[Functional alterations in central nervous system of prehepatic portal hypertensive rats]. / Cambios funcionales en el sistema nervioso central de ratas hipertensas portales prehepaticas.

Prehepatic Portal Hypertension (PH) leads to morphologic changes in the rat Central Nervous System, including alterations of the blood brain barrier (BBB), and astrogliosis and angiogenesis in CA1 and CA4 hyppocampal fields. The present study investigates functional changes in portal hypertensive rats. Wistar Kyoto rats were used (240 g/bw) and allotted in two groups: GI (n = 8) portal hypertensive rats obtained through a regulated stenosis of the portal vein (Groszmann), and GII (n = 6), sham-operated rats. We have analyzed: BBB integrity with the Trypan Blue diffusion method (TB, Reynolds), protein concentration (PC) in Cerebrospinal Fluid (CSF) and plasma (Bradford method), electroencephalographic activity (EEG), cerebral edema expressed as brain water content (gravidimetric test), and behavior: Animex, righting reflex, pain reflex and Rotarod. TB was positive in GI in peripheral vascular areas in hippocampus, PC in CSF (ug/ml)(mean +/- SED) was GI: 40.6 +/- 6.8 and GII: 16.5 +/- 4.2 (p < 0.005), and the plasma levels were (mg/ml): GI: 108.8 +/- 7.6 and GII: 87.4 +/- 2 (NS). The EEG showed a higher power of the delta band in hypertensive rats (GI: 0.551 +/- 0.033 and GII: 0.342 +/- 0.031, p < 0.008), but water content was not different between GI and GII (water%/per/g/tissue) (GI: 79.21 +/- 0.2, GII: 78.95 +/- 0.18). These results, showing functional changes in the BBB and brain activity without behavioral alterations, suggest the development of a subclinic form of hepatic encephalopathy in our model of PH rats.

Cambios funcionales en el sistema nervioso central de ratas hipertensas portales prehepaticas. / [Functional alterations in central nervous system of prehepatic portal hypertensive rats]

Prehepatic Portal Hypertension (PH) leads to morphologic changes in the rat Central Nervous System, including alterations of the blood brain barrier (BBB), and astrogliosis and angiogenesis in CA1 and CA4 hyppocampal fields. The present study investigates functional changes in portal hypertensive rats. Wistar Kyoto rats were used (240 g/bw) and allotted in two groups: GI (n = 8) portal hypertensive rats obtained through a regulated stenosis of the portal vein (Groszmann), and GII (n = 6), sham-operated rats. We have analyzed: BBB integrity with the Trypan Blue diffusion method (TB, Reynolds), protein concentration (PC) in Cerebrospinal Fluid (CSF) and plasma (Bradford method), electroencephalographic activity (EEG), cerebral edema expressed as brain water content (gravidimetric test), and behavior: Animex, righting reflex, pain reflex and Rotarod. TB was positive in GI in peripheral vascular areas in hippocampus, PC in CSF (ug/ml)(mean +/- SED) was GI: 40.6 +/- 6.8 and GII: 16.5 +/- 4.2 (p < 0.005), and the plasma levels were (mg/ml): GI: 108.8 +/- 7.6 and GII: 87.4 +/- 2 (NS). The EEG showed a higher power of the delta band in hypertensive rats (GI: 0.551 +/- 0.033 and GII: 0.342 +/- 0.031, p < 0.008), but water content was not different between GI and GII (water

/per/g/tissue) (GI: 79.21 +/- 0.2, GII: 78.95 +/- 0.18). These results, showing functional changes in the BBB and brain activity without behavioral alterations, suggest the development of a subclinic form of hepatic encephalopathy in our model of PH rats.

An immunocytochemical study on the distribution of two G-protein-gated inward rectifier potassium channels (GIRK2 and GIRK4) in the adult rat brain.

G-protein-gated inward rectifier potassium channels mediate the synaptic actions of numerous neurotransmitters in the mammalian brain, and were recently shown to be candidates for genetic mutations leading to neuronal cell death. This report describes the localization of G-protein-gated inward rectifier potassium channel-2 and G-protein-gated inward rectifier potassium channel-4 proteins in the rat brain, as assessed by immunocytochemistry. G-protein-gated inward rectifier potassium channel-2 immunoreactivity was widely distributed throughout the brain, with the strongest staining seen in the hippocampus, septum, granule cell layer of the cerebellum, amygdala and substantia nigra pars compacta. In contrast, G-protein-gated inward rectifier potassium channel-4 immunoreactivity was restricted to some neuronal populations, such as Purkinje cells and neurons of the globus pallidus and the ventral pallidum. The presence of G-protein-gated inward rectifier potassium channel-2 immunoreactivity in substantia nigra pars compacta dopaminergic neurons was confirmed by showing its co-localization with tyrosine hydroxylase by double immunocytochemistry, and also by selectively lesioning dopaminergic neurons with the neurotoxin 6-hydroxydopamine. At the cellular level both proteins were localized in neuronal cell bodies and dendrites, but clear differences were seen in the degree of dendritic staining among neuronal groups. For some neuronal groups the staining of distal dendrites (notably dendritic spines) was strong, while for others the cell body and proximal dendrites were preferentially labelled. In addition, some of the results suggest that G-protein-gated inward rectifier potassium channel-2 protein could be localized in distal axonal terminal fields. A knowledge of the distribution of G-protein-gated inward rectifier potassium channel proteins in the brain could help to elucidate their physiological roles and to evaluate their potential involvement in neurodegenerative processes in animal models and human diseases.

Comparative expression of the inward rectifier K+ channel GIRK2 in the cerebellum of normal and weaver mutant mice.

The main target for degeneration associated with the weaver mutation is the cerebellum. Expression of the GIRK2 mRNA and protein was studied in cerebellum of 12- and 22-day-old normal and weaver mice. In 12-day-old mice, GIRK2 is expressed at highest levels in the external granule layer (EGL) and in lower levels in the newly forming internal granule layer (IGL). In the weaver cerebellum, a high hybridization signal and dark immunostaining was observed in the EGL due to the higher density of non-migrated cells. In 22-day-old weaver cerebella, there are only few remaining granule cells existing as scattered cells within the IGL and molecular layer. GIRK2 is expressed in these neurons but the majority of cells expressing GIRK2 in these cerebella are Purkinje cells that are also affected by the weaver mutation (position, shape) but have not died. Normal cerebellar granule neurons but not homozygous mutant neurons in primary cultures and cerebellar slices of 8-day-old mice displayed inward rectifier K+ currents. Taken together, these findings suggest that cell loss in the weaver cerebellum is not directly related to a differential content of GIRK2 in the affected neurons during development. The lethal effect of the weaver mutation in specific neurons is probably due to a combination of the abnormal function of the inward rectifier K+ channels and other factors specific to the vulnerable neurons.

Absence of neurotoxicity of chronic L-DOPA in 6-hydroxydopamine-lesioned rats.

We investigated the effects of 6 months' oral treatment with L-dihydroxy-phenylalanine (L-DOPA)/carbidopa on the remaining dopaminergic neurones of the substantia nigra pars compacta (SNC) and the ventral tegmental area (VTA) of rats with moderate or severe 6-hydroxydopamine (6-OHDA)-induced lesions and sham-operated animals. Using a radioimmunohistochemical method we counted tyrosine hydroxylase (TH)-radioimmunoreactive cells in the SNC and the VTA in emulsion-coated sections and measured the remaining surface area of both structures on autoradiograms. The sole difference observed was a significant increase of the remaining surface area of TH radioimmunolabelling in the SNC of moderately lesioned rats treated with L-DOPA/carbidopa compared with the untreated animals, while the rest of the parameters recorded, in both structures and groups of animals, were unchanged. This suggest that in vivo, this treatment is not toxic either to healthy dopaminergic neurones of the ventral mesencephalon or to those surviving after a 6-OHDA lesion.

Turning behavior induced by injections of glutamate receptor antagonists into the substantia nigra of the rat.

We have found recently that muscimol microinjections into the subthalamic nucleus produce contralateral turning activity [Murer and Pazo (1993) NeuroReport, 4:1219-1222]. To test the hypothesis that a reduced glutamate action on substantia nigra pars reticulata neurons mediates this turning response, we examined the effect of unilateral intranigral microinjections of the AMPA/kainate receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX) and the competitive N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP-5). DNQX and AP-5 both produced a dose-dependent contralateral turning response, while vehicle administration did not induce turning activity. Application of glutamate receptor antagonists at adjacent regions of the mesencephalic tegmentum were also ineffective. Coadministration of NMDA or AMPA significantly reduced the turning response induced by AP-5 or DNQX, respectively. Lesions of the nigrostriatal pathway by 6-hydroxydopamine did not modify the response to DNQX or AP-5 administration into the nigra. However, their behavioral effects were significantly reduced by a lesion of the ipsilateral subthalamic nucleus. Our results show that the blockade of a tonic input acting on AMPA/kainate and NMDA receptors located at the substantia nigra produces contralateral turning behavior. The effect seems to involve pars reticulata cells since this area remains unchanged after destruction of dopaminergic neurons. The subthalamic nucleus seems to be the endogenous source of the agonist acting on the nigral glutamate receptors related to turning behavior.

D1 and D2 receptors and circling behavior in rats with unilateral lesion of the entopeduncular nucleus.

The role of D1 and D2 striatal dopamine receptors on circling behavior was studied in a normosensitive model obtained by unilateral kainic acid lesion of the entopeduncular nucleus. In this model, the sensitivity of striatal dopamine receptors was preserved, because kainic acid destroyed the neurons of the entopeduncular nucleus and left undamage the fibers of passage and axon terminals. Systemic administration of SKF 38393 to these animals fails to induce circling activity. In contrast, administration of quinpirole elicited rotation toward the lesioned side, which was increased by concurrent injection of SKF 38393. This behavior was inhibited by pretreatment with either a specific D1 (SCH 23390) or D2 (-sulpiride) antagonist. The apomorphine also induced ipsilateral circling that was abolished by pretreatment with D1 or D2 antagonists. The above results suggest that coactivation of both D1 and D2 striatal dopamine receptors are necessary to induce rotation in this normosensitive model.

Changes in pancreatic exocrine secretion after repeated haloperidol administration.

The effect of repeated administration of haloperidol on the pancreatic secretion was studied in urethane-anesthetized Swiss mice. Haloperidol (2 mg/kg) injected daily i.p. for 7 days, increase the volume and protein content of the basal pancreatic juice significantly. This secretory activity was partially blocked by i.p. injection of atropine (5 mg/kg), both in control and treated animals. The volume of the secretory response to bethanechol, a cholinergic agonist, was decreased by haloperidol without any change in amylase release. From these findings it is concluded that repeated haloperidol treatment produces an increase of basal pancreatic secretion, which is probably the result of changes in the sensitivity of dopamine receptors of the gland.

The sialagogue response of striatal dopamine receptors to L-dopa is not influenced by castration or chronic estrogen treatment.

The secretory response of salivary glands to L-dopa, elicited by stimulation of dopamine receptors in the striatum and the circling behavior induced by apomorphine in animals bearing a unilateral kainic lesion of the entopeduncular nucleus, was studied in intact and ovariectomized female rats. Castration did not modify the sialagogue response to L-dopa, while the turning behavior was significantly increased. Daily administration of 17-beta-estradiol benzoate during 7 days to ovariectomized rats decreased the circling activity to the level of intact female rats, while the salivary secretion to L-dopa was unaffected. The above findings suggest that the sialagogue response induced by L-dopa may be due to the interaction of this agonist with D1 striatal receptors, whose activity is not influenced by estrogens. However, we cannot rule out any possible alteration in the metabolism and/or presynaptic conversion of L-dopa to dopamine by estrogen treatment. The changes in turning behavior may be attributed to an antidopaminergic effect of estrogens and/or, like L-dopa, to modifications in the metabolism of apomorphine induced by the hormone.