Medial Olfactory Tubercle Research Articles

Distinct limbic dopamine regulation across olfactory-tubercle subregions through integration of in vivo fast-scan cyclic voltammetry and optogenetics.

The olfactory tubercle (OT), an important component of the ventral striatum and limbic system, is involved in multi-sensory integration of reward-related information in the brain. However, its functional roles are often overshadowed by the neighboring nucleus accumbens. Increasing evidence has highlighted that dense dopamine (DA) innervation of the OT from the ventral tegmental area (VTA) is implicated in encoding reward, natural reinforcers, and motivated behaviors. Recent studies have further suggested that OT subregions may have distinct roles in these processes due to their heterogeneous DA transmission. Currently, very little is known about regulation (release and clearance) of extracellular DA across OT subregions due to its limited anatomical accessibility and proximity to other DA-rich brain regions, making it difficult to isolate VTA-DA signaling in the OT with conventional methods. Herein, we characterized heterogeneous VTA-DA regulation in the medial (m) and lateral (l) OT in "wild-type," urethane-anesthetized rats by integrating in vivo fast-scan cyclic voltammetry with cell-type specific optogenetics to stimulate VTA-DA neurons. Channelrhodopsin-2 was selectively expressed in the VTA-DA neurons of wild-type rats and optical stimulating parameters were optimized to determine VTA-DA transmission across the OT. Our anatomical, neurochemical, and pharmacological results show that VTA-DA regulation in the mOT is less dependent on DA transporters and has greater DA transmission than the lOT. These findings establish the OT as a unique, compartmentalized structure and will aid in future behavioral characterization of the roles of VTA-DA signaling in the OT subregions in reward, drug addiction, and encoding behavioral outputs necessary for survival.

Activation of the dopaminergic pathway from VTA to the medial olfactory tubercle generates odor-preference and reward.

Odor-preferences are usually influenced by life experiences. However, the neural circuit mechanisms remain unclear. The medial olfactory tubercle (mOT) is involved in both reward and olfaction, whereas the ventral tegmental area (VTA) dopaminergic (DAergic) neurons are considered to be engaged in reward and motivation. Here, we found that the VTA (DAergic)-mOT pathway could be activated by different types of naturalistic rewards as well as odors in DAT-cre mice. Optogenetic activation of the VTA-mOT DAergic fibers was able to elicit preferences for space, location and neutral odor, while pharmacological blockade of the dopamine receptors in the mOT fully prevented the odor-preference formation. Furthermore, inactivation of the mOT-projecting VTA DAergic neurons eliminated the previously formed odor-preference and strongly affected the Go-no go learning efficiency. In summary, our results revealed that the VTA (DAergic)-mOT pathway mediates a variety of naturalistic reward processes and different types of preferences including odor-preference in mice.

DREADD-Induced Silencing of the Medial Olfactory Tubercle Disrupts the Preference of Female Mice for Opposite-Sex Chemosignals(1,2,3).

Attraction to opposite-sex pheromones during rodent courtship involves a pathway that includes inputs to the medial amygdala (Me) from the main and accessory olfactory bulbs, and projections from the Me to nuclei in the medial hypothalamus that control reproduction. However, the consideration of circuitry that attributes hedonic properties to opposite-sex odors has been lacking. The medial olfactory tubercle (mOT) has been implicated in the reinforcing effects of natural stimuli and drugs of abuse. We performed a tract-tracing study wherein estrous female mice that had received injections of the retrograde tracer, cholera toxin B, into the mOT were exposed to volatile odors from soiled bedding. Both the anterior Me and ventral tegmental area sent direct projections to the mOT, of which a significant subset was selectively activated (expressed Fos protein) by testes-intact male (but not female) volatile odors from soiled bedding. Next, the inhibitory DREADD (designer receptors exclusively activated by designer drugs) receptor hM4Di was bilaterally expressed in the mOT of female mice. Urinary preferences were then assessed after intraperitoneal injection of either saline or clozapine-N-oxide (CNO), which binds to the hM4Di receptor to hyperpolarize infected neurons. After receiving CNO, estrous females lost their preference for male over female urinary odors, whereas the ability to discriminate these odors remained intact. Male odor preference returned after vehicle treatment in counterbalanced tests. There were no deficits in locomotor activity or preference for food odors when subject mice received CNO injections prior to testing. The mOT appears to be a critical segment in the pheromone–reward pathway of female mice.

Laminar and spatial localization of the islands of Calleja in mice

The islands of Calleja (IC) are dense clusters of cells localized within the ventral striatum. The IC have been described as variable in both number and localization from animal-to-animal, however, a quantitative investigation of this variability is unavailable. Further, it is presently unknown whether the IC occupy select areas of the olfactory tubercle (OT), the ventral striatum structure which possesses the IC in mice. To address these questions, we examined the IC of adult C57bl/6 mice. As previously noted, we found substantial inter-hemispheric and inter-mouse variations in the total number of IC. While the IC were observed in all three cell layers of the OT, the bulk of IC occupied layer iii. The span of the IC along the anterior–posterior and medial–lateral axes of the OT was variant. Further, localizations of the IC within the OT also differed across animals. Notably, the probability of observing an IC in the medial OT was greater than that of observing one in the lateral. These data provide a fundamental characterization of both differences and similarities regarding the IC in mice and will be informative for future in vivo studies seeking to perturb and possibly record from the IC. Further, we predict that inter-animal diversity in the IC may be a mechanism for inter-animal differences in behavior, especially reward-related and motivational behaviors.

P.6.c.019 Persistent microglia activation contributes to the depressive/psychotic-like phenotype induced by adolescent THC exposure in rats

Rodents rely upon their olfactory modality to perceive opposite-sex pheromonal odors needed to motivate courtship behaviors. Volatile and nonvolatile components of pheromonal odors are processed by the main (MOS) and accessory olfactory system (AOS), respectively, with inputs converging in the medial amygdala (Me). The Me in turn targets the mesolimbic dopamine system, including the nucleus accumbens core (AcbC) and shell (AcbSh), the ventral pallidum (VP), medial olfactory tubercle (mOT) and ventral tegmental area (VTA). We hypothesized that pheromone-induced dopamine (DA) release in the ventral striatum (particularly in the mAcb and mOT) may mediate the normal preference of female mice to investigate male pheromones. We made bilateral 6-OHDA lesions of DA fibers innervating either the mAcb alone or the mAcb + mOT in female mice and tested estrous females’ preference for opposite-sex urinary odors. We found that 6-OHDA lesions of either the mAcb alone or the mAcb + mOT significantly reduced the preference of sexually naïve female mice to investigate breeding male urinary odors (volatiles as well as volatiles + nonvolatiles) vs. estrous female urinary odors. These same neurotoxic lesions had no effect on subjects’ ability to discriminate between these two urinary odors, on their locomotor activity, or on their preference for consuming sucrose. The integrity of the dopaminergic innervation of the mAcb and mOT is required for female mice to prefer investigating male pheromones.

Neuroanatomical circuitry mediating the sensory impact of nicotine in the central nervous system

Direct actions of nicotine in the CNS appear to be essential for its reinforcing properties. However, activation of nicotinic acetylcholine receptors (nAChRs) on afferent sensory nerve fibers is an important component of addiction to, and withdrawal from, cigarette smoking. The aim of the present study was to identify the neuroanatomical substrates activated by the peripheral actions of nicotine and to determine whether these sites overlap brain structures stimulated by direct actions of nicotine. Mouse brains were examined by immunohistochemistry for c-Fos protein after intraperitoneal injection of either nicotine hydrogen tartrate salt (NIC; 30 and 40 μg/kg) or nicotine pyrrolidine methiodide (NIC-PM; 20 and 30 μg/kg). NIC-PM induced c-Fos immunoreactivity (IR) at multiple brain sites. In the brainstem, c-Fos IR was detected in the locus coeruleus, laterodorsal tegmental nucleus, and pedunculotegmental nucleus. In the midbrain, c-Fos IR was observed in areas overlapping the ventral tegmental area (VTA), which includes the paranigral nucleus, parainterfascicular nucleus, parabrachial pigmental area, and rostral VTA. Other structures of the nicotine brain-reward circuitry activated by NIC-PM included the hypothalamus, paraventricular thalamic nucleus, lateral habenular nucleus, hippocampus, amygdala, accumbens nucleus, piriform cortex, angular insular cortex, anterior olfactory nucleus, lateral septal nucleus, bed nucleus of stria terminalis, cingulate and medial prefrontal cortex, olfactory tubercle, and medial and lateral orbital cortex. NIC, acting through central and peripheral nAChRs, produced c-Fos IR in areas that overlapped NIC-PM-induced c-Fos-expressing sites. These neuroanatomical data are the first to demonstrate that the CNS structures that are the direct targets of nicotine are also anatomical substrates for the peripheral sensory impact of nicotine.

6-Hydroxydopamine lesions of the anteromedial ventral striatum impair opposite-sex urinary odor preference in female mice

Rodents rely upon their olfactory modality to perceive opposite-sex pheromonal odors needed to motivate courtship behaviors. Volatile and nonvolatile components of pheromonal odors are processed by the main (MOS) and accessory olfactory system (AOS), respectively, with inputs converging in the medial amygdala (Me). The Me in turn targets the mesolimbic dopamine system, including the nucleus accumbens core (AcbC) and shell (AcbSh), the ventral pallidum (VP), medial olfactory tubercle (mOT) and ventral tegmental area (VTA). We hypothesized that pheromone-induced dopamine (DA) release in the ventral striatum (particularly in the mAcb and mOT) may mediate the normal preference of female mice to investigate male pheromones. We made bilateral 6-OHDA lesions of DA fibers innervating either the mAcb alone or the mAcb+mOT in female mice and tested estrous females’ preference for opposite-sex urinary odors. We found that 6-OHDA lesions of either the mAcb alone or the mAcb+mOT significantly reduced the preference of sexually naïve female mice to investigate breeding male urinary odors (volatiles as well as volatiles+nonvolatiles) vs. estrous female urinary odors. These same neurotoxic lesions had no effect on subjects’ ability to discriminate between these two urinary odors, on their locomotor activity, or on their preference for consuming sucrose. The integrity of the dopaminergic innervation of the mAcb and mOT is required for female mice to prefer investigating male pheromones.

A quantitative comparison of the efferent projections of the anterior and posterior subdivisions of the medial amygdala in female mice

In rodents, many aspects of sociosexual behavior are mediated by chemosignals released by opposite-sex conspecifics. These chemosignals are relayed via the main (MOS) and accessory olfactory systems (AOS) to the medial amygdala (Me). The Me is subdivided into anterior (MeA) and posterior (MeP) subnuclei, and lesions targeting these regions have different effects on proceptive courtship behaviors in female mice. Differential behavioral effects of MeA vs. MeP lesions could reflect a difference in the projections of neurons located in these Me subnuclei. To examine this question, we injected female mice with the anterograde tracer, Fluoro-Ruby into either the MeA or MeP and quantified labeled puncta in 11 forebrain target sites implicated in courtship behaviors using confocal fluorescence microscopy. We found that the MeP more densely innervates the medial and intermediate regions of the posterior bed nucleus of the stria terminalis (pBNST) and the posteromedial cortical amygdala (PMCo), while the MeA more densely innervates the horizontal diagonal band of Broca (HDB) and the medial olfactory tubercle (mOT), a region that may be a component of the circuitry responsible for olfactory-mediated motivated behaviors.

Long-term effects of cariprazine exposure on dopamine receptor subtypes

All clinically effective antipsychotics are known to act on the dopaminergic system, and previous studies have demonstrated that repeated treatment with antipsychotics produced region-specific changes in dopamine receptor levels. Cariprazine is a dopamine D₃ and D₂ receptor partial agonist with preferential binding to D₃ receptors. We examined the effects of chronic cariprazine administration on dopamine receptor levels. Rats were administered either vehicle or cariprazine (0.06, 0.2, or 0.6 mg/kg) for 28 days. Dopamine receptor levels were quantitated using autoradiographic assays on brain tissue sections from the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIPP), olfactory tubercle (OT), and islands of Calleja (ICj). Chronic treatment with cariprazine did not alter D₁ receptor levels in any brain region tested. Cariprazine increased D₂ receptor levels in mPFC (27%-43%), NAc (40%-45%), medial (41%-53%) and lateral (52%-63%) CPu, and HIPP (38%). Cariprazine dose-dependently upregulated D₃ receptor levels in ICj (32%-57%), OT (27%-67%), and NAc shell (31%-48%). Repeated cariprazine treatment increased D₄ receptor in NAc (53%-82%), medial (54%-98%) and lateral (58%-74%) CPu, and HIPP (38%-98%). Similar to other antipsychotics, cariprazine upregulated D₂ and D₄ receptor levels in various brain regions. Cariprazine was unique among antipsychotics in increasing D₃ receptor levels, which may support its unique psychopharmacologic properties.

Amyloid β Peptide-(1–42) Induces Internalization and Degradation of β2 Adrenergic Receptors in Prefrontal Cortical Neurons

Emerging evidence indicates that amyloid β peptide (Aβ) initially induces subtle alterations in synaptic function in Alzheimer disease. We have recently shown that Aβ binds to β(2) adrenergic receptor (β(2)AR) and activates protein kinase A (PKA) signaling for glutamatergic regulation of synaptic activities. Here we show that in the cerebrums of mice expressing human familial mutant presenilin 1 and amyloid precursor protein genes, the levels of β(2)AR are drastically reduced. Moreover, Aβ induces internalization of transfected human β(2)AR in fibroblasts and endogenous β(2)AR in primary prefrontal cortical neurons. In fibroblasts, Aβ treatment also induces transportation of β(2)AR into lysosome, and prolonged Aβ treatment causes β(2)AR degradation. The Aβ-induced β(2)AR internalization requires the N terminus of the receptor containing the peptide binding sites and phosphorylation of β(2)AR by G protein-coupled receptor kinase, not by PKA. However, the G protein-coupled receptor kinase phosphorylation of β(2)AR and the receptor internalization are much slower than that induced by βAR agonist isoproterenol. The Aβ-induced β(2)AR internalization is also dependent on adaptor protein arrestin 3 and GTPase dynamin, but not arrestin 2. Functionally, pretreatment of primary prefrontal cortical neurons with Aβ induces desensitization of β(2)AR, which leads to attenuated response to subsequent stimulation with isoproterenol, including decreased cAMP levels, PKA activities, PKA phosphorylation of serine 845 on α-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor subunit 1 (GluR1), and AMPA receptor-mediated miniature excitatory postsynaptic currents. This study indicates that Aβ induces β(2)AR internalization and degradation leading to impairment of adrenergic and glutamatergic activities.

Amphetamine Administration into the Ventral Striatum Facilitates Behavioral Interaction with Unconditioned Visual Signals in Rats

BackgroundAdministration of psychomotor stimulants like amphetamine facilitates behavior in the presence of incentive distal stimuli, which have acquired the motivational properties of primary rewards through associative learning. This facilitation appears to be mediated by the mesolimbic dopamine system, which may also be involved in facilitating behavior in the presence of distal stimuli that have not been previously paired with primary rewards. However, it is unclear whether psychomotor stimulants facilitate behavioral interaction with unconditioned distal stimuli.Principal FindingsWe found that noncontingent administration of amphetamine into subregions of the rat ventral striatum, particularly in the vicinity of the medial olfactory tubercle, facilitates lever pressing followed by visual signals that had not been paired with primary rewards. Noncontingent administration of amphetamine failed to facilitate lever pressing when it was followed by either tones or delayed presentation or absence of visual signals, suggesting that visual signals are key for enhanced behavioral interaction. Systemic administration of amphetamine markedly increased locomotor activity, but did not necessarily increase lever pressing rewarded by visual signals, suggesting that lever pressing is not a byproduct of heightened locomotor activity. Lever pressing facilitated by amphetamine was reduced by co-administration of the dopamine receptor antagonists SCH 23390 (D1 selective) or sulpiride (D2 selective).ConclusionsOur results suggest that amphetamine administration into the ventral striatum, particularly in the vicinity of the medial olfactory tubercle, activates dopaminergic mechanisms that strongly enhance behavioral interaction with unconditioned visual stimuli.

Intracranial self-administration of MDMA into the ventral striatum of the rat: differential roles of the nucleus accumbens shell, core, and olfactory tubercle.

Behavioral and anatomical data suggest that the ventral striatum, consisting of the nucleus accumbens and olfactory tubercle, is functionally heterogeneous. Cocaine and D: -amphetamine appear to be more rewarding when administered into the medial olfactory tubercle or medial accumbens shell than into their lateral counterparts, including the accumbens core. We sought to determine whether rats self-administer the popular recreational drug (+/-)-3,4-methylenedioxymethamphetamine (MDMA) into ventrostriatal subregions and whether the medial olfactory tubercle and medial accumbens shell mediate MDMA's positive reinforcing effects more effectively than their lateral counterparts. Rats receiving 30 mM MDMA into the medial olfactory tubercle, medial accumbens shell, or accumbens core, but not the lateral tubercle or lateral shell, showed higher self-administration rates than rats receiving vehicle. The medial shell supported more vigorous self-administration of MDMA at higher concentrations than the core or medial olfactory tubercle. In addition, intra-medial shell MDMA self-administration was disrupted by co-administration of the D1 or D2 receptor antagonists SCH 23390 (1-3 mM) or raclopride (3-10 mM). Our data suggest that the ventral striatum is functionally heterogeneous. The medial accumbens shell appears to be more important than other ventrostriatal subregions in mediating the positive reinforcing effects of MDMA via both D1- and D2-type receptors. Together with previous data, our data also suggest that unidentified actions of MDMA interfere with the positive reinforcing effects of dopamine in the medial olfactory tubercle.

Projections from the posterolateral olfactory amygdala to the ventral striatum: neural basis for reinforcing properties of chemical stimuli.

BackgroundVertebrates sense chemical stimuli through the olfactory receptor neurons whose axons project to the main olfactory bulb. The main projections of the olfactory bulb are directed to the olfactory cortex and olfactory amygdala (the anterior and posterolateral cortical amygdalae). The posterolateral cortical amygdaloid nucleus mainly projects to other amygdaloid nuclei; other seemingly minor outputs are directed to the ventral striatum, in particular to the olfactory tubercle and the islands of Calleja.ResultsAlthough the olfactory projections have been previously described in the literature, injection of dextran-amines into the rat main olfactory bulb was performed with the aim of delimiting the olfactory tubercle and posterolateral cortical amygdaloid nucleus in our own material. Injection of dextran-amines into the posterolateral cortical amygdaloid nucleus of rats resulted in anterograde labeling in the ventral striatum, in particular in the core of the nucleus accumbens, and in the medial olfactory tubercle including some islands of Calleja and the cell bridges across the ventral pallidum. Injections of Fluoro-Gold into the ventral striatum were performed to allow retrograde confirmation of these projections.ConclusionThe present results extend previous descriptions of the posterolateral cortical amygdaloid nucleus efferent projections, which are mainly directed to the core of the nucleus accumbens and the medial olfactory tubercle. Our data indicate that the projection to the core of the nucleus accumbens arises from layer III; the projection to the olfactory tubercle arises from layer II and is much more robust than previously thought. This latter projection is directed to the medial olfactory tubercle including the corresponding islands of Calleja, an area recently described as critical node for the neural circuit of addiction to some stimulant drugs of abuse.

The Functional Divide for Primary Reinforcement of D-Amphetamine Lies between the Medial and Lateral Ventral Striatum: Is the Division of the Accumbens Core, Shell, and Olfactory Tubercle Valid?: Figure 1.

When projection analyses placed the nucleus accumbens and olfactory tubercle in the striatal system, functional links between these sites began to emerge. The accumbens has been implicated in the rewarding effects of psychomotor stimulants, whereas recent work suggests that the medial accumbens shell and medial olfactory tubercle mediate the rewarding effects of cocaine. Interestingly, anatomical evidence suggests that medial portions of the shell and tubercle receive afferents from common zones in a number of regions. Here, we report results suggesting that the current division of the ventral striatum into the accumbens core and shell and the olfactory tubercle does not reflect the functional organization for amphetamine reward. Rats quickly learned to self-administer D-amphetamine into the medial shell or medial tubercle, whereas they failed to learn to do so into the accumbens core, ventral shell, or lateral tubercle. Our results suggest that primary reinforcement of amphetamine is mediated via the medial portion of the ventral striatum. Thus, the medial shell and medial tubercle are more functionally related than the medial and ventral shell or the medial and lateral tubercle. The current core-shell-tubercle scheme should be reconsidered in light of recent anatomical data and these functional findings.

A five-minute, but not a fifteen-minute, conditioning trial duration induces conditioned place preference for cocaine administration into the olfactory tubercle

The establishment of conditioned place preference (CPP) with intracranial injections requires specific injection sites, drug doses, and conditioning trial durations. We examined the role of conditioning trial duration in CPP with cocaine injections into the medial olfactory tubercle. Only those rats that had spent 5 min in the compartments showed CPP for cocaine, while rats that had been removed immediately or spent 15 min following cocaine injections did not show CPP. Effective conditioning trial durations for CPP induced by intracranial cocaine injections are apparently much shorter than those typically used for intracranial injections of other drugs of abuse.

Ventral striatal anatomy of locomotor activity induced by cocaine, D-amphetamine, dopamine and D 1/D 2 agonists

The ventral striatum appears to play a critical role in mediating motoric effects (i.e. ambulatory activity and rearing) of psychostimulants such as cocaine. We evaluated whether sub-regions of the ventral striatum play differential roles in locomotion and rearing induced by various dopaminergic drugs. Injections of D-amphetamine and dopamine stimulated locomotion and rearing with a similar potency at each of the sub-regions: the core, medial shell or medial tubercle. However, injections of mixtures of the D 1- and D 2-type agonists SKF 38393 and quinpirole or cocaine into the medial olfactory tubercle or the medial shell of the nucleus accumbens induced marked locomotion and rearing, while these injections into the core induced little or no locomotion or rearing. Furthermore, cocaine injections into the lateral or posterior tubercle produced marginal locomotion and rearing, while cocaine injections into regions just dorsal to these tubercle sites, the lateral portion of the shell or the ventral pallidum, did not produce any stimulating effect. We conclude that dopaminergic compounds induce vigorous locomotion and rearing in both core and shell; the relative roles of the core and shell differ depending on chemical compounds. Similar to the nucleus accumbens, the olfactory tubercle, particularly the medial portion, also mediates these behaviors induced by dopaminergic compounds. The medial ventral striatum (i.e. the medial tubercle and medial shell) plays a more important role in cocaine-induced locomotion and rearing than the lateral ventral striatum (i.e. the core, lateral shell and lateral tubercle). Moreover, the differential effects of cocaine between the medial and lateral portions of the shell on locomotion and rearing suggest more than two functional units (the core vs. the shell) within the accumbens.

Differential regional zif268 messenger RNA expression in an escalating dose/binge model of amphetamine-induced psychosis

Amphetamine-induced psychosis is most often associated with a high-dose multiple binge pattern of stimulant abuse. To simulate these conditions in rats, we used an escalating dose/binge administration paradigm. Animals were pretreated with escalating doses of amphetamine (1.0–8.0 mg/kg) over four days, then exposed to nine daily binges (8.0 mg/kg every 2 h; four injections/day). Other animals received either multiple injections of saline, saline followed by acute amphetamine (8.0 mg/kg) or single daily injections of amphetamine (8.0 mg/kg) in parallel with the escalating dose/binge treatment. One hour after the last injection, all animals were decapitated and regional brain activation patterns were assessed using in situ hybridization with antisense probes for zif268. Acute amphetamine resulted in a significant elevation of zif268 messenger RNA in both the nucleus accumbens and dorsal striatum. However, whereas after single daily amphetamine treatment this index was no longer elevated above control levels in the dorsal striatum, multiple binge exposures were required for the nucleus accumbens to return to baseline. Agranular insular cortex and medial olfactory tubercle zif268 messenger RNA expression was also markedly increased after acute amphetamine treatment but, unlike the nucleus accumbens and dorsal striatum, this increase was not significantly attenuated by either single daily injection or multiple binge treatment. Zif268 messenger RNA expression in the lateral nucleus of the amygdala also remained elevated above baseline after binge treatment. The possible relationships of these changes in zif268 messenger RNA regional expression patterns to the development of psychosis in high-dose stimulant abusers are discussed.

Effects of the Trichothecene Mycotoxin T-2 Toxin on Neurotransmitters and Metabolites in Discrete Areas of the Rat Brain

T-2 toxin has been shown to affect the central nervous system. Only recently have attempts been made to characterize the neurochemical perturbations associated with T-2 intoxication. To examine the effect of T-2 on regional brain biogenic monoamines and selected metabolites, male rats were dosed orally with T-2 toxin in corn oil at 0.1, 1.0 or 2.5 mg/kg body weight. At 2, 6 and 10 hr post-dosing, rats were killed, brains were collected and stored at −80° until analysed. Brain nuclei, including nucleus raphe magnus, paraventricular nucleus, locus coeruleus, substantia nigra, medial forebrain bundle, nucleus accumbens and olfactory tubercle, were analysed. T-2 treatment increased 5-hydroxy-3-indoleacetic acid and serotonin throughout the brain, and produced a transient increase in norepinephrine in the nucleus raphe magnus and a temporary decrease in the substantia nigra. Regional dihydroxyphenylacetic acid concentration was affected, with increased DOPAC observed in the locus coeruleus, medial forebrain bundle and paraventricular nucleus of the hypothalamus, and decreased DOPAC in the olfactory tubercles. No regional changes in epinephrine or dopamine were observed. Few treatment differences were observed, with the 0.1 mg/kg body weight T-2, 2% of the LD 50, significantly affecting brain monoamines. It had been suggested that neurological manifestations of T-2 toxin are the result of brain hypoxia; however, the altered brain monoamine profile observed at doses that do not alter heart function, suggests the brain is a primary site of trichothecene action.

Selective Expression of Dopamine D3Receptor mRNA in Proliferative Zones during Embryonic Development of the Rat Brain

We studied by in situ hybridization histochemistry the expression of D3 receptor (D3R) mRNA at various stages of rat brain development. The first expression of D3R mRNA was detected at embryonic day 14 (E14) in the striatal and rhinencephalic neuroepithelia and throughout the tectal neuroepithelium. From E16 to E19 D3R mRNA expression extended along a rostrocaudal axis to additional proliferative ventricular zones of the basal forebrain, including the neuroepithelia of the olfactory bulb, nucleus accumbens, septum, and amygdala, whereas D1 and D2 receptor (D1R and D2R) mRNAs were expressed predominantly by migrating neuroblasts and/or differentiating striatal neurons. Only a few neuroblasts, migrating in the lateral cortical stream or developing as cerebellar Purkinje cells, expressed D3R mRNA from E18. At birth D3R expression mRNA appeared in differentiating neuronal fields of the nucleus accumbens and medial mamillary body primordia and on P5 reached a distribution similar to that found in adult. In addition, a transient upregulation was detected on P5 in the medial mamillary bodies, parietofrontal cortex, and olfactory tubercle. In the adult brain D3R gene expression continued in the striatal proliferative subventricular zone. The late expression D3R mRNA in neurons, after achievement of dopamine innervation, supports the existence of a regulating factor released from dopamine neurons, as suggested by denervation studies in the adult. The sustained and abundant D3R gene expression, predominantly in germinative neuroepithelial zones actively involved in neurogenesis of most basal forebrain structures, supports the hypothesis of a neurogenetic but minor morphogenetic modulatory role for the D3R during CNS development.

Alteration of local cerebral glucose utilization following intravenous administration of heroin in Fischer 344 rats

The 2-deoxyglucose method was used to study the effects of acute administration of small intravenous doses of heroin on rates of glucose utilization in rat brain to identify small brain regions that may be involved in the acute behavioral effects of heroin. In contrast to previous studies which have used relatively large doses, the doses of heroin used in this study have been shown to be self-administered [Martin, T.J., Dworkin, S.I. and Smith, J.E., Alkylation of μ-opioid receptors by β-funaltrexamine in vivo: comparison of the effects on in situ binding and heroin self-administration in rats., J. Pharmacol. Exp. Ther., 272 (1995) 1135–1140.]. Administration of 18 μg/kg of heroin resulted in higher rates of glucose utilization in the medial olfactory tubercle, anterior nucleus accumbens and dorsolateral caudate while having no other effects on limbic structures compared to saline-treated animals. Conversely, the rate of glucose utilization was lower than control in the habenula, dorsal raphe, and central gray following adminstration of 18 μg/kg of heroin. Administration of two higher doses (60 and 100 μg/kg) resulted in lower rates of glucose utilization in the thalamus, habenula, inferior colliculus, dorsal raphe and central gray compared to saline. The higher rates of glucose utilization in the limbic areas were specific for the lowest dose of heroin, whereas the effect of lowering the rate of glucose utilization compared to control in the thalamus and inferior colliculus were an increasing function of dose. In the habenula and dorsal raphe, however, the dose-effect function was inverted. These data indicate that the alterations of glucose utilization in rat brain by heroin are site-specific and the systems involved as well as the nature of the alteration differs for individual doses of heroin.