Postsynaptic supersensitivity after 6-hydroxy-dopamine induced degeneration of the nigro-striatal dopamine system

Self-stimulation and local injections of 6-hydroxydopamine into the rat brain: enhanced behavioral depressive effects of alpha-methylparatyrosine

The effects of intracerebral injections of 6-OHDA on self-stimulation were examined. Small amounts of 6-OHDA were injected either in the area ventralis tegmenti (AVT) or laterally in the pedonculus cerebellaris superior (PCS), then all rats were implanted in the AVT. In spite of marked depletion of brain catecholamines, self-stimulation learning was not altered by PCS 6-OHDA injections, whereas, AVT 6-OHDA injections produced a small perturbance. The administration of low doses of AMPT which had no observable effect in control rats, produced a severe depression of self-stimulation rates in 6-OHDA pretreated rats. The depressive effect of AMPT is always more important in rats injected with 6-OHDA in the AVT than those injected at the level of PCS. The respective role of noradrenergic and dopaminergic neurons in AVT self-stimulation are discussed.

Apomorphine-induced and pilocarpine-induced hypothermia in mice: drug interactions and changes in drug sensitivity after caudate nucleus lesions

1 Apomorphine and pilocarpine each produced dose-dependent hypothermic effects in mice. However, the dose-response curve for pilocarpine was steeper than that for apomorphine.2 Bilateral lesions of the caudate nucleus produced a permanent decrease in sensitivity to apomorphine but had no effect on sensitivity to pilocarpine.3 Apomorphine and pilocarpine had synergistic effects; i.e. the hypothermic effect was greater following a combination of the drugs than following either drug alone.4 The effect of apomorphine was antagonized by either haloperidol or scopolamine; only scopolamine antagonized the effect of pilocarpine.5 These results suggest that a mechanism involving dopaminergic neurones in the caudate nucleus has a modulatory role in temperature regulation.

Possible modulating influence of frontal cortex on nigro-striatal function

1. After administration of (+)-amphetamine, rats with unilateral ablations of the frontal cortex rotated either ipsilaterally or contralaterally as a function of time after surgery.2. At early postoperative intervals (1-7 days), rotation was towards the side of the lesion.3. At later times (15-30 days), rotation was towards the intact side.4. Repeated testing with amphetamine appeared to slow the time-course of changes in rotational behaviour.5. These results suggest that a dopaminergic nigro-striatal system is modulated by the frontal cortex and that unilateral removal of the latter produces a denervation supersensitivity of the former.

Changes on recovery in the concentrations of tryptophan and the biogenic amine metabolites in the cerebrospinal fluid of patients with affective illness

The concentration of the acid metabolites of dopamine, and 5-hydroxytryptamine (5-HT), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) respectively, were estimated in the cerebrospinal fluid of patients suffering from either unipolar or bipolar affective illness, both before and after recovery. Significantly low concentrations of HVA and 5-HIAA (P<0·01 and 0·05 respectively) were found in the unipolar depressed group and these did not return to normal on recovery. Depressed bipolar patients had levels within normal limits. In bipolar manic patients the HVA concentration fell on recovery to a level significantly lower (P<0·05) than controls. There was no difference in the levels of tryptophan in the CSF of any of the groups of patients nor was there any alteration on recovery. There was a high correlation between 5-HIAA and HVA in the same CSF. These findings are against the amine hypothesis which postulated in depression a lowered concentration of transmitter amine at synaptic junction.

Analysis of the effects of apomorphine and bulbocapnine in relation to the proposed dopamine receptor

On rat isolated vas deferens, apomorphine was found to be l/5th as active as dopamine. Reserpine or cocaine pretreatment failed to reduce the response to apomorphine. Low concentrations of apomorphine which do not cause contraction of the tissue, antagonize the effects of dopamine. The effects of dopamine were antagonized equally by phentolamine or apomorphine. On rabbit aortic strips 4 × 10−4M apomorphine repeated at 45 min intervals induces pronounced tachyphylaxis. During the tachyphylactic period dopamine was not inhibited to a significantly greater extent than was phenylephrine. Bulbocapnine tested against dopamine and phenylephrine yielded identical pA2 values of 6. Only at 10−5M was bulbocapnine observed to produce a preferentially greater blockade of dopamine. Dopamine or isoprenaline-induced relaxations of aortic strips were not blocked by bulbocapnine. Dopamine and 3 times 10−6M bulbocapnine increased the chronotropic effects in atria. Apomorphine and higher doses of bulbocapnine produced rate decelerating effects. On atria low doses of apomorphine were equally effective in reducing the effects of dopamine or histamine. These results are discussed in light of the proposal that the effects of apomorphine and bulbocapnine involve dopamine receptor interactions. In all three tissues there was no clear cut evidence of specific dopamine receptors.