192

results in receptor phosphoryla- tion at tyrosine, serine and threo- nine residues. Thus, the EGF- receptor may be susceptible to the action of three protein kinases, i.e. its own kinase activity, protein kinase C and a kinase modulated by the cAMP-dependent kinase or this latter itself. The biological significance of these covalent modifications of the EGF receptor is not yet clear. Interestingly, however, vasopressin s and plate- let-derived growth factor 9 also decrease the affinity of the EGF receptor.

A stimulatory action of insulin on insulin-like growth factor II- binding, in isolated adipocytes, has been shown by several groups. Oppenheimer et al. 1° observed that the stimulatory action of insulin, on insulin-like growth factor II, is associated with a 60% increase in the concentration of receptors in the plasma membrane with a concomitant 40% decrease in the receptor density in the micro- somes. In an elegant study, Ward-

azala et al. 11 showed that such changes in receptor density in the different cell fractions are due to receptor recycling. Interestingly, these insulin-induced changes in the steady state distribution of insulin-like growth factor recep- tors between the intraceUular pool and the plasma membrane are similar to those produced by insulin on the glucose transport system. It is also noteworthy that in other models, activation of protein kinase C by phorbol di- esters induces hyperphosphoryla- tion and reversible regulation of the number of transferrin mem- brane receptors, probably involv- ing receptor cycling, between dif- ferent cell compartments 12 .

J. ADOLFO GARCIA-SAINZ

Departamento de Bioenergdtica, Centro de Investigaciones en Fisiologfa Celular, Univer- sidad Nacional Aut6noma de Mdxico. 04510, M~xico, DF.

References 1 Sibley, D. R., Nambi, P., Peters, J. R. and

Lefkowitz, R. J. (1984) Biochem. Biophys.

TIPS - M a y 1985

Res. Commun. 121, 973-979

2 Stader, J. M., Nambi, P., Shorr, R. G. L., Sawyer, D.F., Caron, M.G. and Lefkowitz, R.J. (1983) Proc. Natl Acad. Sci. USA 80, 3173-3177

3 Pessin, J.E., Gitomer, W., Oka, Y., Oppenheimer, C. L. and Czech, M. P. (1983) J. Biol. Chem. 258, 7386-7394

4 Arner, P., Hellmer, J., Ewerth, S. and Ostman, J. (1984) Biochem. Biophys. Res. Commun. 122, 97-102

5 Davis, R. J. and Czech, M. P. (1984) J. Biol. Chem. 259, 8545--8549

6 Cochel, C., Gill, G. N., Meisenhelder, J., Cooper, J. A. and Hunter, T. (1984) J. Biol. Chem. 259, 2553-2558

7 Iwashita, S. and Fox, C. F. (1984) J. Biol. Chem. 259, 2559-2567

8 Rozengurt, E., Brown, K.D. and Pettican, P. (1981) J. Biol. Chem. 256, 716- 722

9 CoUin, M. K. L., Sinnett-Smith, J. W. and Rozengurt, E. (1983) J. Biol. Chem. 258, 11689-11693

10 Oppenheimer, C. L., Pessin, J.E., Massague, J., Gitomer, W. and Czech, M. P. (1983) J. Biol. Chem. 258, 4824-4830

11 Wardzala, L. J., Simpson, I. A., Rechler, M. M. and Cushman, S. W. (1984) Biol. Chem. 259, 8378-8383

12 May, S. W., Jacobs, S. and Cuatrecasas, P. (1984) Proc. Natl Acad. Sci. USA 81, 2016-2020

Opioid--catecholamine and opioid- cholinergic interactions in memory regulation

Post-training administration of opiate receptor blockers, the best studied of which is naloxone, enhances memory of many aver- sive and non-aversive behaviors. This effect was originally describ- ed more or less simultaneously by Gallagher, McGaugh and by our group six years ago (see Refs 1-3); it was later confirmed in 13 laboratories from five different countries s tudying 23 different tasks in at least four different species, including man (see Refs 1, 3, 4). The administration of opioid peptides, the best studied of which is 13-endorphin, usually produces an opposing effect (retrograde am- nesia), and there is reason to be- lieve that the facilitatory influence of naloxone on memory is due to an antagonism of endogenous 13- endorphin released in the brain during training 2,4,5,6.

13-Endorphin-containing fibers originate in the medial basal hypothalamus and project to peri- ventricular structures, to the amy- gdala, the medial septal area, and to the locus coeruleus. These areas

include noradrenergic and cholin- ergic fiber terminals. Early studies have suggested that 13-endorphin and naloxone exert their influences on memory primarily by inhibit- ing and disinhibit ing brain cate- cholaminergic synapses, respec- tively. It has been shown that the post-training effect of naloxone is blocked by concomitant adminis- tration of haloperidol or propra- nolol, or pretreatment with (x- methyl p-tyrosine 2, 6-hydroxy- dopamine 1, or DSP-46. These data were consistent with findings showing inhibitory influences of endogenous opioids on catechol- aminergic terminals or on the cell bodies of the noradrenergic neur- ons of the locus coeruleus (see Refs 1, 2).

However, Baratti and his group have produced recent evidence showing that central cholinergic muscarinic systems may also be involved in the post-training ac- tion of naloxone 5 and ~-endor- phin 6,7 on memory processes. The memory facilitation of a one-trial inhibitory avoidance task caused

by naloxone in mice is antagoniz- ed by i.p. administration of atro- pine but not methylatropine, mec- amylamine or hexamethonium. Further, there is mutual potentia- tion of the enhancing effects of naloxone and the muscarinic agon- ist oxotremorine. The effect of oxotremorine is not antagonized by morphine, suggesting that opioid systems affect cholinergic systems and not vice versa 5. The memory impairment caused by ~- endorphin in the same task and species is prevented by oxotre- morine or by the centrally active anticholinesterase agent physo- stigmine, but is unaffected by neostigmine or hexamethonium 7.

The results obtained by Baratti and his coworkers are consistent with the large body of evidence suggesting a role for central cholin- ergic systems in memory processes (see Ref. 8); and when taken together with the previous obser- vations on interactions between opioid and catecholamine systems in memory regulation 1,2,6, point to the fact that memory, in all prob- ability, does not depend on the isolated operation of any single brain neurotransmitter system, but rather on the concerted func- tion of many such systems and of peripherally-acting hormones as weU 2-4. The design of suitable

~ 1985, Elsevier Science Publishers B.V., Amsterdam 0165-6147/85/$02.00

TIPS - M a y 1985

therapeut ic agents to alleviate am- nesic disorders will have to wai t unti l more is known about how these systems interact wi th one another, and what systems are pr imar i ly affected (if this were the case) in the many different forms of amnesia seen in man or even in laboratory animals 9.

I V A N I Z Q U I E R D O

Laboratorio de Neuroquimica, Departamento de Bioquimica, Instituto de Biociencias,

UFRGS (centro), 90000 Porto Alegre, RS, Brazil.

References 1 GaUagher, M. (1984) in Neurobiology of

Learning and Memory (Lynch, G., McGaugh, J.L. and Weinberger, N., eds), pp. 368-373, Guilford, New York

2 Izquierdo, I., Perry, M. L. S., Dias, R. D., Souza, D. O., Elisabetsky, E., Carrasco, M. A., Orsingher, O. A. and Netto, C. A. (1981) in Endogenous Peptides and Learn- ing and Memory Processes (Martinez, J. L. Jr, Jensen, R., Messing, R. B., Rigter, H. and McGaugh, J. L., eds), pp. 269-290, Academic Press, New York

193

3 McGaugh, J. L. (1983) Ann. Rev. Psychol. 34, 297-323

4 McGaugh, J. L. and Gold, P. E. (1985) in Psychoendocrinology (Levine, S. and Brush, F. R., eds), (in press), Academic Press, New York

5 Baratti, C. M., Introini, I.B. and Huygens, L. (1984) Behav. Neurol. Biol. 40, 155-169

6 Introini, I. B. (1984) PhD Thesis, Univer- sity of Buenos Aires

7 Introini, I. B. and Baratti, C. M. (1984) Behav. Neurol. Biol. 41, 152-163

8 Davies, P. (1985) Ann. N.Y. Acad. Sci., (in press)

9 Izquierdo, I. (1984) Trends Pharmacol, Sci. 5, 493-494

This and that: ruminations on stress, pitfalls and pressure

THE S P O N T A N E O U S L Y h y p e r t e n s i v e (SH) ra t d e r i v e d b y O k a m o t o has b e c o m e a w i d e l y u s e d m o d e l in r e s e a r c h on h y p e r t e n s i o n . Th i s is p r i m a r i l y b e c a u s e , d e s p i t e e x t e n s i v e s t u d y , w e k n o w as l i t t le of t he c a u s a t i o n of h y p e r t e n s i o n in t he S H rat as w e d o of e s s e n t i a l h y p e r t e n s i o n in h u m a n s .

The SH rat is normotens ive at birth. After the first month of life, however, blood pressure slowly climbs, reaching or exceed- ing 220 rnm Hg systolic. An int r iguing but unexplored aspect of the model is that the heart to body weight ratio is significantly elevated from birth, compared to normotens ive Wistar rats.

Wright and McCumbee 7 have now reported the isolation of a dialysable substance from ery- throcyte membranes of SH rats which raises blood pressure on injection into normotens ive rats. Systolic pressure rose some 20-30 mm Hg, the increase pers is t ing for 18 days following the last injec- tion. A complication, however,

was that the sal ine-injected con- trols also showed a transient but significant elevation of blood pressure.

The substance also increased the uptake of calcium by aorta from normotensive rats. Vascular smooth muscle from SH rats takes up calcium more readily than smooth muscle from normoten- sive rats, so this action of the dialysate may provide a clue to the mechanism of b lood pressure ele- vation. Again, however, interpre- tation is complicated by the find- ing that erythrocyte membrane preparat ions from normotensive Wistars also s t imulated aortic cal- cium uptake, albeit to a lesser degree.

These f indings are intr iguing. They would be more so if such reports could range beyond more phenomenology and give some indicat ion of the chemical natures of the humoral agents involved. It has, after all, already been re- ported that pups from normoten- sive dams suckled by SH dams develop elevated blood pressure, suggest ing that a humoral agent secreted into the milk may be responsible. Is the agent ther- mostable? How long can it be left on the bench wi thout activity being lost? How about enrich- ment by chromatography, using calcium uptake as a bioassay, and UV spectroscopy? How about GC- MS on an enriched sample? Is it fair to whet our appeti tes with a whiff of the cooking from the kitchen, leaving us to guess what is on the menu? Purine supreme? Catechol surprise? Pept ide pie? Even heavy metal goulash?

T H E URINE of d o m e s t i c a t e d a n i m a l s has p r o v e d a c o r n u c o p i a of c h e m i c a l t r ea su re s . A n d r o s t e r o n e , t e s t o s t e rone , a n d e s t r o n e are a f ew of t he m o l e c u l a r p u z z l e s c h e m i s t s h a v e f i s h e d ou t of t h i s r e n e w a b l e f lu id for t h e i r p r o f e s s i o n a l de l ec t a t ion .

The t radi t ion continues. 'Diaze- pam-l ike ' compounds have now been isolated from bovine ur ine 1, perhaps accounting for the placid nature of the beast. The authors are to be congratulated for the com- pleteness of their investigations. Not only were structures der ived for all compounds , but those prov- ing to be novel were verif ied by synthesis . Three compounds ex- h ib i t ing activi ty in a benzodiaze- p ine receptor b ind ing assay were shown to be isoflavans. One, equo| , had been previously iso- lated t c o m mare 's urine, but the other two were novel; 3 ' ,7-dihv-

droxyisoflavan and 4 ' -hydroxy-7- methoxyisof lavan (Fig. 1). These compounds had approximate ICs0 in the 10-sM range, 3--4 orders of magni tude less than diazepam

itself. A fourth compound enhanced

the b ind ing of diazepam. This compound was a chlorocarbazole (Fig. 2). At 1raM, the carbazole almost doubled the b ind ing of d iazepam. The authors claim this is the first isolation of a carbazole from a mammal ian source.

The authors also isolated two

R2

R30

Fig. 1. Novel diazepam-like compounds in bovine urine.

R~ = H; R2 = OH; R3 = H: 3',7-dihydroxyisoflavan

R1 = OH; R2 = H; R3 = CH3: 4"-hydroxy-7-methoxyisoflavan

~) 1985, Elsevier Science Publishers B.V., Amsterdam 0165 - 6147/85/$02.00