Investigations on drug produced and subjectively experienced discriminative stimuli. 2. Loperamide, an antidiarrheal devoid of narcotic cue producing actions.
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Administration, Oral↗
Biomedical subjects
F C Colpaert
Publications and source records attributed to F C Colpaert.
Narcotic withdrawal like mouse jumping produced by amphetamine and L-DOPA.
Upward jumping in mice that resembled the narcotic-withdrawal syndrome was produced by a combination of amphetamine (4 mg/kg) and L-DOPA (400 mg/kg) administration. Neither drug alone caused that jumping. Pretreatment with haloperidol (0.16 mg/kg) or pimozide (0.08 mg/kg) but not with phentolamine (10mg/kg) effectively blocked amphetamine-dopa jumping. After DOPA there was an increase in the brain levels of DOPA, dopamine and norepinephrine. Amphetamine, ineffective in itself, enhanced DOPA-induced elevation of brain DOPA and dopamine without affecting brain norepinephrine levels.
Amphetamine↗
Differential response control by isopropamide: a peripherally induced discriminative cue.
The peripherally acting anticholinergic drug isopropamide (0.02 mg/kg s.c.) is shown to produce a discriminative stimulus complex in rats. In rats trained to discriminate isopropamide from saline, dexetimide and methylscopolamine were generalized with isopropamide treatment. The results indicate that drug discrimination learning does not necessarily require a central drug action.
Animals↗
The ventromedial hypothalamus and the control of avoidance behavior and aggression: fear hypothesis versus response-suppression theory of limbic system function.
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Aggression↗
Reversal by a central antiacetylcholine drug of pimozide-induced inhibition of mouse-jumping in amphetamine-dopa treated mice.
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Acetylcholine↗
The narcotic cue: evidence for the specificity of the stimulus properties of narcotic drugs.
Various non-narcotic drugs with intrinsic stimulus properties were found not to be generalized with fentanyl treatment in rats trained to discriminate fentanyl (0.04 mg/kg, s.c., t-30') from its solvent (s.c., t-30'). In contrast, five typical narcotic analgesics yielded dose-dependent generalization with fentanyl treatment. The results evidence the specific character of the narcotic cue in rats.
Animals↗
A critical study on RO-4-1284 antagonism in mice.
Ro-4-1284 is found to produce ptosis, hypothermia, sedation and miosis in mice, and the antagonsim to these symptoms is investigated. The study reports the differential effects of various pharmacologically distinct classes of compounds. The relevance of this type of experiments to possible antidepressant drug activity is discussed.
2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
On the narcotic cuing action of fentanyl and other narcotic analgesic drugs.
Using a food-reinforced two-levers operant procedure, rats could be trained to discriminate fentanyl (1.25 mg/kg, p.o., t-60') from solvent (1 ml/100 g B.W., p.o.,t60)treatment. The administration of the other narcotic analgesics bezitramide, dextromoramide, methadone and morphine produced a dose-related stimulus generalization with the standard fentanyl treatment. The results further evidence the validity of the narcotic cue.
Analgesics, Opioid↗
Effects of VMH lesions on CAR learning in cats.
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Animals↗
Potentiation of jumping behavior by aminophylline in mice treated with threshold doses of amphentamine and dopa.
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Aminophylline↗
Regulation of metallothionein-III (GIF) mRNA in the brain of patients with Alzheimer disease is not impaired.
Contradictory results have been reported on the downregulation and role of the brain-specific protein metallothionein-III (MT-III, GIF) in Alzheimer disease (AD). In this article, the importance of MT-III downregulation in AD brain was re-evaluated in temporal and frontal cortex, hippocampus, and cerebellum of 11 AD patients and two groups of five and six control subjects, respectively. Reverse transcription-polymerase chain reaction (RT-PCR) was used to quantify the levels of MT-III mRNA relative to the levels of three constitutive RNAs: beta-actin, glyceraldehyde-3-phosphate dehydrogenase (G3PDH), and ribosomal RNA 18S (rRNA 18S). The distribution of MT-III was similar to that of each of the three constitutive RNAs. The relative levels of each of these RNAs was high in brain regions examined in both AD patients and control subjects. Our findings do not support a downregulation of MT-III mRNA in the frontal cortex as well as the temporal cortex and hippocampus of AD patients. However, the level of MT-III mRNA was not constant in the investigated samples, suggesting that MT-III mRNA regulation could be controlled by factors other than AD pathology. Brain-derived neurotrophic factor (BDNF) mRNA levels were hardly detectable by RT-PCR in human brain tissue; a trend for a decrease was apparent in the temporal cortex of AD patients. In conclusion, the content of MT-III mRNA in the brain of AD patients was not detectably impaired, whereas BDNF mRNA may be affected.
Actins↗
Apomorphine as a discriminative stimulus, and its antagonism by haloperidol.
At a non-stereotypogenic dose (0.16 mg/kg, s.c.), apomorphine was shown to produce a discriminative stimulus in rats. The apomorphine-produced stimulus was found to be effectively antagonized by haloperidol. It is suggested that apomorphine's ability to stimulate central dopamine receptors is directly related to its cueing action.
Animals↗
How efficacious are 5-HT1B/D receptor ligands: an answer from GTP gamma S binding studies with stably transfected C6-glial cell lines.
The intrinsic activity of a series of 5-hydroxytryptamine (serotonin, 5-HT) receptor ligands was analysed at recombinant h5-HT1B and h5-HT1D receptor sites using a [35S]GTP gamma S binding assay and membrane preparations of stably transfected C6-glial cell lines. Compounds either stimulated or inhibited [35S]GTP gamma S binding to a membrane preparation containing either h5-HT1B or h5-HT1D receptors. The potencies observed for most of the compounds at the h5-HT1B receptor subtype correlated with their potencies measured by inhibition of stimulated cAMP formation on intact cells. Apparent agonist potencies in the [35S]GTP gamma S binding assay to C6-glial/h5-HT1D membranes were, with the exception of 2-[5-[3-(4-methylsulphonylamino)benzyl-1 2,4-oxadiazol-5-yl]-1H-indol-3-yl] ethanamine (L694247), 5- to 13-times lower than in the cAMP assay on intact cells. This suggests that receptor coupling in the h5-HT1D membrane preparation is less efficient than that in the intact cell. It further appeared that 6-times more h5-HT1D than h5-HT1B binding sites were required to attain a similar, maximal (73%), 5-HT-stimulated [35S]GTP gamma S binding response: Hence, the h5-HT1B receptor in C6-glial cell membranes could be more efficiently coupled, even though some compounds more readily displayed intrinsic activity at h5-HT1D receptor sites [e.g. dihydroergotamine and (2'-methyl-4'-(5-methyl[1,2,4]oxadiazol-3-yl)biphenyl-4-carboxylic acid [4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]amide (GR127935)]. Efficacy differences were apparent for most of the compounds (sumatriptan, zolmitriptan, rizatriptan, N-methyl-3-[pyrrolidin-2(R)-ylmethyl]-1H-indol-5-ylmethyl sulfonamide (CP122638), dihydroergotamine, naratriptan and GR127935) that stimulated [35S]GTP gamma S binding compared to the native agonist 5-HT. The observed maximal responses were different for the h5-HT1B and h5-HT1D receptor subtypes. Few compounds behaved as full agonists: L694247, zolmitriptan and sumatriptan did so at the h5-HT1B receptor and only L694247 at the h5-HT1D receptor. GR127935 (10 microM) exerted little effect on [35S]GTP gamma S binding via h5-HT1B receptors (10% stimulation), but potently (pA2: 9.11) antagonized h5-HT1B receptor-stimulated [35S]GTP gamma S binding. Ketanserin and methiothepin inhibited [35S]GTP gamma S binding (by 13-28%) in the absence of an agonist, but were potent and competitive antagonists in the presence of an agonist via h5-HT1B (methiothepin) and h5-HT1D (methiothepin and ketanserin) receptors. The results document the utility of using [35S]GTP gamma S binding studies to assess agonist efficacy, and to characterize 5-HT1B/D receptor ligands as apparently neutral antagonists and inverse agonists at the G-protein level.
Cell Line↗
Paradoxical signal transduction in neurobiological systems.
Information processing in neurobiological systems is commonly thought to rely on the assessment of a signal-to-noise ratio as the key mechanism of signal detection; it assumes and requires that both signal and noise are concurrently available. An alternative theory holds that detection proceeds by the system appreciating any instantaneous input by the input's departure from the moving average of past activity. The evidence reviewed here suggests that this latter transduction mechanism provides a unique, formal account of the highly dynamic, neuroadaptative plasticity (i.e., tolerance, dependence, sensitization) that ensues upon mu-opioid receptor activation. The mechanism would appear already to operate with the receptor-G protein coupling that occurs upon agonist binding to mu-opioid receptors, and also with highly integrated responses such as whole-organism analgesia. The mechanism may perhaps operate ubiquitously with further neuronal and non-neuronal, cell surface, and intracellular-signaling systems, and may govern the experience-dependent regulation of synaptic strength. The transduction mechanism defines a continuously evolving process; the process's most peculiar feature is that it makes any input generate not one but two outcomes that are paradoxical, or opposite in sign.
Analgesics↗