5-HT2C Receptors Localize to Dopamine and GABA Neurons in the Rat Mesoaccumbens Pathway

The serotonin 5-HT2C receptor (5-HT2CR) is localized to the limbic-corticostriatal circuit, which plays an integral role in mediating attention, motivation, cognition, and reward processes. The 5-HT2CR is linked to modulation of mesoaccumbens dopamine neurotransmission via an activation of γ-aminobutyric acid (GABA) neurons in the ventral tegmental area (VTA). However, we recently demonstrated the expression of the 5-HT2CR within dopamine VTA neurons suggesting the possibility of a direct influence of the 5-HT2CR upon mesoaccumbens dopamine output. Here, we employed double-label fluorescence immunochemistry with the synthetic enzymes for dopamine (tyrosine hydroxylase; TH) and GABA (glutamic acid decarboxylase isoform 67; GAD-67) and retrograde tract tracing with FluoroGold (FG) to uncover whether dopamine and GABA VTA neurons that possess 5-HT2CR innervate the nucleus accumbens (NAc). The highest numbers of FG-labeled cells were detected in the middle versus rostral and caudal levels of the VTA, and included a subset of TH- and GAD-67 immunoreactive cells, of which >50% also contained 5-HT2CR immunoreactivity. Thus, we demonstrate for the first time that the 5-HT2CR colocalizes in DA and GABA VTA neurons which project to the NAc, describe in detail the distribution of NAc-projecting GABA VTA neurons, and identify the colocalization of TH and GAD-67 in the same NAc-projecting VTA neurons. These data suggest that the 5-HT2CR may exert direct influence upon both dopamine and GABA VTA output to the NAc. Further, the indication that a proportion of NAc-projecting VTA neurons synthesize and potentially release both dopamine and GABA adds intriguing complexity to the framework of the VTA and its postulated neuroanatomical roles

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Glucose injections into the dorsal hippocampus or dorsolateral striatum of rats prior to T-maze training: Modulation of learning rates and strategy selection

The present experiments examined the effects of injecting glucose into the dorsal hippocampus or dorsolateral striatum on learning rates and on strategy selection in rats trained on a T-maze that can be solved by using either a hippocampus-sensitive place or striatum-sensitive response strategy. Percentage strategy selection on a probe trial (P(crit)) administered after rats achieved criterion (nine of 10 correct choices) varied by group. All groups predominately exhibited a response strategy on a probe trial administered after overtraining, i.e., after 90 trials. In experiment 1, rats that received intrahippocampal glucose injections showed enhanced acquisition of the T-maze and showed increased use of response solutions at P(crit) compared with that of unimplanted and artificial cerebral spinal fluid (aCSF)-treated groups. These findings suggest that glucose enhanced hippocampal functions to accelerate the rate of learning and the early adoption of a response strategy. In experiment 2, rats that received intrastriatal glucose injections exhibited place solutions early in training and reached criterion more slowly than did aCSF controls, with learning rates comparable to those of unoperated and operated-uninjected controls. Relative to unoperated, operated-uninjected and glucose-injected rats, rats that received intrastriatal aCSF injections showed enhanced acquisition of the T-maze and increased use of response solutions at P(crit). The unexpected enhanced acquisition seen after striatal aCSF injections suggests at least two possible interpretations: (1) aCSF impaired striatal function, thereby releasing competition with the hippocampus and ceding control over learning to the hippocampus during early training trials; and (2) aCSF enhanced striatal functioning to facilitate striatal-sensitive learning. With either interpretation, the results indicate that intrastriatal glucose injections compensated for the aCSF-induced effect. Finally, enhanced acquisition regardless of treatment was accompanied by rapid adoption of a response solution for the T-maze

Distribution of FG- TH- and GAD-67-labeled cells in the VTA.

<p>Schematic representation of the location of cells labeled for FG alone (black squares), FG+TH (blue circles), FG+GAD-67 (green triangles) and FG+TH+GAD-67-labeled cells (red stars) in the [A] rostral (∼bregma −5.14 mm), [B] middle (∼bregma −5.67 mm), and [C] caudal (∼bregma −6.30 mm) levels of the VTA <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. Insets display schematic diagrams depicting the location of VTA (shaded) relative to surrounding brain areas (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone-0020508-g005" target="_blank">Fig. 5</a> for abbreviations) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. Data represent the number and distribution of cells counted in one rostral, middle or caudal section from a animal injected with FG in the NAc shell.</p

Distribution of FG- TH- and 5-HT_2CR-labeled cells in the VTA.

<p>Schematic representation of the location of cells labeled for FG alone (black squares), FG+TH (blue circles), FG+5-HT_2CR (green triangles) and FG+TH+5-HT_2CR-labeled cells (red stars) in the [A] rostral (∼bregma −5.12 mm), [B] middle (∼bregma −5.67 mm), and [C] caudal (∼bregma −6.30 mm) levels of the VTA <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. Insets display schematic diagrams depicting the location of VTA (shaded) relative to surrounding brain areas [interpeduncular nucleus (IP); interpeduncular fossa (IPF); medial laminiscus (ml); mammillary peduncle (mp); mammillothalamic tract (MT) substantia nigra pars compacta, dorsal tier (SNCD); substantia nigra pars compacta, medial tier (SNCM); substantial nigra reticulata (SNR)] <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. Data represent the number and distribution of cells counted in one rostral, middle or caudal section from an animal injected with FG in the NAc shell.</p

Colocalization of GAD-67 and 5-HT_2CR immuonoreactivity with FG-labeled cells in the VTA.

<p>[<b>A</b>] Representative composite photomicrograph of the middle level of the VTA displaying the overlay of FG (blue), GAD-67-IR (red) and 5-HT_2CR-IR (green). Inset displays the schematic diagram of the middle VTA (shaded area) and surrounding brain areas (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone-0020508-g003" target="_blank">Fig. 3</a> for abbreviations) at bregma -5.64 mm <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. High magnification images of the boxed region in panel A depict FG labeling [blue; B], GAD-67-IR [red, C], and 5-HT_2CR-IR [green, D], as well as the overlay of images in B, C, and D to demonstrate colocalization [E]. Filled arrows (<b></b>) indicate cells triple-labeled for FG+GAD-67+5-HT_2CR cells, while the open arrows (<b></b>) indicate a cell double-labeled for FG+5-HT_2CR; as noted in the text, cells labeled for FG+GAD-67 alone were not often detected in the area represented by the boxed region. Scale bars  = 20 µm. Note: Portions of IP nucleus present in the composite photomicrograph in panel A were removed from the image prior to incorporation into the figure.</p

Primary antibodies employed in the experiments.

<p>Primary antibodies employed in the experiments.</p

Colocalization of TH and GAD-67 immuonoreactivity with FG-labeled cells in the VTA.

<p>[A] Representative composite photomicrograph of the middle level of the VTA displaying the overlay of FG (blue), TH-IR (green) and GAD-67-IR (red). Inset displays the schematic diagram of the middle VTA (shaded area) and surrounding brain areas (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone-0020508-g003" target="_blank">Fig. 3</a> for abbreviations] at bregma -5.64 mm. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020508#pone.0020508-Paxinos1" target="_blank">[17]</a>. High magnification images of the boxed region in panel A depict FG labeling [blue, B], TH-IR [green, C], and GAD-67-IR [red, D], as well as the overlay of images in B, C, and D to demonstrate colocalization [E]. Filled arrows (<b></b>) indicate a cell triple-labeled for FG+TH+GAD-67, open arrows (<b></b>) indicate a cell double-labeled for FG+TH, solid arrows () indicate a cell double-labeled for FG+GAD-67, and the arrowheads () point to a cell double-labeled for TH+GAD-67 in the absence of FG; Scale bars  = 20 µm. Note: Portions of IP nucleus present in the composite photomicrograph in panel A were removed from the image prior to incorporation into the figure.</p