L. Cass Terry

Cocaine: evidence for supraspinal, dopamine-mediated, non-opiate analgesia

Cocaine (25 mg/kg i.p.) produces analgesia in the rat within 5 min and for a duration of 90 min as determined by the formalin test or for 30 min as determined by the hot plate test. Cocaine analgesia is unaffected by doses of naloxone that are sufficient to attenuate morphine analgesia in both tests. Chlorpromazine (3 mg/kg i.p.), SCH 23390 (100 micrograms/kg i.p.; a D1 dopamine receptor antagonist), and eticlopride (75 micrograms/kg i.p.; a D2 dopamine receptor antagonist) each attenuate cocaine analgesia in both tests at doses that alone do not affect performance in either test. Measurements of blood pressure and heart rate indicate that cocaine analgesia is not due to the activation of baroreceptor reflex afferents. We conclude that cocaine is a supraspinally acting, dopamine-mediated, non-opiate analgesic in the rat.

Immunocytochemical localization of cathepsin D in rat neural tissue.

The localization of cathepsin D (CD) in normal adult rat neural tissue was determined with an indirect immunoperoxidase technique utilizing rabbit anti rat brain CD followed by a horseradish peroxidase conjugate of the Fab portion of goat antirabbit IgG. The immunoreactive enzyme protein was distributed predominantly in a granular pattern, presumably lysosomal, in neurons and choroid plexus epithelium. Smaller amounts were detected in oligodendrocytes and ependymal cells. The neuronal localization included the perikaryon and its processes, was widely distributed, and displayed a range of staining intensities in different anatomical areas. Immunoreactive CD was heavily concentrated in brain stem and spinal cord motoneurons, large neurons of the caudate nucleus, neurons of several nuclear groups, especially the paraventricular and supraoptic, in the hypothalamus, and neurons of superior cervical and dorsal root ganglia. CD was also readily detected in brain stem sensory neurons, pyramidal cells of the hippocampus, inferior olive and Purkinje cells, but was absent or present in very small quantities in the granule cells of the cerebellar cortex, the more superficial layers of the neocortex, and smaller neurons of the caudate nucleus. This distribution suggests that CD may have a major role in specific chemical events in neural functions and peptidergic pathways and could be involved in the alterations of certain neural structures in disease states.

Role of central epinephrine in regulation of anterior pituitary hormone secretion

Hypothalamic regulation of anterior pituitary hormones is thought to be mediated by the release of stimulatory and/or inhibitory peptides that are, in turn, regulated by catecholaminergic neurons. The recent development of selective epinephrine (EPI) synthesis inhibitors has made it possible to disrupt central EPI neurotransmission without affecting norepinephrine or dopamine. These compounds were used in the present investigation to assess the involvement of brain EPI systems in regulation of GH, LH, and prolactin (PRL) in male and ovariectomized female rats. Inhibition of central EPI synthesis (1) inhibited episodic and morphine-, but not clonidine-induced GH release, and (2) blocked the LH surge induced by estrogen and progesterone, but did not affect episodic LH release in hormonally untreated rats. Inhibition of peripheral (adrenal) EPI synthesis had no effect on these hormones. Results of these studies suggest an excitatory role for EPI in regulation of GH and LH secretion, mediated by stimulation of GH-releasing hormone and LHRH, respectively. EPI does not appear to have a major function in regulation of PRL secretion.

Dopamine D-1 and D-2 Receptor Antagonists Potentiate Analgesic and Motor Effects of Morphine

To examine the role of dopamine receptor subtypes mediating analgesic and motor responses to opioids, rats were pretreated with either saline or a selective D-1 or D-2 dopamine receptor antagonist 10 min prior to morphine (12 mg/kg IP). Analgesic response latency was determined using the hot plate test (52.5 degrees C and 55 degrees C), and catalepsy was assessed using the abnormal posture test. Morphine increased analgesic response latency to 44.5 +/- 7.9% of the maximum possible response, but had no cataleptic effect in the abnormal posture test. Pretreatment with either the D-1 antagonist, SCH 23390 (50-100 micrograms/kg), or the D-2 antagonist, eticlopride (20-150 micrograms/kg), potently enhanced morphine analgesia as measured on the 52.5 degrees C hot plate. Peak analgesic responses to morphine increased to 100 +/- 0% and 91.9 +/- 7.5% of maximum with the highest doses of SCH 23390 and eticlopride, respectively. These treatments also produced catalepsy. Increasing the hot plate temperature to 55 degrees C reduced response latency in groups treated with either dopamine receptor antagonist plus morphine. This indicates that the animals were capable of responding at a shorter latency and demonstrates that motor impairment cannot account for potentiation of morphine analgesia by D-1 and D-2 antagonists at 52.5 degrees C. These results show that the relationship between dopamine and opioids with respect to analgesic and motor systems involves both dopamine receptor subtypes.

Regulation of Episodic Growth Hormone Secretion by the Central Epinephrine System STUDIES IN THE CHRONICALLY CANNULATED RAT

Catecholamines are postulated to regulate growth hormone (GH) secretion by their influence on the release of two hypothalamic substances, somatostatin, which inhibits GH release, and GH-releasing factor, as yet unidentified. Extensive pharmacologic studies in man and animals indicate a stimulatory effect of central norepinephrine and dopamine on GH, but the function of epiphephrine (EPI) is uncertain. Furthermore, many of the agents used to study the role of catecholamines in GH regulation are not selective in that they affect adrenergic as well as nor-adrenergic and/or dopaminergic neurotransmission. In the present investigation, central nervous system (CNS) EPI biosynthesis was selectively interrupted with the specific norepinephrine N-methyltransferase inhibitors, SK & F 64139 (Smith, Kline & French Laboratories) and LY 78335, (Eli Lilly & Co. Research Laboratories) and the effects of central EPI depletion on episodic GH secretion in the chronically cannulated rat model were determined. Inhibition of CNS EPI synthesis with SK & F 64139 caused complete suppression of episodic GH secretion and concomitantly reduced the EPI level in the hypothalamus without affecting dopamine or norepinephrine. Administration of LY 78335 produced similar effects on pulsatile GH. Morphine-induced, but not clonidine-induced, GH release also was blocked by SK & F 64139. These results indicate that (a) the central EPI system has a major stimulatory function in episodic GH release, (b) morphine-induced GH release is mediated by the central EPI system, and (c) clonidine stimulates GH release by activation of postsynaptic alpha-adrenergic receptors. Drugs that affect CNS adrenergic systems have a potential role in the diagnosis and treatment of disorders of GH secretion.

Clearance of Immunoreactive Somatostatin by Perfused Rat Liver

Other investigators have demonstrated that concentrations of immunoreactive somatostatin (IRS) are higher in blood from the hepatic portal vein or its tributaries than in blood from the hepatic or peripheral systemic veins of man and animals. This suggests that there is hepatic extraction of IRS from the portal system in vivo. In the rat, portal vein plasma IRS is reported to be heterogeneous and to contain, in part, a 1,600 mol wt form of IRS which is immunochemically similar to synthetic somatostatin and not significantly bound to high molecular weight plasma protein. Our study was undertaken to determine directly whether unbound synthetic cyclic somatostatin was cleared by the rat liver perfused through the hepatic portal vein in vitro with a recirculating, plasma-free, erythrocyte-containing perfusate. At 37 degrees C and pH 7.40, perfusate IRS, at initial concentrations (1,728 pg/ml) within the range previously reported in rat portal venous blood, was removed by the liver at a rate commensurate with first-order kinetics. Hepatic clearance was 0.84+/-0.04 ml/min per g postperfusion wet weight (SE). Hepatic extraction was 36+/-2%, and t((1/2)) was 20.0+/-1.3 min. Recovery of IRS from the perfusate without the liver was >85%, excluding significant degradation by the medium. Clearance, extraction, and t((1/2)) of IRS were not changed by an unphysiologic IRS concentration (621,500 pg/ml), or by pharmacologic concentrations of insulin (8.2 muM) or glucagon (2.9 muM). The t((1/2)) was prolonged significantly to 28.2+/-1.9 and 45.6+/-4.7 min during perfusions at liver temperatures of 25 degrees and 16 degrees C, respectively. At 37 degrees C, the t((1/2)) was also significantly increased to 28.7+/-3.2 and 24.2+/-1.1 min at perfusate pH 7.06 and 6.78, respectively. These studies indicate that the rat liver clears unbound IRS from the perfusate by a first-order kinetic process that is (a) unsaturable at pharmacologic concentrations, (b) temperature-sensitive and, to a lesser extent, influenced by lowered pH, and (c) not affected by insulin and glucagon. The liver would appear to play an important role in the metabolism of the 1,600 mol wt form of somatostatin. Clearance of endogenous IRS by the liver should be considered in the interpretation of IRS concentrations in the peripheral systemic veins.

Differential effects of chronic partial myelotomies on monoamine levels in cat spinal cord

The concentrations of 5-hydroxytryptamine (5-HT), norepinephrine (NE) and dopamine (DA) were measured in samples of lumbar and cervical spinal cords from 6 cats with chronic (over 2 months) lesions of the thoracic spinal cord and from 7 unoperated cats. Lesions confined to the dorsal thoracic spinal cord significantly lowered lumbar concentrations of NE, but not 5-HT, compared with control lumbar or matched paired cervical samples. Both NE and 5-HT were significantly reduced by dorsal or ventral lesions that involved tissue ventral to the central canal. Only the largest lesion could be shown to reduce lumbar DA concentration.

A dilutional microassay for serum ionized calcium using ion-selective electrodes☆

Abstract A microassay for serum ionized calcium was developed and characterized with commercially available instrumentation that employs conventional electrochemical, ion-selective electrode, methodology. The microassay consists of diluting serum with an appropriate concentration and volume of tris(hydroxymethyl)aminomethane at physiological pH and ionic strength. The diluent was capable of buffering serum throughout the normal and pathologic ranges of pH and the performance characteristics of the microassay were independent of serum protein concentration. An application of the method is provided and the results support the view that calcium may be involved in cysteamine-induced attenuation of episodic growth hormone secretion in male rats.