The role of the ascending 5-hydroxytryptaminergic pathways in timing behaviour: further observations with the interval bisection task

This experiment examined the effect of destroying the 5-hydroxytryptaminergic (5HTergic) pathways on rats' ability to discriminate between two durations. Rats received injections of 5,7-dihydroxytryptamine into the median and dorsal raphe nuclei or sham lesions. They were trained to press lever A following a 2-s presentation of a light and lever B following an 8-s presentation of the light. For some rats, the levers were inserted into the chamber immediately after stimulus presentation (no-poke-requirement); for others, the levers were not inserted until a flap covering the food tray positioned midway between the levers had been depressed (poke-requirement). When stable performance was attained, probe trials were introduced in which the light was presented for intermediate durations. Logistic functions were derived relating percent choice of lever B to log stimulus duration. Under the no-poke-requirement condition, the bisection point (duration yielding 50% choice of lever B) was shorter in the lesioned rats than in the control rats. Under the poke-requirement condition, this effect of the lesion was attenuated. There was no effect of the lesion on the Weber fraction under either condition. The levels of 5HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. It is proposed that rats may attain accurate timing under the interval bisection task by moving from one lever to the other during stimulus presentation; this movement may be facilitated by destruction of the 5HTergic pathways. Accurate timing is still possible when this movement is suppressed by the introduction of a poke requirement; however, in this case timing is not affected by 5HT depletion.     

Facilitated acquisition of a temporal discrimination following destruction of the ascending 5-hydroxytryptaminergic pathways

This experiment examined the effect of destroying the 5-hydroxytryptaminergic (5HTergic) pathways on the acquisition and performance of discrimination between two brief time intervals. Rats that had received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei, and sham-lesioned control rats were trained in a series of discrete trials to press lever A following a 200-ms presentation of a light stimulus and lever B following an 800-ms presentation of the same stimulus. Both groups gradually acquired accurate performance, attaining 80%–85% accuracy by the end of 40 sessions. The lesioned group learnt the task significantly faster than the control group. When stable performance had been attained, probe trials were introduced in which the light was presented for intermediate durations. Both groups showed sigmoid functions relating percent choice of lever B to log stimulus duration. The bisection point (duration corresponding to 50% choice of lever B) did not differ significantly between the two groups; however, the Weber fraction was significantly smaller in the lesioned group than in the control group. The levels of 5HT and 5-hydroxy-indole-acetic acid were markedly reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. The results indicate that destruction of the 5HTergic pathways facilitates acquisition of a temporal discrimination. The lack of an effect of the lesion on the bisection point contrasts with our previous finding using longer stimulus durations; it is suggested that different behavioural processes may underlie millisecond-range and second-range temporal discrimination, and that these may be differently affected by 5HT depletion.     

Effect of lesions of the ascending 5-hydroxytryptaminergic pathways on timing behaviour investigated with an interval bisection task

Seventeen rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei: 12 rats received sham injections. The rats were trained in a series of discrete trials to press lever A following a 2-s presentation of a light stimulus and to press lever B following an 8-s presentation of the same stimulus. Both groups learnt the task rapidly and maintained >90% accuracy throughout the experiment. When stable performance had been attained, probe trials were introduced in which the light was presented for intermediate durations. Both groups showed sigmoid functions relating percent choice of lever B to log stimulus duration. The bisection point (duration corresponding to 50% choice of lever B) was significantly shorter in the lesioned group than in the control group. There was no significant difference between the slopes of the psychophysical functions or the Weber fractions derived for the two groups. The levels of 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid in the parietal cortex, hippocampus, amygdala, nucleus accumbens and hypothalamus were markedly reduced in the lesioned group, but the levels of noradrenaline and dopamine were not significantly affected by the lesion. The results confirm the involvement of 5HTergic function in timing behaviour, but suggest that destruction of these pathways does not disrupt the capacity for temporal discrimination.     

Effects of chlordiazepoxide on discrimination performance

Chlordiazepoxide (0, 5, and 10 mg/kg), administered on eight successive sessions, significantly impaired the reinforcement-cued discrimination performance of male Sprague-Dawley rats. This performance partially recovered on two postdrug (saline) session. The discrimination impairment was due to less inhibition of responding during no-go phases and lower response rates during go phases of the task by the drugged than control animals.     

The effect of nicotine on the swimming speed of pre-trained rats through a water alley

Summary In sessions of ten runs each, swimming time of rats through a 4 m long water alley was measured. Four doses of nicotine (0.05; 0.1; 0.2; 0.4 mg/kg given intraperitoneally 30 minutes before testing) were tested in sessions with a braking load on the tails of the animals either in all 10 runs of a session, or in every second run, or in none of the 10 runs. Regardless of the swimming condition, nicotine produced a considerable, and at doses of 0.1 mg/kg and over, significant decrease of performance in the first two runs. From the third to the 10th run, the changes caused by nicotine were smaller and differed depending on the swimming conditions.A dose of 0.1 mg nicotine/kg improved performance in the without-load-sessions and the without-load-runs of the alternating sessions, while both 0.1 and 0.2 mg/kg improved performance of the with-load-runs of the alternating sessions. Performance in the without-load-sessions and the without-load-runs was depressed by 0.4 mg/kg and that in the with-load-sessions by 0.2 and 0.4 mg/kg.     

Studies on the constituents of Scutellaria species (XXI): constituents of the leaves of Scutellaria strigillosa Hemsley

From the leaves of Scutellaria strigillosa, 14 compounds, chrysin, apigenin, 5,7,2-trihydroxyflavone, norwogonin, ursolic acid, 6-hydroxy-4-stigmasten-3-one, 6-hydroxy-4,22-stigmastadien-3-one, 2 R,4 R,8 R--tocopherol, (S)-5,5 -bi--tocopheryl, (R)-5,5 -bi--tocopheryl, solanachromene, tocopherylquinone, jodrellin T, and 14,15-dihydrojodrellin T were isolated. The structures were determined on the basis of chemical and spectral data.     

A new technique for the investigation of some analgesic drugs on a reflexive behavior in the rat

Summary The analgetic action of a series of analgesic and psychotropic agents was tested in a situation in which variable intensities of electric shock to a rat's feet were used to elicit two distinguishable reflexive responses: a flinching response at low shock values, and a jumping response at higher shock values,By using a modified method of limits, reliable threshold for the two responses were obtained.Chlorpromazine, perphenazine, morphine, codeine, nalorphine and acetylsalicylate were found to raise the threshold to jump, but had little or no effect on the threshold to flinch.PIH, JB 835, iproniazid, reserpine, tetrabenazine, and amphetamine were found to have no effect on either the jump or the flinch thresholds.A combination of amphetamine and codeine was found to produce a synergistic potentiation. A combination of morphine and nalorphine was found to produce an antagonism.The results were discussed in terms of Beecher's hypothesis that the analgetic action of drugs is due to a diminution of the emotional components of an animal's reaction to pain and in terms of the relationship of brain amine change to analgetic action.     

Clockwise hysteresis or proteresis

The authors propose the word proteresis to designate the clockwise hysteresis, i.e., when an effect increases more rapidly than the observed drug concentrations. Such a phenomenon has been recently described for aspirin and nicotine. Indeed hysteresis means which comes after, while proteresis, the greek symmetrical word, means which comes earlier, a more appropriate term for the described situation.     

Dopamine inhibits prostaglandin F2α-induced depolarization of rabbit jejunal arteries via activation of DA1-receptors

Summary In rabbit jejunal arteries, the membrane potential of single smooth muscle cells decreased on the application of noradrenaline 3 mol/1. LY 171555 1 mol/1 did not change, whereas SKF 38393 10 mol/1 reversed the effect of noradrenaline. When prostaglandin F₂ (PGF₂) was used to evoke depolarization in the presence of prazosin 0.1 mol/1, rauwolscine 1 mol/1 and propranolol 1 mol/1, both SKF 38393 10 mol/1 and dopamine 10 mol/1 repolarized the membrane. SCH 23390 1 mol/1 antagonized the effects of SKF 38393 10 mol/1 and dopamine 10 mol/1. Thus, the change in membrane potential is mediated by a DA₁-recep-tor.     

A method to shorten the training phase of drug discrimination

Rats were trained to discriminate drug from no drug in a two-lever, food-reinforced task. One group was trained with cocaine (10 mg/kg) and a second group was trained with pentylenetetrazol (20 mg/kg). A method designed to shorten the time required for the training phase of drug discrimination experiments was assessed in subgroups for each drug. In one subgroup, single training sessions were conducted daily. In the other subgroup, a second session (either drug or saline) was conducted on days for which the first condition was saline. The training conditions were presented in an irregular sequence, with the same condition occurring in no more than two consecutive sessions. Rats trained by the accelerated method learned the discrimination in fewer days, with no decrement in acquisition per session, suggesting that drug discrimination training can be accomplished more rapidly by reducing inter-session interval.     

“Go here-go there” performance after amphetamine: The importance of the response requirement in successive discrimination

Marmosets were trained on a task involving simultaneous and successive visual discrimination performance where responses were required on all trials. performance of this task was not affected by low doses of amphetamine. From this it is concluded that amphetamine does not cause a narrowing of attention and that the disruptive effect of amphetamine on the go-no go successive discrimination task already reported is due to a loss of response inhibition rather than to difficulties in the recognition of stimuli presented without a comparison stimulus.     

Acute morphine dependence: Effects observed in shock and light discrimination tasks

Alterations in shock discrimination accuracy in the rat, indicative of hyperalgesia, have been noted 1–3 days following a single injection of morphine. To establish the extent to which these withdrawal-like effects were specific to the shock discrimination paradigm, rats were trained in two separate discrimination tasks. The discriminative stimuli (S^D's) for correct lever presses were mild electric shocks of different intensities in one task and were short duration lights over the levers in the other. After achieving comparable accuracy levels in the two tasks, the animals were injected SC with 30 mg/kg morphine sulfate and performance levels assessed 1, 2, 3, and 7 days later. Shock discrimination accuracy was significantly enhanced on post-morphine day 2, while accuracy in the light position task was not significantly affected on any of the post-morphine test days. The results indicated that increased pain sensitivity, as well as other signs of dependence, can occur following acute exposure to morphine.     

Bedeutung der N- und α-Methylierung für die Affinität von Brenzcatechinaminen zu den adrenergischen Receptoren

Summary 1. N-methylation of dopamine yielding epinine means potentiation of the -adrenergic pressor action in the cat. It is only N-methylation which renders dopamine to a direct acting -sympathomimetic amine: the positive inotropic effect of epinine on the isolated electrically driven guinea pig auricle remained uninfluenced by pretreatment of the animals with reserpine, whereas the dose-response curve of dopamine was shifted to the right.The blood pressure lowering effect of epinine after phenoxybenzamine was—in contrast to that of dopamine—abolished by pronethalol.—N-methylation of noradrenaline doubled the affinity for the -receptors of the heart.2. Also by -methylation dopamine gains affinity to the adrenergic -receptors (heart and vessels): d--methyldopamine, an exclusively directly acting catecholamine, had a 40 times stronger inotropic action than dopamine on reserpinized auricles; the action of l--methyldopamine, a mainly indirectly acting amine, was only 4 times stronger than dopamine.-methylnoradrenaline, although having the same inotropic activity as noradrenaline, had a 10 times stronger depressor action than noradrenaline in the cat pretreated with phenoxybenzamine.By -methylation, the -adrenergic pressor effect of dopamine as well as that of noradrenaline was enhanced only in the range of lower doses since the dose-response curves of the -methylated compounds were generally less steep than those of the non-methylated catecholamines, indicating a lower intrinsic activity of the -methylated derivatives.3. The N- and -methylated catecholamines -methylepinine and -methyladrenaline resp. were blood pressure lowering agents per se, because both methylgroups additively enhanced the affinity to the vascular -receptors. -methylepinine was the most potent -sympathomimetic on the heart in the dopamine series (dopamine < d--methyldopamine epinine < dl--methylepinine). However, in the noradrenaline series the twofold methylated compound -methyladrenaline had the lowest positive inotropic action (d(–)-adrenaline > d(–)-noradrenaline (–)erythro--methylnoradrenaline > (–) erythro--methyladrenaline).4. From the results the following conclusions are drawn: The N- as well as the -methyl-group exerts and +I-effect on the ammonium group. Thereby, protonation will be increased which leads to an enhanced affinity of the resp. catecholamine to the adrenergic - and -receptor. Since the -CH₃ group—dependant upon its steric configuration—also causes a steric hindrance at the receptor site, the increase in affinity due to the +I-effect is partially neutralized. By that the lower intrinsic affinity of the -methylated compounds as indicated by the different slope of their pressor dose-response curves, is also readily explained. Furtheron it is intelligible why -methylation enhanced the -adrenergic activity in the less potent dopamine series (preponderance of the +I-effect), whereas it lowered the affinity to the cardiac -receptors in the noradrenaline series (preponderance of the steric hindrance).5. Although -methyladrenaline was the least potent -sympathomimetic of the noradrenaline series in the guinea pig heart, it was the most potent compound in lowering the cat's blood pressure. Therefore, it seems to be questionable whether the cardiac and the vascular -receptors and/or the mechanisms by which they induce the pharmacodynamic actions are identical.

Über einen Teil der Ergebnisse wurde auf der 7. Frühjahrstagung der Deutschen Pharmakologischen Gesellschaft in Mainz, 24.–27. April 1966, berichtet (Palm, Langeneckert u. Holtz, 1966).     

The metabolism of the amyloid precursor protein and its relevance to Alzheimer's disease

Summary The pathology of Alzheimer's disease is primarily characterized by the deposition of -amyloid/A peptide as the major component of senile or neuritic plaques. The A peptide is produced as a result of proteolytic cleavage of the transmembrane protein precursor, APP, during its normal cellular metabolism. The free amino terminus of the A peptide is generated by an endopeptidic cleavage between Met⁶⁷¹-Asp⁶⁷² by a protease termed -secretase. Increased cleavage at this site takes place in a rare, inherited double mutation (Lys⁶⁷⁰-Met⁶⁷¹ to Asn⁶⁷⁰-Leu⁶⁷¹), leading to increased A production and consequent development of Alzheimer's disease on an accelerated time scale in the affected individuals, underscoring the pathological importance of -secretase activity. Cellular studies provide direct evidence that inhibition of -secretase activity would appear to be effective in inhibiting A production as a rational approach to developing therapeutics for the disease.     

Differential Effects of Sulfate and Sulfobutyl Ether of β-Cyclodextrin on Erythrocyte Membranes in Vitro

The hemolytic activity of -cyclodextrin (-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of -CyD; the membrane disrupting abilities decreased in the order of -CyD > 2-hydroxypropyl--CyD (HP--CyD) > sulfobutyl--CyD (SB--CyD) >> -CyD sulfate (S--CyD). Under pre-hemolytic concentrations, both -CyD and SB--CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S--CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S--CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike -CyD, S--CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three - CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB--CyD and S--CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent -CyD and HP--CyD.     

Effects of chlordiazepoxide and pentobarbital on conflict behavior in rats

A punishment discrimination (conflict) was conditioned in rats by simultaneously rewarding with food (sweetened, condensed milk) and punishing with shock all lever responses made in the presence of an auditory stimulus. Chlordiazepoxide and pentobarbital were administered in order to compare degrees of attenuation of conflict behavior relative to the production of behavioral debilitation. Chlordiazepoxide produced the maximum attenuation at doses that produced only minimum debilitation. In general, conflict attenuation (anti-anxiety) was greater under chlordiazepoxide while general debilitation (behavioral toxicity) was greater for pentobarbital.     

Factors in the estimated response of acne vulgaris to antibiotics

Summary The data of a double-blind cooperative trial of thiamphenicol (TP), tetracycline (TE) and placebo (PL) in a two-week oral treatment of acne vulgaris were subjected to a study of the observers' attitudes. The study provided no evidence that the PL-optimistic doctors judged either antibiotic more favorably than the PL-pessimistic. A technique for analyzing factorial experiments when the data are frequencies m unbalanced groups was used in a computerized form to evaluate the effects of the oral treatments as well as the interactions with the factors Sex, Severity and Topical treatment. The advantage of TP (63% satisfactory responses) over PL (34%) was proved beyond doubt, irrespective of any factors studied; the addition of a topical treatment is a useful cofactor only in the severe forms in female patients. The advantage of TE (50% overall satisfactory responses) over PL was detected in female patients only. This finding, as well as the potent action of TP, are discussed in view of the acne ameliorating mechanism/s of these antibiotics.     

Antagonism by γ-aminobutyric acid of the stimulant effect of angiotensin II on cardiac sympathetic ganglia in spinal dogs

Summary The effects of angiotensin II and neuro-aminoacids administered through the right subclavian artery (i. a.) to the cardiac sympathetic ganglia were investigated in spinal dogs. Angiotensin II (1–8 g) elicited a dose-dependent positive chronotropic effect which was reduced after i. a. injection of saralasin (100g). The effect of angiotensin II was not reduced after combined treatment with either hexamethonium (10 mg/kg) plus atropine (0.1 mg/kg) or hemicholinium-3 (5 mg/kg) plus preganglionic stimulation. The dosedependent response to angiotensin II of heart rate was inhibited by GABA (50, 500g), GABOB (500g) and muscimol (50, 100g). The inhibition of the response to angiotensin II by a small dose of GABA (50g), but not by a high one (500g), was antagonized by i. a. injection of picrotoxin (2 mg). The positive chronotropism induced by bethanechol (25, 50g) and a small dose of acetylcholine (25g) were significantly inhibited by a high dose (500g) but not by a low dose (50g) of GABA. These results confirm that angiotensin II stimulates cardiac chronotropism by acting on the angiotensin II receptor located at the cardiac ganglia and show that this stimulant effect is antagonized by GABA.     

Cyclodextrins as Nasal Absorption Promoters of Insulin: Mechanistic Evaluations

The safety and effectiveness of cyclodextrins (CD) as nasal absorption promoters of peptide-like macromolecules have been investigated. The relative effectiveness of the cyclodextrins in enhancing insulin nasal absorption was found to be in the descending order of dimethyl--cyclodextrin (DMCD) > -cyclodextrin (-CD) > -cyclodextrin (-CD), hydroxypropyl--cyclodextrin (HPCD) > -cyclodextrin (-CD). A direct relationship linking absorption promotion to nasal membrane protein release is evident, which in turn correlates well with nasal membrane phospholipid release. The magnitude of the membrane damaging effects determined by the membrane protein or phospholipid release may provide an accurate, simple, and useful marker for predicting safety of the absorption enhancers. In order to estimate further the magnitude of damage and specificity of cyclodextrin derivatives in solubilizing nasal membrane components, the enzymatic activities of membrane-bound 5-nucleotidase (5-ND) and intracellular lactate dehydrogenase (LDH) in the perfusates were also measured. HPCD at a 5% concentration was found to result in only minimal removal of epithelial membrane proteins as evidenced by a slight increase in 5-ND and total absence of LDH activity. On the other hand, 5% DMCD caused extensive removal of the membrane-bound 5-ND. Moreover, intracellular LDH activity in the perfusate increased almost linearly with time. The cyclodextrins are also capable of dissociating insulin hexamers into smaller aggregates, and this dissociation depends on cyclodextrin structure and concentration. Enhancement of insulin diffusivity across nasal membrane through dissociation may provide an additional mechanism for cyclodextrin promotion of nasal insulin absorption.     

Interaction between discrimination of drug states and external stimuli

Rats learned a two-choice operant response by discriminating differences between external stimuli, internal (drug-produced) stimuli, or a combination of these two types of stimuli. Separate groups of rats were used for each stimulus condition. A tactile and visual external cue was superior to the ethanol-saline cue in producing stimulus control, but the group receiving both drug and external stimulus cues performed in a manner very similar to the external cue-only group. The two stimulus sources thus did not add to promote more rapid or complete discrimination. After acquisition of discrimination, previously coincident drug and external stimulus states were reversed to determine which stimulus source had more behavioral control. This test for stimulus selectivity indicated that the external stimulus had essentially complete control of response choice.