Subicular lesions cause dendritic atrophy in CA1 and CA3 pyramidal neurons of the rat hippocampus.

The subiculum is a major source of output projections from hippocampus to cortical and subcortical regions. Our previous studies have demonstrated the selective loss of CA1 pyramidal neurons of the hippocampus, and operant and spatial learning impairment in subicular lesioned rats [Govindaiah et al. (1997) Brain Res. 745, 121-126; Laxmi et al. (1999) Brain Res. 816, 245-148]. In the present study, the effect of ibotenate lesions of the subiculum on the dendritic morphology of CA1 and CA3 pyramidal neurons of the hippocampus was investigated in 30-day-old male Wistar rats. The ventral subiculum was lesioned bilaterally with multiple injections of ibotenic acid, stereotaxically. The dendritic branching points and intersections were studied in apical and basal dendrites up to 320 and 160 microm, respectively, in Golgi-impregnated CA1 and CA3 pyramidal neurons of the hippocampus. The results revealed a significant (P<0.001) decrease in the number of dendritic branching points, intersections and total number of dendrites in both apical and basal dendrites of CA1, as well as CA3 pyramidal neurons of the hippocampus. It is surprising that the subicular lesions caused dendritic atrophy of CA3 neurons without affecting the cell density. The results of the present study demonstrate the dendritic atrophy of hippocampal neurons following selective subicular lesions. This might be responsible for the impairments in operant and spatial learning tasks in these rats as observed in our earlier studies. In addition, hippocampal damage is also associated with an impairment in the process of the active monitoring of movements in space, rather than place learning per se [Whishaw (1998) Neurosci. biobeh. Rev. 22, 209-220]. Accordingly, further studies are required to correlate the differential effect of subicular lesions on impairments in learning and movement in space in rats.

Ventral subicular lesion alters rhythmical slow wave activity (theta) of CA1 area of hippocampus and entorhinal cortex.

The present study demonstrates the effect of ibotenic acid lesioning of ventral subiculum on the theta activity of CA1 area of hippocampus and the entorhinal cortex during REM sleep. Ibotenic acid lesioning of ventral subiculum, has increased the absolute power with no noticeable change in the relative power of theta of the CA1 area. In contrast, it has decreased both the absolute and relative power of entorhinal cortical theta. Subicular output may serve to modulate the synchronous neuronal activity of entorhinal cortex and CA1 pyramidal cells during REM sleep.

Deficits in operant behavior and alteration of CA1, CA3 hippocampal dendritic arborization due to subicular lesions.

The deficits in operant behavior and the alterations in dendritic arborizations of Cornu Ammonis 1 and Cornu Ammonis 3 (CA1 and CA3) hippocampal areas were investigated in subicular lesioned rats. The subjects were female Wistar rats aged 120 days, and were divided into four groups: one serving as age-matched untrained control, a second group received training and sham lesioning, a third group were only trained, and the fourth group were first trained and then subjected to subicular lesions. The rats were food-deprived 24 hours prior to operant behavior training sessions. Two training sessions for operant behavior with continuous reinforcement of 10 minutes duration per day were done during the shaping session, following which rats were allowed 10 minutes of operant food reward for 10 days. On the eleventh day, only the operant behavior and sham-operated rats were used for subicular lesion and sham surgery, respectively. After 72 hours of surgical recovery, operant behavioral testing was performed daily as before for a further period of 10 days. Later, all groups of rats were killed and the hippocampus was processed for rapid Golgi staining. Our results suggest that subicular lesions produce a significant reduction in operant learning. Further, the Golgi studies revealed a reduction in dendritic branching points and intersections of apical and basal CA1, CA3 neurons in lesioned rats.

Effects of vigabatrin on sleep-wakefulness cycle in amygdala-kindled rats.

PURPOSE: Our aim was to study the effect of prolonged administration of vigabatrin (VGB) on sleep-wakefulness cycle in kindled seizure-induced rats. METHODS: Adult male Wistar rats were implanted stereotaxically with electrodes for kindling and polysomnography. The rats were divided into two groups, kindled and VGB-treated kindled rats. VGB was administered intraperitonially every day for 21 days, and polysomnographic recordings were taken after doses 1, 7, 14, and 21. The drug effects were evaluated by comparing the records of kindled and drug-treated kindled rats. RESULTS: The VGB-administered kindled rats showed an increase in total sleep time (TST) due to an increase in total non-rapid eye movement (NREM) and light slow-wave sleep stage I (SI) with a decrease in wakefulness. The number of episodes and REM onset latencies were found to be decreased after drug treatment. CONCLUSIONS: It can therefore be concluded that VGB has a somnolence-inducing effect and that it might mediate its anticonvulsant effect by altering sleep architecture through sleep-regulating areas.

Amelioration of fornix lesion induced learning deficits by self-stimulation rewarding experience.

Intracranial self-stimulation (ICSS) rewarding experience is known to modulate learning and memory and induce morphological and neurochemical changes in hippocampus. Therefore, we studied the effect of ICSS on the hippocampus-dependent operant and the spatial learning tasks in rats with bilateral electrolytic lesioning of fornix. Bilateral lesioning of fornix induced deficits in acquisition and performance of both the tasks, whereas exposure to 10 days of ICSS experience from ventral tegmental area reversed these behavioural deficits. Hence, we propose that the ICSS experience ameliorates the fornix lesion induced behavioural deficits, by inducing neuronal plasticity in the hippocampus which may act as a compensatory mechanism for the deficits produced by the lesioning of fornix.

Increased numerical density of synapses in CA3 region of hippocampus and molecular layer of motor cortex after self-stimulation rewarding experience.

Self-stimulation has been considered as an intensely rewarding behavioural experience, being perhaps even more influential than feeding or sexual behaviour. Our earlier studies have demonstrated a self-stimulation rewarding experience-induced increase in dendritic branching points, intersections and spine densities in CA3 hippocampal and layer V motor cortical pyramidal neurons. In the present study, we report self-stimulation-induced alterations in the numerical density of synapses in the hippocampus and motor cortex. A self-stimulation experience was provided 1 h daily for a period of 10 days through bipolar electrodes, implanted bilaterally in the lateral hypothalamus and substantia nigra-ventral tegmental area, stereotaxically. The results revealed a significant (P < 0.001) increase in the number of synapses in the CA3 region of hippocampus and the molecular layer of the motor cortex in self-stimulation-experienced rats. The increased synaptic number may be due to the activation of afferent pathways to the hippocampus and motor cortex following self-stimulation, which may lead to the induction of long-term potentiation. Long-term potentiation is known to cause structural changes by strengthening the existing synapses or resulting in the formation of new synapses. These changes may be related to the improved cognitive functions observed in self-stimulation-experienced rats.

Self-stimulation rewarding experience induced alterations in dendritic spine density in CA3 hippocampal and layer V motor cortical pyramidal neurons.

Self-stimulation rewarding experience induced alterations in the numerical density of spines in CA3 hippocampal and layer V motor cortical pyramidal neurons in adult male Wistar rats was evaluated. Self-stimulation experience was provided 1 h daily over a period of 10 days through stereotaxically implanted bipolar stainless steel electrodes bilaterally in lateral hypothalamus and substantia nigra-ventral tegmental area. After 10 days, rats were killed and the hippocampus and motor cortex were processed for rapid Golgi staining procedure. The dendritic spine densities were studied in CA3 hippocampal and layer V motor cortical pyramidal neurons. The spine densities were quantified in five successive segments of 15.2 microm up to a distance of 76 microm. Apical dendrites were classified as mainshaft, sub branch, oblique shaft-I, oblique shaft-II, primary branch; and basal dendrites as main shaft, primary branch and secondary branch. A grand total of 864 CA3 hippocampal and 1008 layer V motor cortical dendrites were analysed for spine counting in different groups of rats. The results revealed a significant (P<0.001; ANOVA, F-test) increase in the number of spines in all the categories of dendrites in apical and basal regions in both hippocampal and motor cortical neurons in self-stimulation group of rats. Such changes were not observed either in sham control, experimenter-administered or normal control groups of rats. The self-stimulation induced increase in the spine density suggests an increase in the postsynaptic receptive field in CA3 hippocampal and layer V motor cortical neurons. This might enhance the efficacy of synaptic transmission in these neurons. Our study clearly demonstrated the self-stimulation rewarding experience induced postsynaptic plasticity in hippocampal and motor cortical pyramidal neurons.

Alterations in the levels of monoamines in discrete brain regions of clomipramine-induced animal model of endogenous depression.

It has been hypothesized that the dysfunction of the serotonergic and catecholaminergic neurotransmission is involved in the pathogenesis of depression. These hypotheses are being tested in a novel rat model of depression developed by the treatment of antidepressant-clomipramine neonatally from postnatal day 8 to 21. After the attainment of adulthood, these rats mimicked the features of the human endogenous depression showing significant decrease in the aggressive behavior and food intake. Biogenic amine estimations in these rats revealed that the levels of serotonin and noradrenaline were decreased significantly (P < 0.001) in frontal cortex, hippocampus, brain stem, septum and hypothalamus, while the levels of dopamine were decreased significantly (P < 0.001) only in the hippocampus compared to normal control and vehicle treated groups of rats. Our results demonstrate the dysfunction of serotonergic and noradrenergic neurotransmission, with lesser involvement of dopaminergic neurotransmission in the clomipramine induced experimental model of depression.

Chronic (-) deprenyl administration alters dendritic morphology of layer III pyramidal neurons in the prefrontal cortex of adult Bonnett monkeys.

Chronic (-) deprenyl (0.2 mg/kg, b.wt; for 25 days) treatment induced alterations in the dendritic morphology of prefrontal cortical neurons in adult Bonnett monkeys were evaluated in the present study. The branching points and intersections in apical and basal dendrites were studied up to a distance of 400 and 200 micrometers, respectively, in Golgi impregnated layer III pyramidal neurons of the prefrontal cortex. Our results revealed a significant (p<0.001) increase in the number of branching points and intersections in both apical and basal dendrites in (-) deprenyl treated monkeys compared to controls. Such an enriched dendritic arborization in prefrontal cortical neurons may be responsible for the enhancement of cognitive functions in Alzheimer disease patients following (-) deprenyl treatment.

Spatial memory impairment in ventral subicular lesioned rats.

The present study examined the effects of ibotenic acid lesions of the ventral subiculum (SUB) on the ability of rats to memorize a rewarded alternation test in a T-maze. Results indicated that rats with ibotenic acid lesions (IL) of the ventral subiculum were impaired in postoperative acquisition of the spatial discrimination task, making more errors than the vehicle treated and normal control rats. In addition, all rats, including the IL group of rats, were able to memorize an acquired spatial behaviour. These findings suggest that the SUB play an important role in spatial information processing in rats.

Sleep-wakefulness alterations in amygdala-kindled rats.

PURPOSE: Our aim was to study the relation between epilepsy and sleep-wakefulness cycles in the amygdala-kindling model of temporal lobe epilepsy. METHODS: Adult male Wistar rats were electrically kindled through bipolar electrodes implanted in the anterior amygdala. Polysomnographic recordings were taken before and after kindled seizures for 6 h. For the studies on the effects of a single, full-blown seizure, recordings were taken immediately after the seizure and daily thereafter until the recordings returned to baseline values. For studies on the effects of five full-blown seizures, recordings were taken immediately after the fifth seizure and then on day 1, 2, 3, 5, 7, 14, 21, and 28. RESULTS: Polysomnographic recordings taken immediately after the first full-blown seizure revealed an initial increase in the duration of deep slow-wave sleep (SII), a decrease in the light slow-wave sleep (SI) stage of non-rapid eye movement (NREM) sleep, and a decrease in the quiet wakefulness (W2) stage of wakefulness. All these parameters returned to baseline values after 24 h. The duration of rapid eye movement (REM) sleep increased and returned to the baseline value after 48 h. Five consecutive full-blown seizures caused an increase in the duration of SII from the day the seizures occured until day 28, whereas the duration of SI decreased for 72 h. The duration of REM sleep, decreased only on the day of the seizures and day 1, while decreases in the number of REM episodes were observed on the day of the seizure, day 2 and day 14. CONCLUSIONS: Our study indicates that even a single, full-blown seizure can cause alterations in the architecture of sleep-wakefulness cycles for a short duration, and that multiple seizures produce long-term effects.

Long-lasting structural changes in CA3 hippocampal and layer V motor cortical pyramidal neurons associated with self-stimulation rewarding experience: a quantitative Golgi study.

Self-stimulation (SS) rewarding experience induced structural changes in CA3 hippocampal and layer V motor cortical pyramidal neurons in adult male Wistar rats has been demonstrated. In the present study, whether these structural changes are transient or of a permanent nature was evaluated. Self-stimulation experience was provided for 1 h daily over a period of 10 days through bilaterally implanted bipolar electrodes in the lateral hypothalamus and the substantia nigra-ventral tegmental area. Following 10 days of SS experience, the rats were sacrificed after an interval of 30 and 60 days for the quantitative analysis of the dendritic morphology in Golgi stained CA3 hippocampal and layer V motor cortical pyramidal neurons. The results revealed a significant increase in the dendritic branching points and intersections in apical and basal dendrites in both types of neurons in 30 days post-SS group compared to sham control. The total number of apical and basal dendrites were significantly increased in both 30 and 60 days post-SS groups of rats. This study suggests that SS experience induced structural changes are sustainable, even in the absence of rewarding experience.

Alterations in the density of excrescences in CA3 neurons of hippocampus in rats subjected to self-stimulation experience.

Self-stimulation (SS) rewarding experience induced alterations in the density of excrescences in the apical dendrites of CA3 neurons were studied in adult male Wistar rats. SS experience was provided daily for an hour over a period of 10 days, through bipolar stainless steel electrodes implanted bilaterally in lateral hypothalamus and substantia nigra-ventral tegmental area. The results revealed a significant (P<0.001) increase in the number of excrescences in both main shaft and sub branches of the apical dendrites in SS experienced group compared to control groups of rats. The increased number of excrescences in CA3 neurons might be due to an enhancement in the synaptic transmission in the mossy fiber pathway following SS experience.

Role of monoamine oxidase type A and B on the dopamine metabolism in discrete regions of the primate brain.

The role of monoamine oxidase (MAO) type A and B on the metabolism of dopamine (DA) in discrete regions of the monkey brain was studied. Monkeys were administered (-)-deprenyl (0.25 mg/kg) or clorgyline (1.0 mg/kg) or deprenyl and clorgyline together by intramuscular injections for 8 days. Levels of DA and its metabolites, dihydroxy phenylacetic acid (DOPAC) and homovanillic acid (HVA) were estimated in frontal cortex (FC), motor cortex (MC), occipital cortex (OC), entorhinal cortex (EC), hippocampus (HI), hypothalamus (HY), caudate nucleus (CN), globus pallidus (GP) and substantia nigra (SN). (-)-Deprenyl administration significantly increased DA levels in FC, HY, CN, GP and SN (39-87%). This was accompanied by a reduction in the levels of DOPAC (37-66%) and HVA (27-79%). Clorgyline administration resulted in MAO-A inhibition by more than 87% but failed to increase DA levels in any of the brain regions studied. Combined treatment of (-)-deprenyl and clorgyline inhibited both types of MAO by more than 90% and DA levels were increased (57-245%) in all brain regions studied with a corresponding decrease in the DOPAC (49-83%) and HVA (54-88%) levels. Our results suggest that DA is metabolized preferentially, if not exclusively by MAO-B in some regions of the monkey brain.

Self-stimulation of lateral hypothalamus and ventral tegmentum increases the levels of noradrenaline, dopamine, glutamate, and AChE activity, but not 5-hydroxytryptamine and GABA levels in hippocampus and motor cortex.

Self-stimulation (SS) rewarding experience induced structural changes have been demonstrated in the hippocampal and motor cortical pyramidal neurons. In the present study, we have evaluated whether these changes are accompanied by neurochemical alterations in the hippocampus and motor cortex in SS experienced rats. Self-stimulation experience was provided one hour daily over a period of 10 days through stereotaxically implanted bipolar stainless steel electrodes, bilaterally in lateral hypothalamus and substantia nigra-ventral tegmental area. Self-stimulation experience resulted in a significant (P < 0.001) increase in the levels of noradrenaline, dopamine, glutamate and AChE activity but not 5-hydroxytryptamine and GABA levels in hippocampus and motor cortex. Such alterations in the levels of neurotransmitters may enhance the cognitive functions in the SS experienced rats.

Chronic (-) deprenyl administration increases dendritic arborization in CA3 neurons of hippocampus and AChE activity in specific regions of the primate brain.

The mechanism by which (-) deprenyl enhances cognitive function in Alzheimer's disease (AD) is not yet understood. (-) Deprenyl (0.2 mg/kg/day) was administered intramuscularly to adult male monkeys (n = 6) for 25 days. Control monkeys (n = 6) received physiological saline by the same route. The activity of acetylcholinesterase (AChE) in different brain regions and the dendritic arborization in CA3 pyramidal neurons of hippocampus were analysed. (-) Deprenyl-treated monkeys showed a significant increase in the AChE activity by 43% (p < 0.001) in the frontal cortex, by 39% (p < 0.025) in the motor cortex, by 66% (p < 0.001) in the hippocampus and by 26% (p < 0.05) in the striatum compared to controls. The branching points and the intersections of both apical and basal dendrites of CA3 hippocampal pyramidal neurons were also significantly increased in (-) deprenyl-treated monkeys. Enhanced AChE activity may increase dendritic arborization in the hippocampus and it may also play a role in improving cognitive functions observed in AD, following (-) deprenyl treatment.

Facilitation of acquisition and performance of operant and spatial learning tasks in self-stimulation experienced rats.

Adult male Wistar rats were implanted bilateraly with bipolar electrodes in substantia nigra-ventral tegmental area (SN-VTA) to experience intracranial self-stimulation (ICSS) for 15 min per day over a period of 10 days. These rats were then assessed for the acquisition and performance of the operant and the spatial learning tasks. ICSS experienced rats showed rapid acquisition of both the operant and the spatial learning tasks. Both the lever press performance for 7 sessions in the operant learning task and mean number of alternations per session in the spatial learning task were significantly higher (p < .001) in ICSS experienced rats compared with controls. The results suggest that prior ICSS experience facilitates the acquisition and performance in both the operant and the spatial learning tasks, which may be due to the structural and neurochemical alterations in the hippocampus induced by ICSS experience.

(-)-Deprenyl attenuates spinal motor neuron degeneration and associated locomotor deficits in rats subjected to spinal cord ischemia.

We have evaluated potential neuroprotection offered by (-)-deprenyl on degenerating motor neurons of the spinal cord when subjected to transient ischemia. Thirty-six healthy adult male Wistar rats were trained for a motor function test in a staircase maze and randomly but equally (n = 6) grouped into normal control, sham control, ischemia (IS), IS rats treated with vehicle (IV), and rats treated with low (0.1 mg/kg) and high (1.0 mg/kg) doses of (-)-deprenyl. (-)-Deprenyl was given intraperitoneally 30 min after the induction of ischemia and thereafter everyday for 14 days. Spinal cord ischemia was produced at the lumbar level in conscious rats by occluding the abdominal aorta just below the branching point of the left renal artery for 30 min. Analysis of the motor performance in all groups of rats revealed a significant (P < 0.001) increase in the time taken to cross the run way of the maze, in i.s. and i.v. rats compared to all other groups of rats. In addition, qualitative and quantitative examination of spinal motor neurons at the lumbar level showed a significant (P < 0.001) decrease in the number of healthy motor neurons in i.s. and i.v. rats compared to controls. Postischemic administration of (-)-deprenyl, at both doses, significantly prevented motor neuron degeneration and the associated locomotor deficits in IS rats.

Subicular lesion induced impairment in operant behaviour and altered dendritic morphology of CA1, CA3 hippocampal neurons.

The effects of bilateral electrolytic subicular lesions were examined on the operant behaviour for food reward on a continuous reinforcement schedule as well as the dendritic morphology of CA1 and CA3 hippocampal areas. The subjects were female Wistar rats 20 days of age and were divided into four groups. 1. Age matched control 2. Sham operated 3. Operant behaviour for food reward and 4. Subicular lesion. Animals were starved twenty-four hours prior to operant behaviour training sessions. Two trial sessions with continuous reinforcement (CRF) of 10 min duration/day were done during training sessions following which the rats were allowed CRF for ten minutes per day for ten days. On the eleventh day, the operant behaviour and sham operated animals were taken up for bilateral subicular lesion and sham surgery respectively. After seventy two hours of surgical recovery, operant behavioural testing was done as before for a further period of ten days. Later all the groups of animals were sacrificed and the hippocampi were processed for rapid Golgi staining technique. Our results suggest that subicular lesions do produce a significant reduction in operant learning behaviour for food reward. Further the Golgi studies revealed a reduction in dendritic branching points and intersections of apical and basal CA1, CA3 neurons in lesioned animals.

Selective reduction of monoamine oxidase A and B in the frontal cortex of subordinate rats.

We have previously shown that subordination causes a reduction in the levels of 5-hydroxytryptamine and dopamine selectively in the frontal cortex [6]. These monoamines are catabolised mainly by the enzyme monoamine oxidase (MAO) which exists in two isoforms; MAO-A and MAO-B. The present study was carried out to determine whether there is any change in the activity of these two iso-enzymes induced by subordination and if any such alteration is confined to the frontal cortex. The animal model of dominance-subordination used was a worker-parasite paradigm in male Wistar rats. The enzyme activities were measured in five brain regions, the frontal cortex, entorhinal cortex, hippocampus, hypothalamus and striatum, using kynuramine as the substrate. Clorgyline and L-deprenyl were used in vitro to block the activities of MAO-A and MAO-B, respectively. There was a significant (P < 0.001) reduction in the activity of MAO-A as well as MAO-B selectively in the frontal cortex of the subordinate animals. This finding may suggest a reduced neurotransmitter turnover in the serotonergic and dopaminergic neurons terminating in the frontal cortex.