Molecular mechanisms of pain: serotonin1A receptor agonists trigger transactivation by c-fos of the prodynorphin gene in spinal cord neurons

By using spinal cord neurons cultured in chemically defined medium, a double labeling procedure, and blockage with antisense oligonucleotides, we show that induction of c-fos and the subsequent transactivation of the prodynorphin gene are coupled events, triggered by serotonin1A receptor agonists. Addition of the specific 1A agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) to the culture, at concentrations similar to that needed for transactivation of the prodynorphin gene, also significantly increases cAMP levels. Furthermore, in rats depleted of serotonin by intrathecal administration of 5,7-dihydroxytryptamine, the induction of prodynorphin after noxious stimulation is dramatically decreased compared with the induction in sham-operated rats. These results suggest that the expression of the prodynorphin gene in spinal cord is under the control of the raphe-spinal efferents containing serotonin.

Transcriptional response to cAMP in brain: specific distribution and induction of CREM antagonists

Changes in cAMP levels are often associated with the modulation of neuronal function. The CREM gene encodes both antagonists and activators of the cAMP-dependent transcriptional response by alternative splicing. CREM transcripts in rat brain show a characteristic pattern of expression, being specific for the inner layer of the cerebral cortex, anterior thalamus, hippocampus, and hypothalamus. Strikingly, the CREM transcripts correspond to the antagonist isoforms in these areas, suggesting a down-regulatory role for CREM in brain; in contrast, the expression of CREM tau and CREB activators is more diffuse and generalized. In the supraoptic nucleus, CREM expression is induced after osmotic stimulus. Importantly, this demonstrates physiological inducibility of CREM, which is novel within the CRE/ATF family.

Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons

This study has analysed by immunocytochemistry the pattern of expression of Fos-related proteins, as well as variations in nuclear size, after the osmotically induced activation of supraoptic nucleus neurons of the rat. In control rats most supraoptic nucleus neurons were Fos-like negative. After acute and chronic dehydration by salt-loading, the number of Fos-like positive neurons increased dramatically. The level of Fos-like immunoreactivity was higher in chronically stimulated rats, and also the neurons of the ventral region of the supraoptic nucleus were more intensely stained than those of the dorsal region. The karyometric analysis was made on electron micrographs. The mean nuclear profile area showed a significant increase in dehydrated rats with respect to the controls (73 +/- 16 microns 2 in those dehydrated for six days vs 54 +/- 13 in controls, mean +/- S.D.). However, no significant differences in this parameter were found when one-day and six-day dehydrated groups were compared. The invagination factor of the nuclear membrane, a nuclear shape indicator, decreased significantly in dehydrated rats, indicating a tendency towards spherical nuclei. It is noteworthy that the nuclear profile perimeter was constant, about 32 microns, in control and osmotically simulated rats. The higher nuclear accumulation of Fos-related antigens after six days of dehydration suggests that in chronically stimulated supraoptic nucleus neurons there is a sustained induction of cell-specific genes. Moreover, the transcription rate of the target genes containing the consensus DNA sequence TGAC/GTCA or c-AMP responsive elements recognition sites may depend upon the nuclear concentration of Fos-related antigens in supraoptic nucleus neurons. Our results also suggest that the initial Fos-related antigen expression and nuclear size increase are triggered concomitantly in supraoptic nucleus neurons after a short period of osmotic stimulation. On the other hand, we propose that nuclear envelope invaginations represent a reservoir of nuclear membrane which allows dynamic changes in nuclear size and shape depending on the metabolic status of the supraoptic nucleus neurons.

Narine occlusion decreases basal levels of Fos protein in the cerebral cortex of the lizard Podarcis hispanica

Immunocytochemical study of cerebral cortex of the lizard Podarcis hispanica using an antibody directed to the M peptide of the rat c-Fos protein showed a distinct pattern of Fos distribution. Abundant Fos-immunoreactive neuronal nuclei were detected in the cell layers of the medial, the dorsal and the lateral cortices, whereas only a few nuclei were found in the cell layer of the dorsomedial cortex. The Fos immunoreactivity was characterized by Western blot analysis of nuclear extracts from lizard brain and showed a distinct band with an apparent molecular weight of 30,000. In band-shift assays, nuclear extracts from lizard brain were shown to contain AP-1 complexes. The basal expression of Fos immunoreactivity is related to sensory olfactory input in the cerebral cortex of the lizard since experiments with olfactory-deprived animals resulted in a complete absence of Fos immunoreactivity in the cortical areas.

Differential expression of the jun family members in rat brain

The transcription factor AP-1 is phorbol ester-regulated and, as such, is considered to be a nuclear target of the signal transduction pathway involving protein kinase C. AP-1 is constituted by the various products of the jun and fos gene family members. These genes belong to the early response class and are inducible in different ways by growth factors, phorbol esters and depolarization. We studied the transcript distribution of c-jun, junB and junD in the rat brain. Our results show that the transcripts for these three genes are differentially distributed in various neuronal tissues. We also provide evidence for developmentally regulated expression of jun genes in post-natal brain. The spatiotemporal pattern of expression of c-jun, junB and junD offers clues to the understanding of the links between gene regulation and neuronal processes.

Independent expression of the alpha and beta c-erbA genes in developing rat brain

Thyroid hormone is important for normal brain development. Cellular responses to thyroid hormone are mediated by multiple nuclear receptors, classified into alpha- and beta-subtypes. In the rat, expression of both the alpha and beta genes results in several translation products. By using cRNA probes common to alpha transcripts or specific for alpha-1 and beta-1, we have studied the distribution of these transcripts in rat brain at different stages of development from embryonic day 14 to adult age by using in situ hybridization histochemistry. On embryonic day 14, the alpha-1 mRNA is already widely expressed at a low level in the developing brain. The alpha-1 mRNA is developmentally regulated and showed a peak in expression during the first 3 postnatal weeks in the cerebral cortex, amygdala, hippocampus, and cerebellum. The probe common to the alpha transcripts detected a widespread distribution and high levels of these forms in the same regions throughout postnatal development. The level of beta-1 mRNA before birth was low or undetectable. The beta-1 transcript showed developmental regulation as well, with a high level at birth in the mitral cell layer of the olfactory bulb, accumbens nucleus, caudate, and hippocampal field CA1 and increasing levels in other regions later during development. Complementary expression of the alpha and beta forms was seen in the cerebral cortex and hippocampus. The differential temporal and spatial distribution as well as coexpression at comparable levels in certain brain regions suggest different roles for the c-erbA proteins during brain development and in the mature animal.

Uncoupled changes in the expression of the jun family members during myeloid cell differentiation

The differentiation into macrophages of the U937 and HL60 human cell lines induced by 4 beta-phorbol 12-myristate 13-acetate (PMA) was accompanied by induction of the expression of the proto-oncogenes c-jun, jun B and jun D. However, expression of the three jun genes was regulated differently during induction of cell differentiation in both U937 and HL60 cells, with the three jun family members being expressed distinctly at different stages of cell differentiation. Whereas jun B transcription was strongly stimulated following treatment with PMA for 30 min, jun D mRNA levels were only increased 6 h after PMA treatment and the content of c-jun mRNA was elevated maximally only 24 h after PMA treatment. The rapid induction of the jun B mRNA level suggests a putative role for this proto-oncogene in the early triggering step of U937 and HL60 cell differentiation induced by PMA. Interestingly, a weak induction of jun B and jun D mRNA levels, but no induction of the c-jun mRNA level, was detected during Me2SO-induced granulocytic HL60 differentiation. These data suggest a different role for each jun proto-oncogene in regulating gene activity and that different transcriptional complexes involving distinct jun proto-oncogenes can be formed during macrophage and granulocytic differentiation.

Molecular pathways of pain: Fos/Jun-mediated activation of a noncanonical AP-1 site in the prodynorphin gene

Noxious stimulation provokes the activation of genes that are thought to play a crucial role in the phenomena of stress and pain. Among these is the prodynorphin gene. By double-labeling in situ hybridization/immunohistochemistry, we show that increased prodynorphin gene expression is preceded, in the same neurons, by an early induction of c-fos. Inspection of the prodynorphin promoter region revealed the presence of several AP-1-like sequences. We demonstrate that only one of these sites is a functional AP-1 element. It is constituted by the noncanonical TGACAAACA sequence, in which the palindromic structure is partly conserved by the 3' terminal CA dinucleotide. Transfection experiments in NCB20 neuroblastoma cells indicated that this site is a target of Fos/Jun trans-activation. Our results suggest that Fos/Jun oncoproteins may function as third messengers in the signal transduction mechanisms of stress/pain processes.

Transient expression of c-fos during the development of the rat cerebral cortex

The present study has explored with immunocytochemical methods the expression of the proto-oncogene c-fos during the pre- and postnatal development of the cerebral cortex of the rat. The immunostaining of the Fos protein follows a strikingly precise spatiotemporal pattern: it occurs uniquely within layer VIb of the developing cerebral cortex, and is transient, lasting only from embryonic day 20 until postnatal day 1. The expression of c-fos in layer VIb may be related to the dynamic changes that occur at this level during development.

Co-induction of jun B and c-fos in a subset of neurons in the spinal cord

Noxious stimulation in vivo provokes the transcriptional activation of several genes which are thought to play an important role in the phenomena of stress and pain. In the rat, the expression of the c-fos proto-oncogene is rapidly induced upon noxious stimulation in defined neurons in the dorsal horn of the spinal cord. Interestingly, expression of the prodynorphin gene, which is thought to be involved in the endogenous mechanisms for pain/stress control, also localizes in the same anatomical area. Fos proteins are known to associate in transcriptional complexes with the products of the jun family constituting nuclear factor AP-1. These considerations prompted us to analyse the expression of the jun gene family members c-jun, jun B and jun D in rats subjected to noxious stimulation. We present data indicating that in unstimulated animals the transcripts of the three genes are differentially expressed and abundant within the various laminas of the lumbar spinal cord. Surprisingly, upon stimulation only the jun B transcript is augmented, being co-localized with Fos in a subset of neurons of the medial dorsal horn.

Expression of c-jun, jun B and jun D proto-oncogenes in human peripheral-blood granulocytes

We have found that purified human peripheral-blood granulocytes express constitutively significant levels of proto-oncogenes c-jun, jun B and jun D mRNA. Upon functional activation of granulocytes by 4 beta-phorbol 12-myristate 13-acetate (PMA), the levels of c-jun, jun B and jun D transcripts were increased. The three jun genes showed a similar time course in their induction by PMA, maximal mRNA levels being reached after 60 min of induction. These results suggest that expression of c-jun, jun B and jun D genes might be involved in terminal granulocyte differentiation or in regulating granulocyte functionality.

Expression of the prodynorphin gene in the developing and adult cerebral cortex of the rat: an in situ hybridization study

A population of cortical neurons contains the opioid peptide dynorphin; the laminar distribution of these neurons in the adult cerebral cortex and their patterns of development are not well known. We have utilized in situ hybridization techniques to localize prodynorphin mRNA-containing neurons. Rats aged from embryonic day (E) 15 through postnatal day (P) 90 were used. Prenatal animals did not show any labeling in the cerebral cortex. By P4, prodynorphin was expressed in a small number of cortical neurons for the first time. The autoradiographic signal was restricted to perikarya. In the frontoparietal cortex, labeled neurons first appeared in layer V and the upper part of layer VI. Subsequently, from P11 onward, the band expanded in an "inside-out" sequence to include layers IV through II. In the posterior cingulate cortex and in the insular and perirhinal cortices, prodinorphin mRNA containing-neurons were located preferentially in layer V. In all cortical areas analyzed, a progressive increase in the packing density of neurons expressing prodynorphin mRNA was observed until P14; it decreased slightly thereafter.

PC12 cells differentiate into chromaffin cell-like phenotype in coculture with adrenal medullary endothelial cells

Previously we described specific in vitro interactions between PC12 cells, a cloned, catecholamine-secreting pheochromocytoma cell line derived from the rat adrenal medulla, and bovine adrenal medullary endothelial cells. We now demonstrate that these interactions induce the PC12 cells to acquire physical and biochemical characteristics reminiscent of chromaffin cells. Under coculture conditions involving direct cell-cell contact, the endothelial cells and the PC12 cells reduced their rates of proliferation; upon prolonged coculture PC12 cells clustered into nests of cells similar to the organization of chromaffin cells seen in vivo. Within 3 days in coculture with endothelial cells, but not with unrelated control cells, PC12 cells synthesized increased levels of [Met]enkephalin. In addition, PC12 cells, growing on confluent endothelial monolayers, failed to extend neurites in response to nerve growth factor. Neither medium conditioned by endothelial cells nor fixed endothelial cells could by themselves induce all of these different phenomena in the PC12 cells. These results suggest that under coculture conditions PC12 cells change their state of differentiation toward a chromaffin cell-like phenotype. The rapid, transient increase in the expression of the protooncogene c-fos suggests that the mechanism(s) inducing the change in the state of differentiation in PC12 cells in coculture with the endothelial cells may be distinct from that described for the differentiation of PC12 cells--e.g., by glucocorticoids. We propose that similar interactions between endothelial cells and chromaffin cell precursors may occur during embryonic development and that these interactions might be instrumental for the organ-specific differentiation of the adrenal medulla in vivo.

Unusual c-fos induction upon chromaffin PC12 differentiation by sodium butyrate: loss of fos autoregulatory function

Induction of PC12 pheochromocytoma cells neuronal differentiation upon treatment with nerve growth factor (NGF) is accompanied by a coupled stimulation of c-fos and c-jun oncogene transcription. We found that induction of c-fos and c-jun proto-oncogene mRNAs levels following the endocrine differentiation of PC12 cells by sodium butyrate is uncoupled. While c-fos mRNA level increased within minutes, the content of c-jun mRNA was significantly elevated only 24 hours after treatment. Continuous presence of sodium butyrate for 72 hours resulted in stable high levels of c-fos and c-jun mRNAs. Gene transcription of the other members of the jun family, jun B and jun D, was not significantly modified at any induction time. The early accumulation of c-fos mRNA was accompanied by increased levels of c-Fos protein. While the NGF-induced c-Fos protein migrates with an apparent homogeneous molecular weight of 62 kDa, the sodium butyrate-stimulated Fos protein is of heterogeneous lower molecular weight. The different gel mobility of the Fos immunoreactive bands induced by sodium butyrate and the sustained Fos mRNA levels after induction suggested that the sodium butyrate-induced c-Fos protein could be non-functional in the autoregulation of the c-fos gene. Gel shift analysis showed unimpaired capacity of the butyrate-induced c-Fos protein to participate in the formation of transcriptional complexes with the Jun/AP-1 protein. However, transfection experiments indicate that the sodium butyrate-induced c-Fos protein is not able to negatively trans-regulate the c-fos promoter.

Expression of cholecystokinin and enkephalin mRNA in discrete brain regions

The levels of preprocholecystokinin mRNA were measured in several regions of rat brain using RNA blot analysis. In both species, high levels of expression were observed in the thalamus, amygdala, neocortical areas and hippocampus. Intermediate levels were observed in the periaqueductal grey, hypothalamus, substantia nigra, ventral tegmental area, and olfactory bulbs; little or no mRNA was detected in the caudate nucleus, nucleus accumbens, olfactory tubercle, cerebellum or a liver control. In contrast, the caudate and olfactory tubercle expressed large amounts of preproenkephalin mRNA. Other regions, such as the periaqueductal grey and olfactory bulbs, expressed both transcripts while regions like the hippocampus contained prominent amounts of preprocholecystokinin mRNA and relatively little preproenkephalin mRNA.

Involvement of spinal monoaminergic pathways in antinociception produced by substance P and neurotensin in rodents

The antinociceptive effects of substance P and of neurotensin have been determined in rodents after depletion of serotonin (5-HT) or noradrenaline (NA) in the spinal cord. The antinociceptive effect of substance P, given intraventricularly, in rats and mice was blocked after depletion of 5-HT in the spinal cord with the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) or with the inhibitor of the synthesis of 5-HT, p-chlorophenylalanine (PCPA), but not after depletion of NA in the spinal cord with the neurotoxin 6-hydroxydopamine (6-OHDA). Conversely, the antinociceptive effect of neurotensin in mice was blocked after lesion of spinal NA pathways with 6-OHDA. When 5-HT spinal pathways of mice were lesioned with 5,7-DHT, neurotensin-induced antinociception was blocked 7 but not 15 days after the lesion. p-Chlorophenylalanine failed to prevent this effect of neurotensin. The results suggest that the antinociceptive effect of substance P depends on the integrity of spinal 5-HT neurones, whereas that of neurotensin depends on spinal NA neurones and, only to a limited extent, on 5-HT neurones. It seems that different descending systems are involved in the antinociception elicited by these two neuropeptides.

Differential activation of spinal cord dynorphin and enkephalin neurons during hyperalgesia: evidence using cDNA hybridization

A unilateral experimental inflammation of the hindlimb produces hyperalgesia to both mechanical and radiant thermal stimuli that is rapid in onset. During this period, parameters of dynorphin biosynthesis are elevated to a much greater degree than those of the enkephalin system. An increase in the content of the peptide dynorphin A(1-8) occurs in the spinal cord segments that receive sensory input from the affected limb. This is accompanied by a rapid (within 24 h) and pronounced increase in the levels of mRNA coding for the dynorphin protein precursor. Maximum elevations (6- to 8-fold) of preprodynorphin mRNA are observed between days 2 and 5 subsequent to the induction of inflammation. Compared to the increase in mRNA, the increase in dynorphin A(1-8) peptide was appreciably delayed and proportionately less; maximal increases in peptide (3-fold) were seen at day 5 of inflammation. Dorsal spinal cord preproenkephalin mRNA is elevated to a lesser degree (50-80%). However, the increase in preproenkephalin mRNA is apparently not enough to yield a measurable increase in the proenkephalin-derived peptide met5-enkephalin-Arg6-Gly7-Leu8, the levels of which showed no significant change during the 14-day inflammatory period. These data suggest the active participation of opioid neurons, especially those containing dynorphin, at the spinal level, in the modulation of sensory afferent input during peripheral inflammatory pain states.

Extraction of peptides from guanidine thiocyanate homogenates used to isolate RNA

A method is described in which the concentrated tissue extract that remains after preparation of RNA in guanidine thiocyanate can be salvaged for simultaneous measurements of neuropeptides by RIA and other neuroactive factors by bioassay. This procedure may be used for assessing alterations in tissue peptide content in addition to mRNA changes in the same tissue sample.

Negative feedback regulation of the content of proenkephalin mRNA in chromaffin cell cultures

The content of proenkephalin messenger RNA (PEmRNA) in cultured bovine adrenal chromaffin cells was reduced in the presence of reserpine (1 nM to 0.1 microM) with a return to basal levels 3 days after removal of the drug. In these cells, the basal release of Met5-enkephalin-Arg6-Phe7 immunoreactivity (MERF-IR) into the medium was significantly decreased when the cultures were pretreated with 0.2 microM reserpine for 3 days. The addition of 0.1 microM etorphine for 3 days also decreased the basal release of MERF-IR without depleting stores of catecholamines. Neither drug modified the total (cells + medium) amount of MERF-IR. In contrast, reserpine was without effect on levels of PEmRNA or release of Met5-enkephalin immunoreactivity (ME-IR) in primary cultures of the striatum of the fetal rat. The present data establish a correlation between inhibition of the secretion of enkephalin and reduced accumulation of its specific mRNA, suggesting a negative feedback inhibition by low molecular weight enkephalins.

Hypotensive effect of naloxone on high blood pressure induced by stress in the rat

A naloxone-reversible enhancement of systolic blood pressure (BP) was induced in rats by application of three different types of stressor, i.e. intense light and sound, cold and foot-shock. In the case of labile high BP provoked by short-term isolation, the opiate antagonist naloxone (1 mg/Kg, i.p.) was also found to reverse hypertension. Naltrexone (2.5 mg/Kg, i.p.) also diminished high BP readings of briefly isolated rats. Conversely, blockade of the opiate receptor with naloxone did not alter elevated BP in cases of established hypertension (spontaneously hypertensive rats, deoxycorticosterone (DOCA)-salt rats and long-term isolated rats). These data can be taken as an evidence of opioid involvement at the onset of high BP readings induced by stress. However, once hypertension becomes established, the opioid system appears to recover its silent features.

Proenkephalin gene expression in the PC12 pheochromocytoma cell line: stimulation by sodium butyrate

The differentiation promoter sodium butyrate increases the content of Met5-enkephalin-Arg6-Gly7-Leu8 (Met5-enk-RGL)-immunoreactive peptides in PC12 pheochromocytoma cells, which, unlike mature adrenomedullary chromaffin cells, contain exceedingly low levels of opioid peptides. These butyrate-induced enkephalin-immunoreactive peptides, which are specific products of the proenkephalin gene, consist principally of two high mol wt forms of amino-terminally extended Met5-enk-RGL. These high mol wt peptides, with apparent mol wt of 20,000 and 10,000, are approximately the same size as the two major immunoreactive peptides found in adult New England Deaconess Hospital rat adrenal. The low mol wt Met5-enk-RGL-immunoreactive peptide found in butyrate-treated cells is similar in size to authentic Met5-enk-RGL, which is not found in the adrenal medulla of the adult rat. When PC12 cells are grown as a tumor in vivo, the amount of Met5-enk-RGL-immunoreactive peptide increased only slightly above the level found in control cells grown in vitro and consisted exclusively of the highest mol wt immunoreactive species. In PC12 cells, the butyrate-stimulated elevation in the content of Met5-enk-RGL-immunoreactive peptides may involve changes in transcription, since the peptide increase is preceded by a 2- to 3-fold increase in the level of proenkephalin mRNA. These results suggest that the PC12 cell line may be useful for investigating those factors that control the initial expression and processing of proenkephalin-derived peptides during embryogenesis.

Analgesic dipeptide derivatives. 3. Synthesis and structure-activity relationships of o-nitrophenyl-modified analogues of the analgesic compound H-Lys-Trp(NPS)-OMe

A series of analogues of the analgesic dipeptide derivative H-Lys-Trp(NPS)-OMe has been designed to determine the influence of the (2-nitrophenyl)sulfenyl (NPS) moiety on the activity. The syntheses and antinociceptive effects of these analogues of general formula H-Lys-Trp(R)-OMe [R = phenylsulfenyl (PS) (9); R = (2-carbomethyoxyphenyl)sulfenyl (CmPS) (10); R = (4-nitrophenyl)sulfenyl (pNPS) (11); R = (2,4-dinitrophenyl)sulfenyl (DNPS) (12); R = [2-(acetylamino)-2-carbomethoxyethyl]sulfenyl (AacCmES) (13); R = [2-(acetylamino)phenyl]sulfenyl (AacPS) (17); R = tert-butylsulfenyl (t-BuS) (23); R = (2-carbomethoxyethyl)sulfenyl (CmES) (24)] are described. Reaction of Z-Lys(Z)-Trp-OMe (3) with PS-, CmPS-, pNPS-, DNPS-, and AacCmES-Cl afforded the corresponding 2-(sulfenyl)tryptophan derivatives, which on treatment with boron-tris(trifluoroacetate)/trifluoroacetic acid or trimethylsilyl iodide in acetonitrile (Me3SiI/CH3CN) provided 9-13, respectively. Sulfenylation of 3 with NPS-Cl gave Z-Lys(Z)-Trp(NPS)-OMe, which, on catalytic hydrogenation of the nitro group using 10% Pd/C followed by acetylation of the resulting amino function and removal of the protecting Z groups, gave 17. Condensation of 2-(tert-butylsulfenyl)- and 2-[(2-carbomethoxyethyl)sulfenyl]tryptophan methyl ester, obtained by reaction of methyl 3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxyla te with the corresponding thiol, with Z-Lys(Z)-OSu afforded Z-Lys(Z)-Trp(t-BuS)-OMe and Z-Lys(Z)-Trp(CmES)-OMe, which on treatment with Me3SiI/CH3CN provided 23 and 24, respectively. Intracerebroventricular administration of 10 elicited a naloxone-reversible antinociceptive effect in mice similar to that of H-Lys-Trp(NPS)-OMe. No analgesia was however found with the phenylsulfenyl or acyclic sulfenyl substituted dipeptides 9, 11, and 17 or 13, 23, and 24. The Trp(DNPS)-containing analogue was neurotoxic. Structure-activity studies indicate that the role of the NPS and CmPS moieties could be related to the adoption of a preferential active conformation.

Regulation of striatal enkephalin turnover in rats receiving antagonists of specific dopamine receptor subtypes

The hypothesis that striatal dopamine regulates enkephalin (ENK) synthesis is supported by the increase of striatal proenkephalin mRNA and ENK after intranigral injection of 6-hydroxydopamine. In order to elucidate which dopamine receptor subtype is operative in the regulation of the dynamic state of ENK, the effect of drugs that block D-1 or D-2 receptor selectively was studied. Daily administration of 140 mumol/kg s.c. of the D-2 antagonist I-sulpiride twice daily for 2 weeks produces a 30% decrease in the content of striatal proenkephalin mRNA and ENK. In contrast, a 50% increase was observed after 2 weeks of treatment with the D-1 antagonist SCH 23390 at 74 nmol/kg s.c. three times a day. Hence, it can be inferred that the endogenous activation of D-1 tonically decreases striatal ENK synthesis. Removal of this neurally mediated regulation either by a specific pharmacologic blockage of D-1 or by lesioning with 6-hydroxydopamine increases the biosynthesis of ENK. The increase of ENK biosynthesis elicited by denervation with 6-hydroxydopamine cannot be due to the endogenous activation of D-2 receptors and must be due to the inactivation of the tonic inhibition exerted by D-1 receptors.

Evidence for a central but not adrenal, opioid mediation in hypertension induced by brief isolation in the rat

Naloxone was found to provoke a hypotensive effect related to the dose on high blood pressure (BP) induced by short-term isolation in young rats. Another opiate antagonist, nalorphine, also reduced the arterial pressure of socially deprived rats. In contrast, naltrexone methylbromide that selectively blocked peripheral opiate receptors did not alter the elevated BP. To investigate whether adrenomedullary opioids were somehow implicated in the development of isolation-induced hypertension, bilaterally adrenalectomized rats were kept under social deprivation for 7 consecutive days. The data obtained indicated that high systolic BP developed in the same manner as in intact rats run in parallel. In conclusion, central opioids appear to be involved in BP elevation due to the stress generated by brief social deprivation in young rats.

Kindling enhances the stimulation of inositol phospholipid hydrolysis elicited by ibotenic acid in rat hippocampal slices

The increment of inositol phospholipid hydrolysis elicited by ibotenic acid (IBO) is greater in hippocampal slices prepared from brain of rats receiving single or repeated hippocampal electrical stimulation or electrically induced amygdala kindling. In the latter group of rats, a potentiation of IBO stimulation of inositol phospholipid hydrolysis was associated with stage 3-4 of kindling according to Racine's scale. This increment returned to normal within one month after withdrawal from electrical stimulations. In both control and stimulated animals, 2-amino-4-phosphonobutyric acid antagonized the increment of inositol phospholipid metabolism elicited by IBO. The stimulation of inositol phospholipid hydrolysis elicited by carbamylcholine and norepinephrine was virtually unaffected by amygdala kindling.