Matthijs G.P. Feenstra

Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathway

In view of mounting evidence that the suprachiasmatic nucleus (SCN) is directly involved in the setting of sensitivity of the adrenal cortex to ACTH, the present study investigated possible anatomical and functional connections between SCN and adrenal. Transneuronal virus tracing from the adrenal revealed first order labelling in neurons in the intermedio‐lateral column of the spinal cord that were shown to receive an input from oxytocin fibres and subsequently second‐order labelling in neurons of the autonomic division of the paraventricular nucleus. The latter neurons were shown to receive an input from vasopressin or vasoactive intestinal peptide (VIP) containing SCN efferents. The true character of this SCN input to second‐order neurons was also demonstrated by the fact that third‐order labelling was present within the SCN, vasopressin or VIP neurons. The functional presence of the SCN–adrenal connection was demonstrated by a light‐induced fast decrease in plasma corticosterone that could not be attributed to a decrease in ACTH. Using intact and SCN‐lesioned animals, the immediate decrease in plasma corticosterone was only observed in intact animals and only at the beginning of the dark period. This fast decrease of corticosterone was accompanied by constant basal levels of blood adrenaline and noradrenaline, and is proposed to be due to a direct inhibition of the neuronal output to the adrenal cortex by light‐mediated activation of SCN neurons. As a consequence, it is proposed that the SCN utilizes neuronal pathways to spread its time of the day message, not only to the pineal, but also to other organs, including the adrenal, utilizing the autonomic nervous system.

The suprachiasmatic nucleus controls the daily variation of plasma glucose via the autonomic output to the liver: are the clock genes involved?

In order to drive tissue‐specific rhythmic outputs, the master clock, located in the suprachiasmatic nucleus (SCN), is thought to reset peripheral oscillators via either chemical and hormonal cues or neural connections. Recently, the daily rhythm of plasma glucose (characterized by a peak before the onset of the activity period) has been shown to be directly driven by the SCN, independently of the SCN control of rhythmic feeding behaviour. Indeed, the daily variation in glucose was not impaired unless the scheduled feeding regimen (six‐meal schedule) was associated with an SCN lesion. Here we show that the rhythmicity of both clock‐gene mRNA expression in the liver and plasma glucose is not abolished under such a regular feeding schedule. Because the onset of the activity period and hyperglycemia are correlated with an increased sympathetic tonus, we investigated whether this autonomic branch is involved in the SCN control of plasma glucose rhythm and liver rhythmicity. Interestingly, hepatic sympathectomy combined with a six‐meal feeding schedule resulted in a disruption of the plasma glucose rhythmicity without affecting the daily variation in clock‐gene mRNA expression in the liver. Taking all these data together, we conclude that (i) the SCN needs the sympathetic pathway to the liver to generate the 24‐h rhythm in plasma glucose concentrations, (ii) rhythmic clock‐gene expression in the liver is not dependent on the sympathetic liver innervation and (iii) clock‐gene rhythmicity in liver cells is not sufficient for sustaining a circadian rhythm in plasma glucose concentrations.

Rapid sampling of extracellular dopamine in the rat prefrontal cortex during food consumption, handling and exposure to novelty.

We report the effects of physiological stimuli on extracellular dopamine (DA) in the medial prefrontal cortex (PFC) of the rat determined on-line in dialysates obtained every 5.5 min. The detection limit for DA was 0.03-0.1 pg/5 microl injection using a conventional HPLC set-up. Basal levels in PFC were at the detection limit, therefore 3 microM nomifensine was included in the Ringer perfusion fluid, producing readily detectable DA levels of 0.9 pg/injection. Perfusion with 3 microM TTX for 30 min decreased DA within 11 min to 10% of control. The routine use of rapid sampling of extracellular DA was applied to study cortical DA release in relation to behaviour. Exposure to a novel environment for 5.5 min led to an increase to 135%. Presentation of a food pellet to food-deprived rats resulted in a rapid increase to 150% within 5.5 min, which lasted 30-40 min, which is 10-20 min more than the time spent eating. Handling the rat for 5.5 min increased DA in PFC within 5.5 min to 160% and in 11 min to 190% of control followed by a 25-min period of a 50% increase, probably reflecting increased arousal. The results suggest that emotional arousal is a common denominator of increased cortical DA release and that responses are graded depending on the intensity of the stimulus.

Novelty-induced increase in dopamine release in the rat prefrontal cortex in vivo: inhibition by diazepam.

The effects of graded stressful conditions on extracellular concentrations of dopamine (DA) in the medial prefrontal cortex of rats were measured in vivo using microdialysis. Picking up the rat twice with a 20-min interval increased extracellular DA to 120%, exposure to a novel environment by placement in a clean cage for 20 min to 150% and holding the rat in the hands for 20 min to over 200%. Diazepam (5 mg/kg) decreased DA to about 75% and attenuated the novelty- and handling-induced increases. Exposure to novelty or handling are easy and simple methods to obtain graded increases of in vivo cortical DA release.

Local activation of metabotropic glutamate receptors inhibits the handling-induced increased release of dopamine in the nucleus accumbens but not that of dopamine or noradrenaline in the prefrontal cortex: comparison with inhibition of ionotropic receptors.

Abstract: On‐line in vivo microdialysis was used to determine the effects of a 16‐min handling period on release of dopamine (DA) in the nucleus accumbens and of DA and noradrenaline (NA) in the medial prefrontal cortex of awake, freely moving rats. DA and NA were determined in one HPLC run. Handling resulted in an immediate and strong increase of both catecholamines in the prefrontal cortex. Maximal values for DA were 295%, and for NA 225%, of controls. DA in the nucleus accumbens was also increased (to 135% of controls) but only after a short delay. Local inhibition of ionotropic glutamate receptors by continuous reversed dialysis of the drugs 6‐cyano‐7‐nitroquinoxaline, d‐2‐amino‐5‐phosphonopentanoic acid, or dizocilpine did not significantly affect handling‐induced increases in cortical DA and NA release. Neither did the agonist of metabotropic glutamate receptors, trans‐(1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (ACPD), or the GABA‐B agonist baclofen. Reversed dialysis of dizocilpine in the nucleus accumbens was equally ineffective, but ACPD inhibited the increase in DA release in this area. Stimulation of metabotropic glutamate receptors in the nucleus accumbens was previously reported to inhibit activation of DA release in that area after stimulation of glutamatergic or dopaminergic afferents. It is concluded that metabotropic receptors in the nucleus accumbens are important for the control of activation of DA release in the accumbens by physiological stimuli but that a similar mechanism is lacking in the prefrontal cortex.

In vivo microdialysis of noradrenaline overflow: effects of α‐adrenoceptor agonists and antagonists measured by cumulative concentration‐response curves

1 The purpose of the present study was to compare the effects of several α‐adrenoceptor agonists and antagonists on cerebral cortical overflow of endogenous noradrenaline (NA) in freely moving rats. One or two days after the implantation of transcerebral dialysis tubes in the frontoparietal cortex, extracellular NA levels were monitored on‐line with high performance liquid chromatography and electrochemical detection. The drugs were applied locally via the dialysis membrane, and effects on NA overflow were determined in cumulative concentration‐response curves. 2 The average basal cortical NA overflow of all experiments was 0.25 pg min−1. The α2‐adrenoceptor agonists caused a concentration‐dependent decrease in NA levels. UK‐14,304 was the most potent and B‐HT 933 the least potent agonist. The maximal decrease in NA overflow was to 10–15% of control levels after UK‐14,304 or moxonidine, to 30% after clonidine and to 50% after B‐HT 933 administration. Continuous activation of the presynaptic α2‐adrenoceptor with 10−6 m UK‐14,304 caused a decrease in NA levels to 40–50% of basal levels. This decrease was reached within 1 h and remained stable for the entire 3 h measurement period. The α1‐adrenoceptor agonists, phenylephrine and methoxamine, induced an increase in NA levels to 225% and 300%, respectively, at a concentration of 10−3 m. 3 Local application of α2‐adrenoceptor antagonists caused an increase in NA levels, with idazoxan being more potent than piperoxan. Yohimbine did not cause any significant change. 4 All drugs used in these in vivo experiments had in vitro recoveries across the dialysis membrane between 10 and 20%. 5 We conclude that microdialysis with local drug application is suitable for the comparison of the pharmacological effects of drugs with affinity for α‐adrenoceptors on cortical NA overflow in vivo, provided that the passage across the membrane is equal for the different drugs.

Noradrenaline and Dopamine Efflux in the Prefrontal Cortex in Relation to Appetitive Classical Conditioning

We trained rats to learn that an auditory stimulus predicted delivery of reward pellets in the Skinner box. After 2 d of training, we measured changes in efflux of noradrenaline (NA) and dopamine (DA) in the medial prefrontal cortex using microdialysis on the third day. Animals were subjected to a normal rewarded session and an extinction session, in which the auditory stimulus was presented alone. In the rewarded session, both NA and DA efflux were increased, but in extinction, only NA was activated. The data suggest that NA has a role in the reaction to reward-predicting stimuli, which complements that of DA.

Role of the prefrontal cortex of the rat in learning and decision making: effects of transient inactivation

Publisher Summary This chapter describes the role of the prefrontal cortex of the rat in learning and decision making. Depending on the authors reviews of prefrontal cortex (PFC) functions in rats have provided lists of behavioral deficiencies following damage of the PFC. They include deficient performance in various delay-type tasks, spatial tasks, inhibition, attention, along with abnormalities in social behavior. When rats with PFC damage are examined for their spatial learning skills in a Morris water maze, no impairments in spatial learning could be detected; however, when the task was changed from an allocentric one to a visual-cued one, rats with damage of the medial PFC were initially impaired. It is assumed that with prefrontal damage, it was more difficult to shift between tasks with different task demands. Evidence supporting this assumption has been obtained, when rats are trained either in a cheeseboard task, or a visual-cued version of that task. Transient inactivation of the medial PFC did not interfere with task acquisition. However, such an inactivation impaired learning when the rats were switched from one version of the task to the other one. It is tempting to relate these findings with the well-known deficiencies described in humans with PFC damage.

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.

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.