over the WKY rat tissues. However, the concentration of MEK in pituitary of SHR rats was 40% lower than that of WKY rats. These studies suggest that the endogenous opioid peptides of both central and peripheral tissues may be important in the regulation of blood pressure in SHR rats.

The opioid peptides. A role in hypertension?

This review is an attempt to highlight evidence that may implicate the endogenous opioid system in the pathogenesis of hypertension in humans. The evidence raised includes biochemical, physiological, pharmacological, and behavioral studies conducted in in vitro and in vivo systems, experimental models of hypertension, and humans with essential hypertension. While the compelling biochemical and pharmacological evidence in experimental animals clearly shows the presence of opioid peptides and their receptors in strategic sites of cardiovascular control and potent cardiovascular response to opioid peptides, opioid antagonists show no consistent blockade or reversal of hypertension in experimental animals or humans. One possible explanation for this phenomenon could be the vast redundancy in systems regulating blood pressure (i.e., the blockade of one system still leaves many other systems fully able to rapidly offset the eliminated system). Regarding the opioid system, the situation is much more complex, since some opioid receptors (mu-type) mediate pressor responses, while other receptors (kappa-type) mediate depressor responses. Therefore, nonselective opioid receptor antagonists (e.g., naloxone), which block both types of receptors, can be devoid of any cardiovascular activity, while a selective mu-receptor antagonist or a selective and potent kappa-receptor agonist may produce the desired antihypertensive effect. A combination of both actions (i.e., a drug that is both a mu-antagonist and a kappa-agonist) might be even more advantageous. Until such compounds are developed, this hypothesis will be hard to prove.

Effect of dermorphin and morphine on the sympathetic and cardiovascular system of the pithed rat

Dermorphin is a recently discovered opioid peptide which is unique in having a D-amino acid in its sequence. Dermorphin binding sites have been shown in central and peripheral organs and central administered dermorphin produces profound autonomic responses. The purpose of this study was to examine the effect of intravenous dermorphin on heart rate and blood pressure of the pithed rat in basal condition and in response to controlled sympathetic stimulation. Also, since dermorphin is a selective mu-receptor agonist, its effects were compared to morphine, an opiate selective for mu receptors. Dermorphin (0.0001-10 mumol/kg, i.v) or morphine (1-10 mg/kg) had no effect on basal heart rate or blood pressure and failed to modify sympatho-adreno-medullary evoked pressor and tachycardic responses. Furthermore, dermorphin or morphine did not affect the increase in plasma norepinephrine and epinephrine in response to spinal cord stimulation. It is concluded that the dermorphin and morphine have no direct peripheral effects on heart rate or blood vessel tone nor do these mu-receptor agonists have any effect on norepinephrine and epinephrine release from the sympathetic nerves and the adrenal medulla in the rat.

Increases in heart rate and blood pressure produced by microinjections of atrial natriuretic factor into the AV3V region of rat brain

Recent studies have provided evidence for the dense localization of atrial natriuretic factor (ANF) in the anteroventral third ventricle (AV3V) region of the rat brain. This area is currently thought to be involved in the regulation of blood pressure and fluid and electrolyte balance. To investigate whether ANF may play a role in central cardiovascular regulation, the effects of microinjection of ANF into the preoptic suprachiasmatic nucleus (POSC), which is located in the AV3V region of the brain, were examined in the present study. Low doses of ANF (2-4 pmol) produced modest elevations in systolic and diastolic pressures, approximately 10-14%, and a small rise in HR of roughly 7%. Higher doses of ANF (20-40 pmol) produced significant increases in systolic (15-19%), mean arterial (12-14%) and pulse (25-36%) pressures. In addition, much larger increases in HR, approximately 20%, were produced by these higher doses of ANF. The onset of effects produced by ANF on BP and HR was seen 15-45 min after injection. Peak effects were usually observed approximately 60-150 min after onset, and the duration of the effect was 2-4 hours, after which time values usually returned to baseline. These studies indicate that ANF produces significant increases in BP and HR when injected at pmol doses into the POSC, and lends support to the idea that this peptide may play an important role in central cardiovascular regulatory mechanisms.

Effects of clonidine, alpha-methyldopa and hydralazine on met-enkephalinergic neurons in cerebral nuclei of spontaneously hypertensive rats

Immunocytofluorescent and microautoradiographic methods were applied to measure met-enkephalin-like immunoreactivity (MELI) and ME receptor binding (MERB) levels in cerebral nuclei of serial brain slices from SHR which received clonidine, alpha-methyldopa and hydralazine at equivalent hypotensive doses. All three drugs increased both MELI and MERB levels in the caudal part of the n. tractus solitarii and its functionally related dorsomedullary nuclei and decreased them in the n. accumbens septi, in accordance with the correspondent change in glucose utilization rates in these nuclei as reported previously. Both CNS-active agents (not hydralazine) also increased MELI and MERB levels in the n. intercalatus and substantia grisea centralis, and they decreased them in the n. ventromedialis hypothalami. Differences in both CNS-active agents were minor. Vasodilative hydralazine alone decreased these levels both in the n. reticularis medialis and n. tegmenti ventralis, and it increased them slightly in the area lateralis hypothalami. The present studies indicate that ME neurons of these dorsomedullary and supramedullary nuclei may act as direct as well as homeostatic controls of blood pressure.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents: II

This survey begins a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1978, but data from many earlier papers are also tabulated.

Cardiovascular effects produced by injections of thyrotropin-releasing hormone in specific preoptic and hypothalamic nuclei in the rat

Microinjection of 1.4 pmol TRH (0.5 ng; 50-150 nl) into both the preoptic suprachiasmatic nucleus (pos) and the A7000-6800 region of the medial preoptic nucleus (pom) produced increases in blood pressure and heart rate of 7% and 19%, respectively; heart rate responses in these two areas were higher than those occurring in other areas tested. TRH induced a significant increase in blood pressure and heart rate in the posterior hypothalamic nucleus (nhp) and increased heart rate only in the anterior (nha) and dorsomedial (ndm) hypothalamic nuclei. A small decrease in both blood pressure and heart rate resulted with TRH injections in the A7400-7050 region of the pom. No changes in respiratory rate or rectal temperature were observed at any site with this dose of TRH. Preliminary studies into the mechanism of the cardiovascular actions of TRH suggested that inhibition of the parasympathetic nerves to the heart make a partial contribution to the TRH-induced heart rate increase in the pos and that adrenal catecholamine release mediates the TRH response in the nhp. Neither methylatropine pretreatment nor adrenalectomy prevented the response to TRH injected into the nha, suggesting that activation of the cardiac sympathetic nerves may mediate TRH actions in this region. In the ndm, neither methylatropine nor adrenalectomy prevented the response to TRH; however, there was a tendency for the response to be less after methylatropine. Therefore, both inhibition of the parasympathetic and activation of the sympathetic nervous systems may contribute to the response observed, but no adrenal involvement could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of adrenalectomy, propranolol and methylatropine on the increase in heart rate induced by injection of dermorphin in the rat anterior hypothalamic nucleus

Anterior hypothalamic injections of 40 pmol dermorphin, a potent opiate receptor agonist, increased heart rate 17% and had no effect on blood pressure in halothane-anesthetized rats. Administration of the beta-receptor antagonist, propranolol, during the peak response to dermorphin, reduced the heart rate to levels not different from pretreatment control; pretreatment with propranolol completely blocked the tachycardia produced by a subsequent injection of dermorphin. In contrast, neither adrenalectomy nor pretreatment with methylatropine altered the response to dermorphin. These data suggest that increased activity of the sympathetic nervous system, primarily to the heart, and not increased release of adrenal catecholamines or inhibition of parasympathetic nervous system activity, is responsible for the increase in heart rate resulting from injection of dermorphin into the anterior hypothalamic nucleus.