Effect of postictal process in motor deficit and monoaminergic concentration in hippocampus, cerebellum, and cortex / Efecto del proceso postictal en el déficit motor y la concentración monoaminérgica en el hipocampo, el cerebelo y la corteza

Abstract Introduction Systemic administration of pentylenetetrazole (PTZ) causes brain damage (BD), and triggers a series of morphological and neurochemical changes, which in turn bring about behavioral, cognitive, and motor deficits. Serotonin (5-HT), dopamine (DA), and noradrenaline (NA) levels are controlled by various brain structures and these levels are related to motor activity; however, the concentration of these neurotransmitters during the postictal process remains unknown. Objective We investigated the concentration of 5-HT, NA and DA in the hippocampus, cerebellum, and cortex on motor deficit during the postictal stage. Method Eighteen male Wistar rats (300 g) assigned to two groups: control (n = 9, saline solution) and experimental (n = 9, PTZ) were used. Myoclonic shakes were counted and motor behavior assessments were recorded during three hours post PTZ injection (90 mg/kg). The cortex, cerebellum, and hippocampus of each rat were dissected to determine the 5-HT, DA, and NA concentration by high performance liquid chromatography. Results PTZ induced a significant increase in total 5-HT and DA levels in the hippocampus and cortex; in the cerebellum there was a significant increase in the concentration of 5-HT and NA. The presence of myoclonic shakes as well as a marked motor deficit in the experimental group were significantly different in comparison to the control. Discussion and conclusion 5-HT modifies the concentration of other monoamines directly involved in motor aspects such as NA and DA in the hippocampus, cerebellum, and cortex during the postictal process.

Resumen Introducción La administración sistémica de pentilentetrazol (PTZ) causa daño cerebral y desencadena una serie de cambios morfológicos y neuroquímicos que a su vez provocan déficits conductuales, cognitivos y motores. Los niveles de serotonina (5-HT), dopamina (DA) y noradrenalina (NA) son modulados por varias estructuras cerebrales y sus concentraciones se relacionan con la actividad motora; sin embargo, se desconoce la concentración de estos neurotransmisores durante el proceso postictal. Objetivo Evaluar la manera en que la concentración de 5-HT, NA y DA en el hipocampo, el cerebelo y la corteza influye en el déficit motor durante la etapa postictal. Método Se utilizaron 18 ratas macho Wistar (300 g), divididas en dos grupos: control (n = 9, solución salina) y experimental (n = 9, PTZ). Se registraron las sacudidas mioclónicas y se evaluó el comportamiento motor durante tres horas después de la inyección de PTZ (90 mg/kg). Se extrajeron la corteza, el cerebelo y el hipocampo de cada rata para determinar la concentración de 5-HT, DA y NA mediante cromatografía líquida de alta resolución. Resultados La administración de PTZ indujo un aumento significativo en los niveles totales de 5-HT y DA en el hipocampo y la corteza; en el cerebelo hubo un aumento significativo en la concentración de 5-HT y NA. Se encontró una diferencia significativa entre el grupo experimental y control con respecto a las sacudidas mioclónicas; asimismo, los animales del grupo experimental mostraron un marcado déficit motor. Discusión y conclusión La 5-HT modula la concentración de otras monoaminas involucradas directamente en aspectos motores tal como NA y DA en el hipocampo, el cerebelo y la corteza durante el proceso postictal.

Histamine H3 receptor activation reduces the impairment in prepulse inhibition (PPI) of the acoustic startle response and Akt phosphorylation induced by MK-801 (dizocilpine), antagonist at N-Methyl-d-Aspartate (NMDA) receptors.

We have investigated the effect of the local activation of histamine H3 receptors (H3Rs) in the rat prefrontal cortex (PFCx) on the impairment of pre-pulse inhibition (PPI) of the startle response induced by the systemic administration of MK-801, antagonist at glutamate N-Methyl-d-Aspartate (NMDA) receptors, and the possible functional interaction between H3Rs and MK-801 on PFCx dopaminergic transmission. Infusion of the H3R agonist RAMH (19.8 ng/1 µl) into the PFCx reduced or prevented the inhibition by MK-801 (0.15 mg/kg, ip) of PPI evoked by different auditory stimulus intensities (5, 10 and 15 dB), and the RAMH effect was blocked by the H3R antagonist/inverse agonist ciproxifan (30.6 ng/1 µl). MK-801 inhibited [3H]-dopamine uptake (-45.4 ±â€¯2.1%) and release (-32.8 ±â€¯2.6%) in PFCx synaptosomes or slices, respectively, and molecular modeling indicated that MK-801 binds to and blocks the rat and human dopamine transporters. However, H3R activation had no effect on the inhibitory action of MK-801 on dopamine uptake and release. In PFCx slices, MK-801 and the activation of H3Rs or dopamine D1 receptors (D1Rs) stimulated ERK-1/2 and Akt phosphorylation. The co-activation of D1Rs and H3Rs prevented ERK-1/2 and Akt phosphorylation, and H3R activation or D1R blockade prevented the effect of MK-801. In ex vivo experiments, the intracortical infusion of the D1R agonist SKF-81297 (37 ng/1 µl) or the H3R agonist RAMH increased Akt phosphorylation, prevented by D1R/H3R co-activation. These results indicate that MK-801 enhances dopaminergic transmission in the PFCx, and that H3R activation counteracts the post-synaptic actions of dopamine.

Sensorimotor Intervention Recovers Noradrenaline Content in the Dentate Gyrus of Cortical Injured Rats.

Nowadays, a consensus has been reached that designates the functional and structural reorganization of synapses as the primary mechanisms underlying the process of recovery from brain injury. We have reported that pontine noradrenaline (NA) is increased in animals after cortical ablation (CA). The aim of the present study was to explore the noradrenergic and morphological response after sensorimotor intervention (SMI) in rats injured in the motor cortex. We used male Wistar adult rats allocated in four conditions: sham-operated, injured by cortical ablation, sham-operated with SMI and injured by cortical ablation with SMI. Motor and somatosensory performance was evaluated prior to and 20 days after surgery. During the intervening period, a 15-session, SMI program was implemented. Subsequently, total NA analysis in the pons and dentate gyrus (DG) was performed. All groups underwent histological analysis. Our results showed that NA content in the DG was reduced in the injured group versus control, and this reduction was reverted in the injured group that underwent SMI. Moreover, injured rats showed reduction in the number of granule cells in the DG and decreased dentate granule cell layer thickness. Notably, after SMI, the loss of granule cells was reverted. Locus coeruleus showed turgid cells in the injured rats. These results suggest that SMI elicits biochemical and structural modifications in the hippocampus that could reorganize the system and lead the recovery process, modulating structural and functional plasticity.

Histamine H3 receptor activation inhibits dopamine synthesis but not release or uptake in rat nucleus accumbens.

We studied the effect of activating histamine H3 receptors (H3Rs) on rat nucleus accumbens (rNAcc) dopaminergic transmission by analyzing [(3)H]-dopamine uptake by synaptosomes, and dopamine synthesis and depolarization-evoked [(3)H]-dopamine release in slices. The uptake of [(3)H]-dopamine by rNAcc synaptosomes was not affected by the H3R agonist RAMH (10(-10)-10(-6) M). In rNAcc slices perfusion with RAMH (1 µM) had no significant effect on [(3)H]-dopamine release evoked by depolarization with 30 mM K(+) (91.4 ± 4.5% of controls). The blockade of dopamine D2 autoreceptors with sulpiride (1 µM) enhanced K(+)-evoked [(3)H]-dopamine release (168.8 ± 15.5% of controls), but under this condition RAMH (1 µM) also failed to affect [(3)H]-dopamine release. Dopamine synthesis was evaluated in rNAcc slices incubated with the l-dihydroxyphenylalanine (DOPA) decarboxylase inhibitor NSD-1015 (1 mM). Forskolin-induced DOPA accumulation (220.1 ± 10.4% of controls) was significantly reduced by RAMH (41.1 ± 6.5% and 43.5 ± 9.1% inhibition at 100 nM and 1 µM, respectively), and this effect was prevented by the H3R antagonist ciproxifan (10 µM). DOPA accumulation induced by preventing cAMP degradation with IBMX (iso-butyl-methylxantine, 1 mM) or by activating receptors for the vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating peptide (PACAP) with PACAP-27 (1 µM) was reduced (IBMX) or prevented (PACAP-27) by RAMH (100 nM). In contrast, DOPA accumulation induced by 8-Bromo-cAMP (1 mM) was not affected by RAMH (100 nM). These results indicate that in rNAcc H3Rs do not modulate dopamine uptake or release, but regulate dopamine synthesis by inhibiting cAMP formation and thus PKA activation. This article is part of the Special Issue entitled 'Histamine Receptors'.

Iron-dextran injection into the substantia nigra in rats decreases striatal dopamine content ipsilateral to the injury site and impairs motor function.

Iron chloride injections into the rat SNc can cause chronic decreases in striatal dopamine (DA) levels. However, changes in striatal DA content after iron-dextran injection into rat SNc have not been completely elucidated. The aim of this work was to measure striatal DA concentrations after iron-dextran injection into the SNc. We divided 40 male Wistar rats into five groups, including control, saline injected then sacrificed 7 days or 30 days later, and iron-dextran injected then sacrificed 7 days or 30 days later. Striatal DA content was measured in control animals and in all animals sacrificed 7 days or 30 days after injection, and motor performance was assessed in iron-dextran and saline injected groups 30 days after injection. The striatal DA levels were determined using HPLC. There were significant (P < 0.05) decreases in DA concentrations in the striatum ipsilateral to the injection site in the iron-dextran treated rats compared to control and saline-injected rats. There were no significant differences in DA concentration between the sham-operated (i.e., saline-injected) and control rats. We also observed motor deficits in the iron-dextran injected rats. The striatal DA reduction observed after iron-dextran injection may be attributable to iron-induced oxidative injury in the SNc. Motor deficits, in turn, may be explained by subsequent disturbances in striatal and cortical dopaminergic neuromodulation.

Pontine and cerebellar norepinephrine content in adult rats recovering from focal cortical injury.

Norepinephrine (NE) plays an important role in motor recovery after brain damage. Most studies concerning NE activity have been performed in the cerebellum, while the role of the pons, the site where the norepinephrinergic locus coeruleus is located, has not yet been elucidated. For this work, we studied the changes in cerebellar and pontine NE content in sham-operated (n = 17), motor cortex injured (n = 6) and recovered rats (n = 12). Motor effects were assessed by means of footprint analysis and sensorimotor evaluation. It was found that after cortical brain damage, the stride length decreases while the stride angle increases after 6 h post-surgery, while the sensorimotor evaluation showed an increase in the motor deficit. Recovery was observed after 24 h. NE content increased in the pons after 6 h and returned to normal levels in recovered rats, with no significant changes observed in the cerebellum. Based on the functional remote inhibition, it is possible that NE exerts an autoinhibitory effect in the pons after motor cortical ablation. On the other hand, the absence of an effect in the cerebellum suggests that cerebellar NE activity related to damage and/or recovery is limited to discrete areas of the structure.

Pontine norepinephrine content after motor cortical ablation in rats.

It has been reported that norepinephrine (NE) plays an important role in recovery after brain damage. However, the role of the pons, the site where the norepinephrinergic locus coeruleus (LC) is located, has not been elucidated. In order to study the changes in the pontine NE content in either noninjured, injured or recovered rats, we used 35 animals trained to walk across to a walkway where their footprints were recorded. Subsequently, 17 trained rats were sham-operated while 18 were injured by means of an ablation of the right motor cortex representative of the hindlimb. From the injured rats, 6 were sacrificed 6 hr before surgery in order to obtain the pons, while all the remaining rats were recorded in the walkway 6, 24 and 48 hr post-surgery. Then, rats were sacrificed by decapitation, the pons was removed and each hemisphere was prepared for the chromatographic analysis of NE. Results showed that after cortical brain damage, the length of the stride decreased while the angle of the stride increased 6 hr post-surgery. Recovery was observed after 24 hr. NE increased in the pons after 6 hr and returned to normal levels when rats had recovered. This suggests that cortical damage elicits NE changes in the LC that could reorganize the system to lead the recovery process. Such findings must be taken in account when pharmacotherapy with antidepressants or antipsychotics that act on norepinephrine-containing neuronal systems are prescribed in patients after stroke.