Emilio J. Marco

Serotonergic innervation of cat cerebral arteries

5-HT and 5-HIAA were measured in cat cerebral arteries by HPLC. Removal of both superior cervical ganglia or simultaneous lesions of dorsal and central raphe nuclei significantly decreased 5-HT levels but not those of 5-HIAA. This suggests that cat cerebral blood vessels are innervated by serotonergic fibers of different origin.

Pharmacological receptors of the cerebral arteries of the goat.

5-Hydroxytryptamine (5-HT), norepinephrine (NE), histamine (H) and potassium (K+) chloride induce dose-dependent changes in tension of the isolated middle crerbral artery of the goat. Vasopressin produces highly variable responses followed by tachyphylaxis; angiotensin II is ineffective over a wide dose range. The order of potencies of these vasoactive agents is 5-HT greater than NE greater than H greater than K+. With regard to their ability to induce maximal contractile responses, the order is: H greater than 5-HT, K+ greater than NE. Lysergic acid diethylamide (LSD) antagonizes the actions of 5-HT in a manner which progresses from surmountability to unsurmountability of the blockade depending on the concentration of LSD. The blockade exerted by LSD is reversed by washing. Phentolamine and diphenhydramine competitively antagonize the actions of NE and H, respectively. The potency of phentolamine and diphenhydramine in the cerebral arteries of the goat is similar to that determined in different tissues obtained from a variety of animal species. It is concluded that the cerebral arteries of the goat possess receptors for biogenic amines, the most effective of which is 5-HT; receptors for vasoactive peptides are ill defined.?25

Serotonin and γ-Aminobutyric Acid Turnover After Injection into the Median Raphe of Substance P and D-Ala-Met-Enkephalin Amide

Abstract: The raphe nuclei [which contain serotonin (5‐HT) cell bodies) are also known to contain axons that store substance P, met‐enkephalin, and γ‐aminobutyric acid (GABA). We have previously shown that GABA has a tonic inhibitory action on 5‐HT turnover. To examine other possible interactions of these neuronal systems, we assessed the effect on 5‐HT turnover of injecting substance P and 2‐n‐ala‐met‐enkephalin into the median raphe nucleus, and the effects of substance P on GABA turnover. Serotonin turnover was increased by 30% in the hippocampus after the injection of substance P (4 μg) into the median raphe, indicating an excitatory effect of substance P on the raphehippocampal system. Local injection of the metabolically stable metenkephalin analog 2‐D‐ala‐met‐enkephalin amide (10 μg) increased the hippocampal steady state content of 5‐hydroxyindoleacetic acid (5‐HIAA) by 60%. The data suggest an excitatory effect of met‐enkephalin within the raphe nucleus. We attempted to estimate GABA turnover from the rate of disappearance of GABA after inhibition of glutamic acid decarboxylase by isoniazid and by the rate of accumulation of GABA after inhibition of GABA transaminase by gabaculine. Isoniazid, which is a competitive inhibitor, had too short and incomplete an action to be of use when injected intranuclearly. Gabaculine, which is an irreversible inhibitor, induced a rapid‐onset increase in GABA content. This accumulation was linear up to 90 min. The injection of gabaculine (80 ng) into the raphe increased GABA content by five times the control values, but hippocampal 5‐HT and 5‐HIAA contents were not significantly changed. Substance P injection increased the GABA turnover by 30%. Gabaculine seems a promising tool for detecting changes in GABA turnover.

Indirect adrenergic effect of histamine in cat cerebral arteries

SummaryHistamine (10(−4 M) induced an increase in the tritium outflow from cat cerebral arteries preloaded with 3H-noradrenaline. Pretreatment with reserpine (3 mg/kg, i.p., total dose) or removal of both superior cervical ganglia two weeks before the experiment abolished that increase. The presence of cocaine or diphenhydramine also prevented the rise in tritium efflux induced by histamine.Histamine (10(−8 M to 10(−3 M) elicited dose-dependent contractions in the isolated posterior communicating artery of the cat which were reduced in the presence of diphenhydramine at all doses except the highest three. The addition of phentolamine to the bath decreased the contractile responses at the doses lower than 10(−6 M. Pretreatment with reserpine or removal of both superior cervical ganglia also diminished the responses at doses of histamine below 10(−6 M and 10(−5 M, respectively. When cocaine was added to the bath there was a decrease in the contraction elicited at all doses except the last one.These results suggest the existence of an indirect adrenergic mechanism in the contractile response to histamine in cat cerebral arteries.

Different influence of superoxide anions and hydrogen peroxide on endothelial function of isolated cat cerebral and pulmonary arteries

1. Exogenous superoxide dismutase (SOD) or catalase did not modify isolated cat middle cerebral arterial basal tone. Catalase but not SOD reduced ACh relaxation. 2. H2O2 induced endothelium-independent relaxation which was abolished by catalase. 3. 3-Amino-1,2,4-triazole (AT) evoked endothelium-dependent contractions and diminished ACh relaxation. 4. Diethyldithio carbamic acid (DETC) induced endothelium-independent relaxation and did not modify ACh vasodilatation. 5. ACh relaxation of cat isolated pulmonary arteries was unaffected by SOD, catalase or AT, and diminished by DETC. 6. Endothelial catalase but neither SOD nor superoxide anions is involved in EDRF cerebral vasodilatation and H2O2 participates in ACh relaxation. In pulmonary arteries, only endothelial SOD activity plays a role.

LESION OF THE DORSAL RAPHE NUCLEUS INDUCES SUPERSENSITIVITY TO SEROTONIN IN ISOLATED CAT MIDDLE CEREBRAL ARTERY

Simultaneous lesions of dorsal and median raphe nuclei were induced after 15 days postjunctional supersensitivity to serotonin in isolated segments of cat middle cerebral artery. The same result was obtained when only the dorsal raphe nucleus was destroyed. The lesion of the median raphe nucleus brought about an increased contractile response to serotonin only at the three first doses used. The contractile response to noradrenaline was unaffected by these treatments. These results suggest the existence of a serotonergic innervation of the cat middle cerebral artery whose main origin might be the dorsal raphe nucleus.

Analysis of the contractile effect of 5-hydroxytryptamine on the isolated posterior communicating artery of the cat

5‐Hydroxytryptamine (5‐HT) induced dose‐dependent increases in tension on the isolated posterior communicating artery (PCA) of the cat were significantly antagonized by lysergic acid diethylamide (LSD, 6 times 10−9 m). In the presence of phentolamine (10−6 m) the contraction induced by the two lowest doses of 5‐HT was significantly reduced. Pretreatment of the animals with reserpine (3 mg kg−1, i.p., total dose) did not modify the dose‐response curve to 5‐HT except for the lowest dose. Removal of both superior cervical sympathetic ganglia 15 days before the experiment brought about a significant increase in the vasoconstriction induced by 5‐HT at all the doses compared with the control. Cocaine (10−6m) induced a significant shift to the left of the dose‐response curve to 5‐HT but the maximum response was the same as in the control. The augmented response to 5‐HT after denervation was partially antagonized by LSD (6 times 10−9 m) but not by phentolamine (10−6 m). These results show that the vasoconstriction elicited by 5‐HT in the PCA of the cat is mainly due to direct stimulation of tryptaminergic receptors. The participation of an indirect adrenergic component in the contractile effects of 5‐HT seems to be negligible.

Adrenergic Mechanisms in Cerebral Blood Vessels: Effect of Tyramine on the Isolated Middle Cerebral Artery of the Goat

Tyramine induces dose-dependent changes in tension of the isolated middle cerebral artery of the goat. Cocaine, phentolamine and reserpine reduce the sensitivity of the tissue to tyramine by factors of 2.8, 3.7 and 3.7, respectively. The norepinephrine (NE) concentration of the arteries of the circle of Willis is 2.10 μg per gram and the corresponding value for the right atria is 1.25 μ per gram. Reserpine pretreatment (0.02 mg/kg/day for three days) reduces the NE concentration of the cerebral arteries to undetectable levels and that of the right atria to 2.4% of the control value. The relatively high concentration of NE of the cerebral arteries of the goat suggests that this tissue receives considerable sympathetic innervation. It is likely that part of the contractile response to tyramine is due to release of endogenous NE from sympathetic stores in the artery. However, some contractile response to tyramine remains after α-adrenergic blockade, reserpine pretreatment and in the presence of cocaine, suggesting that in addition to an indirect action (release of NE) tyramine also possesses a direct stimulatory effect in cerebral arteries.

Tryptophan hydroxylase activity in rat brain base arteries related to innervation originating from the dorsal raphe nucleus.

Background and Purpose Tryptophan hydroxylase activity was assayed in cell-free extracts of rat brain base arteries as marker of a serotonergic innervation. Methods Estimation of the enzymatic activity was made in untreated male Sprague-Dawley rats (n=53) and in those who underwent destruction of the dorsal and median raphe nuclei (n=10). Results Tryptophan hydroxylase activity was measured in rat cerebral arteries. The time-dependent 5-hydroxytryp-tophan production was undetectable in the absence of tryptophan or 6-methyltetrahydropterine and in the presence of 6-fluorotryptophan, and it was significantly reduced in the presence of p-chlorophenylalanine. Destruction of the dorsal raphe nucleus but not the median raphe nucleus brought about a significant reduction in enzyme activity. Conclusions These results suggest that rat cerebral arteries receive a serotonergic innervation arising from the dorsal raphe nucleus.

Different Influence of Endothelium in the Mechanical Responses of Human and Cat Isolated Cerebral Arteries to Several Agents

Abstract— The present work was undertaken to elucidate the role of the vascular endothelium in the changes of isometric tension elicited by different compounds in isolated cylinders of human and cat cerebral arteries and cat pulmonary arteries. Endothelium removal by rubbing significantly reduced the relaxing response to acetylcholine (ACh) of isolated segments of all the arteries. The same treatment did not modify the contraction elicited by 5‐hydroxytryptamine (5‐HT) in the human and cat cerebral segments but increased the contractile effect of the amine in cat pulmonary arteries. The mechanical responses to vasopressin, ATP and adenosine in isolated segments of cat cerebral arteries were unaffected after removing the endothelial layer. L‐Arginine, but not D‐arginine (10−5 M), enhanced significantly the relaxation induced by increasing doses of ACh in unrubbed cat cerebral arteries whereas it did not modify the response to ACh in rubbed ones. However, L‐arginine had no effect on the dose‐response curve to 5‐HT in both kinds of preparation and did not change the tone in precontracted unrubbed cat cerebral segments. These results suggest that the endothelium of the cerebrovascular bed plays a minor role in regulating the mechanical response induced by several vasoactive agents, although it retains its ability to produce an endothelium‐derived relaxing factor.