Intracellular studies on the dopamine-induced firing inhibition of neostriatal neurons in vitro: evidence for D1 receptor involvement

Intracellular recordings were obtained from rat neostriatal slices. Bath-applied dopamine (1-10 microM) produced a reversible inhibition of the action potentials evoked by direct stimulation and a decrease in the amplitude of the intrastriatally evoked depolarizing postsynaptic potentials. No change in membrane potential was detected during the application of 1-10 microM dopamine. Dopamine application also produced a decrease in anomalous rectification in the depolarizing direction. This subthreshold inward rectification was abolished by tetrodotoxin, but not by calcium-free and cadmium (0.1-1 mM)-containing solutions. The dopamine-induced decrease in excitatory postsynaptic potential amplitude was evident at resting membrane potential or at more positive levels, but was absent at hyperpolarized values of the membrane potential. Addition of bicuculline (50-500 microM) to the medium did not affect the inhibitory action of dopamine. The inhibitory action of dopamine also persisted in calcium-free and cadmium-containing solutions. The adenosine 3',5'-cyclic monophosphate analogue, 8-bromo-adenosine 3',5'-cyclic monophosphate (0.1-1 mM), mimicked the effects produced by D1 receptor activation. Bath application of 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF 38393) (1-10 microM), a selective D1 dopaminergic agonist, mimicked the effects of micromolar concentrations of dopamine. The D2 dopaminergic agonists, 4,4a,5,6,7,8,8a,9-octahydro-5-n-propyl-2H-pyrazolo-3,4-g-quinoline (LY 171555) and bromocriptine (both at 10 nM-10 microM), had no effects on neostriatal cells. The inhibition induced by micromolar doses of dopamine or SKF 38393 was antagonized by bath applications of R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin++ +-7-ol (SCH 23390; 0.1-10 microM), a D1-selective antagonist, but not by sulpiride (10 nM-10 microM), a D2 antagonist. We conclude that the inhibitory effect of dopamine on rat striatal neurons is postsynaptically mediated by the activation of D1 dopaminergic receptors via the reduction of a voltage-dependent tetrodotoxin-sensitive inward conductance.

Responses of intracellularly recorded cortical neurons to the iontophoretic application of dopamine

Considering that a well-defined dopaminergic projection from the mesencephalic structures to the rat frontal cortex has been demonstrated, the purpose of this research was to study the action of iontophoretically applied dopamine (DA) on intracellularly recorded rat frontal neurons. The stimulation of the substantia nigra (SN) and the ventral tegmental area (VTA) evoked EPSP-IPSP sequences in these cells. About 50% of the tested neurons, widely distributed in all the frontal cortex, responded to DA application and no difference in the response to DA was observed between neurons with monosynaptic inputs and neurons with polysynaptic inputs. The catecholamine depolarized the cell membrane and decreased the firing rate, generally without significant changes in membrane resistance, as already observed in rat and cat striatal cells. In some neurons the decrease of the spikes preceded the membrane depolarization. Considering the complex effect of DA on the electrical properties of these neurons, these results seem to be indicative of a mechanism of action dependent on metabolic changes.

Dopamine decreases cell excitability in rat striatal neurons by pre- and postsynaptic mechanisms

The mechanism by which dopamine (DA) decreases the amplitude of the EPSP-IPSP sequences evoked by cortical stimulation was investigated by means of electrophysiological and biochemical methods. Intracellular recordings indicate that DA decreases the amplitude of the excitatory and inhibitory events by reducing the increase in membrane conductance measured at the peaks of the EPSP-IPSP. The non-synaptic input resistance was not modified. In addition the catecholamine (+50/+200 nA balanced current) was shown to decrease the action of glutamate (-30/-80 nA balanced current) and GABA (+40/+100 nA balanced current) when iontophoretically applied. These observations suggest that DA interferes with the excitatory (glutamatergic) and inhibitory (GABAergic) transmission at the postsynaptic site in striatal neurons. However, the depression of cellular excitability elicited by DA could not be ascribed only to its interaction with synaptic transmission at the postsynaptic level. In fact the catecholamine also inhibited spike frequency driven by depolarizing pulses and decreased the depolarization-induced release of glutamate at the presynaptic site, as shown by biochemical experiments with striatal synaptosomal preparations. A neuromodulatory role of DA in the depression of the excitability of striatal neurons by presynaptic and postsynaptic mechanisms is suggested.

Paraquat- and rotenone-induced models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder mainly characterized by a loss of dopaminergic (DA) neurons in the substantia nigra pars compacta. In recent years, several new genes and environmental factors have been implicated in PD, and their impact on DA neuronal cell death is slowly emerging. However, PD etiology remains unknown, whereas its pathogenesis begins to be clarified as a multifactorial cascade of deleterious factors. Recent epidemiological studies have linked exposure to environmental agents, including pesticides, with an increased risk of developing the disease. As a result, over the last two decades the "environmental hypothesis" of PD has gained considerable interest. This speculates that agricultural chemicals in the environment, by producing selective dopaminergic cell death, can contribute to the development of the disease. However, a causal role for pesticides in the etiology of PD has yet to be definitively established. Importantly, most insights into PD pathogenesis came from investigations performed in experimental models of PD, especially those produced by neurotoxins. This review presents data obtained in our laboratories along with current views on the neurotoxic actions induced by the two most popular parkinsonian pesticide neurotoxins, namely paraquat and rotenone. Although confined to these two chemicals, mechanistic studies underlying dopaminergic cell death are of the utmost importance to identify new drug targets for the treatment of PD.

Dopamine modulates CA1 hippocampal neurons by elevating the threshold for spike generation: an in vitro study

Intracellular recordings were obtained from CA1 neurons of rat hippocampal slices preparation. Dopamine applied by perfusion (10(-5)-10(-7) M), microdrop (10(-4) M) and iontophoresis (+80, +200 nA balanced current) inhibited "spontaneous" and evoked action potentials. An increase in current injection restored the evoked action potentials which appeared unmodified. Membrane potential was not modified in 60% of the neurons; in the remaining ones, a slow depolarization was observed. Membrane resistance, measured at rest, was not modified by dopamine. Calcium-mediated events such as bursting activity and afterhyperpolarization, mainly in the late component, were also attenuated by the catecholamine. These effects were antagonized by domperidone, a dopaminergic antagonist. Calcium spikes, evoked in tetrodotoxin- and tetraethylammonium-poisoned slices, were reversibly inhibited by dopamine. Since an increase in the amplitude of a depolarizing pulse of injected current was able to evoke both sodium and calcium action potentials suppressed by dopamine without change in shape or duration, it is concluded that this catecholamine depresses cellular excitability by altering the interaction between membrane voltage and sodium and calcium entry and the subsequent increase in potassium conductance.

The brain as a target organ of gonadal steroids

Gonadal steroids have many effects in the central nervous system. Through a feedback mechanism, they influence the synthesis and release of hypothalamic gonadotropin-releasing hormone (GnRH) and/or pituitary gonadotropic hormones (luteinizing hormone, LH, and follicle stimulating hormone, FSH). Endogenous opioid peptides (EOPs) represent one of the key factors modulating the activity of sex steroids on the hypothalamus-pituitary-gonadal (HPG) axis. In particular, these peptides control the secretion of LH by inhibiting the activity of the hypothalamic neurons which produce GnRH. The EOP effect is dependent on the steroid hormone milieu, as shown by different responses to naloxone administration, both in animals and in humans. For the naloxone-induced increase in LH secretion to occur, relatively high levels of sex steroids are required. In humans, LH release is absent before sexual maturation. In fertile women, naloxone administration increases LH levels in the luteal phase but not in the follicular phase. In the postmenopausal period, naloxone has no effect on LH release; estrogen/progestin therapy does restore the LH response.

α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors in spinal cord motor neurons are altered in transgenic mice overexpressing human Cu,Zn superoxide dismutase (Gly93→Ala) mutation

There are many evidences implicating glutamatergic toxicity as a contributory factor in the selective neuronal injury occurring in amyotrophic lateral sclerosis (ALS). This neurodegenerative disorder is characterized by the progressive loss of motor neurons, whose pathogenesis is thought to involve Ca(2+) influx mediated by alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors (AMPARs). In the present study we report alterations in the AMPARs function in a transgenic mouse-model of the human SOD1(G93A) familial ALS. Compared with those expressed in motor neurons carrying the human wild type gene, AMPAR-gated channels expressed in motor neurons carrying the human mutant gene exhibited modified permeability, altered agonist cooperativity between the sites involved in the process of channel opening and were responsible for slower spontaneous synaptic events. These observations demonstrate that the SOD1(G93A) mutation induces changes in AMPAR functions which may underlie the increased vulnerability of motor neurons to glutamatergic excitotoxicity in ALS.

Electrical stimulation of mesencephalic cell groups (A9-A10) produces monosynaptic excitatory potentials in rat frontal cortex

Electrical stimulation of the ventral tegmental area and substantia nigra produces monosynaptic and polysynaptic excitatory postsynaptic potentials in rat frontal neurons that can be recorded intracellularly. The electrophysiological characteristics of the monosynaptic responses and the possibility that dopamine (DA) mediates these events are discussed.

Effect of steroid hormones and antihormones on hypothalamic beta-endorphin concentrations in intact and castrated female rats

The aim of the present study was to evaluate the effects of estrogens and androgens on hypothalamic beta-endorphin (beta-EP) concentrations. Intact or castrated female rats were chronically (2 weeks) treated with estrogen (estradiol benzoate) and/or antiestrogens (clomiphene, cyclophenil or epimestrol), and with androgens (dihydrotestosterone or dehydroepiandrosterone sulphate) and/or antiandrogen (cyproterone acetate). A group of rats treated with vehicle were studied as comparison. The beta-EP concentrations were measured by radioimmunoassay on acidic extracts of rat hypothalami. The administration of clomiphene and cyclophenil significantly reduced hypothalamic beta-EP concentrations in intact rats, while both drugs or estradiol benzoate increased the peptide concentration in castrated rats. Both intact and castrated rats treated with epimestrol showed hypothalamic beta-EP concentrations higher than vehicle treated rats. The estradiol-induced increase of beta-EP was not changed by the concomitant administration of antiestrogens. The administration of dihydrotestosterone significantly decreased beta-EP concentrations in both intact and castrated female rats, while the treatment with dehydroepiandrosterone sulphate only slightly decreased beta-EP levels in intact female rats. The cyproterone acetate-chronically treated rats showed higher beta-EP concentrations than vehicle-treated rats and these changes were reversed by the concomitant addition of dihydrotestosterone or dehydroepiandrosterone sulphate. These results showed that estrogens play a positive role while androgens negatively influence the hypothalamic beta-EP concentrations in female rats, supporting the view that central beta-EP might be a target of gonadal steroid feedback signals.

Short-latency scalp somatosensory evoked potentials and central spine to scalp propagation characteristics during peroneal and median nerve stimulation in multiple sclerosis

Peripheral (cauda-lumbar, wrist-Erb, Erb-cervical) and central (cauda-vertex, cervical-scalp) nervous impulse propagation velocities and times to peroneal and median nerve stimulation were investigated in 34 patients suffering from definite (17 cases), probable (6 cases) and possible (11 cases) forms of multiple sclerosis (MS). In 6 cases short- and intermediate-latency scalp somatosensory evoked potentials to peroneal nerve stimulation were recorded with 'open' (1-5000 Hz, -6 dB) bandpass filters and subsequently digitally filtered through a 'narrow' bandpass (200-5000 Hz, -6 dB). The lumbar response was abnormal in 2.95% of legs, while the Erb response was always within normal limits. The cauda-vertex conduction was altered in 75% of the examined limbs (86.2% definite, 58.3% probable, 63.6% possible MS). Absent scalp responses to peroneal stimulation were often encountered during narrow bandpass recording (54.9%), while a slowed central conduction was less frequent (33.3%). Scalp responses when recorded with open bandpass were always identifiable, being delayed in 3 out of 6 cases. In 5 of these the short-latency wavelets were either absent or showed a prolonged interpeak time even when open filter records were normal. Median nerve SEPs were altered in 60.3% of cases, more frequently because of a delayed scalp response or of a prolonged cervical-scalp conduction time than because of an absent cervical or scalp response. When peroneal and median nerve data were considered together, the rate of abnormality rose to 88.2% of patients. Due to their length, afferent pathways from the lower limb might suffer from a loss of high frequency impulse coding as an early sign of defective impulse propagation.

Multiple opiate receptors on neurons of the mammalian central nervous system. In vivo and in vitro studies

Experiments were performed in rat spinal cord cells in vivo and on hippocampal pyramidal cells in vitro. These investigations suggest that acute and chronic treatment renders the neurons subsensitive to opiate alkaloids without altering their sensitivity to opioid peptides. The experiments performed in the dorsal horn of the spinal cord provide evidence that in this structure mu- and delta-receptors may also be localized on the same cell. The evidence for the existence of distinct types of opiate receptors as originally proposed by (1) and suggested by the differing pattern of opiate and opioid peptide activity in various assay systems has been substantiated by investigations involving the selective development of tolerance and the protection of a particular receptor subtype by chemical manipulation. Furthermore, they have been characterized by the use of low concentrations of radiolabelled agonists and antagonists and through the ability of GTP to influence differentially their binding to the opiate receptor (for refs. see: 2). Recently autoradiographic techniques were able to provide direct evidence by mu- and delta-receptors in the mammalian brain (3; 4; 5; 6; and cits. therein). The presence of multiple opiate receptors located on the same cell is suggested by the present study.

Norgestimate increases pituitary and hypothalamic concentrations of immunoreactive beta-endorphin

Progesterone is a potent hormone acting on the female reproductive tract and influencing a series of other functions. Recent studies revealed a correlation between progesterone and brain neurotransmitters and neuropeptides. Our study evaluated the possible effect of norgestimate, a new progestin, on hypothalamic and pituitary beta-endorphin (B-EP) concentration in castrated female rats. Ovariectomy was performed under ethyl ether anesthesia. Treatment was started 3 weeks after surgery. Norgestimate, estradiol benzoate or norgestimate plus estradiol benzoate were administered. The two steroids were dissolved in sesame oil and injected (s.c.) every day for 2 weeks. Pituitary and hypothalamus B-EP concentrations were measured by radioimmunoassay. Our studies showed that norgestimate increases the pituitary and hypothalamic B-EP concentration in female rats, reaching values higher than controls and estrogen-treated rats. Because B-EP has an important role in reproductive function, both modulating gonadotropin secretion and sexual behavior, the present results lead to the hypothesis that norgestimate affecting B-EP concentrations may influence central functions.

The action of glycine on rat epileptic foci

The action of glycine (Gly) intravenously injected on rat epileptic foci induced by strychnine or penicillin topically applied, was compared with that of GABA. Gly (450 mg/kg i.v.) produced a complete block of the spiking activity. The inhibitory action of GABA (80 mg/kg), in terms of threshold and duration, was stronger than the action of Gly. The same inhibitory effect was also observed if these amino acids were applied topically or intracisternally. These results are consistent with the possibility that Gly has a role in the rat cortical inhibition.

Hormonal treatments modulate pulsatile plasma growth hormone, gonadotrophin and osteocalcin levels in postmenopausal women

Oestrogen plays a role in modulating growth hormone (GH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and osteocalcin secretion in women. Indeed, the postmenopausal period is characterized by changes in plasma GH, LH, FSH and osteocalcin levels. The aim of the present study was to investigate the changes in the secretory patterns of these hormones in postmenopausal women under different therapeutic regimens. A total of 20 subjects took part in the study. They were subdivided into four groups comprising 5 untreated postmenopausal women (time since menopause 1-5 years), 5 postmenopausal women receiving steroid hormone replacement therapy, 5 postmenopausal women receiving salmon calcitonin and 5 fertile women with regular menstrual cycles. Blood samples were collected every 15 min for 4 h and hormone levels were measured by radioimmunoassay. Plasma GH levels fell in the postmenopausal women, but were restored under oestrogen-progestogen treatment. The pulsatile patterns of plasma LH and FSH did not show significant differences in the treated and untreated women. Plasma osteocalcin levels showed episodic fluctuations and mean levels decreased under steroid hormone or calcitonin treatment. No significant correlation was observed between plasma GH and osteocalcin or gonadotrophin levels or body mass index.

Action of morphine on rat cortical neurons intracellularly recorded in vivo: evidence for an excitatory postsynaptic effect which is naloxone insensitive

The action of morphine, applied either iontophoretically (40-200 nA balanced current) or systemically (5-10 mg/kg, intraperitoneally) to rat cortical neurons, was investigated in vivo, using intracellular electrodes. Morphine increased the apparent input resistance and increased the number of both spontaneous and evoked action potentials. Several cells, which normally generated single spikes, generated bursting potentials; neurons with bursting activity increased their activity. Naloxone, iontophoretically or systemically applied, did not reverse or prevent the morphine-induced excitation. The iontophoretic administration of cadmium suggested that the effects of morphine were due, at least in part, to a postsynaptic site of action. It is suggested that the increase of cellular excitability induced by morphine could contribute to its production of seizures in cortex.

[A case of cerebral stroke caused by a spontaneous dissection of the internal carotid with rapid resolution]

We describe a case of acute stroke due to a spontaneous carotid dissection. Doppler sonography performed 12 hours after stroke and repeated in the following days suggested a dissection of the right internal carotid artery, then confirmed by angiography. The dissection could be unrecognized because of a complete normalization of the flow within the fifth day. This case shows the importance of performing an early ultrasonic examination in stroke patients.

O-204 Non-invasive AI image analysis unlocks the secrets of oocyte quality and reproductive potential by assigning ‘Magenta’ scores from 2-dimensional (2-D) microscope images

Study question

Can an Artificial Intelligence (AI) software tool, utilizing 2-D image analysis of mature oocytes, prospectively correlate an oocyte score to utilizable blastocyst development?

Summary answer

Oocyte Magenta scores show a statistically significant difference in blastocyst development between the highest (7.1-10) and lowest (1.0-4.0) scored oocytes [46.1% vs 26.6%; p < 0.005].

What is known already

Unlike sperm (WHO 2010) or embryos (Gardner blastocyst grading), there is no validated visual oocyte scoring system used in clinical practice. Embryologists have been unsuccessful in correlating oocyte morphological features to reproductive potential. A valuable oocyte scoring system should be able to correlate higher scores with improved embryological outcomes. Although not possible by the human eye, a non-invasive oocyte AI assessment tool (Magenta) has accomplished this feat in retrospective studies. This study applied the Magenta network at two IVF clinics in real-time; representing one of the few prospective AI studies in our field, and the only one focusing on oocytes.

Study design, size, duration

This prospective, multi-center study was conducted from September - November 2021 by TRIO Fertility (Toronto, Canada) and CARE Fertility (Sheffield and Nottingham, UK), utilizing the oocyte AI image analysis tool, Magenta. Magenta was created with a convolutional neural network trained on 16,373 oocyte images and corresponding outcomes. Inclusion criteria was all IVF-ICSI patients who consented to participate without severe male factor (testicular or epididymal sources). Results are based on 392 images of oocytes (46 patients).

Participants/materials, setting, methods

Non-invasive, light microscope images were taken of mature oocytes post-denudation, prior to ICSI, utilizing an image capture software. Images were uploaded and analyzed by Magenta, scoring each oocyte on a scale of 1-10, and remained in a blinded folder to the IVF clinics. De-identified patient outcomes were collected to analyze blastocyst development correlation with Magenta scores. Oocytes were handled as per good laboratory practice, without extended periods outside the incubator or disruption to standard protocols.

Main results and the role of chance

Oocyte images were analyzed by Magenta to score each oocyte on a scale of 1-10. There was a total of 46 patients representing 392 oocytes from both TRIO (26, 280) and CARE (20, 112). The scoring spectrum was divided into 3 tiers (1.0-4.0: 188 oocytes; 4.1-7.0: 128 oocytes; 7.1-10: 76 oocytes). A utilizable blastocyst was defined as a Gardner grade of 2BB or greater on Day 5 or 3BB or greater by Day 6 of embryo development and of adequate quality for transfer, freezing or PGT-A biopsy.  

The blastocyst development (positivity) rate was 26.6% (1.0-4.0), 32.0% (4.1-7.0) and 46.1% (7.1-10), with mean Magenta scores of 2.4, 5.5 and 8.2, respectively. The lowest and highest tier of Magenta scores were accordingly found to have the lowest and highest blastocyst rates, which was statistically significant (p-value < 0.005) by a Two-Proportions Z-test. 

Overall, oocytes that developed into a utilizable blastocyst had a higher mean Magenta score (5.0) than oocytes that did not develop into a utilizable blastocyst (4.3); (p-value <0.05) by a Welch’s Two Sample t-test. 

Limitations, reasons for caution

Sample size is currently limited for this ongoing, prospective study. Therefore, additional male factor (non-surgical sperm sources) and possible poor images have not been removed from the current analysis. Furthermore, AI neural network accuracy is restricted by the amount of data it is trained on.

Wider implications of the findings

Magenta has enabled visual oocyte assessments that will provide IVF-ICSI patients with insights into their oocyte quality; resulting in counselling benefits and the ability to make more informed, personalized decisions regarding future treatment plans. AI will inevitably improve the IVF process and prospective validation studies are critical in its evolution.

Trial registration number

Not applicable.