Matthew P. Gardner

A Gene for an Extended Phenotype

An insect virus gene controls the behavior of the dying host to increase dispersion of the virus. Manipulation of host behavior by parasites and pathogens has been widely observed, but the basis for these behaviors has remained elusive. Gypsy moths infected by a baculovirus climb to the top of trees to die, liquefy, and “rain” virus on the foliage below to infect new hosts. The viral gene that manipulates climbing behavior of the host was identified, providing evidence of a genetic basis for the extended phenotype.

Asenapine exerts distinctive regional effects on ionotropic glutamate receptor subtypes in rat brain.

Asenapine, a new pyschopharmacologic agent being developed for the treatment of schizophrenia and bipolar disorder, has a unique human receptor binding signature with strong affinity for dopaminergic, α‐adrenergic, and, in particular, serotonergic receptors raising the possibility of interactions with glutamatergic receptors. Changes in ionotropic glutamate (Glu) N‐methyl‐D‐aspartic acid (NMDA) receptors and 2‐amino‐3‐(3‐hydroxy‐5‐methyl‐isoxazol‐4‐yl)propionic acid (AMPA) receptors in rat forebrain regions were quantified after repeated administration of multiple doses of asenapine (0.03, 0.1, or 0.3 mg/kg, subcutaneous, twice/day) or vehicle for 4 weeks. Brain sections were collected from the medial prefrontal cortex (mPFC), dorsolateral frontal cortex, caudate putamen (CPu), nucleus accumbens (NAc), and hippocampus (HIP), and processed for in vitro receptor autoradiography. Four weeks of treatment with 0.03, 0.1, or 0.3 mg/kg of asenapine significantly (P < 0.01) decreased binding of [3H]MK‐801 to NMDA/MK‐801 modulatory sites in NAc (by 27%, 29%, and 26%, respectively), medial CPu (by 25%, 28%, and 24%), and lateral CPu (by 24%, 31%, and 26%). In contrast, the same doses of asenapine did not alter binding of [3H]glycine to NMDA/glycine modulatory sites in any of the brain regions examined. [3H]AMPA binding to AMPA receptors was selectively and significantly (P < 0.001) elevated in hippocampal CA1 (41%) and CA3 (40%) regions but only at the highest dose tested. These results indicate that chronic treatment with asenapine has region‐specific and dose‐dependent effects on ionotropic Glu‐receptor subtypes in rat forebrain, which might contribute to the unique psychopharmacologic properties of asenapine. Synapse 63:413–420, 2009.

Effects of repeated risperidone exposure on serotonin receptor subtypes in developing rats

Risperidone is an atypical antipsychotic drug that is widely prescribed to young patients with different psychotic disorders. The long-term effects of this antipsychotic agent on neuronal receptors in developing brain remain unclear and require further investigation. In this study, we examined the effects of long-term treatment of risperidone on two serotonin receptor subtypes in brain regions of juvenile rat. Levels of 5-HT(1A) and 5-HT(2A) receptors in forebrain regions of juvenile rats were quantified after 3 weeks of treatment with three different doses of risperidone (0.3, 1.0 and 3.0mg/kg). Findings were compared to previously reported changes in 5-HT receptors after risperidone treatment (3.0mg/kg) in adult rat brain. The three doses of risperidone selectively and dose-dependently increased levels of 5-HT(1A) receptors in medial-prefrontal and dorsolateral-frontal cortices of juvenile animals. The higher doses (1.0 and 3.0mg/kg) of risperidone also increased 5-HT(1A) receptor binding in hippocampal CA(1) region of juvenile but not adult rats. In contrast, the three doses of risperidone significantly reduced 5-HT(2A) labeling in medial-prefrontal and dorsolateral-frontal cortices in juvenile as well as in adult animals in an equipotent fashion. 5-HT(1A) and 5-HT(2A) receptors in other forebrain regions were not altered by repeated risperidone treatment. These findings indicate that there are differential effects of risperidone on 5-HT(1A) and 5-HT(2A) receptors in juvenile animals, and that the 5-HT system in developing animals is more sensitive than adults to the long-term effects of risperidone.

Pathogenesis of Lymantria dispar multiple nucleopolyhedrovirus in L. dispar and mechanisms of developmental resistance.

Lymantria dispar has a long historical association with the baculovirus Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), which is one of the primary population regulators of L. dispar in the field. However, host larvae exhibit strong developmental resistance to fatal infection by LdMNPV; the LD50 in newly moulted fourth instars is 18-fold lower than in the middle of the instar (48-72 h post-moult). Using a recombinant of LdMNPV expressing lacZ, we examined the key steps of pathogenesis in the host to explore mechanisms of developmental resistance. At the midgut level, we observed reduced primary midgut infections in mid-fourth instars, indicating increased sloughing of infected cells. Additional barriers were observed as the virus escaped the midgut. Mid-fourth instars had higher numbers of melanized foci of infection associated with the midgut, apoptotic tracheal epidermal cells and haemocytes, and reduced numbers of infected haemocytes later in infection. Our results show that the co-evolutionary relationship between L. dispar and LdMNPV has resulted in both midgut-based and systemic antiviral defences and that these defences are age-dependent within the instar. This age-related susceptibility may contribute to how the virus is maintained in nature and could influence management of L. dispar by using the virus.

Synthesis and Dopamine Receptor Affinities of N-Alkyl-11-hydroxy-2-methoxynoraporphines: N-Alkyl Substituents Determine D1 versus D2 Receptor Selectivity

We developed a procedure to synthesize a series of N-alkyl-2-methoxy-11-hydroxynoraporphines from thebaine and evaluated their binding affinities at dopamine D1 and D2 receptors in rat forebrain tissue. At D2 receptors, the most potent 10,11-catechol-aporphine was (R)-(-)-2-methoxy-N-n-propylnorapomorphine (D2, Ki = 1.3 nM; D1, Ki = 6450 nM), and the most selective and potent 11-monohydroxy aporphine was (R)-(-)-2-methoxy-11-hydroxy-N-n-propylnoraporphine (D2, Ki = 44 nM; D1, Ki = 1690 nM). In contrast, the N-methyl congeners (R)-(-)-2-methoxy-11-hydroxy-N-methyl-aporphine (D1 vs D2, Ki = 46 vs 235 nM) showed higher D1 than D2 affinity, indicating that N-alkyl substituents have major effects on D2 affinity and D2/D1 selectivity in such 2-methoxy-11-monohydroxy-substituted aporphines.

Synthesis and binding studies of 2-O- and 11-O-substituted N-alkylnoraporphines.

We synthesized several novel 2-O- or 11-O-substituted N-alkylnoraporphines and assessed their affinities at dopamine D(1) and D(2), and serotonin 5-HT(1A) receptors in rat forebrain tissue. Tested compounds displayed moderate to high affinities to D(2) receptors but low affinities to D(1) and 5HT(1A) receptors. The findings accord with previous evidence of a lipophilic cavity on the surface of the D(2) receptor to accommodate N-alkyl moieties of aporphines. The most D(2)-potent (K(i)=97 nM) and selective novel agent (>100-fold vs. D(1) and 5-HT(1A) sites) was R(-)-2-(2-hydroxyethoxy)-11-hydroxy-N-n-propylnoraporphine (compound 11).

Synthesis and neuropharmacological evaluation of esters of R(-)-N-alkyl-11-hydroxy-2-methoxynoraporphines.

We synthesized several esters of R(-)-N-alkyl-11-hydroxy-2-methoxynoraporphines, assessed their affinities at dopamine D(1) and D(2) receptors in rat forebrain tissue and quantified their effects on motor activity in normal adult male rats. Tested compounds displayed moderate to high affinities to D(2) receptors but low affinities to D(1) receptors. The most D(2)-potent (K(i)=18.9nM) and selective novel agent (>529-fold vs D(1) sites) was R(-)-2-methoxy-11-acetyloxy-N-n-propylnoraporphine (compound 4b). At moderate doses, the compound proved to have prolonged behavioral locomotor activity.

Developmental effects of antipsychotic drugs on serotonin receptor subtypes

Antipsychotic medications are increasingly prescribed to pediatric and adolescent patients with psychotic diseases in spite of limited knowledge on the long‐term effects of dissimilar antipsychotic drugs on developing brain. In this study, we quantified the levels of two major serotonin 5‐HT1A, and 5‐HT2A receptors in brain regions of developing rats after 3 weeks of treatment with typical (fluphenazine) and atypical (clozapine and olanzapine) antipsychotics, and compared to similarly treated adult rats treated with olanzapine, risperidone, and quetiapine examined in previous studies. Fluphenazine, clozapine, and olanzapine all increased 5‐HT1A receptors in medial prefrontal cortex (MPC) and dorsolateral frontal cortex (DFC) of juvenile and adult rats. Clozapine and olanzapine also increased 5‐HT1A labeling in hippocampal CA1 and CA3 regions of juvenile but not adult animals. Repeated treatments with clozapine and olanzapine, but not fluphenazine, decreased 5‐HT2A receptors in MPC and DFC in developing and mature animals. In addition, both clozapine and olanzapine selectively reduced 5‐HT2A labeling in hippocampal CA1 and CA3 regions of juvenile animals. These findings suggest that forebrain 5‐HT receptor subtypes in juvenile animals are more sensitive than adults to the long‐term effects of antipsychotic drugs, which may account for differences in clinical effects of antipsychotic drugs between young vs. adult psychiatric patients.