Cadmium inhibits stimulus-response coupling in skate (Raja erinacea) electric organ.

1. The effects of cadmium on stimulus-response coupling in the skate (Raja erinacea) electric organ were examined. 2. Cadmium decreased the evoked electrical discharge and the evoked release of 3H-ACh in a concentration-related fashion. 3. Cadmium (100 microM) also blocked voltage-dependent 45Ca uptake. 4. Both d-tubocurarine and nifedipine blocked Ca uptake and evoked potential, but not 3H-ACh release, thus most of the 45Ca uptake measured was post-synaptic through L Ca channels. 5. Nickel, cadmium, and verapamil inhibited 3H-ACh release and evoked potential, indicating a block of pre-synaptic T Ca channels.

Parasympathetic effects on in vivo rat heart can be regulated through an alpha 1-adrenergic receptor.

A prejunctional mechanism involving an alpha 1-adrenergic receptor may exert control on the release of acetylcholine from parasympathetic nerve endings in the heart. To test this hypothesis in vivo, rats were prepared for electrical stimulation of the vagus nerves. Blood pressures and heart rates were monitored, and the animals were treated with alpha-agonists and alpha-antagonists. The alpha 1-selective agonist phenylephrine significantly attenuated vagally induced bradycardia in a dose-dependent fashion (ED50 = 19 micrograms/kg). This is consistent with the hypothesis that there is alpha-adrenergic inhibition of ACh release. In contrast, the alpha 2-selective agonist, BHT-920, caused no change in heart rate during vagal stimulation. The effects of phenylephrine to raise heart rate and blood pressure during vagal stimulation were blocked by the alpha 1-selective antagonist prazosin (ID50 approximately 1 microgram/kg) but not by the alpha 2-selective antagonists yohimbine and rauwolscine. This further supports an alpha 1 assignment to the prejunctional adrenergic receptor mechanism, which can regulate the release of acetylcholine from cardiac parasympathetic neurons.

Effects of amnesic doses of reserpine or syrosingopine on mouse brain acetylcholine levels.

The effects of reserpine and syrosingopine on mouse whole brain acetylcholine levels were examined. At 2 or 24 hr following injection, the brains were removed and analyzed by mass spectrometry. No differences were found between drug-treated and control mice in the acetylcholine content of the brain at either time interval. The results suggest that whole brain acetylcholine levels do not predict the amnesic effects of either reserpine or syrosingopine.

Incorporation of 15N-leucine amine into ATP of fast-twitch muscle following stimulation.

During intense contraction conditions, ATP content in fast-twitch muscle rapidly decreases (approx. 50%) by the deamination of AMP to IMP and NH3. During recovery, the ATP content returns to normal by the reamination of IMP from aspartate. We evaluated whether the donor amine may be obtained from branched chain amino acid uptake by perfusing muscle in situ with 1.0 mM [15N]-leucine during a 1 hr recovery. [15N]-enriched adenine nucleotide accounted for 14% to 24% of the IMP reaminated, depending on whether [15N]-leucine was provided only during the recovery period or, in addition, 30 min prior to stimulation. Thus, the uptake of leucine by fast-twitch muscle may provide an important source of amine for adenine nucleotide resynthesis following contractions.

Biochemical correlates of morphine withdrawal. 2. Effects of clonidine.

Naloxone-precipitated morphine withdrawal in the rat has been shown to deplete adrenal epinephrine and to increase adrenal and locus ceruleus tyrosine hydroxylase activities. Administration of clonidine (0.1 - 1.0 mg/kg) through the first 6 hr of withdrawal blocked adrenal epinephrine depletion in a dose-dependent fashion. Clonidine also blocked the increases in tyrosine hydroxylase activity seen in the adrenal and locus ceruleus during withdrawal. Clonidine attenuated the weight loss and inhibited the diarrhea during withdrawal. The alpha-2 adrenergic antagonist yohimbine reversed the effects of clonidine in blocking withdrawal. Morphine withdrawal caused only a slight depletion of epinephrine in the denervated adrenal; however, clonidine (0.3 mg/kg) prevented this decrease. These results suggest that clonidine suppresses adrenal and central adrenergic function during morphine withdrawal. This effect occurs through an alpha-2 adrenergic mechanism, possibly at the level of the locus ceruleus although clonidine appears to also have a direct effect on the adrenal medulla. The results are discussed in terms of adrenergic mechanisms of opiate withdrawal and the actions of clonidine on this syndrome.

Biochemical correlates of morphine withdrawal. 1. Characterization in the adrenal medulla and locus ceruleus.

Adrenal catecholamines and their synthesizing enzymes were monitored during morphine treatment and after naloxone-precipitated morphine withdrawal in the rat. At 2 and 6 hr of withdrawal epinephrine content was reduced to approximately 50 and 45% of control. Five days after withdrawal a significant overshoot in adrenal epinephrine concentration was observed. Morphine treatment increased adrenal tyrosine hydroxylase activity to 160% of control. Precipitation of withdrawal with naloxone further increased adrenal tyrosine hydroxylase activity to 240% of control after 1 day; the enzyme activity returned to control values at day 7. Similar effects, but of lesser magnitude, were observed with locus ceruleus tyrosine hydroxylase activity. No increase in adrenal dopamine-beta-hydroxylase activity was seen until day 3 of withdrawal and this activity peaked at 5 days to 160% of control values. Adrenal phenylethanolamine-N-methyltransferase activity was unchanged during the time course studied. Splanchnicotomy caused depletion of adrenal epinephrine to 60% of control. Morphine withdrawal in these animals caused a further (23%) decrease in epinephrine content. These data show that epinephrine is selectively released from the adrenal medulla during naloxone-precipitated morphine withdrawal in the rat and that this release has both a direct and a centrally mediated component. The possible mechanisms underlying these biochemical changes are discussed.

The distribution of acetylcholine and choline in guinea pig heart.

The regional distributions of acetylcholine (ACh) and choline (Ch) in the guinea pig heart were investigated with a pyrolysis-mass fragmentography technique. Using ACh as a marker for cholinergic neurons, we have described a pattern of parasympathetic innervation in the guinea pig heart. This distribution is very similar to that suggested by studies using several different cholinergic indicators in various species. Atrial areas receive richer parasympathetic innervation than ventricular areas, with the right portions receiving more than the left. The nodal areas were the most abundantly innervated regions examined. Ch content is not a good indicator for cholinergic innervation as the regional distribution of ACh and Ch throughout the guinea pig heart are not strongly associated.

In vivo acetylcholine turnover in rat heart.

The in vivo uptake of choline (Ch) and synthesis of acetylcholine (ACh) in rat heart were studied using a pyrolysis mass fragmentography (PMF) method. Deuterium labeled Ch was pulse injected (i.v.) into anesthetized rats. Labeled and unlabeled Ch and ACh were measured by PMF in hearts at various times following injection. From these data we calculated the specific activities of Ch and ACh, rate constants for ACh and turnover rates of ACh. After an initial equilibration period of approximately 2 min, the specific activities of Ch and ACh decayed in a parallel manner with half-times of 28.2 and 28.8 min respectively. Between 2 and 60 min the calculated ACh turnover rate was 0.144 nmol/g/min. Unlike brain Ch, heart Ch levels are very stable with time following sacrifice. No advantage was found in using microwave irradiation to stabilize heart ACh and Ch content.

The effect of reserpine, syrosingopine, and guanethidine on the retention of discriminated escape reversal: peripherally administered catecholamines cannot reverse the reserpine amnesia in this situation.

In a series of experiments, the effects of reserpine, syrosingopine, and guanethidine on retention of a discriminated escape reversal training were investigated in mice. The peripherally and centrally acting reserpine produced amnesia while the primarily peripherally acting compounds, syrosingopine or guanethidine, did not produce amnesia even when given in high dosages or when training was given with low footshock. Unlike in the passive avoidance situation, peripherally administered norepinephrine or dopamine was not able to attenuate the reserpine-induced amnesia. The results were discussed in terms of the role of biogenic amines in memory formation.

Catecholamine levels in the whole brain and the probability of memory formation are not related.

Amnesia was induced with reserpine or was blocked with 1-dopa and 5-hydroxytrptophan before or after passive avoidance training in mice. The levels of dopamine and norepinephrine in the whole brain were measured in corresponding groups with gas chromatography-mass spectrometry. No correlation was found between retention and the levels of these catecholamines in the brain.

Effects of ethanol on rat brain and heart acetylcholine.

Single doses of ethanol caused increased levels of acetylcholine in the brains of fed and fasted rats; heart acetylcholine levels were not affected.

Cat heart acetylcholine: structural proof and distribution.

The distribution of acetylcholine (ACh) in the cat heart was investigated by a pyrolysis-gas chromatography (PGC) method. The hearts were dissected into various regions and homogenized in acetonitrile in the presence of propionylcholine, internal standard. Following extraction with toluene and hexane, the choline esters were precipitated as the enneaiodide complex. The isolated choline esters were analyzed by PGC, and the peak corresponding to ACh was quantified. The compound extracted from heart tissue that eluted with the retention time of authentic ACh was identified by mass spectrometry as dimethylaminoethylacetate, the pyrolysis product of ACh. ACh concentrations were found to be higher in the atria than the ventricles. In both the atria and the ventricles, a higher content of ACh was found in the right than the left portions: right ventricle, 5.0 compared to left ventricle, 2.0 nmol/g; and right atrium, 16.8 compared to left atrium, 11.3 nmol/g. Some cats were subjected to a bilateral cervical vagotomy 3 wk before removal and analysis of heart tissue. Hearts from vagotomized cats contained less ACh than controls in the right ventricle (-31%), right atrium (-54%), SA node (-42%), and papillary muscle (-53%), but no decreases were found in the left ventricle, left atrium, or interventricular septum.