Time course of certain behavioral changes after hippocampal damage and their alteration by dopaminergic intervention into nucleus accumbens

The Hole-Board Test in Mutant Mice

First described by Boissier and Simon in (Ther Recreat J 17:1225-1232, 1962), the hole-board has become a recognized test of anxiety and spatial memory. Benzodiazepines acting at the GABA_A-BZD site increase hole-pokes in rats and mice, indicating a loss in behavioral inhibition concordant with the behavior of mutant mice deficient in the GABA transporter. Hole-poking also depends on arousal mechanisms dependent on dopaminergic transmission, as indicated by drug and null mutant studies. In addition, the behavior is modified in natural and null mutants affecting the cerebellum as well as null mutants affecting neuropeptides, growth factors, cell adhesion, and inflammation. Further research is required to determine convergences between genetic and pharmacological effects.

Electroencephalographic, cognitive, and neurochemical effects of LY3130481 (CERC-611), a selective antagonist of TARP-γ8-associated AMPA receptors

6-[(1S)-1-[1-[5-(2-hydroxyethoxy)-2-pyridyl]pyrazol-3-yl]ethyl]-3H-1,3-benzothiazol-2-one (LY3130481 or CERC-611) is a selective antagonist of AMPA receptors containing transmembrane AMPA receptor regulatory protein (TARP) γ-8. This molecule has been characterized as a potent and efficacious anticonvulsant in an array of acute and chronic epilepsy models in rodents. The present set of experiments was designed to assess the effects of LY3130481 on the electroencephelogram (EEG), cognitive function, and neurochemical outflow. LY3130481 disrupted food-maintained responding in rats and spontaneous alternation in a Y-maze in mice. In rat fear conditioning, LY3130481 caused a deficit in trace (hippocampal-dependent), but not in delay fear conditioning. Although these effects on cognitive performances were observed, the known cognitive-impairing anticonvulsant, topiramate, did not always produce deficits under these assay conditions. LY3130481 produced modest increases in wake times in rats. In addition, LY3130481 was able to attenuate some impairing effects of standard antiepileptic drugs. The motor-impairing effects of the lacosamide were attenuated by LY3130481 as was the decrease in non-rapid-eye movement sleep induced by carbamazepine. Evaluation of the effect of LY3130481 on neurotransmitter and metabolite efflux in the rat medial prefrontal cortex, using in vivo microdialysis, revealed significant increases in the pro-cognitive and wake-promoting neurotransmitters, histamine and acetylcholine, as well as in serotonin, telemethylhistamine, 5-HIAA, HVA and MHPG. LY3130481 thus presents a novel behavioral profile that will have to be evaluated in patients to fully appreciate its implications for therapeutics. LY3130481 is currently under clinical development as CERC-611 as an antiepileptic.

Striatum on the anxiety map: Small detours into adolescence

Adolescence is the most sensitive period for the development of pathological anxiety. Moreover, specific neural changes associated with the striatum might be related to adolescent vulnerability to anxiety. Up to now, the study of anxiety has primarily focused on the amygdala, bed nucleus of the stria terminalis (BNST), hippocampus and ventromedial prefrontal cortex (vmPFC), while the striatum has typically not been considered as part of the anxiety system. This review proposes the addition of the striatum, a complex, multi-component structure, to the anxiety network by underscoring two lines of research. First, the co-occurrence of the adolescent striatal development with the peak vulnerability of adolescents to anxiety disorders might potentially reflect a causal relationship. Second, the recognition of the role of the striatum in fundamental behavioral processes that do affect anxiety supports the putative importance of the striatum in anxiety. These behavioral processes include (1) attention, (2) conditioning/prediction error, and (3) motivation. This review proposes a simplistic schematic representation of the anxiety circuitry that includes the striatum, and aims to promote further work in this direction, as the role of the striatum in shaping an anxiety phenotype during adolescence could have critical implications for understanding and preventing the peak onset of anxiety disorders during this period. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Chronic psychosocial stress impairs learning and memory and increases sensitivity to yohimbine in adult rats

BACKGROUND

It is well known that intense and prolonged stress can produce cognitive impairments and hippocampal damage and increase noradrenergic activity in humans. This study investigated the hypothesis that chronic psychosocial stress would affect behavior, drug sensitivity, and hippocampal-dependent learning and memory in rats. The work provides a novel connection between animal and human studies by evaluating the effects of stress on a rat's response to yohimbine, an alpha(2) adrenergic receptor antagonist.

METHODS

Rats were exposed to a cat for 5 weeks and randomly housed with a different group of cohorts each day (psychosocial stress). The effects of the stress manipulations were then assessed on open field behavior, spatial learning and memory in the radial arm water maze and the behavioral response to a low dose of yohimbine (1.5 mg/kg).

RESULTS

Stressed rats displayed impaired habituation to a novel environment, heightened anxiety, and increased sensitivity to yohimbine. In addition, the stressed rats exhibited impaired learning and memory.

CONCLUSIONS

There are commonalities between the current findings on stressed rats and from studies on traumatized people. Thus, psychosocial stress manipulations in rats may yield insight into the basis of cognitive and neuroendocrine disturbances that commonly occur in people with anxiety disorders.

A neurobiological basis for substance abuse comorbidity in schizophrenia

It is commonly held that substance use comorbidity in schizophrenia represents self-medication, an attempt by patients to alleviate adverse positive and negative symptoms, cognitive impairment, or medication side effects. However, recent advances suggest that increased vulnerability to addictive behavior may reflect the impact of the neuropathology of schizophrenia on the neural circuitry mediating drug reward and reinforcement. We hypothesize that abnormalities in the hippocampal formation and frontal cortex facilitate the positive reinforcing effects of drug reward and reduce inhibitory control over drug-seeking behavior. In this model, disturbances in drug reward are mediated, in part, by dysregulated neural integration of dopamine and glutamate signaling in the nucleus accumbens resulting form frontal cortical and hippocampal dysfunction. Altered integration of these signals would produce neural and motivational changes similar to long-term substance abuse but without the necessity of prior drug exposure. Thus, schizophrenic patients may have a predilection for addictive behavior as a primary disease symptom in parallel to, and in many, cases independent from, their other symptoms.

Novelty-evoked elevations of nucleus accumbens dopamine: dependence on impulse flow from the ventral subiculum and glutamatergic neurotransmission in the ventral tegmental area

In vivo microdialysis in freely moving rats was used to monitor novelty-evoked elevations in extracellular dopamine in the nucleus accumbens septi (NAS) and to examine the role of the ventral subiculum of the hippocampus and glutamatergic transmission in the ventral tegmental area (VTA) on these elevations. Exposure to novel stimuli evoked investigatory activity and increased nucleus accumbens dopamine. Unilateral injections of the sodium channel blocker tetrodotoxin (0.16 ng/0.5 microL) into the ventral subiculum ipsilateral to the dialysed NAS abolished novelty-evoked elevations in dopamine. Injections of tetrodotoxin into the contralateral VS did not prevent novelty-evoked elevations in nucleus accumbens dopamine. Unilateral perfusion (via microdialysis) of the ionotropic glutamate receptor antagonists kynurenic acid (1 mM) into the ipsilateral but not the contralateral VTA blocked novelty-evoked elevations in nucleus accumbens dopamine. Neither unilateral injections of tetrodotoxin nor unilateral perfusion of kynurenic acid disrupted investigatory behaviour. These data indicate that phasic elevations in nucleus accumbens dopamine evoked by exposure to unconditioned novel stimuli are dependent on impulse flow from the hippocampus and glutamatergic transmission in the VTA.

The cardiovascular effects of amperozide: interactions with cocaine

Amperozide is a 5-HT2A receptor antagonist that significantly reduces the acquisition and expression, by rats, of a cocaine conditioned place preference. In order to rule out the possibility that amperozide affects a cocaine conditioned place preference due to effects on blood pressure or heart rate, the cardiovascular effects of amperozide were investigated. Alternating cumulative doses of amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) or saline and phenylephrine (8 microg kg(-1)) were administered through the femoral vein of awake freely-moving Sprague-Dawley rats and blood pressure and heart rate were recorded from the femoral artery. A single dose of cocaine (5.0 mg kg(-1)) was administered after all the amperozide or saline doses were given. Amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) did not have any significant effect on blood pressure compared to the saline control treatment to the same animals. However, 0.5 mg kg(-1) amperozide significantly decreased heart rate at 5 and 10 min. after administration. but higher doses did not further depress heart rate. Amperozide did not affect the increased blood pressure and decreased heart rate caused by phenylephrine. an alpha1-adrenoceptor agonist. In addition, amperozide did not affect the cardiovascular response to an intravenous dose of 5.0 mg kg(-1) cocaine. These results suggest that amperozide does not cause direct cardiovascular effects. The mechanism by which the lowest dose of amperozide caused a decrease in heart rate is unknown. Amperozide affects neither alpha-adrenoceptor mediated vasoconstriction nor the increased sympathetic activity caused by the peripheral and central effects of cocaine. The significance of these results, in terms of locomotor activity and the cocaine conditioned place preference paradigm, is discussed.

Kainic acid lesions enhance locomotor responses to novelty, saline, amphetamine, and MK-801

Intracerebroventricular (i.c.v.) administration of kainic acid (KA) to rats produces neuronal loss in the hippocampus and other areas of the limbic system. The present study demonstrates that i.c.v. KA enhances the locomotor response to novelty and saline injection, as well as to amphetamine and MK-801. Sixteen to 18 days after i.c.v. administration of KA or vehicle, lesioned and control rats were placed in a novel cage, and locomotor activity and grooming were recorded for 30 min prior to and 60 min following a subcutaneous injection of saline, D-amphetamine, or MK-801. In response to the novel cage and after each injection, KA rats exhibited increased locomotor activity relative to controls. Grooming behavior was found to be elevated in the KA rats when compared to controls, but only in response to the novel cage and saline injection. The possibility that damage to the limbic system disrupts dopaminergic regulation of locomotor behavior is discussed, as well as implications for neuropathology in schizophrenia.

From an animal model of an attentional deficit towards new insights into the pathophysiology of schizophrenia

The paper presents an animal model of schizophrenic-like attentional deficit, consisting of an inability to ignore irrelevant stimuli. It is based on the paradigm of latent inhibition (LI), in which animals learn to ignore repeatedly presented stimuli not followed by meaningful consequences. In a series of experiments it was demonstrated that the capacity to ignore irrelevant stimuli is lost in rats treated with systemic or intra-accumbens injections of amphetamine, in normal volunteers given amphetamine, in high "psychosis-prone" persons, in acute schizophrenic patients and in untreated male adult rats that were raised until weaning under conditions of extremely restricted stimulation. In addition, LI is lost following the disruption of the hippocampal input to the nucleus accumbens. In all of the above conditions tested for antagonism by anti-psychotic drugs a loss of LI is reversed. On the basis of these results we propose an animal model which accommodates a neurodevelopmental dysfunction, hippocampal pathology, mesolimbic DA overactivity, vulnerability to stress, and gender differences, all of which have been postulated as factors in the pathophysiology of schizophrenia.

Behavioral and anatomical consequences of unilateral fornix lesions and the administration of nimodipine

Male Wistar rats subjected to unilateral fimbria-fornix transection by mechanical knife cut or to sham operations were tested in a water maze and in an open field. Half the animals in each group were treated with either 0.06 mg/kg nimodipine or vehicle, administered i.p. for 7 days, beginning the day of surgery. Animals were sacrificed and brains were processed for acetylcholine esterase (AChE) histochemistry. In the water maze, lesioned rats showed a significant impairment relative to the sham-operated animals. Nimodipine treatment did not improve performance. There were no differences among the groups in the observed frequencies of the open field behaviors of locomotion, hole-poke, rearing and grooming. A significant reduction of AChE-positive cell bodies was found in the medial septal region on the side of the lesion. There were no differences in water maze performance among groups of rats treated with 0.0, 0.5, 1.0, or 5.0 mg/kg nimodipine for 7 days, beginning the day of fimbria-fornix transection, in an attempt to determine any dose-dependent effect of the drug.

Amperozide--a new putatively antipsychotic drug with a limbic mode of action on dopamine mediated behaviour

Amperozide, a new putatively antipsychotic drug, was found to exert a functional selectivity for the limbic system of the brain. Thus, amperozide was as active as both classical and atypical neuroleptics on hypermotility induced by a low dose of amphetamine. On the other hand, amperozide did not produce catalepsy, nor did it reverse amphetamine-induced stereotypies. Moreover, amperozide inhibited exploratory behaviour in mice. The present results indicate an antipsychotic effect of amperozide, with a minimal risk for EPS when used in the clinic.

The effects of unilateral destruction of fimbria-fornix and supracallosal pathways in the rat

Rats with unilateral lesions of either the supracallosal regions (including the dorsal cingulate cortex) and the fimbria-fornix either on the same (S) or the opposite (O) sides of the brain were studied in a 16-hole open field without pharmacologic intervention and, subsequently, after 0.1 and after 1.0 mg/kg scopolamine HBr. Their performances were compared with those of unoperated control animals subjected to the same testing regime. Certain of their behaviors were compared with those of a larger number of animals with bilateral hippocampal destruction (and their control groups) from prior studies. Unilateral lesions of fimbria-fornix and supracallosal afferents to the hippocampal formation produced a decrease in hole poking activity relative to control animals. A further decrease in hole-poking behavior, coupled with increased locomotion, was observed in rats with fimbria-fornix and cingulate cortex lesions on opposite sides of the brain (group O). The smaller dose of scopolamine accentuated these effects. Indeed, the behavior of group O after scopolamine treatment was similar to animals with large bilateral hippocampal lesions. The large dose of scopolamine induced stereotyped rearing or hole poking in the brain-damaged animals but not in the control group. These findings suggest that both the fimbria-fornix and the supracallosal pathway is necessary for normal hippocampal function and that the behavioral deficit is greater when these structures are damaged on the opposite sides of the brain.

Altered grooming responses to stress in rats exposed prenatally to ethanol

The effects of prenatal alcohol exposure on grooming, locomotion, and rearing in response to stress were examined in adult rats whose mothers consumed a liquid diet containing 35% ethanol-derived calories (EDC). Offspring of both pair-fed 0% EDC mothers and ad libitum chow-fed mothers were included as controls. In Experiment 1, females groomed more than males following placement into a novel test chamber, but no differences due to prenatal treatment were observed. Ethanol-exposed animals groomed more than controls following the stress of a forced 1-min swim (Experiment 2), but when rats tested in Experiment 1 were observed again after forced swim stress (Experiment 3), no differences due to prenatal treatment or sex were observed. Experiment 4 examined the effects of pretreatment with 1 mg/kg naloxone on novelty-induced grooming and as in Experiment 1 prenatal treatment did not affect grooming responses. Females again groomed significantly more than males and naloxone reduced grooming equally for all groups. The results suggest that novelty-induced grooming is a sex-influenced behavior, with females grooming more than males, and that animals exposed prenatally to alcohol and tested as adults may have altered responses to certain stressors (i.e., forced swim) under specific conditions. The altered grooming response of alcohol-exposed rats to swim stress can be eliminated by preexposing them to novelty stress.

Colchicine-induced granule cell loss in rat hippocampus: selective behavioral and histological alterations

Bilateral injection of 3.5 micrograms of colchicine into two levels of the dentate gyrus produced a selective loss of dentate granule cells and persistent behavioral effects in male Fischer rats. Histological analysis confirmed that this dosage of colchicine resulted in the selective loss of most granule cells in both superior and inferior blades of the dentate gyrus near the injection sites, while sparing pyramidal cells in CA1, CA2, CA3, and CA4, and GABAergic interneurons throughout the hippocampus. Rats injected with colchicine were significantly more active than cerebrospinal fluid-injected controls 2, 7, 14, 21 and 28 days after treatment. Behavioral reactivity, assessed by the magnitude of the acoustic startle response and the latency to respond in a hot-plate test, was not affected at any of these time points. Retention of a step-through passive avoidance task was impaired in the colchicine group one month after surgery. Their step-through latencies were significantly shorter than control latencies, and they exhibited more partial entries during the retention test. Acquisition and performance in a radial-arm maze, measured up to 3 months after surgery, were also impaired by colchicine. Animals injected with colchicine required more trials to acquire the task and were less accurate in the task even after their performance had stabilized. These data suggest that the hippocampus modulates motor behavior and cognitive function. The results of these experiments also support the use of colchicine as a means of defining the functional and anatomical consequences following selective destruction of the granule cell population of the dentate gyrus.

Disrupted patterns of consummatory behavior in rats with fornix transections

The feeding and drinking behavior was examined in male rats with fornix transections and sham-operated control rats. Total food and water consumption was recorded but supplemented by a pattern analysis of feeding and drinking behavior. The behavior of the rats was continuously monitored during four hour morning and afternoon sessions under ad lib access and during a two hour session following adaptation to a restricted access feeding schedule. Rats with fornix transections were more active and exhibited increased frequencies of rearing, eating and drinking. The increased meal frequency in rats with fornix transections was accompanied by decreased meal durations and a reduction in the length of intermeal intervals. Total food and water consumption was unaffected by fornix transection as were the duration of sleep bouts and the frequencies of grooming, sleeping and carrying shavings. Fornix transections also reduced food carrying and food hoarding but only under conditions of restricted food access. The results suggest that fornix transection does not alter major homeostatic regulatory mechanisms nor does it alter the components of feeding and drinking behavior. Fornix transection alters, instead, the organization of microregulatory feeding and drinking patterns.

The effects of Org 2766 on the performance of sham, neocortical, and hippocampal-lesioned rats in a food search task

The behavioral effects of an ACTH4-9 variant, Org 2766, given for one week postoperatively at a dose of 1 microgram/rat daily, were evaluated in animals given hippocampal, neocortical, or "sham" lesions. After the week during which the injections were given, the animals were tested for 5 days in a food-search task in which food was hidden in two recessed holes in the floor. On the next day the ability of the rats to find food in these same two baited holes was tested in the presence of 14 additional holes that were not baited. On the following day, the animals were tested again, this time with all 16 holes baited. To assess the long-term effects of Org 2766 treatment, the animals were tested once again 2-3 months later in the same apparatus with 16 empty holes. In general, rats with lesions restricted to the neocortex were severely impaired in the task and were unaffected by prior treatment with Org 2766. Animals with hippocampal damage quickly learned the task and were hyperactive. During the test session with 16 baited holes they showed differential behavioral changes suggesting attentional deficits not seen in "sham" operated rats. These deficits were attenuated by prior Org 2766 treatment, whereas the lesion-induced hyperactivity was not. Treatment with Org 2766 impaired all aspects of performance of "sham" operated animals.

Selective attention and the brain: a hypothesis concerning the hippocampal--ventral striatal axis, the mediation of selective attention, and the pathogenesis of attentional disorders

The mechanisms mediating selective attention are not currently known. Dysfunctional selective attention is a common and prominent finding in a variety of medical and psychiatric conditions. A hypothesis is developed that efferents from the hippocampal formation are the final common pathway of processes which determine the noteworthiness of both exteroceptive and interoceptive stimuli, and that dysfunction of these efferents is a common pathway for a variety of anatomical, electrophysiological, and neurochemical lesions. This hypothesis suggests that clinical syndromes of disordered attention may be caused by various lesions of efferent connections from hippocampal formation to nucleus accumbens. The hypothesis further addresses the possibility that the threshold of hippocampus to various classes of stimuli may change on a diurnal and phasic basis. Experimental evidence that bears on the hypothesis is reviewed and experimental implications of the hypothesis are explored.

Suppression of corticosterone synthesis alters the behavior of hippocampally lesioned rats

The suppression of corticosterone synthesis with metyrapone (25 mg/kg) reduced the hyperactivity and altered the exploratory activity of hippocampally lesioned animals (HPC) in the open field to the level of cortical and sham controls (Experiment 1). In a second experiment, corticosterone (600 micrograms/kg) pretreatment 2 h, but not 1 h, before metyrapone partially restored the hyperactivity of HPC animals that had been decreased by the corticosteroid-suppressant drug. Alterations in exploratory behavior induced by metyrapone were also prevented by corticosterone pretreatment. The results suggest that the suppression of corticosterone in hippocampally lesioned animals produces a normalization of behavior that can be prevented by pretreatment with corticosterone.

Hippocampus modulates self-stimulation reward from the ventral tegmental area in the rat

Rats with electrodes in the ventral tegmental area were tested for the threshold of intracranial reward using a rate insensitive self-stimulation procedure. It was found that an electrolytic lesion of a part of the dorsal hippocampus induced a marked decrease in the variation of thresholds across rats, while the mean reward level did not change. This indicates that a factor is removed, by the hippocampal lesion, which causes differences in reward between individual rats. It is suggested that the mesolimbic dopaminergic system is involved in this modulatory influence of the hippocampus on reward.

Neurochemical and behavioral consequences of acute, uncontrollable stress: effects of dietary tyrosine

Acute, uncontrollable stress increases norepinephrine (NE) turnover in the rat's brain (thereby depleting NE) and diminishes the animal's subsequent tendency to explore a novel environment. We determined whether supplemental dietary tyrosine could prevent some of these changes. Rats given a control diet or diets enriched with tyrosine or tyrosine plus valine were exposed to tail-shock stress or to no stress over a 60-min period. Exposure to the stress caused an increase in NE turnover, decreasing NE and increasing 3-methoxy-4-hydroxy-phenylethylene glycol sulfate (MHPG-SO4) concentrations within the locus coeruleus, hypothalamus and hippocampus. No changes were detected in serotonin (5-HT) levels or turnover. Behavioral deficits following the stress were observed using measures of locomotion and of exploration in a novel open-field environment: stressed animals displayed much less spontaneous motor activity, hole-poking or frequency of standing on their hind legs than control animals. Animals receiving the tyrosine-enriched diet displayed neither the stress-induced depletion of NE nor the behavioral depression. These preventive effects of tyrosine were abolished by co-administration of valine, a large neutral amino acid that competes with tyrosine for transport across the blood-brain barrier. Since tyrosine alone, in animals not subjected to stress, did not change NE turnover nor the behaviors studied, our observations affirm that catecholaminergic neurons respond to the precursor amino acid only when they are physiologically active. Supplementary tyrosine may be useful therapeutically in people exposed chronically to stress.

Tyrosine prevents behavioral and neurochemical correlates of an acute stress in rats

Exposure of rats to an acute, uncontrollable stressor can increase brain norepinephrine (NE) turnover and decrease locomotor and exploratory behavior. We examined the ability of exogenous tyrosine, NE's amino acid precursor, to protect rats from developing these neurochemical and behavioral changes when stressed. Animals pretreated with saline or tyrosine (200 mg/kg, i.p.) were subjected to tail shock (15 v, 2 mA, 5 sec/30 sec) or to no shock during a 60-min period. Exposure to shock depleted NE and increased its turnover [as indicated by altered NE and 3-methoxy-4-hydroxy-phenylene-glycol sulfate levels (MHPG-SO4)] within the locus coeruleus, the hippocampus and the hypothalamus. Behavioral deficits were observed using measures of locomotion, standing on hind legs, and hole-poking in an open-field apparatus. Animals given tyrosine before shock displayed neither shock-induced NE depletion nor the deficits in locomotion and hole-poking; brain MHPG-SO4 levels tended to be greater than after shock alone. These observations suggest that the stress caused NE to be released from some neurons more rapidly than it could be restored by synthesis or reuptake, thereby impairing noradrenergic transmission and NE-dependent exploratory behaviors. Tyrosine administration presumably enhanced the transmitter's synthesis in stressed animals, thereby preventing both the neurochemical and the behavioral deficits.

Differentiation of basal ganglia dopaminergic involvement in behavior after hippocampectomy

Large bilateral aspiration lesions of the hippocampus in rats lead to a variety of changes in spontaneous behavior measured in an open field/hole board, relative to sham and neocortically lesioned controls. These changes include increased locomotion, and decreased grooming frequency and rearing bout duration. When animals were injected with the dopamine (DA) agonist 3,4-dihydroxyphenylamino-2-imidazoline (DPI: 0.5, 1.0 and 5.0 microgram) into the nucleus accumbens one week after surgery, the behavior of hippocampally lesioned rats was restored to levels not different from control lesioned rats. Haloperidol injections (0.05, 0.1 and 0.5 microgram) into the caudate nucleus were not able to do this. Further, DPI injected into the caudate month after surgery was also able to attenuate some of the effects of hippocampal damage. On the other hand, haloperidol injections into the nucleus accumbens did not influence behavior. The results are interpreted in terms of hippocampal lesion-induced alteration of a balance in basal ganglia DA systems, indicated by modified response to pharmacological intervention and which mediate the behavioral effects of the lesion.

Hippocampal damage: effects on dopaminergic systems of the basal ganglia

Although the research topics discussed in this chapter cover a substantial range of areas, methods, and behaviors, there is a consistent central issue: the alterations of brain and behavior subsequent to hippocampal lesions. The initial hypothesis that important secondary changes occur in the basal ganglia after hippocampal lesions has been sustained, at least in part, but other and unexpected results have been obtained that both clarify and mystify at the same time. The restoration of normal locomotion to animals with hippocampal damage by the application of a DAi agonist, DPI, to n. accumbens certainly supports our general idea, but the fact that membrane and transmitter changes in accumbens are transitory needs to be explained and perhaps related to alterations in DA receptor populations. The fact that intra-accumbens DPI can restore ACTH-induced excessive grooming at 28 days after hippocampal damage supports the idea that progressive changes are occurring in DA receptors in n. accumbens, but we need to know their nature more precisely. To do this, however, will probably require advances in our general knowledge of central DA receptors. One of the more interesting aspects of our observations is that the intra-accumbens administration of DPI restores normal behavioral patterns in several types of behaviors, especially locomotion and the excessive grooming response. These two behaviors are not closely linked in nature because large changes can occur in them independently, given appropriate conditions for testing. On the basis of available evidence both of these behaviors seem linked to activities in forebrain DA systems. This would further support the idea that the hippocampus modulates DA activities in basal ganglia systems. The results that suggest the presence of multiple sites for the central induction of grooming were also unexpected. As evidence mounts in support of this idea, it is likely that the one located in n. accumbens is more influenced by hippocampal destruction than the region(s) affected by icv neuropeptide administration. The interactions that take place in the basal ganglia can be extensive. Afferents from the entirety of the neocortical surface, the limbic system, and the projections from the brainstem DA cell groups meet in the striatum and ventral striatum. The efferents from this region not only reach motor cortical and subcortical sites but also project back onto diffusely projecting monoaminergic cells of the brainstem.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in open-field behaviors following septal lesions in rats

Sixteen rats were tested for 10 min in an open field on postoperative Days 6--7, 11--12, 19--20, and 38--39, under two conditions of illumination. Septal lesions produced alterations in activity, rearing, and grooming that changed over the repeated tests. Septal rats initially had low activity scores that increased over testing to a level higher than that of controls, low rearing behavior that increased over sessions but always remained below control levels, and low grooming scores that became equivalent to controls by postoperative Days 38--39. These findings indicated that repeated testing given only postoperatively in an open field resulted in hyperactivity, decreased rearing, but no differential effect in grooming. The time course of change in these three behaviors was not identical.

Activity and exploratory behavior after lesions of the medial entorhinal cortex in the woodmouse (Apodemus sylvaticus)

The effects of bilateral electrolytic lesions of the entorhinal cortex were studied in male adult woodmice. Experiments were designed to allow separate analysis of the basal activity level and exploratory behavior. Activity recording was conducted in three situations: (a) 24-hr wheel running in the home cage pre- and postoperatively; (b) 24-hr activity composition in a large enclosure over 4 days, 5 to 9 days postoperatively; and (c) sequence and duration of visits in a residential plus maze 11 to 14 days postoperatively. Medial entorhinal cortex lesion involving the para- and presubiculum increased the 24-hr amount of movements in the enclosure (b) without increasing wheel running in any situation (a or b). This lesion also enhanced the locomotor reactivity to being introduced into the plus maze and impaired exploratory behavior. This last effect was equally apparent when the whole situation was new or when part of the familiar maze was modified. Lesioned woodmice did notice the new element but did not show active focalization of their behavior on that element. Data showed that lesion induced hyperactivity and changes of exploratory behavior were not necessarily associated. Novelty detection was performed but it is not clear now on what information this discrimination was based.

Catecholamine alterations in basal ganglia after hippocampal lesions

Rats were given sham, cortical, or hippocampal lesions and sacrificed 7 or 28 days following surgery. Levels of norepinephrine, dopamine, and the major dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA), were assayed in 3 brain regions. At day 7 there was a decrease in dopamine utilization and a decrease in norepinephrine levels in the nucleus accumbens after hippocampal damage but both of these measures returned to normal levels by day 28. In the neostriatum HVA levels decreased at day 7 after hippocampal damage. The utilization of dopamine in the neostriatum was decreased at day 28 in animals that received neocortical lesions but this was not observed in animals with hippocampal destruction. No effects of any lesion at any day were found in the olfactory tubercle region, the third brain region analyzed. It is thought that the removal of hippocampal and neocortical input to the basal ganglia influences catecholamine function reflected in the loss and subsequent recovery of dopamine utilization.