Plasticity of hippocampal and motor cortical pyramidal neurons induced by self-stimulation experience.

The self-stimulation (SS) induced neuronal plasticity was observed in CA3 hippocampal and layer V motor cortical pyramidal neurons. SS experience was allowed daily for a total of 1 hour for 10 days through four bipolar electrodes implanted bilaterally in lateral hypothalamus (LH) and substantia nigra-ventral tegmental area (SN-VTA) in adult male Wistar rats. Examination of pyramidal neurons stained by rapid Golgi technique was made in a total of 1,600 neurons out of 80 rats consisting of 4 groups. The dendritic intersections were quantified upto 200 and 120 microns radial distances in apical and basal dendrites respectively. The CA3 hippocampal and layer V motor cortical pyramidal neurons of SS group revealed significant increase (P < 0.001, two-way ANOVA) in dendritic intersections in both apical and basal dendrites, compared to normal control (NC), sham control (SH) and experimenter-administered (EA) group of animals. These results demonstrate that SS experience promotes increase in dendritic length in hippocampal and motor cortical pyramidal neurons.

Avances en la fisiología de los ganglios basales / Advances in basal ganglia physiology

La organización del sistema de los Ganglios Basales está basada en una serie de circuitos paralelos, funcionalmente segregados pero que comparten un modelo básico común. La principal fuente de aferencias al sistema proviene de casi todas áreas corticales, sensitivo-motoras, asociativas y límbicas, siendo la corteza frontal el receptor final más importante de su actividad aferente. A través de la desinhibición selectiva de los circuitos apropiados, los Ganglios Basales especifican la combinación y secuencia de respuestas más adecuadas a los estímulos, sensoriales o endógenos que motivan una reacción del SNC. Se revisan las evidencias básicas que dan pie a esta interpretación así como a la comprensión de las principales manifestaciones clínicas del sistema

Effect of lesions of areas of brain--stimulation reward of one region of brain on operant behaviour for receiving electrical stimulation into sites of another region and on operant behaviour for food reward.

It was aimed to study the effects of lesions of a self-stimulation (SS) area of one region of brain on the SS of another region, and on feeding behaviour in adult Wistar rats (males). The two regions proposed for study were the lateral hypothalamus (LH) and the substantia nigra-ventral tegmental area (SN-VTA). The objective was to elucidate whether each region had its own neural organization for SS behaviour or not, and whether the neural substrates of SS behaviour and feeding behaviour were one, or separate. Four bipolar electrodes were implanted bilaterally in LH and SN-VTA in each rat, and their SS pedal press rates for rewarding electrical stimulations were characterised. The rats were also trained in operant conditioning paradigm for receiving reward of food grains in FR-30 schedule. Their free-field food intake in home cages was measured. Later, electrolytic lesions of the four electrode sites were made one after another at 2-day intervals through the same biopolar electrodes. After each lesioning, the SS of the same and of the other electrode sites, and the operant performance of FR-30 food reward schedule, and daily free-field food intake (in home cage) were determined. Lesions of the LH SS site always disrupted SS-of contralateral LH but not of SN-VTA SS. Lesions of SN-VTA had not modified contralateral SN-VTA SS. A study of effects of ipsilateral lesions of LH SS site on SN-VTA SS, or of lesions of SN-VTA SS site on LH SS, revealed a range of changes, as were also effects on the FR-30 operant performance and daily food intake. Medium size lesions of SS area made in one region affected the SS of that area but not usually the SS of the other region. Large lesions of one region affected the SS of the other regions also. With large lesions, feeding behaviour also was affected, firstly of the operant type and secondly the free-field type.

Comparative assessment of pedal pressing rates of self-stimulation of hypothalamus and midbrain with both square wave and sine wave stimulus parameters.

In Wistar rats, the regional differences of pedal pressing rates of self-stimulation (SS) of lateral hypothalamus (LH) and substantia nigra-ventral tegmental area (SN-VTA) were assessed with electrodes implanted in both regions in each subject. Average of SS rates of SN-VTA sites was significantly higher than that of LH sites, tested with both sine wave and square wave types of stimuli. There was no significant difference in SS rates between males and females, and also in the females between different days of oestrus cycles. The high rates of robust SS observed in this study relative to SS rates reported in past literature were probably due not only to the placements of electrodes in the main substrates of SS, but also to the parameters of stimulus used (0.25 sec trains of sine waves through bipolar electrodes).

Bilateral microinjection of ethosuximide into the substantia nigra does not prevent amygdala-kindled seizures

Male Wistar rats were sugjected to daily sessions of electrical amygdala kindling until a generalized seixure was observed on five consecutive days. Bilateral microinections (0.5 micronl) of ethosuximide (ETX) (10 pg/micronl) or saline were then administered though guide cannulas into the substantia nigra (pars reticulata). No significant difference was observed between the ETX (N = 8) and saline (N = 8) groups in duration of afterdischarge or in the latency for stage 5 generalized seizures. Our results indicate that ETX applied to the substantia nigra is not effective in suppressing amydala-kindled seizure

Investigation of influence of diazepam, valproate, cyproheptadine and cortisol on the rewarding ventral tegmental self-stimulation behaviour.

Experiments were carried on in the Wistar rats having self-stimulation (SS) electrodes implanted chronically in substantia nigra-ventral tegmental area (SN-VTA) to examine whether modulations of GABAergic, serotonergic, histaminergic, dopaminergic, and glucocorticoid neuronal receptor functions will affect or not the brain reward system and the SS behaviour. The modulators are the wellknown drugs: diazepam which is a facilitator of some of the GABA receptors, and used clinically for its tranquilizing, anxiolytic, sedative-hypnotic and anti-convulsant properties; sodium valproate which is known to enhance the GABA synapse function, and used clinically for its anti-convulsant property; haloperidol which is a dopaminergic receptor (D2) blocker, and clinically used for its anti-psychotic property; cyproheptadine which is both anti-histaminic and anti-serotonergic (blocks 5-HT2 receptor), used clinically for its antihistaminic and other beneficial properties; and hydrocortisone which is the stress-resisting glucocorticoid having direct effects on both brain and body cells, used clinically for the wide-ranging glucocorticoid therapeutic effects. The results revealed that systemic administration of these drugs, except haloperidol, caused no significant influence on the SS behaviour, thereby indicating that these nondopaminergic drugs have no effect on brain-reward system and also these categories of synaptic actions are not likely to be involved in the primary organization of the mechanisms of the brain-reward system.

Effects of both 6-hydroxydopamine-induced and electrolytic lesion of the substantia nigra on the rotational behavior and audiogenic seizures in the rat

1. Twenty-eight male albino rats were evaluted for audiogenic seizure sensitivity by systematic observation and the recording of behavior by ethological methods. The animals were subjected to high-intensity acoustic stimulation and their behavior was evaluated by reference to an audiogenic severity index (SI). Animals were classified as susceptible (S) or resistant (R) depending on the SI value. R. animals were: 1) subjected to chemical lesion of the substantia nigra compacta with 6-hydroxydopamine (60HDA), followed by SI quantitation, contralateral electolytic lesion osf the substantia nigra reticulata and new SIevaluation (N = 10) received 0,9% saline followed by SI evaluation, contralateral sham (mechanical) lesion and new SI calculation; 3) another group (N = 10) was subjected to unilateral electrolytical lesion of the substantia nigra reticulata and SI evaluation. 2. Effects of asymmetry were observed after chemical or electrolytic lesions, but these alterations correlated only with increased audiogenic sensitivity in rats with electrolytic lesions in the substantia nigra reticulada. No bhevioral changes were observed in any of the cocntrols. The amplhetamine-induced rotational behavior presented a definite left pattern (ipsilateral to the 60HDA lesion) for the animals with bilateral lesions, with an asymmetry index of 98%, whereas the sham-lesioned controls showed a 60% asymmetry index which was not significant. 3. The relationship between asymmetry and ssimultaneous audiogenic sensitivity may correspond to changes in the basal ganglia possibly in the hypersensitive postsynaotic portions of the substantia nigra reticulata efferents

A novel, fully automated rotometer for the study of turning behavior: comparison of results under different experimental conditions

Se describe un rotámetro totalmente automático destinado a la cuantificación del comportamiento rotatorio en ratas con lesión unilateral del sistema nigroestiado. Las partes fundamentales del rotámetro son: a) sensor compuesto a su vez por un disco perforado que reproduce la rotación del animal mediante giro homólogo y dos células infrarrojo, con emisor y receptor cada una de ellas; b) microprocesador que transforma los pulsos de las células fotoeléctricas en información computadorizada, memoriándola; c) impressora comercial conectada al microprocesador. La confiabilidad, utilidad y validez del rotámetro se ensayó en distintos grupos experimentales de ratas adultas. La destrucción unilateral de la zona compacta de la sustantia nigra con 6-hidroxidopamina o ácido Kaínico intracerebrales, produce rotación contralateral bajo administración de apomorfina (0.5 y 1 mg/Kg, s.c.). En cambio la apomorfina provoca rotación homólateral a la lesión en animales con destrucción electrolítica (1.5 mA, 15 s) de la nigra. Para obtener una actividad rotatoria significativa, la lesión electrolítica debe ubicarse en la región externa del núcleo (365+53.4 vueltas/60m en lesión externa (n=5); 97.3ñ19.5 en lesión interna (n=3); t=2.31, p<0,05. Apomorfina 0.5 mg/Kg, s.c.). En animales con lesión unilateral del caudado por ácido iboténico intracerebral, se observa rotación homolateral tanto a la apomorfina como a la bromocriptina tanto a la apomorfina como a la bromocriptina (10 y 30 mg/Kg, i.p.). Se comprueban dif

Conditioned turning and functional recovery after unilateral substantia nigra lesion in rats

In order to invetigate whether conditioned circling interferes with recovery from turning induced by unilateral substantia nigra (SN) lesion, rats were trained to turn either ipsi-or contralateral to the lesioned side before and after the lesion was made. Two yoked groups served as controls. The number of turns contralateral to the trained side was significantly lower in relation to the pre-lesion value for the ipsilateral trained group and remained so until the end of the experiment. A partial recovery was observed on the 19th post-lesion day for the contralateral trained group. The results are discussed in terms of additive effects from training and the lesion symptoms