Decreased hypothalamic serotonin levels in adult rats treated neonatally with clomipramine.

Early postnatal treatment with the antidepressant drug clomipramine has repeatedly been shown to lead to behavioural and physiological changes in adult rats. To provide some neurochemical correlates to these studies we have measured a number of monoaminergic parameters in the brains of adult (one year old) rats that were treated twice daily with 15 mg/kg clomipramine from postnatal day 2-14. The most consistent finding was that the hypothalamic levels of serotonin (5-HT) were decreased and those of the dopamine metabolite dihydroxyphenylacetic acid (DOPAC) were increased in rats irrespectively whether they went through a range of behavioural and physiological tests or not. The numbers of beta-adrenoceptors in the frontal cortex and of alpha 2-adrenoceptors in the amygdala/piriform cortex were not changed. The decrease in hypothalamic 5-HT concentrations appears to be up to now the most consistent neurochemical alteration in adult rats that were neonatally treated with antidepressant drugs. It is, however, not clear what the relation is with the functional changes in these rats, that are proposed by some authors as an animal model for depression.

Activity-dependent plasticity of inhibitory and excitatory amino acid transmitter systems in cultured rat cerebral cortex.

Chronic suppression of spontaneous bioelectric activity in cultures of dissociated fetal rat cerebral cortex increases neuronal cell death and results in electrophysiological changes which indicate an altered balance between excitatory and inhibitory neurotransmission in culture. To delineate whether alterations in neurotransmitter release could underlie this imbalance, we investigated the effects of chronic tetrodotoxin (TTX) treatment on the content and release of glutamate, aspartate and gamma-aminobutyric acid (GABA) in culture. Chronic TTX treatment decreased the content of all amino acids investigated. However, only GABA was decreased relative to the neuronal marker NSE (neuron-specific enolase), indicating a disproportionate loss of GABA production following chronic silencing. Depolarization-induced release of GABA, glutamate and aspartate increased about 10-fold between 7 and 21 days in control cultures. Chronic TTX treatment significantly increased the depolarization-induced release of glutamate and aspartate at 7 days in vitro relative to control levels. At all ages it caused a two-fold increase in the ratio of evoked excitatory amino acid release to that of GABA. These observations suggest that chronic silencing of developing neocortex cell cultures increases the ratio of excitatory to inhibitory synaptic activity either by differential cell death or by reduced synaptic efficiency, on which a decrease in GABA neurotransmission appears to play a major role. Since similar mechanisms may be involved in activity-dependent plasticity in vivo, these cultures provide a useful model to analyse this phenomenon at the cell biological and molecular level.

Neonatal lesions of the ventral tegmental area affect monoaminergic responses to stress in the medial prefrontal cortex and other dopamine projection areas in adulthood.

A mean decrease of dopamine (DA) to 20% and serotonin to 25-30% of control levels was found in the medial prefrontal cortex (mPFC) and amygdala/piriform cortex (A/PC) of adult rats with neonatal lesions of the ventral tegmental area (VTA). The metabolites were less decreased suggesting an increased activity of the remaining terminals. Moderate decreases to 30-75% were detected for DA and serotonin in the nucleus accumbens, olfactory tubercle and striatum. Footshock stress in control animals resulted in a strong increase (200% of control) in DA metabolites in mPFC and A/PC. The noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in A/PC was strongly increased to 240%. When stress was given to the neonatally VTA-lesioned animals these neurochemical responses were reduced compared to the nonlesioned rats. In the case of DA in the mPFC this was clearly due to a loss of stress response in the severe lesion group where DA is depleted to less than 20% of control. The stress-induced small increases in DA metabolism in tubercle, accumbens and striatum and serotonin metabolism in the striatum (20-40%) were entirely lost, while the MHPG increase in the A/PC was blunted. The present results suggest that moderate and severe lesions of DA and serotonin alter or prevent the normal activation of these transmitter systems and even of the noradrenergic system to stress.

Early postnatal clonidine treatment results in altered regional catecholamine utilisation in adult rat brain.

Clonidine is a clinically used antihypertensive which has been suggested to produce physiological changes in children after exposure in utero. The aim of our study was to test the hypothesis that chronic exposure of the developing brain to an alpha 2-adrenergic agonist like clonidine would influence the adult neurochemical setting of central monoamine neurotransmitter systems. Male rat pups were treated from postnatal day 8 to 21 twice daily with saline or with 0.1 mg/kg clonidine. After the last injection on day 21, brain regional catecholamine utilisation was determined using synthesis inhibition with alpha-methyl-p-tyrosine in a subgroup of the pups. The expected decrease in noradrenaline utilisation after clonidine was observed, although statistical significance was not reached in a number of brain regions. Dopamine utilisation was not affected. The other pups were left to reach young adulthood and catecholamine utilisation was measured on day 90. Noradrenaline utilisation on day 90 was significantly decreased in two regions: the medulla-pons and the mesolimbic (dopamine projection) areas. Dopamine utilisation was decreased in the hypothalamus and increased in the amygdala and the cerebellum. These adult neurochemical alterations corroborate previous findings of adult behavioural, physiological and central biochemical alterations in rats exposed to clonidine in early postnatal life.

Chronic propranolol treatment in developing rats: acute and lasting effects on monoamines and beta-adrenergic receptors in the rat brain.

During early postnatal development rat pups were treated twice daily with the beta-adrenergic antagonist propranolol (15 mg/kg) in order to study the acute and long-lasting effects of early blockade of noradrenergic beta-mediated neurotransmission. Treatments from postnatal days 1-10 or days 11-20 did not induce alterations in the number of beta-adrenergic receptors as measured three days after the last injection, nor could lasting effects be shown at 60 days of age. The day 1-10 treatment, however, had a significant effect on the regional brain levels of noradrenaline (NA) and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), measured 90 min after the last injection. The metabolite had increased by 40% in all brain regions examined. On day 60, the MHPG concentrations were still increased when compared to postnatally saline-treated animals. Propranolol treatment from day 11-20 only marginally increased MHPG on day 20 and induced no lasting differences. These results suggest that propranolol treatment during the first ten days of life produces a long-lasting increase in NA metabolism, possibly reflecting an increased neuronal NA turnover.

Sex differences in the effects of inescapable footshock on central catecholaminergic and serotonergic activity.

In two experiments sex differences in changes in central noradrenergic, dopaminergic and serotonergic activity were measured immediately after a 30-min session of inescapable footshocks. In Experiment 1 concentrations of noradrenaline, dopamine, serotonin and their major metabolites were determined in the frontal cortex, hypothalamus, amygdala, striatum, mesencephalon and the medulla-pons area. Inescapable shock increased the activity of all 3 transmitter systems, as evidence by increased metabolite concentrations in specific brain areas. Shock-induced increments in metabolite levels were larger in females than in males, especially for the serotonergic system. In addition, shock presentation resulted in a decrement in the noradrenaline content in most areas studied. In the frontal cortex, noradrenaline was reduced by inescapable shock in males but not in females. In Experiment 2, sex-dependent neurochemical consequences of predictable versus unpredictable shocks were studied in the frontal cortex and the medulla-pons area. Similar to Experiment 1, both brain parts showed large shock-induced increments in the activity of the catecholaminergic systems. Differential effects of predictable and unpredictable shock were not found (frontal cortex) or were rather small (medulla-pons) and appeared sex-dependent for serotonin in this area. The sex differences in neurochemical change found in the first experiment were largely replicated in the second experiment. The relevance of the observed sex differences in central neurotransmitter reactivity for sex differences in behavior is discussed.

Widespread alterations in central noradrenaline, dopamine, and serotonin systems in the Brattleboro rat not related to the local absence of vasopressin.

A comprehensive study of monoamine transmitter and metabolite concentrations measured by HPLC was undertaken in female (vasopressin-deficient) Brattleboro rats as compared to Long Evans rats. Noradrenaline was significantly increased in 8 out of 13 dissected brain regions, whereas concentrations of the metabolite 3-methoxy-4-hydroxyphenylglycol were not altered. The increases were not restricted to areas which are normally innervated by vasopressin-containing neurons. Serotonin was increased in 6 and dopamine in 4 regions and this was accompanied in some areas by increases in the metabolites 5-hydroxyindolacetic acid and dihydroxyphenylacetic acid. Only in the striatum, cerebellum, and the medulla-pons no changes could be detected in any of the compounds of interest. These results show that the long term absence of vasopressin in Brattleboro rats appears to be associated with increases in monoamine transmitter contents and decreased metabolite/transmitter ratios. The regional distribution of these changes does not bear any relationship to the regional distribution of vasopressin cell bodies or nerve endings.

Monoamine and metabolite levels in the prefrontal cortex and the mesolimbic forebrain following neonatal lesions of the ventral tegmental area.

Monoamine metabolism was determined in the medial prefrontal cortex (mPFC) and the limbic forebrain (LFB) of adult rats following neonatal lesions of the ventral tegmental area. The dopamine (DA) and serotonin (5-HT) levels were decreased down to 30% in both the mPFC and the LFB. The noradrenaline (NA) level was also significantly decreased, but only in the mPFC of the right hemisphere. The metabolite/transmitter ratios of DA and 5-HT, but not of NA, were greatly increased in the depleted mPFC, but not in the LFB, which suggests an increased activity of the remaining cortical DA and 5-HT fibres in the mPFC.