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Notes: THOUGHT AND LANGUAGE IN THE PHILOSOPHY OF THE ENLIGHTENMENT

Notes: Abstract: Chronic in vivo exposure of rats to ethanol in a complete liquid diet for 14 or 21 days produced a behavioral tolerance to the acute injection of ethanol. After 21 days, but not 14 days, of chronic exposure, there was a significant increase in the maximum density of striatal D1 and D2 dopamine receptors without a change in these receptors' affinities. A 24-h withdrawal from the 21-day exposure did not alter the observed increase in density. Both the level and duration of ethanol exposure appear to be important variables for demonstration of an increase in striatal D1 and D2 dopamine receptors.

Notes: Abstract: Extracellular levels of endogenous serotonin (5-HT) and its major metabolite, 5-hydroxyindoleacetic acid (5-HIAA), were measured in the caudate-putamen of anesthetized and awake rats using intracerebral microdialysis coupled to HPLC with fluorimetric detection. A dialysis probe (of the loop type) was perfused with Ringer solution at 2 μl/min, and samples collected every 30 or 60 min. Basal indole levels were followed for up to 4 days in both intact and 5,7-dihydroxytryptamine (5,7-DHT) lesioned animals. Immediately after the probe implantation, the striatal 5-HT levels were about 10 times higher than the steady-state levels that were reached after 7-8 h of perfusion. The steady-state baseline levels, which amounted to 22.5 fmol/30 min sampling time, remained stable for 4 days. In 5,7-DHT-denervated animals, the steady-state levels of 5-HT, measured during the second day after probe implantation, were below the limit of detection (〈10 fmol/60 min). However, during the first 6h post-implantation, the 5-HT output was as high as in intact animals, which suggests that the high 5-HT levels recovered in association with probe implantation were blood-derived. As a consequence, all other experiments were started after a delay of at least 12 h after implantation of the dialysis probe. In awake, freely moving animals, the steady-state 5-HT levels were about 60% higher than in halothane-anesthetized animals, whereas 5-HIAA was unaffected by anesthesia. KCI (60 and 100 mM) added to the perfusion fluid produced a sharp increase in 5-HT output that was eight-fold at the 60 mM concentration and 21-fold at the 100 mM concentration. In contrast, 5-HIAA output dropped by 43 and 54%, respectively. In 5,7-DHT-lesioned animals, the KCl-evoked (100 mM) release represented less than 5% of the peak values obtained for the intact striata. Omission of Ca2+ from the perfusion fluid resulted in a 70% reduction in baseline 5-HT output, whereas the 5-HIAA levels remained unchanged. High concentrations of tetrodotoxin (TTX) added to the perfusion medium (5-50 μM) resulted in quite variable results. At a lower concentration (1 μM), however, TTX produceda 50% reduction in baseline 5-HT release, whereas the 5-HIAA output remained unchanged. The 5-HT reuptake blocker, indalpine, increased the extracellular levels of 5-HT sixfold when added to the perfusion medium (1 μM), and threefold when given intraperitoneally (5 mg/kg). By contrast, the 5-HIAA level remained unaffected during indalpine infusion. Application of TTX (1 μM) under simultaneous 5-HT uptake blockade induced a decrease in 5-HT output by 62–71%. p-Chloroamphetamine (2.5 mg/kg, i.p.) induced a 12-fold increase in 5-HT release and reduced the 5-HIAA output by about 50%. The p-chloroamphetamine-induced increase in 5-HT release was 10 times lower in the 5,7-DHT-denervated striatum. Pargyline (75 mg/kg, i.p.) increased the extracellular levels of 5-HT 11-fold within 6 h, and reduced the 5-HIAA levels by 80%. The 5-HT receptor agonist, 5-methoxy-N,N-dimethyltryptamine (1 mg/kg, i.p.), produced an immediate reduction of about 50% in 5-HT release and a small (11 %) decrease in 5-HIAA output. It is concluded (1) that intracerebral microdialysis coupled to HPLC with fluorimetric detection provides a useful method for the study of extracellular 5-HT and 5-HIAA levels; (2) that steady-state levels of 5-HT and 5-HIAA recovered in the dialysis perfusate are neuronally derived, but these steady-state levels are reached only after a minimum of 7–8 h after probe implantation; (3) that changes in striatal extracellular levels of 5-HT are closely related to changes in serotonergic synaptic activity; and (4) that extracellular levels of 5-HIAA are a poor indicator of synaptic activity, and instead primarily reflect intraneuronal metabolism.

Notes: Although prior studies have supported the validity of measuring total muscarinic receptor binding in postmortem brain, there has not been a study of postmortem effects on muscarinic receptor subtypes, M1 and M2, defined by high and low affinity for pirenzepine, respectively. We have examined in rat brain the effect of postmortem delay at room temperature, storage at 4°C and-20°C, and multiple freeze/thaw cycles on total muscarinic binding, measured with [3H]quinuclidinylbenzilate ([3H]QNB) and on M1 muscarinic binding, measured with [3H]pirenzepine ([3H]-Pir). We found that delay at room temperature up to 4 h, or storage at 4°C for 24 h or at-20°C for 4 weeks, or 3 freeze/thaw cycles had no effect on [3H]QNB or [3H]Pir binding. Exposure of brain to room temperature for 15 h, however, led to an increase in [3H]QNB binding, without change in [3H]Pir. Scatchard analysis showed an increase in binding sites without a change in affinity. We conclude that [3H]-QNB and [3H]Pir are valid measures of total and M1 muscarinic binding, respectively, under these circumstances, but that caution must be used in the interpretation of indirect measures of M2 binding.

Notes: Abstract: Administration to male rats of a single dose of 17β-estradiol valerate (8-500 μg/rat) or implantation of a pellet containing 17β-estradiol (0.5-50 mg/rat) increased serum 17β-estradiol levels in a dose-dependent relationship when measured on the sixth day after adminstration. At the same time, after these doses, the serum rat prolactin (rPRL) levels were doubled and the striatal 3,4-dihydroxyphenyl-ethylamine (DA, dopamine) receptor densities were increased 20%. A single dose of 17β-estradiol valerate of 4 μg/ rat or less did not alter serum 17β-estradiol or rPRL levels or the striatal DA receptor density. After the single injection of 17β-estradiol valerate (125 μg/rat) the serum 17β-estra-diol levels peaked at 1 day, the serum rPRL levels peaked at 2 days, and the striatal DA receptor density elevation peaked from 4 to 8 days. Implantation of a pellet containing 17β-estradiol (25 mg/rat) produced a constant elevation of serum 17β-estradiol levels from 1 to 10 days. Whereas the serum rPRL levels were continuously elevated about twofold, the densities of the striatal DA receptors were increased significantly by 20-25% only from 4 to 8 days after pellet implantation. These results indicate that striatal DA receptor density rises and returns to control levels during the constant elevation of serum 17β-estradiol and rPRL levels. These results, in comparison with those from the literature, suggest that in male rats the elevation of rPRL levels leads to the increase in striatal DA receptor density and that a substantial sex difference exists in rats in the regulation of striatal DA receptor density after 17β-estradiol administration.

Notes: Abstract: Specific cell surface insulin binding to embryonic chick neural retina cells has been demonstrated in vivo. Kinetics of insulin binding as well as hormonal specificity were similar to those reported for other vertebrate cells and tissues, both neural and nonneural. When surface insulin binding to retinal cells was studied as a function of embryonic age, a developmental relationship was observed. Scatchard analysis revealed that the number of cell surface insulin receptors decreased approximately 75% between days 10 and 16 of embryonic development. Receptor affinities remained fairly constant for this period.

Notes: Calmodulin (CaM)-sensitive adenylate cyclase has recently been purified extensively from bovine brain. In this study, the sensitivity of the CaM-sensitive adenylate cyclase to adenosine and adenosine analogs was examined. The highly purified enzyme preparation retained sensitivity to inhibition by adenosine and adenosine analogs with ribose ring modifications, but not to those with purine ring modifications. Adenosine inhibition of this enzyme was not dependent on GTP and was noncompetitive with respect to ATP. Enzyme that had been dissociated from functional guanine nucleotide binding protein interactions by gel filtration in the presence of the zwitterionic detergent 3-[3-(cholamido-propyl)-dimethylammonio]-propanesulfonate and Mn2+ retained sensitivity to adenosine inhibition. The Ki for adenosine inhibition of the CaM-sensitive adenylate cyclase was approximately 2.6 × 10-4M. 5′-Guanylylimi-dodiphosphate and CaM did not affect the Ki of 3′-deoxy-adenosine for the enzyme, but the presence of Ca2+ in the millimolar range raised the Ki by a factor of 5. These results show that the CaM-sensitive form of adenylate cyclase from bovine brain is subject to adenosine inhibition, and strongly suggest that this inhibition is due to interaction of ligands with a purine-specific (“P”) site located on the catalytic subunit of the enzyme.