The Balance of MU-Opioid, Dopamine D2 and Adenosine A2A Heteroreceptor Complexes in the Ventral Striatal-Pallidal GABA Antireward Neurons May Have a Significant Role in Morphine and Cocaine Use Disorders.

The widespread distribution of heteroreceptor complexes with allosteric receptor-receptor interactions in the CNS represents a novel integrative molecular mechanism in the plasma membrane of neurons and glial cells. It was proposed that they form the molecular basis for learning and short-and long-term memories. This is also true for drug memories formed during the development of substance use disorders like morphine and cocaine use disorders. In cocaine use disorder it was found that irreversible A2AR-D2R complexes with an allosteric brake on D2R recognition and signaling are formed in increased densities in the ventral enkephalin positive striatal-pallidal GABA antireward neurons. In this perspective article we discuss and propose how an increase in opioid heteroreceptor complexes, containing MOR-DOR, MOR-MOR and MOR-D2R, and their balance with each other and A2AR-D2R complexes in the striatal-pallidal enkephalin positive GABA antireward neurons, may represent markers for development of morphine use disorders. We suggest that increased formation of MOR-DOR complexes takes place in the striatal-pallidal enkephalin positive GABA antireward neurons after chronic morphine treatment in part through recruitment of MOR from the MOR-D2R complexes due to the possibility that MOR upon morphine treatment can develop a higher affinity for DOR. As a result, increased numbers of D2R monomers/homomers in these neurons become free to interact with the A2A receptors found in high densities within such neurons. Increased numbers of A2AR-D2R heteroreceptor complexes are formed and contribute to enhanced firing of these antireward neurons due to loss of inhibitory D2R protomer signaling which finally leads to the development of morphine use disorder. Development of cocaine use disorder may instead be reduced through enkephalin induced activation of the MOR-DOR complex inhibiting the activity of the enkephalin positive GABA antireward neurons. Altogether, we propose that these altered complexes could be pharmacological targets to modulate the reward and the development of substance use disorders.

Transcranial focal electrical stimulation reduces seizure activity and hippocampal glutamate release during status epilepticus.

Previously we demonstrated that noninvasive transcranial focal electrical stimulation (TFS) with sub-effective doses of diazepam reduces status epilepticus (SE)-induced neuronal damage. However, it was unclear if this neuroprotective effect is a consequence of the decrease in the glutamate release. The aim of the present study was to evaluate the effects of TFS on γ-Aminobutyric acid (GABA) and glutamate release in the hippocampus during pilocarpine-induced SE. After pilocarpine administration, the rats showed progressive behavioral changes that culminated in SE with a significant increase of GABA and glutamate (95 and 128% respectively), even more evident at the end of the experiment (120 and 182% respectively), 5 hours after pilocarpine injection and was associated with the prevalence of high-voltage rhythmic spikes and increased spectral power in the 4-90 Hz bands. The TFS application during the SE decreased the convulsive expression, the prevalence of high-voltage rhythmic spikes and spectral power in 4-8 Hz and 30-90 Hz bands. These effects were associated with lower release of GABA and glutamate in the hippocampus. These results support the anticonvulsive and neuroprotective effects induced by TFS.

Amino acid tissue levels and GABAA receptor binding in the developing rat cerebellum following status epilepticus.

Incidence of status epilepticus (SE) is higher in children than in adults and SE can be induced in developing rats. The cerebellum can be affected after SE; however, consequences of cerebellar amino acid transmission have been poorly studied. The goal of this study was to determine amino acid tissue concentration and GABA(A) receptor binding in the immature rat cerebellum after an episode of SE. Thirteen-day-old (P13) rat pups received intraperitoneal injections of lithium chloride (3 mEq/kg). Twenty hours later, on P14, SE was induced by subcutaneous injection of pilocarpine hydrochloride (60 mg/kg). Control animals were given an equal volume of saline subcutaneously. Animals were killed 24h after SE induction, the cerebellum was quickly removed, and the vermis and hemispheres were rapidly dissected out on ice. Amino acid tissue concentrations in the vermis and hemispheres were evaluated by HPLC and fluorescent detection. GABA(A) receptor binding in the medial vermis was analyzed by in vitro autoradiography. SE increased the tissue levels of the inhibitory amino acids taurine (80%) and alanine (91%), as well as glutamine (168%) in the cerebellar hemisphere; no changes were observed in the vermis. SE did not modify GABA(A) receptor binding in any cerebellar lobule from the vermis. Our data demonstrate that SE produces region-specific changes in amino acid concentrations in the developing cerebellum.

Vulnerability of postnatal hippocampal neurons to seizures varies regionally with their maturational stage.

The mechanism of status epilepticus-induced neuronal death in the immature brain is not fully understood. In the present study, we examined the contribution of caspases in our lithium-pilocarpine model of status epilepticus in 14 days old rat pups. In CA1, upregulation of caspase-8, but not caspase-9, preceded caspase-3 activation in morphologically necrotic cells. Pretreatment with a pan-caspase inhibitor provided neuroprotection, showing that caspase activation was not an epiphenomenon but contributed to neuronal necrosis. By contrast, upregulation of active caspase-9 and caspase-3, but not caspase-8, was detected in apoptotic dentate gyrus neurons, which were immunoreactive for doublecortin and calbindin-negative, two features of immature neurons. These results suggest that, in cells which are aligned in series as parts of the same excitatory hippocampal circuit, the same seizures induce neuronal death through different mechanisms. The regional level of neuronal maturity may be a determining factor in the execution of a specific death program.

El pretratamiento agudo y subcrónico con farmacos anticonvulsivantes modifica las crisis generalizadas inducidas por el pentilenetetrazol en el ratón / The acute and subchronic pretreatment with antiepileptic drugs modifies the pentylenetetrazol- induced generalized seizures in mice

Objetivo: El incremento en el contenido de GABA cerebral o la administración de un agente GABA-mimético se emplea como un tratamiento antiepiléptico eficaz. Sin embargo, se sugiere que el empleo de farmacos que alteran continuamente la transmisión sinoptica puede afectar al sistema nervioso. En el presente estudio se evaluaron los efectos del pretratamiento agudo (una administración) y subcrónico (administraciones diarias por 7 días) de diazepam (DZP; 10 mg/kg, ip), gabapentina (GBP, 100 mg/kg, vo) y vigabatrina (VGB, 500 mg/kg, vo) en las crisis generalizadas inducidas por pentilenetetrazol (PTZ, 80 mg/kg ip). Materiales y métodos: Ratones macho de la cepa taconic (20-25 g) recibieron tratamiento agudo y subcrónico de DZP, GBP o VGB y 24 h después de la última administración se aplicó PTZ. Se evaluaron las latencias a la primera crisis clónica, a la fase tónica así como la incidencia de muerte. Resultados: El pretratamiento agudo con DZP protegió 100 por ciento a los animales de los efectos del PTZ, mientras que su administración subcrónica redujo la latencia a la crisis clónica (21 por ciento; p<0.05), la fase tónica (27 por ciento, p<0.05) y muerte (37 por ciento, p<0.05). La aplicación aguda de VGB protegió 100 por ciento a los animales de los efectos del PTZ, mientras que su aplicación subcrónica aumentó la latencia a las crisis clónicas (32 por ciento, p<0.05), aunque facilitó la aparición de la crisis tónica (55 por ciento, p<0.05) y la muerte (58 por ciento, p<0.05). La administración aguda de GBP elevó la latencia a la crisis clónica (52 por ciento, p<0.05), mientras que su administración subcrónica no modificó el efecto producido por PTZ. Conclusiones: Estos resultados sugieren que el pretratamiento agudo y subcrónico de farmacos que incrementan la transmisión GABAérgica modifican diferencialmente la susceptibilidad a las crisis por PTZ y que su administración repetida puede facilitar la producción de crisis convulsivas.

Objetives: The increased GABA content or administration of a centrally active GABA-mimetic agent have been used as a efficacious anticonvulsant therapeutic approach. However, it has been suggested that the use of drugs that continually and noncontingently alter synaptic transmission could alter at the nervous system. The present study was carried out to investigate the effects of acute (one administration) and subchronic (7 daily administrations) treatments with Diazepam (DZP; 10 mg/kg, ip), Gabapentin (GBP, 100 mg/kg. vo) and Vigabatrin (VGB, 500 mg/kg, vo) on pentylenetetrazol-induced generalized seizures (PTZ, 80 mg/kg, ip). Materials and methods: Male Taconic mice (20-25 g) received acute or subchronic treatment with DZP, VGB or GBP and 24 h after the last administration, the effects of PTZ (latency to the clonus, forelimb extension and death incidence) were evaluated. Results: Acute DZP protected all animals (100 percent) to the convulsant effects of PTZ, whereas subchronic DZP decreased the latency to the clonic (21 percent; p<0.05), tonic (27 percent, p<0.05) and death (37 percent, p<0.05). The acute treatment with VGB protect all animals (100 percent) to the effects of PTZ, whereas its subcronic administration enhanced the latency to clonus (32 percent, p<0.05), but facilitated the appearance of tonic seizures (55 percent, p<0.05) and death (58 percent, p<0.05). The acute administration of GPB increased the latency to clonus (52 percent, p<0.05), whereas its subchronic treatment did not modify the PTZ-induced effects. Conclusions: The present results indicate that the acute pretreatment with drugs enhancing GABAergic transmission differently modifies the seizure susceptibility, and that the subchronic administration may facilitate the seizure activity.

Do single seizures cause neuronal death in the human hippocampus?

The question of whether repeated single seizures cause neuronal death in the adult human brain is of great clinical importance and might have broad therapeutic implications. Reviewed here are recent studies on the effects of repeated single seizures (in the absence of status epilepticus) on hippocampal volume and on neuronal death markers in blood and in surgically ablated hippocampi.