Rat brain concentrations of 5-hydroxytryptamine following acute and chronic administration of MAO-inhibiting antidepressants

1. Groups of male Sprague-Dawley rats were injected once daily with phenelzine (15 mg/kg) or tranylcypromine (10 mg/kg) and killed 6 h after drug administration on days 1, 2, 8 and 19.

2. Brains were analyzed for MAO activity by a radiochemical procedure and for 5-HT concen- trations by an electron-capture gas Chromatographic procedure.

3. Both drugs affected 5-HT concentrations in a similar manner—a significant increase of 5-HT over control levels by day 1, with levels still increasing between days 8 and 19, having attained concentrations approximately 5 times control values by day 19.     

Changes in brain catecholamine levels following DL-dopa are not potentiated by deuterium substitution

1. Adult male Wistar rats were treated with either DL-dopa, D₃-DL-dopa or vehicle and sacrificed at various time intervals after treatment. Brain dopamine and noradrenaline concentrations were measured using quantitative mass spectrometric analysis.

2. After treatment with DL-dopa or D₃-DL-dopa, total dopamine levels increased above control values; however, no differences were observed between the two drug treatments. Total noradrenaline levels were not significantly altered by treatment with either DL-dopa or D₃-DL-dopa.

3. Deuterium substitution did not appear to affect catechol ami ne deamination or β-hydroxylation .     

Brain levels of 5-hydroxytryptamine, tryptamine and 2-phenylethylamine in the rat after administration of N-cyanoethyltranylcypromine

1. Brain levels of 5-hydroxytryptamine (5-HT), tryptamine (T), 2-phenylethylamine (PEA) and monoamine oxidase activity at 5, 15, 30, 60, 120 and 240 min were determined in male Sprague-Dawley rats after intraperitoneal injection of the “pro-drug” N-2-cyanoethyltranylcypromine (CE-TCP, dose 0.1 mMole/kg).

2. Analyses of 5-HT, T and PEA were performed on an electron-capture gas Chromatograph with a capillary column. Activity of MAO-A and MAO-B was measured using a radiochemical method.

3. Results indicate substantial inhibition of MAO in rat brain after intraperitoneal administration of CE-TCP, leading to elevated levels of 5-HT, T and PEA as early as 5 min after drug administration.

4. Increases in brain levels of the trace amines T and PEA were much greater (approximately 40 and 100 times control levels, respectively) than with 5-HT (approximately 1.8 times control level) 240 min after administration of CE-TCP.     

Cell cultures as models for studying neural functions

1. Two cell culture systems were used for studies of neural functions in vitro. A neuronal hybrid cell line (neuroblastoma x glioma hybrid cells) and primary glial-rich cultures of newborn murine brain.

2. The level of cyclic AMP in both systems is regulated by two groups of hormones, those that stimulate and those that inhibit formation of cyclic AMP.

3. Among the inhibitory hormones active on the hybrid cells are opioids. Therefore the cells are being used in the elucidation of action of opioids.

4. The list of stimulating and inhibitory hormones regulating the primary glial-rich cultures includes several peptide hormones such as the gastro- intestinal peptides secretin and vasoactive intestinal peptide, the calcaemic hormones parathyrin and calcitonin, adrenocorticotropin and melanotropins, and somatostatin.

5. Noradrenaline (via - and (β-adrenergic receptors) and adenosine (via A₁) and A₂ receptors) inhibit and stimulate cyclic AMP synthesis in the primary glial-rich cultures.

6. Bradykinin slowly hyperpolarizes the hybrid cells and elicits formation of cyclic GMP. Both responses desensitize rapidly.

7. Substance P increases the permeability of hybrid cells for Na⁺, as measured by using ¹⁴C-guanidinium as substitute for Na⁺.

8. Hybrid cells actively accumulate taurine, an amino acid that appears to fulfill important functions in the nervous system.

9. The transport of taurine across the plasma membrane is highly specific for and strictly dependent on Na⁺.

10. The pumped power station hypothesis of taurine action in the nervous system views taurine gradient plus taurine carrier as a transport system for the elimination of sodium from neurons during phases of high neuronal activity.     

Adenosine''s role in the central actions of the benzodiazepines

1. The hypothesis that inhibition of adenosine uptake may play an important role in the central actions of the benzodiazepines is presented.

2. The evidence supporting this hypothesis is discussed.

3. Brain concentrations of the benzodiazepines are adequate for inhibition of adenosine uptake.

4. Benzodiazepines, such as R015-1788 and R05-4864, which do not enhance γ-aminobutyric acid binding, may exert some of their central effects by inhibiting the uptake of adenosine.     

Red cell choline in Korsakoff psychosis

1. Red blood cell (RBC) choline was measured in 48 male patients with Korsakoff psychosis secondary to alcoholism and in 19 age-matched male controls using gas chromatographymass spectrometry.

2. The variance in RBC choline was significantly different between Korsakoff patients and controls (p < 0.002).

3. RBC choline was significantly higher in Korsakoff patients compared with controls (p < 0.02).

4. There was no significant correlation between age and RBC choline.

5. Higher RBC choline levels suggest differences in membrane transport properties. Differences in membrane properties may indicate a neuronal membrane vulnerability to the toxic effect of alcohol or to thiamine deficiency which lead to the degenerative changes associated with Korsakoff psychosis.     

The Calcium entry blockers: Anti-manic drugs?

1. The reported property of calcium antagonists as antimanic drugs has been investigated in three models of hyperactivity in mice.

2. The hyperactivity was induced by amphetamine, oxolinic acid or reserpine after inhibition of monoamine oxydase (MAO).

3. Nicardipine (a dihydropyridine derivative) reduces the three hyperactivities, verapamil (a diphenylalkylamine derivative) reduces only oxolinic acid hyperactivity, and diltiazem (a benzothiazepine derivative) was active except in the MAOI-reserpine test. Levome-promazine used as a reference drug reduced the three hyperactivities.

4. The three calcium entry-blockers reduce the different hyperactivities at doses which already decrease motor activity. And so, it seems that their action was not specific. On the contrary, levomepromazine antagonizes MAOI-reserpine induced hypermotolity at a dose which is not sedative.

5. These results do not strengthen the property of calcium antagonists as antimanic drugs.     

Functional and biochemical basis for multiple muscarinic acetylcholine receptors

1. The novel antimuscarinic compound pirenzepine (PZ) has generated considerable interest in the basis and the implications of muscarinic acetylcholine receptor (mAChR) heterogeneity.

2. [³H]PZ has been used extensively to identify and characterize the putative M₁ (high affinity for PZ) mAChR subtype, which predominates in central nervous system (CNS) and ganglia.

3. The heterogeneity sensed by PZ is not identical to the heterogeneity sensed by agonists.

4. Differences in effector coupling do not necessarily provide a simple explanation for the molecular basis of these putative M₁ and M₂ subtypes.

5. Therapeutic and untoward effects of muscarinic drugs may be mediated by independent mAChR subpopulations which may be pharmacologically exploited to produce more highly selective as well as efficacious new drugs.     

Determination of meta- and para-hydroxyphenylacetic acid levels in single caudate nuclei by selected metastable peak monitoring: a new sensitive gas chromatographic-mass spectrometric procedure

The levels of meta- and para-hydroxyphenylacetic acids in rat brain caudate nuclei have been determined by a new gas chromatography-mass spectrometric (GC-MS) procedure in which metastable transitions specific to the derivatized acids are observed. The method is more sensitive than previous procedures and allows determination of the acid concentrations using single caudate nuclei. The levels of the meta- and para-isomers were found to be 9.2 ± 1.5 and 43 ± 3.7 ng/g, respectively.     

Specificity of the combined dexamethasone suppression and TRH/TSH tests in melancholia

1. Subjects for this study were 61 acute psychiatric inpatients. Forty two (42) qualified for a RDC diagnosis of Major Depressive Disorder (MDD) and 19 for other disorders.

2. After a 7–10 days drug withdrawal period patients were subjected to the dexamethasone suppression and TRH/TSH tests. TSH was measured using a RIA. Cortisol was measured using a CPB technique.

3. Eighteen (18) of the 42 MDD patients and 1 of the 19 others had an abnormal DST (sensitivity 43%, specificity 94%). Twenty two (22) depressed patients and 4 others had a blunted TSH response (sensitivity 52%, specificity 79%). Thirteen (13) depressives and none of the others had abnormal responses to both tests (sensitivity 31%, specificity 100%).

4. DST nonsuppression alone and blunted TSH response alone were not a function of severity of illness, sex, age of onset, family history or RDC subtype.

5. The 13 MDD patients with the combined neuroendocrine abnormality were more severely depressed, had longer episodes of illness, were older and had a later age of onset of their first episode.

6. Our results add support to the suggestion that serial neuroendocrine challenge studies might be of particular relevance and significance in the diagnosis and management of elderly psychotic depressed patients.     

H-Clonidine binding to membranes of platelets prepared under physiological conditions

(1) A reproducible binding assay has been established to measure ₂-adrenoreceptors on membranes of human platelets prepared under physiological conditions.

(2) Washed platelet suspensions were obtained from fresh blood by a modified method (Mustard et al., 1972) and membranes were prepared by mechanical homogenization.

(3) ³H-clonidine, a selective ₂-adrenoreceptor agonist was selected as the ligand in a concentration range of 2–64 nM. Specific binding of ³H-clonidine was defined as the difference between total bound radioactivity and that not displaced by excess cold clonidine (6.4 × 10⁻⁵M).

(4) Platelets from 14 healthy young male volunteers were analysed using this technique, and one high affinity binding site, with K_D and B_max values in the reported range was found (K_D: 10.14 ± 1.95 nM; B_max: 428 ± 33 fmol/mg protein (Mean) ± S.E.M.).

(5) This technique will be used in future studies that will examine ₂-adrenoreceptor changes in specific subgroups of depressed patients.     

Comparative autoradiographic distribution of calcium channel antagonist binding sites for 1,4-dihydropyridine and phenylalkylamine in rat, guinea pig and human brain

1. The autoradiographic distribution of calcium channel antagonist binding sites for 1,4-dihydropyridine and phenylalkylamine has been investigated in rat, guinea pig and human brain.

2. 1,4-dihydropyridine([³H] (+) PN200-110) and phenylalkylamine ([³H] (−) D-888) binding sites are identically distributed in the brain of the three mammalian species studied.

3. High densities of calcium antagonist binding sites are present in brain areas enriched in synaptic contacts such as the hippocampus, cortex and striatum. Low to moderate densities of sites are found in other regions such as the thalamus, hypothalamus and brain stem.

4. These data demonstrate the existence of specific calcium antagonist binding sites in mammalian brain including man. These sites are discretely distributed with highest concentrations present in the hippocampus and cortex. Moreover, the similar distribution of binding sites for [³H](+)PN200-110 and [³H](−) D-188 suggests that 1,4-dihydropyridine and phenylalkylamine bind to the same receptor site complex in mammalian brain.     

Analysis of thromboxane B3 converted from eicosapentaenoic acid in human platelet rich plasma by gas chromatography/mass spectrometry

Gas chromatographic mass spectrometric determination of thromboxane B3 (TXB3) synthesized from platelet is described. Eicosapentaenoic acid (EPA) was added to human platelet rich plasma and after the reaction the exstraction was carried out. Plasma thromboxanes were run through an Amberlite XAD-2 and SEP-PAK silica cartridge, and then chromatographed using silicagel thin layer plate to remove interfering materials, such as 6-keto-prostaglandin F1 alpha. Extracted thromboxanes were converted into the methoxime-dimethylisopropylsilylmethyl ester derivatives and they were measured by gas chromatography/ammonia chemical ionization mass spectrometry. Three peaks were obtained on the gas chromatogram which were presumed to be 3-series metabolite product TXB3 and their related substances. Results indicates the human platelet may easily convert EPA to TXB3 by adding EPA to PRP without adding arachidonic acid.     

The effect of acute and chronic administration of desmethylimipramine on responses to stress in rats

1. Rats were given single or repeated injection of desmethyllmipramine (DMI) and subjected to a single session of restraint or footshock stress.

2. The degree of anorexia and plasma corticosterone elevation in response to the stress was measured.

3. Repeated but not single injection of DMI was found to reduce the anorectic response to restraint and footshock but not to affect the corticosterone response to restraint.

4. It is concluded that repeated DMI treatment has differential effects on responses to acute stress.     

The effects of administration of meta-tyramine and para-tyramine on dopamine and its metabolites in the rat striatum

1. Para-tyramine administration decreased the release of dopamine as indicated by the decline in 3-MT concentrations, increased HVA concentrations at 30 and 60 min and decreased DA concentrations at the same times. DOPAC concentrations declined after 60 min.

2. Meta-tyramine reduced the synthesis of dopamine thus causing a decrease in the concentrations of all its metabolites by 60 min post injection.

3. The failure of the deaminated products of the tyramines to affect the concentrations of dopamine and its metabolites suggested that the effects produced by either meta or paratyramine were due to the amines and not due to interference with various transport mechanisms.

4. Para-tyramine and meta-tyramine may achieve their actions on dopamine neurotransmission by different mechanisms. Para-tyramine may act as a partial agonist reducing DA release ext raneuronally (the decrease in 3-MT levels) or by displacing DA intraneuronally as evidenced by the decline in DA concentrations or increase in HVA concentrations. Metatyramine appears to inhibit the synthesis of dopamine.     

Antagonism of physostigmine induced hypothermia and neuroendocrine changes following exposure to different environmental temperatures

1. The magnitude of physostigmine-induced hypothermia increased with decreasing environmental temperature.

2. The hypothermic response was accompanied by significant changes in plasma levels of corticosterone, glucose and fatty acids.

3. Central cholinergic mediation appears to be a significant component of physostigmine-induced hypothermia and neuroendocrine changes at moderate temperature.

4. At lower ambient temperatures cholinergic blockers produced less antagonism of physostigmine-induced effects.

5. The decreased effectiveness of cholinergic blockers at low environmental temperatures and the increased plasma fatty acid levels under almost all conditions studied may be of importance in considering long term therapy with cholinergic agonists.     

N-Acetylserotonin in the central nervous system

1. N-acetylserotonin has been identified by immunohistochemistry in specific brain areas separate from melatonin and serotonin. N-acetylserotonin is widely distributed within the brain stem, cerebellum and hippocampus and in the brain stem it is contained within reticular formation nuclei and motor nuclei. Like serotonin, N-acetylserotonin appears to be derived from tryptophan as tryptophan hydroxylase inhibition leads to a lowering in innunoreactive N-acetylserotonin in brain and blood. Beta adrenergic drugs influence N-acetylserotonin neurons with beta adrenergic agonists causing a rise in immunoreactive N-acetylserotonin. The presence of N-acetylserotonin in brain has been confirmed by gas chromatography, mass spectrometry and radioimmunoassay.

2. At this point little is known of the possible role of N-acetylserotonin in the brain. In the hippocampus N-acetylserotonin is present in granule cells and its appearance parallels the appearance of those cells. High affinity binding of tritiated N-acetylserotonin is found in brain and in various brain areas and this radioligand appears to label serotonergic receptors. Preliminary iontophoretic studies performed on hippocampal slices indicate an inhibitory action of N-acetylserotonin on glutamate induced firing of pyramidal cells.

3. Taken together these findings suggest that N-acetylserotonin may have a role in the central nervous system distinct from that of being a precursor for melatonin. If this hypothesis is correct it would suggest that indoleamines have certain similarities to catecholamines. Thus for the catecholamines, dopamine, norepinephrine and epinephrine form a synthetic sequence and yet have independent roles as neurotransmitters and/or hormones. The three indoleamines serotonin, N-acetylserotonin and melatonin also form a synthetic sequence and these three substances may also have independent roles as neurotransmitters and/or hormones.     

Increasing membrane polyunsaturated fatty-acid content augments cyclic AMP formation and prostaglandin production in NIE-115 neuroblastoma

1. Addition of linoleic acid (50 μM) to culture medium significantly increases levels of polyunsaturated fatty acids (PUFA) in membrane phospholipids of NIE-115 neuroblastoma.

2. Basal levels of cyclic AMP are elevated significantly in supplemented ceils.

3. Exogenous prostaglandins (PG) PGE₁ and PGD₂ stimulate cAMP formation in NIE-115 neuroblastoma.

4. Supplemented cells produce higher levels of PGE and PGD than do control cultures.

5. Inclusion of cyclooxygenase inhibitors in culture medium does not block elevation of cyclic nucleotide in supplemented cells.

6. Endogenous PG production and receptor activation cannot account for increased cAMP in EFA-supplemented neuroblastoma.     

The effect of a putative antidepressant, an O2-substituted derivative of barbitone on apomorphine induced hypomotility

1. The effects of the chronic administration of barbitone and its O₂-substituted isopropyl derivative (0₂IB) was studied on the hypomotility induced in rats by the acute administration of a low dose of apomorphine.

2. Neither drug was found to selectively antagonize the hypomotility caused by acute apomorphine administration.

3. No correlation could be found between the behavioural effects of the barbiturates and changes in the concentrations of biogenic amines and GABA in four discrete brain regions.

4. The results of this study do not support the conclusions of previous acute studies in which O₂IB has been shown to have an antidepressant profile.     

An open clinical trial of clonazepam in the treatment of patients with recurrent panic attacks

1. Imipramine, phenelzine and alprazolam have each been shown to be efficacious in the treatment of panic disorder and in agoraphobia with panic attacks.

2. Clonazepam, a 1,4 benzodiazepine derivative used mainly in neurology as an anti-epileptic, has specific pharmacodynamic and pharmacokinetic properties which would make it an advantageous antipanic agent.

3. We report 8 cases of recurrent panic attacks which were successfully treated with clonazepam.