Effects of adenosine agents on apomorphine-induced yawning in rats

Exploring the neurobiology of the premonitory phase of migraine preclinically - a role for hypothalamic kappa opioid receptors?

Background

The migraine premonitory phase is characterized in part by increased thirst, urination and yawning. Imaging studies show that the hypothalamus is activated in the premonitory phase. Stress is a well know migraine initiation factor which was demonstrated to engage dynorphin/kappa opioid receptors (KOR) signaling in several brain regions, including the hypothalamus. This study proposes the exploration of the possible link between hypothalamic KOR and migraine premonitory symptoms in rodent models.

Methods

Rats were treated systemically with the KOR agonist U-69,593 followed by yawning and urination monitoring. Apomorphine, a dopamine D1/2 agonist, was used as a positive control for yawning behaviors. Urination and water consumption following systemic administration of U-69,593 was also assessed. To examine if KOR activation specifically in the hypothalamus can promote premonitory symptoms, AAV8-hSyn-DIO-hM4Di (Gi-DREADD)-mCherry viral vector was microinjected into the right arcuate nucleus (ARC) of female and male KOR^CRE or KOR^WT mice. Four weeks after the injection, clozapine N-oxide (CNO) was administered systemically followed by the assessment of urination, water consumption and tactile sensory response.

Results

Systemic administration of U-69,593 increased urination but did not produce yawning in rats. Systemic KOR agonist also increased urination in mice as well as water consumption. Cell specific Gi-DREADD activation (i.e., inhibition through Gi-coupled signaling) of KOR^CRE neurons in the ARC also increased water consumption and the total volume of urine in mice but did not affect tactile sensory responses.

Conclusion

Our studies in rodents identified the KOR in a hypothalamic region as a mechanism that promotes behaviors consistent with clinically-observed premonitory symptoms of migraine, including increased thirst and urination but not yawning. Importantly, these behaviors occurred in the absence of pain responses, consistent with the emergence of the premonitory phase before the headache phase. Early intervention for preventive treatment even before the headache phase may be achievable by targeting the hypothalamic KOR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01497-7.

On the Emergence of Tremor in Prodromal Parkinson's Disease

Clinical, neuropathological and neuroimaging research suggests that pathological changes in Parkinson's disease (PD) start many years before the emergence of motor signs. Since disease-modifying treatments are likely to be most effective when initiated early in the disease process, there has been significant interest in characterizing prodromal PD. Some people with PD describe autonomic symptoms at the time of diagnosis suggesting that autonomic dysfunction is a common feature of prodromal PD. Furthermore, subtle motor signs may be present and emerge prior to the time of diagnosis. We present a series of patients who, in the prodromal phase of PD, experienced the emergence of tremor initially only while yawning or straining at stool and discuss how early involvement of autonomic brainstem nuclei could lead to these previously unreported phenomena. The hypothalamic paraventricular nucleus (PVN) plays a central role in autonomic control including bowel/bladder function, cardiovascular homeostasis and yawning and innervates multiple brainstem nuclei involved in autonomic functions (including brainstem reticular formation, locus ceruleus, dorsal raphe nucleus and motor nucleus of the vagus). The PVN is affected in PD and evidence from related phenomena suggest that the PVN could increase tremor either by increasing downstream cholinergic activity on brainstem nuclei such as the reticular formation or by stimulating the locus ceruleus to activate the cerebellothalamocortical network via the ventrolateral nucleus of the thalamus. Aberrant cholinergic/noradrenergic transmission between these brainstem nuclei early in PD couldlead to tremor before the emergence of other parkinsonian signs, representing an early clinical clue to prodromal PD.

How yawning switches the default-mode network to the attentional network by activating the cerebrospinal fluid flow

Yawning is a behavior to which little research has been devoted. However, its purpose has not yet been demonstrated and remains controversial. In this article, we propose a new theory involving the brain network that is functional during the resting state, that is, the default mode network. When this network is active, yawning manifests a process of switching to the attentional system through its capacity to increase circulation of cerebrospinal fluid (CSF), thereby increasing clearance of somnogenic factors (prostaglandin D(2), adenosine, and others) accumulating in the cerebrospinal fluid.

Treatment with AC pulsed electromagnetic fields improves olfactory function in Parkinson's disease

Olfactory dysfunction is a common symptom of Parkinson's disease (PD). It may manifest in the early stages of the disease and infrequently may even antedate the onset of motor symptoms. The cause of olfactory dysfunction in PD remains unknown. Pathological changes characteristic of PD (i.e., Lewy bodies) have been demonstrated in the olfactory bulb which contains a large population of dopaminergic neurons involved in olfactory information processing. Since dopaminergic drugs do not affect olfactory threshold in PD patients, it has been suggested that olfactory dysfunction in these patients is not dependent on dopamine deficiency. I present two fully medicated Parkinsonian patients with long standing history of olfactory dysfunction in whom recovery of smell occurred during therapeutic transcranial application of AC pulsed electromagnetic fields (EMFs) in the picotesla flux density. In both patients improvement of smell during administration of EMFs occurred in conjunction with recurrent episodes of yawning. The temporal association between recovery of smell and yawning behavior is remarkable since yawning is mediated by activation of a subpopulation of striatal and limbic postsynaptic dopamine D2 receptors induced by increased synaptic dopamine release. A high density of dopamine D2 receptors is present in the olfactory bulb and tract. Degeneration of olfactory dopaminergic neurons may lead to upregulation (i.e., supersensitivity) of postsynaptic dopamine D2 receptors. Presumably, small amounts of dopamine released into the synapses of the olfactory bulb during magnetic stimulation may cause activation of these supersensitive receptors resulting in enhanced sense of smell. Interestingly, in both patients enhancement of smell perception occurred only during administration of EMFs of 7 Hz frequency implying that the release of dopamine and activation of dopamine D2 receptors in the olfactory bulb was partly frequency dependent. In fact, weak magnetic fields have been found to cause interaction with biological systems only within narrow frequency ranges (i.e., frequency windows) and the existence of such frequency ranges has been explained on the basis of the cyclotron resonance model.

Yawning and stretching induced by transcranial application of AC pulsed electromagnetic fields in Parkinson's disease

Yawning is considered a brainstem regulated behavior which is associated with changes in arousal and activity levels. Yawning and stretching are dopamine (DA) mediated behaviors and pharmacological studies indicate that these behaviors are associated with increased DA release coupled with stimulation of postsynaptic DA-D2 receptors. Despite their relation to the dopaminergic system, yawning and stretching are poorly documented in untreated or treated patients with Parkinson's disease (PD). A 49 year old fully medicated female patient with juvenile onset PD is presented in whom recurrent episodes of yawning and stretching developed during transcranial administration of AC pulsed electromagnetic fields (EM Fs) of picotesla flux density. These episodes have not been observed previously in this or other patients during treatment with levodopa or DA receptor agonists or in unmedicated PD patients during treatment with AC pulsed EMFs. It is suggested that yawning and stretching behavior resulted in this patient from a synergistic interaction between EMFs and DA derived from levodopa supplementation with EMFs possibly facilitating the release of DA and simultaneously activating postsynaptic DA-D2 receptors in the nigrostriatal dopaminergic pathways. In addition, it is postulated that the release of ACTH/MSH peptides from peptidergic neurons in the brain upon stimulation of the DA-D2 receptors reinforced the yawning and stretching behavior.

Differential effects of selective adenosine A1 and A2A receptor agonists on dopamine receptor agonist-induced behavioural responses in rats

The effects of the systemic (i.p.) administration of the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the selective adenosine A2A receptor agonist sodium 2-p-carboxyethyl)phenylamino-5'-N-carboxamidoadenosine (CGS 21680) on different dopamine receptor agonist-induced behaviours were studied in the male rat. CGS 21680 (1 micromol/kg), but not CPA, was found to counteract the stereotypies induced by the non-selective dopamine receptor agonist apomorphine (0.25 mg/kg s.c.). Low doses of CGS 21680 (0.1 micromol/kg) and high doses of CPA (3 micromol/kg) counteracted yawning induced by the dopamine D2 selective agonist quinpirole (0.05 mg/kg). On the other hand, low doses of CPA (0.3 micromol/kg) antagonized grooming induced by the selective dopamine D1 receptor-selective agonist SKF 38393 (10 mg/kg i.p.), while CGS 21680 was ineffective. These results are consistent with the proposed existence of a selective antagonistic modulation of dopamine D1 and D2 receptors by adenosine A1 and A2A receptors, respectively. The ability of CGS 21680 to counteract apomorphine-induced stereotypies is weaker compared to its previously reported antagonistic effect of amphetamine-induced motor activity. This supports the hypothesis that adenosine A2A receptor agonists may be potential antipsychotic drugs with a low potential for extrapyramidal side effects.

Effect of adenosine receptor agonists and antagonists on morphine-induced catalepsy in mice

Effects of adenosine receptor agonists and antagonists on morphine-induced catalepsy in mice were investigated. The adenosine agonists, NECA (5'-N-ethylcarboxamidoadenosine) and S-PIA (S(+)-N6-(2-phenylisopropyl)adenosine) in doses which did not induce any response, increased the cataleptogenic effect produced by morphine. However, the morphine response was decreased and increased by the lower and higher doses of the adenosine receptor agonist, CHA (N6-cyclohexyladenosine), respectively. The adenosine receptor antagonist, theophylline, decreased, but 8-phenyltheophylline increased, the response induced by morphine. Naloxone inhibited the catalepsy induced by morphine or morphine + NECA but not that induced by NECA alone. It is concluded that adenosine A2 receptor activation increases, while adenosine A1 receptor stimulation decreases, the morphine cataleptogenic response. The response to morphine may be mediated through opioid and adenosine receptor mechanisms.

Adenosine receptor agents and conditioned place preference

1. The effects of different doses of the adenosine agonists N5-ethylcarboxamido-adenosine (NECA), R-isomer of N6-phenylisopropyladenosine (R-PIA), and N6-cyclohexyladenosine (CHA) or of the antagonists theophylline and 8-phenyltheophylline (8-PT) on conditioned place preference (CPP) have been studied. 2. The results show that R-PIA and CHA induced conditioned place aversion (CPA) whereas NECA induced conditioned place preference (CPP). 3. Low doses of theophylline elicit CPP, but high doses of the drug induced CPA. 8-PT also produced the CPP. 4. The responses of R-PIA and CHA but not NECA was decreased by theophylline and 8-PT administration. 5. It is concluded that the induction of CPP an CPA by adenosine antagonsists may be mediated by different adenosine receptors.