Successful treatment of neonatal hemochromatosis as gestational alloimmune liver disease with intravenous immunoglobulin.

Neonatal hemochromatosis (NH) is a rare, often fatal disorder characterized by liver failure and hepatic and extrahepatic iron overload. Clinical manifestations can occur in utero or immediately after birth. Evidence suggests that most cases are due to a gestational disease with transplacental transfer of maternal IgG antibodies targeting the fetal liver resulting in immune injury. The alloimmune target is believed to be a fetal hepatocyte cell surface antigen, with subsequent complement activation resulting in severe loss of hepatocytes and fetal iron overload. This cascade of events leads to acute liver failure and neonatal death. With gestational alloimmune liver disease (GALD) being the mechanism of liver injury in most cases of NH, a new paradigm of treatment with intravenous immunoglobulin (IVIG) and exchange transfusion has been successfully used. We describe an extremely ill newborn with NH successfully treated with three doses of IVIG.

Cocaine reduces cytochrome oxidase activity in the prefrontal cortex and modifies its functional connectivity with brainstem nuclei.

Cocaine-induced psychomotor stimulation may be mediated by metabolic hypofrontality and modification of brain functional connectivity. Functional connectivity refers to the pattern of relationships among brain regions, and one way to evaluate this pattern is using interactivity correlations of the metabolic marker cytochrome oxidase among different regions. This is the first study of how repeated cocaine modifies: (1) mean cytochrome oxidase activity in neural areas using quantitative enzyme histochemistry, and (2) functional connectivity among brain regions using inter-correlations of cytochrome oxidase activity. Rats were injected with 15 mg/kg i.p. cocaine or saline for 5 days, which lead to cocaine-enhanced total locomotion. Mean cytochrome oxidase activity was significantly decreased in cocaine-treated animals in the superficial dorsal and lateral frontal cortical association areas Fr2 and Fr3 when compared to saline-treated animals. Functional connectivity showed that the cytochrome oxidase activity of the noradrenergic locus coeruleus and the infralimbic cortex were positively inter-correlated in cocaine but not in control rats. Positive cytochrome oxidase activity inter-correlations were also observed between the dopaminergic substantia nigra compacta and Fr2 and Fr3 areas and the lateral orbital cortex in cocaine-treated animals. In contrast, cytochrome oxidase activity in the interpeduncular nucleus was negatively correlated with that of Fr2, anterior insular cortex, and lateral orbital cortex in saline but not in cocaine groups. After repeated cocaine specific prefrontal areas became hypometabolic and their functional connectivity changed in networks involving noradrenergic and dopaminergic brainstem nuclei. We suggest that this pattern of hypofrontality and altered functional connectivity may contribute to cocaine-induced psychomotor stimulation.

Activation of alpha1-adrenoceptors enhances glutamate release onto ventral tegmental area dopamine cells.

The ventral tegmental area (VTA) plays an important role in reward and motivational processes that facilitate the development of drug addiction. Glutamatergic inputs into the VTA contribute to dopamine (DA) neuronal activation related to reward and response-initiating effects in drug abuse. Previous investigations indicate that alpha1-adrenoreceptors (α1-ARs) are primarily localized at presynaptic elements in the ventral midbrain. Studies from several brain regions have shown that presynaptic α1-AR activation enhances glutamate release. Therefore, we hypothesized that glutamate released onto VTA-DA neurons is modulated by pre-synaptic α1-AR. Recordings were obtained from putative VTA-DA cells of male Sprague-Dawley rats (28-50 days postnatal) using voltage clamp techniques. Phenylephrine (10 µM) and methoxamine (80µM), both α1-AR agonists, increased AMPA receptor-mediated excitatory postsynaptic currents' (EPSCs) amplitude evoked by electrical stimulation of afferent fibers (p<0.05). This effect was blocked by the α1-AR antagonist prazosin (1 µM). Phenylephrine decreased the paired-pulse ratio (PPR) and increased spontaneous EPSCs' frequencies but not their amplitudes suggesting a presynaptic locus of action. No changes in miniature EPSCs (0.5µM, tetrodotoxin [TTX]) were observed after phenylephrine's application which suggests that α1-AR effect was action potential dependent. Normal extra- and intracellular Ca(2+) concentration seems necessary for the α1-AR effect since phenylephrine in low Ca(2+) artificial cerebrospinal fluid (ACSF) and depletion of intracellular Ca(2+) stores with thapsigargin (10 µM) failed to increase the AMPA EPSCs' amplitude. Chelerythrine (1µM, protein kinase C (PKC) inhibitor) but not Rp-cAMPS (11 µM, PKA inhibitor) blocked the α1-AR activation effect on AMPA EPSCs, indicating that a PKC intracellular pathway is required. These results demonstrated that presynaptic α1-AR activation modulates glutamatergic inputs that affect VTA-DA neuronal excitability. α1-AR action might be heterosynaptically localized at glutamatergic fibers terminating onto VTA-DA neurons. It is suggested that drug-induced changes in α1-AR could be part of the neuroadaptations occurring in the mesocorticolimbic circuitry during the addiction process.

Parthenolide Blocks Cocaine's Effect on Spontaneous Firing Activity of Dopaminergic Neurons in the Ventral Tegmental Area.

Chronic cocaine administration leads to catecholamine reuptake inhibition which enhances reward and motivational behaviors. Ventral Tegmental Area dopaminergic (VTA DA) neuronal firing is associated with changes in reward predictive signals. Acute cocaine injections inhibit putative VTA DA cell firing in vertebrates. Parthenolide, a compound isolated from the feverfew plant (Tanacetum parthenium), has been shown to substantially inhibit cocaine's locomotion effects in a planarian animal model (Pagán et al., 2008). Here we investigated the effects of parthenolide on the spontaneous firing activity of putative VTA DA neurons in anesthetized male rats (250-300g). Single-unit recordings were analyzed after intravenous (i.v.) parthenolide administration followed by 1mg/kg i.v. cocaine injection. Results showed that parthenolide at 0.125 mg/kg and 0.250mg/kg significantly blocked cocaine's inhibitory effect on DA neuronal firing rate and bursting activity (p< 0.05, two way ANOVA). We propose that parthenolide might inhibit cocaine's effects on VTA DA neurons via its interaction with a common binding site at monoamine transporters. It is suggested that parthenolide could have a potential use as an overdose antidote or therapeutic agent to cocaine intoxication.

Alpha-2 noradrenergic receptor activation inhibits the hyperpolarization-activated cation current (Ih) in neurons of the ventral tegmental area.

The ventral tegmental area (VTA) is the source of dopaminergic projections innervating cortical structures and ventral forebrain. Dysfunction of this mesocorticolimbic system is critically involved in psychiatric disorders such as addiction and schizophrenia. Changes in VTA dopamine (DA) neuronal activity can alter neurotransmitter release at target regions which modify information processing in the reward circuit. Here we studied the effect of alpha-2 noradrenergic receptor activation on the hyperpolarization-activated cation current (I(h)) in DA neurons of the rat VTA. Brain slice preparations using whole-cell current and voltage-clamp techniques were employed. Clonidine and UK14304 (alpha-2 receptor selective agonists) were found to decrease I(h) amplitude and to slow its rate of activation indicating a negative shift in the current's voltage dependence. Two non-subtype-selective alpha-2 receptor antagonists, yohimbine and RS79948, prevented the effects of alpha-2 receptor activation. RX821002, a noradrenergic antagonist specific for alpha-2A and alpha-2D did not prevent I(h) inhibition. This result suggests that clonidine might be acting via an alpha-2C subtype since this receptor is the most abundant variant in the VTA. Analysis of a second messenger system associated with the alpha-2 receptor revealed that I(h) inhibition is independent of cyclic AMP (cAMP) and resulted from the activation of protein kinase C. It is suggested that the alpha-2 mediated hyperpolarizing shift in I(h) voltage dependence can facilitate the transition from pacemaker firing to afferent-driven burst activity. This transition may play a key role on the changes in synaptic plasticity that occurs in the mesocorticolimbic system under pathological conditions.

Noradrenergic modulation of the hyperpolarization-activated cation current (Ih) in dopamine neurons of the ventral tegmental area.

Alterations in the state of excitability of midbrain dopamine (DA) neurons from the ventral tegmental area (VTA) may underlie changes in the synaptic plasticity of the mesocorticolimbic system. Here, we investigated norepinephrine's (NE) regulation of VTA DA cell excitability by modulation of the hyperpolarization-activated cation current, Ih, with whole cell recordings in rat brain slices. Current clamp recordings show that NE (40 microM) hyperpolarizes spontaneously firing VTA DA cells (11.23+/-4 mV; n=8). In a voltage clamp, NE (40 microM) induces an outward current (100+/-24 pA; n=8) at -60 mV that reverses at about the Nernst potential for potassium (-106 mV). In addition, NE (40 microM) increases the membrane cord conductance (179+/-42%; n=10) and reduces Ih amplitude (68+/-3% of control at -120 mV; n=10). The noradrenergic alpha-1 antagonist prazosin (40 microM; n=5) or the alpha-2 antagonist yohimbine (40 microM; n=5) did not block NE effects. All NE-evoked events were blocked by the D2 antagonists sulpiride (1 microM) and eticlopride (100 nM) and no significant reduction of Ih took place in the presence of the potassium channel blocker BaCl2 (300 microM). Therefore, it is concluded that NE inhibition of Ih was due to an increase in membrane conductance by a nonspecific activation of D2 receptors that induce an outward potassium current and is not a result of a second messenger system acting on h-channels. The results also suggest that Ih channels are mainly located at dendrites of VTA DA cells and, thus, their inhibition may facilitate the transition from single-spike firing to burst firing and vice versa.

AMPA and NMDA receptors in P2 fractions of cocaine and cocaine-prazosin-treated rats.

Cocaine sensitization results in the development of increased locomotion and stereotypy. It is accompanied by changes in glutamatergic trasmission that appear to be region-specific. The purpose of this article was to determine the effect(s) of cocaine and prazosin plus cocaine treatments on ionotropic glutamate receptors in rat cerebral cortex (CTX) and prefrontal cortex (PFC). Cocaine-sensitized rats (15 mg/kg, i.p. once for 5 days), withdrawn (7 days) and later challenged with a single cocaine dose, showed region-specific in NMDA-2A and Glu-R2 in the CTX and PFC membranes in cocaine- and prazosin-treated rats when compared to the saline controls. Co-administration of prazosin inhibits sensitization and changes in NMDA 2A and Glu-R2. Furthermore, prazosin inhibits the effect of cocaine in CTX and PFC on [(3)H]FW (AMPA agonist) binding when compared to controls. In cortex, cocaine treatment causes a marked increase in total binding, while in PFC there is a significant decrease. In both regions, cocaine-prazosin treatment attenuates the effects of cocaine. These results suggest that cocaine affects ionotropic glutamate receptors (NMDA and AMPA) and that prazosin inhibits such effects in a region-specific form in rat brain.

Effects of cocaine administration on VTA cell activity in response to prefrontal cortex stimulation.

The repeated use of psychostimulants in humans has been associated with progressive enhancement of anxiety, panic attacks, and eventually paranoid psychosis. The appearance of such behaviors has been termed behavioral sensitization, which forms part of the basic pathological mechanisms involved in drug addiction. Psychostimulants act via a circuit involving the ventral tegmental area (VTA), prefrontal cortex (PFC), and nucleus accumbens. The PFC sends glutamatergic projections that activate dopaminergic neurons in the VTA. These projections provide an extremely important excitatory drive necessary for the development of sensitization. The effects of cocaine administration on the response of dopaminergic VTA cells to activation of the PFC have not been reported. Here the effects of acute cocaine administration on VTA cell response to PFC stimulation are examined. Statistical analysis of the changes in spontaneous activity and evoked response revealed a significant decrease in spontaneous activity at 1.0 mg/kg i.v. after cocaine treatment compared to baseline levels. The net effect was an increase in signal-to-noise ratio. Treatment with MK-801 at a dose of 2 mg/kg showed that the excitatory response was, at least partially, NMDA-mediated. Prazosin pretreatment (0.5 mg/kg i.p.) did not prevent a significant decrease in spontaneous activity brought about by cocaine (15 mg/kg, i.p.). Nonetheless, prazosin alone induced a significant decrease in the response to PFC stimulation when compared to baseline. In addition, iontophoretic application of norepinephrine (NE) onto VTA cells revealed that NE potentiated (19.2%), enhanced (26.9%), or suppressed (46.2%) the glutamate-evoked response in VTA cells. The results suggest that a possible role of cocaine in the process of sensitization might be to amplify the PFC-induced excitation at the VTA. Since the iontophoretic release of NE in almost half of the sampled cells produced similar effects to those of cocaine it may suggest a possible NE-mediated mechanism for cocaine actions.

Effects of intravenous cocaine administration on cerebellar Purkinje cell activity.

The goal of the present study was to investigate the effects of intravenous cocaine administration on cerebellar Purkinje cell firing. Extracellular neuron activity was recorded and cells were locally excited with spaced microiontophoretic pulses of glutamate. Glutamate-evoked and spontaneous discharges were compared before and immediately following cocaine administration. Cocaine injections (1. 0 and 0.25 mg/kg, i.v.) induced a reversible suppression of both spontaneous activity and glutamate-evoked excitation. Procaine was ineffective in producing similar actions. Cocaine only inhibited glutamate-induced excitation in animals pre-treated with reserpine (5 mg/kg, i.p.). Propranolol injections (10 mg/kg, i.p.) were ineffective in blocking cocaine-induced inhibitions. Yohimbine (5 mg/kg, i.p.) pre-treatment abolished cocaine-induced suppressions of either spontaneous or glutamate-evoked excitation. Therefore, cocaine administration decreases Purkinje cell spontaneous and glutamate-evoked discharges by a mechanism involving alpha(2)-adrenoceptor activation. It is suggested that by changing the normal function of the cerebellum cocaine can produce drug-related alterations in overt behavior and cognition.

Chronic imipramine treatment induces downregulation of alpha-2 receptors in rat's locus coeruleus and A2 region of the tractus solitarius.

Imipramine is an effective antidepressant agent that blocks the reuptake of monoamines. In order to understand some of its basic mechanisms of action, we investigated the effects of chronic imipramine administration (10 mg/kg, i.p.; 21 days) on the alpha-2 receptor population of several brain sites. Alpha-2 receptor density was estimated by in vitro autoradiography using [3H]Idazoxan. The densitometric analysis revealed a decreased receptor density in the A2 region of the tractus solitarius (20%) and locus coeruleus (16%). No changes were observed in the amygdala, pyriform cortex, periacueductal gray and the bed nucleus of the stria terminalis. These results suggest that chronic imipramine treatment selectively modulates the alpha-2 receptor population localized in the brain stem norepinephrine-rich nuclei and not in the population present on limbic structures innervated by noradrenergic terminal projections. The possible physiological consequences of this selective modulation of alpha-2 receptors are discussed.

Cocaine actions in a central noradrenergic circuit: enhancement of cerebellar Purkinje neuron responses to iontophoretically applied GABA.

Many recent studies have implicated the mesolimbic dopaminergic pathway as the central neurotransmitter system which is most likely responsible for the euphoria and abuse potential associated with cocaine self-administration. Nevertheless, cocaine also has well established interactions with the norepinephrine- and serotonin-containing pathways of the brain. In order to begin assessing potential non-dopamine-mediated actions of cocaine in central circuits, we have initiated a series of experiments using the cerebellar Purkinje neuron as an electrophysiological test system. The strategy was to use the same experimental protocols employed in previous investigations of noradrenergic influences on putative amino acid transmitter action to examine the effects of exogenously applied cocaine on gamma-aminobutyric acid (GABA)-induced depressant responses of Purkinje cells. Accordingly, the inhibitory responses of Purkinje neurons to microiontophoretically applied GABA were examined before and after systemic or local iontophoretic administration of cocaine. Drug-induced changes in the spontaneous firing rate and GABA responsiveness of individual cells were assessed by quantitative analysis of perievent histograms. The results indicate that, like norepinephrine, cocaine at parenteral or iontophoretic doses subthreshold for producing direct suppression of spontaneous discharge can augment Purkinje neuron responses to GABA. Such potentiating effects of cocaine on GABA-mediated inhibition were not evident in animals pretreated with the selective noradrenergic toxins DSP-4. These findings indicate that cocaine can enhance central neuronal responsiveness to GABA in a manner identical to that shown previously for norepinephrine. Such actions in noradrenergic target circuits throughout the brain could contribute to the net behavioral response observed following cocaine administration.

Effects of systemically and locally applied cocaine on cerebrocortical neuron responsiveness to afferent synaptic inputs and glutamate.

The goal of the present study was to determine the effects of systemically or locally applied cocaine on rat somatosensory cortical neuron responsiveness to afferent synaptic inputs or putative transmitter application and to compare these results with previously observed actions of endogenous cortical monoamines on the same parameters of neuronal function. Individual cells in rat cortex were activated by stimulation of thalamocortical afferents or local iontophoretic application of glutamate. Extracellularly recorded responses to these stimuli were monitored before and after parenteral or microiontophoretic administration of cocaine. The results indicate that while high doses (greater than 2.0 mg/kg i.p.) of the drug can suppress both evoked and spontaneous activity of cortical neurons, low doses (0.5 mg/kg i.p.) can selectively enhance stimulus-evoked discharge. These facilitating effects can also be observed during iontophoretic application of cocaine directly onto recorded cells, thus suggesting that at least a component of the drug's influence on neuronal responsiveness is mediated by local actions at synapses within the cortex. Of the 3 major endogenous cortical monoamines whose synaptic reuptake is influenced by cocaine, the actions reported here mimic those described previously for norepinephrine but not those of dopamine or serotonin. As such these findings suggest that cocaine may enhance the responsiveness of sensory cortical neurons to afferent synaptic inputs via its ability to activate noradrenergic modulatory mechanisms within the cerebrocortical circuitry.

Antikindling effects of locus coeruleus stimulation: mediation by ascending noradrenergic projections.

Electrical stimulation of the noradrenergic locus coeruleus (LC) delays the generalization of partial seizures during amygdaloid kindling by increasing the time spent in the earliest stages of seizure development. To determine whether noradrenergic axons projecting to the midbrain and forebrain are involved in this antikindling effect, we examined the effects of lesions of the dorsal noradrenergic bundle, induced by intracerebral infusions of 6-hydroxydopamine (6-OHDA), on kindling and the antikindling action of stimulation of the LC. Stimulation of the LC during amygdaloid kindling increased the number of afterdischarges (ADs) spent in the early stages of partial seizure and decreased the number of ADs spent in later stages of generalized seizure, as has been described previously. LC-stimulated rats also displayed longer durations of AD during early stages of kindling. The antikindling effect of LC stimulation was blocked by lesions of the dorsal bundle, whereas the facilitatory effects of LC stimulation on generalization and on the duration of AD were unaffected by the lesions. These results suggest that the antikindling action of LC stimulation is mediated by the ascending projections of noradrenergic neurons, presumably through enhanced release of noradrenaline. On the other hand, the facilitatory effects of LC stimulation on the development of later stages of seizure and on the duration of AD appear to be independent of the ascending dorsal bundle.

Transient elevation of locus coeruleus alpha 2-adrenergic receptor binding during the early stages of amygdala kindling.

Enhancement of noradrenergic neurotransmission retards, but does not prevent, the development of kindling. The firing activity of noradrenergic locus coeruleus (LC) neurons is partially regulated by axon collateral recurrent inhibition mediated via alpha 2-adrenergic receptors. We tested the hypothesis that LC autoinhibitory alpha 2-adrenergic receptors may change during the kindling process thereby altering LC excitability. Specific binding of the alpha 2-adrenergic receptor antagonist [3H]RX781094 (idazoxan) was measured in the LC of rats at 3 different stages of kindling development using in vitro neurotransmitter receptor autoradiography techniques. Specific [3H]RX781094 binding was elevated significantly in rats kindled to two Class 1 kindled motor seizures. No differences in binding were observed in animals kindled to Class 3 or Class 5 kindled motor seizures. Saturation of binding experiments indicated that the increase in binding following two Class 1 kindled motor seizures was due to an increase in the total number of alpha 2-receptors without a change in the affinity of the binding site for [3H]RX781094. The transient increase in number of LC alpha 2-adrenergic receptors is consistent with the idea that noradrenergic neurotransmission inhibits the early progress of kindling development, but then subsequently becomes ineffective in maintaining the inhibition during later stages of kindling development.

The effect of amygdala kindled seizures on locus coeruleus activity.

Locus coeruleus (LC) neuronal activity was recorded in anesthetized and in awake behaving rats during the production of amygdala afterdischarges (AD's) using kindling protocol. Both LC multiple and single unit discharges were temporally correlated with the appearance of AD's in the amygdala. Seizures were manifested in single unit activity as significant increases in firing rate. In awake animals, a bursting pattern of discharges was observed. We postulate that the observed changes in the LC activity pattern may have a modulatory role in the development of kindled seizures.

Effect of locus ceruleus stimulation on the development of kindled seizures.

The effects of locus ceruleus stimulation on amygdala kindling development were investigated. Twenty to thirty minutes of locus ceruleus stimulation was delivered prior to each amygdala kindling session. Locus ceruleus-stimulated animals spent a significantly longer time in stage 1 than did nonstimulated or reticular formation stimulated controls. However, the total number of stimulations to produce the first stage 5 did not differ between groups. The afterdischarge duration in locus ceruleus-stimulated animals increased even though the behavioral stages did not progress. There appeared to be an uncoupling of the electrographic and behavioral manifestations of the kindling process in the locus ceruleus-stimulated animals. These data support the view of an inhibitory role of the central noradrenergic system in the development of kindled seizures.