Neonatal handling in rats induces long-term effects on dynorphin peptides.

The effects of neonatal handling on the opioid dynorphin peptides in the brain and pituitary gland of Sprague-Dawley rats were investigated. Ten weeks after the neonatal handling, handled rats had higher tissue levels of dynorphin A and B in the hypothalamus, pituitary gland and striatum and slightly higher dynorphin B levels in the hippocampus, medulla oblongata and midbrain as compared with non-handled controls. The results indicate a persistent upregulation of the dynorphin system in certain brain areas after neonatal handling, which could contribute to the behavioural changes in these rats observed later in life. Observation in the open field and the elevated plus-maze tests confirmed behavioural effects of neonatal handling, i.e. showing that handled rats exhibit attenuated fearfulness in novel environments as compared with non-handled rats.

Environmental enrichment results in higher levels of nerve growth factor mRNA in the rat visual cortex and hippocampus.

Evidence for structural modifications in the brain following environmental changes have been provided during the last decades. The most pronounced alterations following environmental manipulations have been found in the visual cortex. These plastic changes are supposed to reflect reorganization of neuronal connections involved in postnatal development and adult adjustments of connections involved in sensori-perceptual processing and learning. Potential candidates to mediate these changes are neurotrophins. Nerve growth factor (NGF) has been associated with cognitive functions and shown to improve the performance of aged rats in spatial learning and memory task. In the central nervous system, NGF is of importance for development and maintenance of cholinergic neurons and atrophy of cholinergic neurons is strongly correlated with learning and memory impairments. Exposure to enriched environmental conditions improves learning and problem-solving ability and results in plastic changes in the brain. This study examined the effect of environmental enrichment on expression of NGF mRNA in the rat visual cortex and hippocampus. Rats housed in groups in a stimulus-rich environment for 30 days had significantly higher levels of NGF mRNA than rats housed individually in single cages without stimulus-enrichment. We have recently presented results showing higher levels of neurotrophin-3 (NT-3) mRNA and improved spatial learning following environmental enrichment, and suggest that an interplay involving the neurotrophins NGF and NT-3 may be mediating experience-induced structural changes.

Environmental enrichment selectively increases 5-HT1A receptor mRNA expression and binding in the rat hippocampus.

Environmental enrichment augments neuronal plasticity and cognitive function and possible mediators of these changes are of considerable interest. In this study, male rats were exposed to environmental enrichment or single housing for 30 days. Rats from the enriched group had significantly higher 5-HT1A receptor mRNA expression in the dorsal hippocampus (62%, 59% and 44% increase in the CA1, CA2 and CA3 subfields, respectively). This was associated with significantly higher [3H]8-OH-DPAT binding in the inferior part of CA1. No changes were seen for 5-HT2A or 5-HT2C receptor mRNAs. The neuronal plasticity detected after environmental change may be mediated, in part, through 5-HT1A receptors.

Effects of neonatal stimulation on later cognitive function and hippocampal nerve growth factor.

This study examined the behavioural and physiological effects of chronic mild stress on neonatally handled and non-handled rats. Neonatally handled and non-handled rats were exposed to chronic mild stress from weaning time to 6 months of age. They were behaviourally tested at 6 months of age, and sacrificed for analysis of nerve growth factor (NGF) in the hippocampus and hypothalamus. In contrast to the reported deleterious effect of acute strong stress, mild stress appeared to stimulate production of NGF in the hippocampus and improve spatial learning in both handled and nonhandled rats. Because neonatal handling produces neuroanatomical changes in the rat hippocampus and enhances cognitive function throughout the rats life span, these results implicate hippocampal NGF in the neuroprotective effects of handling.

Expression of neurotrophin-3 mRNA in the rat visual cortex and hippocampus is influenced by environmental conditions.

Environmental enrichment results in structural changes in the brain. Recent findings indicate involvement of neurotrophins in neuronal plasticity. This study examined the effect of environmental complexity on the levels of neurotrophin-3 (NT-3) mRNA in the rat visual cortex and hippocampus, studied by in situ hybridization. Rats housed in groups in a complex, stimulating environment had significantly higher levels of NT-3 mRNA in the visual cortex and the hippocampus than rats housed in individual cages without stimulating objects. These results indicate a possible role for NT-3 in synaptic plasticity.

Influence of place learning on somatostatin levels in the rat brain following environmental deprivation.

We have previously reported increased somatostatin levels in the cerebral cortex of rats housed in impoverished environment and subsequently subjected to a behavioural testing procedure, consisting of open-field exposure and spatial learning. The aim of the present study was to evaluate the degree of neurochemical specificity of the activation of somatostatin neurotransmission and to examine whether the altered levels were due to learning stimulation. Adult rats, previously housed individually for 30 days, were exposed to repeated sessions of a spatial learning task (2 days or 14 days) or repeated sessions of free swimming (14 days). The training sessions of the 14 day group consisted in recurrently changed position of the platform in a learning-set paradigm. Our data showed increased somatostatin immunoreactivity, and unchanged substance P immunoreactivity in the posterior part of the cerebral cortex. However, somatostatin levels increased to a similar extent following 14 days of repeated spatial learning sessions as free swimming sessions. We conclude that the activity of the cortical somatostatin system appears to be sensitive to environmentally induced sensorimotor stimulation in general, rather than learning per se. Thus, external stimulation of early clinical dementia patients with preserved sensorimotor receptivity, in an attempt to restore cognitive function, might be associated with altered somatostatin levels.

Glucocorticoid receptor and NGFI-A gene expression are induced in the hippocampus after environmental enrichment in adult rats.

Environmental manipulation alters hippocampal glucocorticoid receptor (GR) expression in neonatal rats, but effects in adults have not been documented. Chronic environmental enrichment (EE) increases nerve-growth factor (NGF) concentrations in the adult rat hippocampus. Here we demonstrate that EE induces GR, but not mineralocorticoid receptor (MR) gene expression in specific hippocampal subfields (CA1 and CA2). This is accompanied by increased expression of mRNA encoding the (NGF-induced) immediate early gene NGFI-A in CA2, whereas expression of NGFI-B mRNA decreased in CA1 and CA2. The nature of any relationship between NGF, the transcription factors and GR remains to be determined, but the results demonstrate that chronic environmental manipulations alter hippocampal GR gene expression in adult rats.

[Early stimulation--good memory in old age?]. / Tidig stimulering--minnesgoda åldringar?

For better or worse, the importance of neonatal stimulation has attracted increasing attention in recent years. Results from animal studies provide a hint of possible beneficial consequences for humans, even in a geriatric context.

Environmental influences on the central nervous system and their implications for the aging rat.

Two methods of providing environmental stimulation that were introduced in the 1950s have guided much research on neurobehavioural plasticity. These are neonatal handling and environmental enrichment. Neonatal handling has been shown to permanently affect behaviour and endocrine responses. Recently this manipulation has been shown to have important influences on the aging individual, protecting the hippocampus from age-related dysfunction and neuronal loss. These effects are mediated, in part, by keeping glucocorticoid levels low. This has been characterised by, among other things, elevated expression of glucocorticoid receptors in the hippocampus. Earlier studies have failed to present convincing evidence for differences in hormonal variables between animals housed in enriched and impoverished environments, and have not consistently reported changes in the hippocampus. Recent data from our laboratories have shown that adult animals housed in enriched environments had, like neonatally-handled rats, higher expression of the gene encoding glucocorticoid receptors in the hippocampus. Taken together with the induction of NGF and NGFIA gene expression in the hippocampus of enriched animals, these results implicate genes encoding transcription factors and glucocorticoid receptors in the cascade of events leading to environmentally induced cerebral changes. In addition, these results suggest that environmental enrichment in adulthood, like neonatal handling, may have the potential to protect the aging hippocampus from glucocorticoid neurotoxicity.

Environmental influence on somatostatin levels and gene expression in the rat brain.

In the present study we have quantified preprosomatostatin-mRNA and somatostatin levels in rat brain following environmental stimulation. Animals were housed for 30 days in an enriched or impoverished environment prior to analysis. After 30 days of housing half of the rats from each environment were behaviourally tested for 3 days. Housing in enriched environment improved performance in a spatial learning situation. The open-field behaviour of these animals was characterized by initially higher rearing scores and a more rapid habituation to novel environment as measured by spontaneous locomotor activity. We found significantly elevated somatostatin levels in the cortex following enriched environment, compared with impoverished environment. Exposure to behavioural testing of impoverished animals led to increased cortical somatostatin levels. Hypothalamic somatostatin levels increased significantly after housing in enriched environment, while the testing procedure had no influence. Our data shows that the somatostatin system in the rat brain was activated in association with cognitive changes, that were induced by housing in an enriched environment.

Subchronic MK-801 treatment to juvenile rats attenuates environmental effects on adult spatial learning.

Treatment with the non-competitive NMDA receptor blocker MK-801 (0.16 mg/kg), given to juvenile rats before and after the exposure to an enriched environment on alternate days for 4 weeks, attenuated the improvements in spatial learning and open field adaptation which resulted from such environmental stimulation. Drug treatment affected the consolidation of experiences as an injection given after exposure to the enriched environment was needed to demonstrate this effect. In addition, MK-801 administration diminished the adverse effect of stimulus deprivation-the slow learning rate normally seen in rats housed in impoverished environment. Radioligand binding studies showed that drug treatment decreased [3H]MK-801 binding sites in cortex. The learning, activity and receptor binding effects were measured 4 months from cessation of the drug treatment and environmental manipulation. The results support the role of NMDA receptors in mediating cognitive changes associated with environmental stimulation.

Immunohistochemical and behaviour pharmacological analysis of rats inoculated intranasally with vesicular stomatitis virus.

A temperature-sensitive mutant of vesicular stomatitis virus was inoculated intranasally into infant Sprague-Dawley rats aged 9 to 17 days. Rats receiving the virus at 9 days of age had an extensive spread of infection throughout the brain and the animals died after a few days. Rats inoculated at day 11 postnatally survived and the infection was limited to the olfactory pathways, hypothalamus, diagonal bands and the anterior raphe nuclei. Stereological measurements showed that the volume of infected neurons constituted 67 +/- 10% of the total neuronal volume in the dorsal raphe nucleus. Double-labelling experiments revealed that both 5-hydroxytryptamine- and substance P-immunoreactive neurons contained the virus antigen. The motor stimulant effect of amphetamine was studied at 3 months post infection. The increase in amphetamine-induced frequency and duration of rearing was significantly attenuated in infected rats and the amphetamine-induced locomotion was slightly reduced.

Hippocampal nerve growth factor levels are related to spatial learning ability in aged rats.

Brain nerve growth factor (NGF) was determined in two groups of aged rats: 'good' and 'poor' performers. The animals were selected out of a population of 40 aged rats (26-28 months old) trained in a spatial learning task. Animals performing well in the test had significantly higher NGF in the hippocampus when compared to 'poor' performers. No differences in the levels of NGF were found in the cortex, septum and cerebellum. The results implicate hippocampal NGF in cognitive functioning of aged rats, and suggests that the forebrain cholinergic neuronal atrophy which has been observed in cognitively impaired aged rats may be due to reduced availability of target-derived NGF.

Delta9-THC as a discriminative cue in pigeons: effects of delta8-THC, CBD, and CBN.

Pigeons, trained to discriminate the effects of i.m. injections of delta9-tetrahydrocannabinol (delta9-THC, 0.25 mg/kg) from the effects of the vehicle in a drug discrimination paradigm, were tested for generalization with the isomeric delta8-THC, cannabidiol (CBD) and cannabinol (CBN). When given in sufficient doses, delta8-THC and CBN were found to substitute for delta9-THC whereas CBD did not. CBD and CBN did not antagonize the stimulus effect of delta9-THC. The combination of CBN and delta9-THC rather appeared to accentuate the drug response.

Characteristics of tetrahydrocannabinol (THC)-produced discrimination in rats.

UNLABELLED: Rats were trained in a T-shaped maze to discriminate the effects produced by i.p. injections of tetrahydrocannabinol (THC) and the no-drug state (state-dependency, StD). Several doses of both Delta8-THC (range: 0.75-5.0 mg/kg) and Delta9-THC (range: 0.75-40.0 mg/kg) were used in order to compare the number of sessions required by the animals until reaching criterion performance. An additional group of rats had to discriminate pentobarbital sodium (20.0 mg/kg) from the no-drug state. RESULTS: THC discrimination was proportional to dose i.e., animals that had to differentiate high doses of THC from no drug acquired the T-maze task faster than animals trained with the lower doses of THC. Acquisition data further suggest that Delta8-THC is somewhat less potent than the Delta9-isomer. Delta9-THC (10.0 mg/kg) produces strong StD, as defined by Overton (1971), since both this group and the barbiturate group reached the criterion within the first 10 training sessions. Time and dose testings suggest that stimulus properties of drugs vary in a quantitative way and that the calculated ED50 values are mainly determined by the training dose used. It was found that the higher the training dose used the higher was the corresponding ED50 value. Hashish smoke can maintain drug responding among THC-trained rats. A lowered content of brain catecholamines and/or serotonin, induced by AMPT (150 mg/kg) and PCPA (310-350 mg/kg), did not lessen Delta9-THC (2.5 mg/kg) discrimination.

Delta 9-tetrahydrocannabinol produced discrimination in pigeons.

In an operant situation pigeons learned to peck one response key 90 min after an injection of 0.25mg/kg delta9-tetrahydrocannabinol (delta9-THC) and another key when trained nondrugged. When tested with doses of delta9-THC lwer than the training dose the birds disciminated 0.20 mg/kg of the drug from the nondrugged state but not 0.15 mg/kg or lower doses. The animals were able to discriminate the drug state from the nondrugged 180 min but not 360 min after the injection At a shorter interval (45 min) both drug and nondrug responding appeared. Cannabinol and cannabidiol (4.0 - 8.0 mg/kg) did not elicit any drug responses, nor did pentobarbital, ditran or amphetamine. Tests with LSD resulted in both drug and nondrug responding. When administering noncannabinoid drugs in combination with delta9-THC 0.15 mg/kg the birds responded at the key associated with the drug state, suggesting interactional effects.

Delta9-tetrahydrocannabinol and pentobarbital as discriminative cues in the Mongolian Gerbil (Meriones unguiculatus)

Male Mongolian gerbils were trained to escape electric shocks in a T-shaped maze contingent upon the presence or absence of certain drug effects (state-dependency; StD). The drug discriminative cues used were those of either delta9-tetrahydrocannabinol (THC) or pentobarbital (P-barb.) vis-à-vis the respective vehicles. Several doses of THC (0.5-16.0 mg/kg) were used and compared with P-barb. (20.0 mg/kg), a dose at which the most rapid drug discrimination occurs in the rat. When drug discrimination was established dose-time- and transfer characteristics for the training drugs were studied. Possible potentiation and antagonism was also examined in the pentobarbital trained gerbils. It was found that none of the THC doses were discriminated as rapidly as that of P-barb. Decreasing the amounts of training drug administered or increasing the injection-test intervals resulted in a decline of the number of drug associated choices. There was a maximum of 40% drug choices between THC and P-barb at the transfer tests. Mixtures of the two compounds increased the number of drug choices in an additive or even more than additive manner. Amphetamine (4.0 mg/kg) did not interact with the P-barb. induced choice responding. The analeptic drug, bemegride was found effective in antagonizing the P-barb. cued choice behavior.

Drug discrimination in rats: the effects of phencyclidine and ditran.

Choice responding in a T-shaped maze has been made contingent upon whether or not rats experienced certain drug effects. The drug discriminative cues used in the present state-dependent (StD) model were those of phencyclidine (PCP) and ditran. The specificity of these cues and their possible drug inhibition and antagonism was studied. It was found that the lower the training dose used the slower the appearance of the drug discriminative formation. Transfer testings with ketamine and cyclohexamine showed that they were interchangeable with PCP. The order of their relative potency was: cyclohexamine greater than PCP greater than ketamine. Atropine transferred to ditran. Administration of compounds not structurally related to the training drugs did not show transfer. Pretreatment with parachlorphenylalanine (p-CPA) or tetrabenazine (TBZ) plus imipramine did not indicate inhibition or antagonism in PCP trained rats. Tacrine (THA) and especially physostigmine effectively antagonized the ditran-induced cues. Yohimbine and neostigmine did not.

Acute and subchronic influences of tetrahydrocannabinols on water and food intake, body weight, and temperature in rats.

Experiment 1. The acute effects of delta9-THC (1.25, 2.50, 5.00, and 10.00 mg/kg) and delta8-THC (1.25, 2.50, 5.00, and 10.00 mg/kg) was an approximately equipotent, dose related depression of water intake in water-deprived rats. Animals given hashish, inhaled as smoke, showed a depression of water consumption comparable to rats given the highest dose of either of the synthetic THCs. Water intake after chevril smoke was similar to that seen after vehicle injections. Experiment 2. A dose related depression of water-and-food intake, and reduction of body weight with a gradual recovery was found in rats, maintained on a Limited Time of drinking schedule (LT, 2 hr) and subchronically (21 days) treated with delta9-THC (1.25, 2.50, or 5.00 mg/kg). From the 22nd day all animals were given the vehicle only for 10 days. There were no indications of withdrawal effects due to the drug termination. Reinstating the drug after the 10 day drug free period suggested an increased sensitivity to THC as compared to the 21st injection. Experiment 3. In non-deprived rats delta9-THC caused similar effect as in Exp. 2, although to less extent. From both experiments it is concluded that there is an inhibition or even loss of body weight and that food intake seems more severely depressed than water intake. The temperature recordings suggest that the predominant consequence of lower, behaviorally, effective doses of THC on rectal temperature of rats is hyperthermia rather than hypothermia. Initially this effect was most pronounced for the lowest dose (1.25 mg/kg) but with repeated injections the two higher doses (2.50 and 5.00 mg/kg) showed hyperthermia to the same extent as the lowest dose. Hypothermia was seen after a high dose of delta8-THC (20.00 mg/kg) but after 3 daily injections this effect was gone.