Normal and abnormal determinants of dopamine receptor ontogeny in the central nervous system

Pramipexole improves depression-like behavior in diabetes mellitus with depression rats by inhibiting NLRP3 inflammasome-mediated neuroinflammation and preventing impaired neuroplasticity

BACKGROUND

Diabetes mellitus (DM) is frequently associated with the occurrence and development of depression, and the co-occurrence of diabetes mellitus with depression (DD) may further reduce patients' quality of life. Recent research indicates that dopamine receptors (DRs) play a crucial role in immune and metabolic regulation. Pramipexole (PPX), a D2/3R agonist, has demonstrated promising neuroprotective and immunomodulatory effects. Nevertheless, the therapeutic effects and mechanisms of action of PPX on DM-induced depression are not clear at present.

METHODS

Depression, DM, and DD were induced in a rat model through a combination of a high-fat diet (HFD) supplemented with streptozotocin (STZ) and chronic unpredictable mild stress (CUMS) combined with solitary cage rearing. The pathogenesis of DD and the neuroprotective effects of DRs agonists were investigated using behavioral assays, enzyme-linked immunosorbent assay (ELISA), hematoxylin-eosin (HE) staining, Nissl staining, Western blotting (WB) and immunofluorescence (IF).

RESULTS

DD rats exhibited more severe dopaminergic, neuroinflammatory, and neuroplastic impairments and more pronounced depressive behaviors than rats with depression alone or DM. Our findings suggest that DRs agonists have significant therapeutic effects on DD rats and that PPX improved neuroplasticity and decreased neuroinflammation in the hippocampus of DD rats while also promoting DG cell growth and differentiation, ultimately mitigating depression-like behaviors.

LIMITATION

Our study is based on a rat model. Further evidence is needed to determine whether the therapeutic effects of PPX apply to patients suffering from DD.

CONCLUSIONS

Neuroinflammation mediated by damage to the dopaminergic system is one of the key pathogenic mechanisms of DD. We provide evidence that PPX has a neuroprotective effect on the hippocampus in DD rats and the mechanism may involve the inhibition of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation by DRs to attenuate the neuroinflammatory response and neuroplasticity damage.

Cognitive and behavioral effects of whole brain conventional or high dose rate (FLASH) proton irradiation in a neonatal Sprague Dawley rat model

Recent studies suggest that ultra-high dose rates of proton radiation (>40 Gy/s; FLASH) confer less toxicity to exposed healthy tissue and reduce cognitive decline compared with conventional radiation dose rates (~1 Gy/s), but further preclinical data are required to demonstrate this sparing effect. In this study, postnatal day 11 (P11) rats were treated with whole brain irradiation with protons at a total dose of 0, 5, or 8 Gy, comparing a conventional dose rate of 1 Gy/s vs. a FLASH dose rate of 100 Gy/s. Beginning on P64, rats were tested for locomotor activity, acoustic and tactile startle responses (ASR, TSR) with or without prepulses, novel object recognition (NOR; 4-object version), striatal dependent egocentric learning ([configuration A] Cincinnati water maze (CWM-A)), prefrontal dependent working memory (radial water maze (RWM)), hippocampal dependent spatial learning (Morris water maze (MWM)), amygdala dependent conditioned freezing, and the mirror image CWM [configuration B (CWM-B)]. All groups had deficits in the CWM-A procedure. Weight reductions, decreased center ambulation in the open-field, increased latency on day-1 of RWM, and deficits in CWM-B were observed in all irradiated groups, except the 5 Gy FLASH group. ASR and TSR were reduced in the 8 Gy FLASH group and day-2 latencies in the RWM were increased in the FLASH groups compared with controls. There were no effects on prepulse trials of ASR or TSR, NOR, MWM, or conditioned freezing. The results suggest striatal and prefrontal cortex are sensitive regions at P11 to proton irradiation, with reduced toxicity from FLASH at 5 Gy.

Maternal immune activation alters sensitivity to action-outcome contingency in adult rat offspring

Epidemiological studies have provided convincing evidence for a role of maternal immune activation in the pathogenesis of neurodevelopmental disorders such as autism and schizophrenia. In recent years, several research groups have capitalised on this discovery and developed animal models such as the maternal immune activation (MIA) model that emulates many phenotypes characteristic of disorders such as schizophrenia. In the present series of experiments we used the MIA model to examine motivation, a core component of the negative symptomatology in schizophrenia. Contrary to what we expected, in the progressive ratio task, which assesses an animals' willingness to work for a reward under increasing effort requirements, we found that MIA rats appeared more motivated than controls. Subsequent tests showed that this seemingly enhanced motivation was not due to an overall increase in responding, nor due to enhanced attribution of incentive salience to reward associated responses. Instead, we found that the increased willingness to work exhibited by MIA animals was due to an inability to detect changes in the contingency between their behaviour and the resulting rewarding outcome. With regard to motivation, the experiments reported here are the first to subject the MIA model to a rigorous experimental analysis of behaviour by parsing underlying processes that give rise to the overt symptoms in psychiatric disease.

Behavioral neurotoxicity in adolescent and adult mice exposed to fenproporex during pregnancy

We investigated the effects of gestational exposure to fenproporex, one of the most used anorectic drugs in Brazil, on the behavior of adolescent and adult pups (30 and 60 days of age, respectively). Pregnant Swiss mice were treated daily, by gavage, with 15 mg/kg of fenproporex chloride or water during the whole gestational period. Male pups were submitted to open-field, forced swimming test, tail suspension test and fenproporexinduced stereotyped behavior. The results demonstrated that gestational exposure to fenproporex induces antidepressant-like effect and decreases fenproporexinduced stereotyped behavior in both adolescent and adult pups. Moreover, fenproporex-exposed adolescent pups tended (P–0.06) to be more active than control pups. Our data show, for the first time, that gestational exposure to fenproporex leads to long-lasting behavioral toxicity in male mice characteristic of altered dopaminergic transmission.

Paradoxical effects of D-amphetamine in infant and adolescent mice: role of gender and environmental risk factors

The psychostimulant D-amphetamine (AMPH) increases generalised activity in adult subjects, while exerting a paradoxical "calming effect" in children with Attention-deficit Hyperactivity Disorder (AD/HD). A number of animal models have been developed to characterise the neurobiological basis of this AMPH action. In this line, the present review summarises recent work on the effects of AMPH on behavioural and physiological parameters in developing mice with a special emphasis on the role of gender and environmental risk factors. Behavioural and neuroendocrine responses to AMPH administration (0, 1, or 3 mg/kg, IP) and their relation to changes in the environment, represented by social stimuli, were studied in infant CD-1 mouse pups of both sexes at three different developmental ages (3, 8, or 18 postnatal (pnd) days). Mouse pups were assessed either in baseline condition or following 24 h maternal deprivation. AMPH exerted a paradoxical effect on CORT secretion only in maternally deprived subjects while affecting behaviour mainly in deprived female subjects, which showed a generalised shift to the left in the dose-response curve to this drug. Unwanted perseverative motor effects and possible dependence states represent side effects of AMPH administration. Further knowledge on these aspects comes from another set of studies where a shortened conditioned place preference (CPP) paradigm was employed to assess the reinforcing properties of AMPH (0, 1, 3.3, or 10 mg/kg) in developing mice on 14-17, 21-24, and 28-31 pnd. Data indicate that AMPH-CPP develops early, mice being able, already at two weeks of age, to acquire a place preference that relies on adult-like sensory, motor, and associative capacities. AMPH-CPP appears earlier in females, compared to males. A detailed analysis of acute D-amphetamine effects evidenced that the drug produces a dose-dependent increase in locomotor activity and in several responses (including stereotypes). These effects appear much larger at both post weaning stages than in preweanlings and are significantly more pronounced in females than in males. Overall these data suggest that AMPH action is dependent on the baseline level of activity and indicate a strong role of gender in the effects of this drug measured early on during development, with females showing greater sensitivity to this drug. A better understanding of AMPH action during the early ontogenetic phases, particularly its interaction with environmental factors, might extend our knowledge on the neurobiological basis of AD/HD, possibly improving the clinical efficacy of psychostimulant drugs.

Differences in D2 dopamine receptor binding in the neostriatum between cats hemidecorticated neonatally or in adulthood

In order to study differences in response to neocortical injury sustained at different ages at the neurotransmitter level, we examined the density in D2 dopamine receptors in the neostriatum of cats hemidecorticated neonatally (N = 4) or in adulthood (N = 4), as well as in intact brains (N = 6). Receptor densities were measured using quantitative autoradiography and [3H]-spiperone binding in 12 regions of the neostriatum and nucleus accumbens septi. We found that the anterior lateral caudate nucleus on both sides of the brain contained a higher D2 receptor density in neonatal-lesioned as compared to adult-lesioned brains. Ipsilateral to the lesion, the increase was 101% (P < 0.05) and contralaterally it amounted to 77% (P < 0.05). Moreover, this region of the ipsilateral caudate nucleus of neonatal-lesioned cats tended to be more densely labeled than that of intact brain by 58% (P < 0.1). D2 receptor densities in adult-lesioned cats did not differ from that of intact controls. Comparison of these data with those of a former morphological study using the same animals suggested that this bilateral elevation of D2 receptor density in neonatally lesioned brains represents a higher mean density of binding sites per neuron. The elevation in the neonatal-lesioned cats might be a response of the striatum to neuroplastic changes in the striatal neuropil, including the corticostriatal afferents, since such changes are different in neonatal- as compared to adult-lesioned cats.

Ontogeny of human brain dopamine receptors. I. Differential expression of [3H]-SCH23390 and [3H]-YM09151-2 specific binding

Dopamine receptor expression in human fetal forebrain (between 6 and 20 weeks of gestation) was measured using tissue-slice receptor autoradiography with the D1-like and D2-like antagonists [3H]-SCH23390 and [3H]-YM09151-2, respectively. Tissue sections were assayed in saturation studies and examined for age- and sex-related changes in Bmax. We made the following observations: (1) the ages at which D1- and D2-like receptors were first expressed in whole forebrain sections could be reliably identified but were not significantly different from one another (gestational age 65 days for D1- vs. 72 days for D2-like receptors); (2) age-related increases in both D1- and D2-like receptors were demonstrated in forebrain and, from the middle of the first to the middle of the second trimester, the Bmax for each ligand increased by an order of magnitude after the onset of the specific binding site's expression; (3) age-related increases in D1-like receptors, but not D2-like receptors, could be demonstrated in cortex; and, (4) in one case of trisomy 18, the Bmax for [3H]-SCH23390 was significantly elevated above the 95% confidence interval when compared to an age-regressed normal sample. Although D2-like receptor density significantly increased with age in forebrain, age-regressed changes in D2-like receptor expression in cortex and striatum did not reach statistical significance. Likewise, a comparison of the mean Bmax's by sex for both ligands in midgestational striatum failed to reach significance. These data corroborate the findings of other investigators who have delineated the ontogeny of dopaminergic systems in other animal species. The regional differences in the expression of dopamine receptor families may be relevant to the role which dopamine may play during normal gestational brain development. Moreover, significant deviations in dopamine receptor expression during gestation (as seen in this one case of trisomy 18) may signify underlying pathological processes that ultimately are manifested by abnormal psychological development and/or cognitive functioning.

Distribution and postnatal ontogeny of adenosine A2A receptors in rat brain: comparison with dopamine receptors

In adult rat brain, adenosine A2A receptors and dopamine D2 receptors are known to be located on the same cells where they interact in an antagonistic manner. In the present study we wanted to examine when this situation develops and compared the postnatal ontogeny of the binding of the adenosine A2A receptor agonist [3H]CGS 21680, the binding of the dopamine D1 receptor antagonist [3H]SCH 23390 and the dopamine D2 receptor antagonist [3H]raclopride. All three radioligands bound to the striatum at birth and this binding increased several-fold during the postnatal period. [3H]SCH 23390 binding developed first (mostly during the first week), followed by [3H]raclopride binding (first to third week) and [3H]CGS 21680 binding (only during second and third week). For all three radioligands the binding tended to decrease between 21 days and adulthood. This occurred earlier and was more pronounced in the globus pallidus than in the other examined structures. The increase in [3H]CGS 21680 binding from newborn to adult was mainly due to four-fold increase in the number of binding sites. The pharmacology of [3H]CGS 21680 binding to caudate-putamen was similar in newborn, one-week-old and adult animals, and was indicative of A2A receptors. The binding was inhibited by guanylyl imidodiphosphate at all ages, indicating that A2A receptors are G-protein-coupled already at birth. In contrast to the large increase in [3H]CGS 21680 binding, there was a decrease in the levels of A2A messenger RNA during the postnatal period in the caudate-putamen. In cerebral cortex [3H]CGS 21680 bound to a different site than the A2A receptor. From birth to adulthood cortical binding of [3H]CGS 21680 increased four-fold and that of the adenosine A1 agonist [3H]cyclohexyladenosine 19-fold. During early postnatal development [3H]SCH 23390 binding was higher in deep than in superficial cortical layers, but this difference disappeared in adult animals. There was binding of both [3H]CGS 21680 and [3H]cyclohexyladenosine to the olfactory bulb, suggesting a role of the two adenosine receptors in processing of olfactory information. [3H]CGS 21680 binding was present in the external plexiform layer and glomerular layer, and increased during development, but the density of binding sites was about one tenth of that seen in caudate putamen. [3H]cyclohexyladenosine showed a very different labelling pattern, resembling that observed with [3H]SCH 23390. Postnatal changes in adenosine receptors may explain age-dependent differences in stimulatory caffeine effects and endogenous protection against seizures. Since A2A receptors show a co-distribution with D2 receptors throughout development, caffeine may partly exert such actions by regulating the activity of D2 receptor-containing striatopallidal neurons.

Antennal lobe neurons of the honey bee, Apis mellifera, express a D2-like dopamine receptor in vitro

We have used the D2-specific dopamine receptor ligand spiperone [N-(p-aminophenethyl) spiperone; NAPS] coupled to the fluorophore 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD) to visualize dopamine receptors expressed in vitro by neurons of the primary antennosensory centers (antennal lobes) of the brain of the honey bee, Apis mellifera. Changes in the percentage of antennal lobe neurons exhibiting spiperone binding sites over time in culture and at different stages of metamorphic adult development have been investigated. Neurons obtained from animals at all stages of development exhibited spiperone binding sites, but only after 2 days or more in vitro. The percentage of antennal lobe neurons in vitro expressing spiperone binding sites increased significantly with the development of the antennal lobe neuropil. Fluorescently labelled spiperone (120 nM) could be displaced effectively by 1 mM dopamine but not by the same concentration of tyramine, octopamine, or serotonin. In addition, the D2 antagonist spiperone and the D2/D1 antagonist fluphenazine were more effective at displacing the fluorescent ligand than the D1-specific antagonist SCH23390. Our results indicate that Apis antennal lobe neurons in culture express a dopamine receptor and that this receptor is more likely to be D2-like than D1-like in nature. The receptor is expressed early in the metamorphic adult development of the antennal lobe neuropil of the brain.

Developmental plasticity in the D1- and D2-mediation of motor behavior in rats depleted of dopamine as neonates

D1- and D2-like antagonist-induced catalepsy and dorsal immobility were studied in pups (Day 10) and weanlings (Days 20, 28, or 35) that received intraventricular injection of 6-OHDA (50 micrograms/hemisphere) or its vehicle solution or postnatal Day 3. The ability of the D1 of D2 antagonists to induce immobility differed as a function of the lesion condition and the age at the time of testing. Moreover, the two behavioral measures exhibited differences in their specific D1 and D2 receptor modulation. Administration of the D1 antagonist SCH 23390 (0.2 or 1.0 mg/kg) or the D2 antagonist clebopride (1.0, 10.0, or 20.0 mg/kg) led to catalepsy and dorsal immobility in intact rats, regardless of test age. Both antagonists induced catalepsy and dorsal immobility in rats depleted of DA when tested on Day 10. However, the effects of each antagonist in DA-depleted rats were ether negligible or significantly less than in controls when animals were tested as weanlings. These data suggest lesion-induced changes in the DA receptor modulation of motor behavior and that this plasticity requires more than a week to become apparent.

Dopamine receptors mediate differential morphological effects on cerebral cortical neurons in vitro

A morphogenic role of neurotransmitters during cellular differentiation in vitro has been demonstrated in recent years. Using in situ hybridization, we confirm the presence of the D1 receptor at E16 and show additionally that the transcript is relatively widespread and present in both proliferative and differentiating areas of the cerebral wall. Because DA receptor expression precedes the arrival of presynaptic terminals during forebrain development, we examined the role of DA in cerebral cortical neuron differentiation in vitro, using immunohistochemical markers of dendrites, microtubule-associated-membrane protein 2 (MAP2) and axons, neurofilament protein (NF-H). Neurite length, cell size, and cell viability in response to D1 and D2 receptor agonists SKF38393 and quinpirole, respectively, and to DA were analyzed in neurons obtained from embryonic (E) day 16 rats. We have shown that 1) paradoxically, DA at different concentrations can either stimulate or inhibit neurite outgrowth; 2) there is a bimodal pattern of DA-induced axonal outgrowth, i.e., at low and high doses; 3) D2 receptor activation induces neurite outgrowth while D1 receptor activation is inhibitory; 4) D2-mediated neurite elongation is preferentially axonal while D1 receptor activation reduces both axonal and dendritic outgrowth; 5) low doses of DA promote the expression of cytoskeletal components of axonal maturation; and 6) D1 receptor activation decreases neuronal size. We suggest that DA may influence cellular differentiation and circuitry formation early in development of the cerebral cortex through receptor-mediated effects on process outgrowth, which could lead to effects on circuit formation.

Developmental and age-related changes in the D2 dopamine receptor mRNA subtypes in rat brain

The influence of ontogeny and aging on the D2 dopamine receptor mRNA in rat brain were examined using in situ hybridization histochemistry and Northern analysis utilizing oligonucleotide probes complementary to the different D2 mRNA subtypes. At birth, there was a high level of D2 dopamine receptor mRNA in corpus striatum relative to that found in the cerebral cortex and other brain areas. The hybridization signal of striatum (using a probe that hybridizes to both the D2A and D2B mRNA) increased during the first two postnatal weeks, reached a peak at day 16, then declined slightly. The D2A mRNA showed a similar distribution and developmental pattern. Intracisternal injection of 6-hydroxydopamine into neonates did not significantly alter the increase of the D2 dopamine receptor mRNAs, suggesting that neuronal input does not influence the ontogenetic development of this mRNA. In striatum, olfactory tubercule and inferior colliculus, the D2A mRNA declined between 3 and 24 months of age. By contrast, there was an age-related increase in the D2A mRNA in the anterior and intermediate lobes of the pituitary. The mRNA for the D2B dopamine receptor showed very low but nevertheless detectable levels in striatum, olfactory tubercule and pituitary. Like with the D2A mRNA, in 24-month-old rats the D2B mRNA declined in striatum and olfactory tubercule and increased in pituitary. These results show that there are differential tissue-related changes in the mRNAs for the D2 dopamine receptor during both development and aging.

Ontogeny of [3H]-SCH23390 and [3H]-YM09151-2 binding sites in human fetal forebrain

In order to determine the gestational age at which binding sites for the dopamine "D1-like" and "D2-like" receptor antagonists, [3H]-SCH23390 and [3H]-YM09151-2, respectively, can be reliably detected in the human and to identify any discrete anatomic distribution of these binding sites, fetal forebrain tissue sections from mid-first (n = 4) and mid-second (n = 4) trimester gestations were used for receptor autoradiography. Specific binding for both ligands was detectable at the earliest fetal age examined (gestational week 6). Age-related increases in maximum saturation binding were demonstrated for both ligands using tissue sections from basal forebrain. The Bmax for both [3H]-SCH23390 and [3H]-YM09151-2 binding increased ten-fold comparing gestational week 6 and gestational week 18 values. In the cortex at gestational day 120, [3H]-YM09151-2 specific binding could be seen at the gray-white matter boundary, which was more prominent by gestational day 140. In contrast, [3H]-SCH23390 specific binding to the cortex at gestational day 120 did not appear to differentiate specific areas and did not increase between gestational days 120 and 140. These preliminary observations in human fetal brain provide evidence that dopamine "D2-like" binding sites can be localized in a discrete cortical area in the course of normal human brain development. Characterizing these binding sites and the population of cells that demonstrates these binding sites may be relevant to neurodevelopmental hypotheses of psychiatric disorders.

Morphogenic potentials of D2, D3, and D4 dopamine receptors revealed in transfected neuronal cell lines

Molecular cloning studies have defined a family of dopamine D2-like receptors (D2, D3, and D4), which are the products of separate genes. Our previous work has shown that stimulation of dopamine D2-like receptors in cultures of fetal cortical neurons increases the extension and branching of neurites. To determine which D2-like receptors possess morphogenic potentials, a clonal mesencephalic cell line (MN9D) was transfected with D2, D3, or D4 receptor subtypes and treated with quinpirole, an agonist of D2-like receptors, and changes in morphological characteristics were quantitated. Stimulation of D2 receptors increased the number and branching of neurites with little effect on neurite extension; stimulation of D3 and D4 receptors increased the branching and extension of neurites. Similar results were found for primary mesencephalic cultures stimulated with quinpirole. These results suggest that the known D2-like receptors have specific developmental roles in regulating neuronal morphogenesis of dopaminergic pathways.

Neural development is regulated by classical neurotransmitters: dopamine D2 receptor stimulation enhances neurite outgrowth

The classical neurotransmitters serotonin and dopamine are thought to be involved in the etiology or treatment of a variety of psychiatric disorders. Recent studies suggest that these neurotransmitters may also have roles as neural morphogens during brain development. Previously, we have demonstrated that stimulation of serotonin 5-HT1A receptors selectively inhibited neurite branching in an in vitro system (Sikich et al 1990). In the present study, the developmental role of dopamine D2 receptors in the control of neurite outgrowth has been investigated by quantitating the morphological response of cortical neurons to agonist stimulation in vitro. Cultures of fetal rat frontal, cortical neurons were shown to express both alternatively spliced forms of D2 receptor messenger RNA (mRNA). The larger mRNA form predominated (D2A444:D2A415 ratio of about 6:1). In a small but significant percentage of these neurons, culture in the presence of the D2 receptor selective agonist, quinpirole, resulted in a three-to ten-fold increase in the length of neurites and in the number of branch points per neurite. These effects were blocked by the D2 receptor antagonists eticlopride and spiperone. Early abnormalities in the stimulation of dopamine or serotonin receptor subtypes could lead to the types of neuroanatomical changes observed in studies of schizophrenia, bipolar affective disorder, and autism. These morphogenic effects of classical transmitters could unite neurodevelopmental and neurotransmitter theories of the etiology of severe psychiatric disorders.

Ontogenetic expression of D2 dopamine receptor mRNA in rat corpus striatum

The ontogenetic expression of the D2 dopamine receptor (D2R) mRNA has been characterized in rat corpus striatum by in situ hybridization histochemistry and Northern and slot blot analyses using oligonucleotide probes directed toward either the D2R-A subtype of the D2R mRNA or to both the D2R-A and D2R-B subtypes of the D2R mRNA. The results showed that both D2R mRNAs were detected in rat striatum at birth, gradually increased until day 16 postnatally (P16), then declined slightly. At early stages of development, the hybridization signal, when viewed under low magnification, was fairly evenly distributed throughout the striatum. However, later in development (P16) a cluster pattern became manifest. Autoradiographic studies using the mu-opiate receptor as an indication of striatal 'patches' in serial, adjacent sections of striatum indicated that the cluster pattern of the D2R mRNA was not associated solely with the patch or matrix compartments of the striatum. A cellular analysis showed that at early developmental stages the quantity of D2R mRNA per cell was very low in striatum. During the first two postnatal weeks, certain subpopulations of striatal neurons evidenced a marked increase in the expression of D2R mRNA per cell. Administration of 6-hydroxydopamine into neonatal rats failed to significantly change the developmental profile of D2R mRNA in the rat striatum of 16- and 32-day-old animals, although the same treatment caused a marked increase in proenkephalin mRNA. These results suggest that the postnatal development of the D2R mRNA in rat striatum correlates well with the ontogeny of the D2 dopamine receptor, that the developmental expression of the D2R mRNA is highly associated with the maturation and differentiation of striatal neurons, and that the development of the D2R mRNA in rat striatum, unlike that of proenkephalin mRNA, can proceed even with reduced dopaminergic afferent input from the substantia nigra.

D2 dopamine receptor gene expression in the rat striatum during ontogeny: an in situ hybridization study

D2 dopamine receptor (D2R) gene expression in the rat striatum was studied by in situ hybridization throughout the pre- and the postnatal period from gestational day 12 to postnatal day 8. D2R mRNA was detected with 35S-labelled oligonucleotide probes, one that hybridized equally to the two isoforms of the D2R mRNA (D2(415) and D2(444)) and the other that hybridized specifically to the large isoform (D2(444)). D2R mRNA was first detected in the striatal primordium at day 14 of gestation with the probe that recognizes indifferently the two isoforms and with the probe specific for the D2(444) mRNA. At day 16, D2R mRNA was present in the lateral part of the striatum and in the germinal ventricular zone lining the lateral ventricle. At day 18, D2R mRNA was found in neurons of the caudate-putamen, the nucleus accumbens, the olfactory tubercle and the subependymal zone lining the lateral ventricle. The microautoradiographic analysis demonstrated that the labelled cells have a neuroblastic and immature aspect before birth. After birth the topography and aspect of labelled cells was similar to the one observed in the adult animals. D2R mRNA was present in neurons of the caudate-putamen, the nucleus accumbens and the olfactory tubercle. In the caudate-putamen there was a latero-medial gradient of labelling. From postnatal day 2 onward the D2R gene was expressed in two striatal cell types, small neurons probably enkephalinergic, and large-sized neurons with prominent cytoplasm, most probably cholinergic.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of dopaminergic D2 receptor messenger RNAs during development

To define the possible roles of multiple types of dopamine D2 receptors, mRNA levels for two forms of D2 receptor were determined during a variety of developmental stages. Transcripts encoding the 444 amino acid form appear as early as embryonic day 14. In contrast, the mRNA encoding the 415 amino acid form of the receptor does not appear until embryonic day 17, and remains a minor form throughout prenatal development. The adult levels of the mRNAs of these two D2 receptor forms are not attained until long after birth.

Somatic and behavioral ontogeny in three rat strains: preliminary observations of dopamine-mediated behaviors and brain D-1 receptors

1. The acquisition of developmental milestones and maturational motor reflexes were compared in three rat strains (culled to 8 pups/litter), F344, Buff and SD. 2. Open field behavior on postnatal day 21 was scored for locomotor activity, rears and center entries. 3. F344 rats, which model ADHD, were the slowest of the three strains in acquiring a number of developmental milestones and in gaining weight; but they were intermediate in their scores for locomotor activity and rearing during open field testing at postnatal day 21. 4. Preliminary autoradiographic data using the D-1 specific ligand [3H]SCH 23390 are included which suggest that D-1 receptors, which display age-dependent changes in concentration and distribution, are relevant to day 21 open field behavior. 5. F344 rats demonstrate developmental "dysmaturation" which is consistent with that observed in children with ADHD in that somatic growth is disproportionately delayed in comparison to neurological and motor maturation.

Prenatal cocaine: maternal toxicity, fetal effects and locomotor activity in rat offspring

Either 30 or 60 mg/kg of cocaine hydrochloride (COC) was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 60 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. None of the treated dams died nor were any gross signs of cocaine toxicity observed. Among the COC-60 dams, there was a reduction in food and water intake at the beginning of treatment; whereas water intake returned to control levels, food intake remained approximately 12% below that of the controls. Compared to the nontreated dams, both COC-treated and pair-fed dams gained significantly less body weight from conception to term. Cocaine had no effect on offspring mortality, birthweight or rate of postnatal growth. Measurement of the ontogeny of motor activity during the first month of life revealed a similar activity pattern for all the groups except for the COC-60 group which showed heightened activity on Days 20 and 23. These findings are discussed in relation to other animal and clinical reports of prenatal cocaine exposure.

Ontogeny of dopaminergic D-2 receptors in the rat nervous system: characterization and detailed autoradiographic mapping with [125I]iodosulpride

[125I]Iodosulpride, a highly selective and sensitive probe for dopamine D-2 receptors, was used to study the expression of these receptors in binding studies performed on membranes and serial autoradiographic sections, throughout pre- and postnatal developmental periods. D-2 receptors were first detected autoradiographically in sensory and sympathetic ganglia at the embryonic age of 12 days, i.e. much earlier than in previous studies. In membrane binding studies, D-2 receptors were found to be modulated by guanylnucleotides as early as at embryonic day 15, suggesting that they were already functionally coupled to a regulatory G protein. The overall development of D-2 receptors in the central nervous system occurred according to a caudorostral gradient and was accompanied by a slightly but significantly increased affinity for dopamine, possibly related to the late expression of a D-2 receptor subclass. The ontogeny of D-2 receptors was compared to that of tyrosine hydroxylase immunoreactivity as reported by others and taken as an index of dopaminergic innervation. Despite some variations due to experimental conditions, this comparison resulted in the definition of various situations. In some major projection areas (e.g. caudate putamen at embryonic day 14) there was a simultaneous appearance of both dopaminergic markers whereas in most others (e.g. n. accumbens or olfactory tubercles at embryonic day 20) the appearance of D-2 receptors was preceded by 1-4 days by that of tyrosine hydroxylase immunoreactivity. However, in a few projection areas (e.g. the bed nucleus of the stria terminalis at embryonic day 21), D-2 receptors appeared 3-4 days earlier than tyrosine hydroxylase immunoreactivity. In areas of dopaminergic perikarya, e.g. substantia nigra and ventral tegmental area, where they largely correspond to somatodendritic autoreceptors, D-2 receptors appeared at embryonic days 17 and 21 respectively, i.e. 3-8 days after tyrosine hydroxylase immunoreactivity, suggesting that dopamine synthesis and release is not feedback regulated by autoreceptors at initial developmental stages. In areas where D-2 receptors are present in the absence of any established dopaminergic innervation (e.g. discrete layers of the hippocampus, cerebellum, parietal cortex or in cranial nerve nuclei), they generally appeared at a late stage, i.e. during the second or even the third postnatal week. Finally, there was transient and roughly concomitant expression of both D-2 receptors and tyrosine hydroxylase immunoreactivity in some areas such as spinal ganglia or the lateral ventricle floor, consistent with a possible development function of dopamine mediated by D-2 receptors.