In each experiment, stimulus position and strength was adjusted t

In each experiment, stimulus position and strength was adjusted to elicit both stimulus-evoked spiking in the presynaptic cartwheel cell and feed-forward inhibition Olaparib in the post-synaptic fusiform neuron. Parallel fiber stimulus-evoked spiking in the presynaptic cartwheel was slightly changed in the absence of background spiking, with a lower probability of spiking on the first stimulus compared to the background spiking condition (compare Figure 8B, middle traces). Complex spikes were also sometimes more readily elicited by stimuli applied on a background of spontaneous firing. This can be attributed to

differences in cartwheel excitability at the different levels of bias current injection. More importantly, the outward component of the postsynaptic fusiform responses to Androgen Receptor Antagonist the second stimulus in the train was

significantly enhanced when the presynaptic cartwheel did not spike spontaneously in all cartwheel-fusiform pairs tested (compare bottom traces in Figure 8B; summary for 1.4 to 6.6 Hz background presynaptic firing rates in Figure 8C; stim 2 mean outward charge with background firing: 1388 ± 208 pA∗ms, no background firing: 2520 ± 366 pA∗ms, p < 0.05, n = 4 pairs). Total charge measurements from traces created by subtracting averaged fusiform currents obtained during background spiking in patch-clamped presynaptic cartwheels from those Adenosine recorded without presynaptic background firing (see example

Figure 8D) demonstrated a clear enhancement of outward charge following the second stimulus (Figure 8E; stim 2 1173 ± 357 pA∗ms). Thus, changing cartwheel spontaneous spiking activity by intracellular current injection alone was sufficient to alter parallel fiber-evoked feed-forward inhibition. In fact, the change in outward current following the second stimulus was remarkably similar to that observed previously in response to NA (compare Figures 1F, 6D, and 8B). These results support the idea that NA enhances feed-forward inhibition by indirectly relieving cartwheel synapses from depression through elimination of spontaneous action potential firing in a small number of connected presynaptic cartwheel cells. In contrast to the effects of NA, the response to the third stimulus was unchanged between the presynaptic background spiking versus no spiking conditions (Figure 8B; outward charge with background firing: 1149 ± 494 pA∗ms, no background firing: 1317 ± 434 pA∗ms, p = 0.14, n = 4 pairs). However, this likely reflected limitations of our experimental approach. In the paired recording experiments shown in Figure 8, parallel fiber stimuli were adjusted to evoke presynaptic cartwheel spikes reliably by the second stimulus in the train under both background spiking and no background spiking conditions.

A number of rat lines also exhibit a

A number of rat lines also exhibit a selleck chemicals correlation between OT and AVP receptor expression levels and specific types of behavior. Notorious examples are the differences identified by Champagne and Meaney (2001) between high- and low-licking and grooming mother rats characterized by more maternal care and lower anxiety and fear levels. These can be associated with higher levels of OT in the medial preoptic area, paraventricular nucleus, lateral septum, amygdala, and BST, the latter two regions well known for their role in anxiety and fear behavior. A similar association was noticed in mice, bred for different levels of nursing

and licking/grooming, between levels of OT and V1a receptors in the lateral septum and frequencies in, respectively, nursing and licking/grooming (Curley et al., 2012). Similarly, LAB/HAB mice and rats show interesting distinctions in AVP and OT signaling that can be related with a large spectrum of different behaviors (Veenema and Neumann, 2007). Such animal models may serve important roles to study similar variations within the human population. The distinct and potentially opposite roles of OT and AVP in the periphery suggest a certain complementary development in the evolution of their functions. In the brain, Forskolin manufacturer expression of OT and AVP takes place in nonoverlapping areas, and though at times juxtaposed, remains distinctly separated

in different sets of neurons. Similarly their receptors are typically expressed in different regions of the brain, and, where these regions are close neighbors, the expression of their receptors occurs in strictly separate sets of neurons. The question therefore arises of whether it is possible to distinguish across these different brain regions

contrasting and Linifanib (ABT-869) complementary roles of the signaling by these neuropeptide receptors. In this section, I will go through the different parts of the brain in which the expression and activation of their receptors have been found and evaluate their functions in light of potential complementary roles. A large number of electrophysiological studies have already been performed on acute neuromodulatory effects of both peptides in various brain areas. At first glance the effects seem diverse and dispersed in many regions, without a clear organizational pattern. Nevertheless, it may be possible to group some of these regions by considering them as part of neuronal circuits that underlie similar functions. For example, subsets of circuits comprise core networks that integrate the behavioral, physiological, and motivational processes related to specific neural “tasks.” Thus, we can identify a core network for social behavior within the limbic system, another network for stress and anxiety, for learning and memory, or more simply sensory and motor tasks (see also Goodson and Kabelik, 2009).

As reported previously (Beattie et al , 2000, Carroll et al , 199

As reported previously (Beattie et al., 2000, Carroll et al., 1999 and Ehlers, 2000), the surface HA-GluA2, which is mainly localized to the somatodendritic domain (Matsuda et al., 2008), rapidly decreased following NMDA stimulation (Figures 4A and 4E). When the GFP-tagged C-terminal fragment of PIP5Kγ661 (PIP5K-CT-WT) was expressed, the NMDA-induced reduction of surface AMPA receptors was blocked (Figures 4B and 4E). Nutlin-3a cost Similarly, the expression of the GFP-tagged dephosphomimetic

mutant of the PIP5Kγ661 C-terminal fragment (PIP5K-CT-S645A), in which Ala replaced Ser 645, blocked NMDA-induced AMPA receptor endocytosis (Figures 4C and 4E). In contrast, expression of GFP-tagged phosphomimetic mutant of the PIP5Kγ661 C-terminal fragment (PIP5K-CT-S645E) failed to do so (Figures 4D and 4E). GST pull-down assays confirmed that wild-type and PIP5K-CT-S645A, but not PIP5K-CT-S645E, bound to β2 adaptin (Figure S5A). These results suggest that overexpression of the wild-type and dephosphomimetic C-terminal PS-341 cost fragment of PIP5Kγ661 interferes with the interaction between endogenous PIP5Kγ661 and AP-2, thereby inhibiting the NMDA-induced AMPA receptor endocytosis. The C

terminus of PIP5Kγ661 is also reported to bind to the μ2 adaptin of AP-2 (Bairstow et al., 2006) and talin (Di Paolo et al., 2002 and Ling et al., 2002). In addition, β2 adaptin binds to clathrin through its ear and hinge domains (Thieman et al., 2009) and to hippocalcin, a protein that translocates to the plasma membrane in the presence of Ca2+ during hippocampal LTD (Palmer et al., 2005). Nevertheless, none of these interactions are reported to be affected by the dephosphorylation of the C-terminal domain of PIP5Kγ661. To examine the specificity of the dephosphorylation-dependent binding of PIP5Kγ661 Org 27569 to β2 adaptin, we performed

GST pull-down assays. Although β2 adaptin bound to GST-CT-WT and GST-CT-S645A with significantly higher affinity than to GST-CT-S645E, μ2 adaptin equally interacted with all GST-fused C-terminal fragments of PIP5Kγ661 (Figure S5A). In addition, although PIP5Kγ661 binding to β2 adaptin was specifically inhibited by the dephophomimetic C-terminal peptide of PIP5Kγ661 (pep-S645A), the clathrin binding to β2 adaptin was not affected by either phophomimetic (pep-S645E) or dephosphomimetic (pep-S645A) peptide (Figure S5B). Furthermore, binding of CT-WT to talin was inhibited by pep-S645A and pep-S645E to the same degree (Figure S5C). The interaction between β2 adaptin and hippocalcin in the presence of Ca2+ was also similarly inhibited by dephosphomimetic or phosphomimetic PIP5Kγ661 C-terminal peptides and fragments (Figures S5D). These results indicate that the dephosphorylated form-specific effect of PIP5Kγ661 (Figure 4) is likely mediated by its specific interaction with β2 adaptin and that this specific interaction is required for NMDA-induced AMPA receptor endocytosis.

A fraction of neurons was significantly modulated by both PFC 4 H

A fraction of neurons was significantly modulated by both PFC 4 Hz and hippocampal theta oscillations (Figure 7B; PFC: 13.7%; CA1: 21.0%; VTA: 16.9%; p < 0.05; Rayleigh test). Plotting all significantly this website jointly modulated neurons showed that the population of phase-locked units occupied a diagonal

(Figure 7C), similar to the joint phase distribution of 4 Hz and theta oscillations (Figure 7A, second panel). The diagonal distribution of the comodulation values is an indication of the interdependent nature of neuronal phase locking to both rhythms. Comparison between jointly modulated predicting and nonpredicting PFC pyramidal neurons revealed that predicting neurons were significantly more strongly comodulated by these rhythms than nonpredicting cells (Figure 7D; p < 0.05; Figure S6). In addition, we found that local gamma oscillations in PFC and hippocampus were modulated by both PFC 4 Hz and CA1 theta oscillations (Figure S7). These findings suggest that PFC neurons, which are active in the working memory part of the task, are temporally coordinated (Jones and Wilson, 2005, Benchenane et al., 2010 and Rutishauser et al., 2010) by 4 Hz and theta oscillations.

The expected results of such coordination are that the synchronously discharging predicting cells can exert a stronger impact on downstream targets that guide behavior, as compared to the less synchronous nonpredicting population. check details Finally, we compared LFP activity Thiamine-diphosphate kinase in PFC and hippocampus during task behaviors and in the home cage during

waking immobility, rapid eye movement (REM) sleep, and slow-wave sleep (Figure S8). PFC 4 Hz power was high during nose poking and running in the central arm and wheel, i.e., during times when working memory was active. PFC 4 Hz power was low during immobility and sleep, including theta-dominated REM sleep. Hippocampal theta power was high during running behavior and REM sleep but low during nose poking, immobility, and slow-wave sleep (Figure S8). Slow-wave sleep in both PFC and hippocampus was dominated by a large 2 Hz peak, a reflection of slow oscillation of non-REM sleep (Steriade et al., 1993). This behavior-dependent dissociation of power changes demonstrates that theta and 4 Hz oscillations are distinct rhythms with characteristically different behavioral correlates and presumably different mechanisms. Our findings demonstrate a triple time control of neurons in the PFC-VTA-hippocampus axis (Figure 8). The 4 Hz rhythm is the dominant pattern in PFC-VTA circuits, effectively modulating both local gamma oscillations and neuronal firing, whereas synchrony of neuronal spikes in the hippocampus is largely under the control of theta oscillations. Through phase coupling, 4 Hz and theta oscillations jointly coordinate gamma oscillations and neuronal assembly patterns in a task-relevant manner.

Identifying their molecular nature offers great promise to unders

Identifying their molecular nature offers great promise to understand neurovascular disorders and to develop novel neurovascular medicine. Second, the role of pericytes has turned out to be more important than previously recognized. Y-27632 research buy Do pericyte abnormalities causally contribute to neurodegeneration and other types of neurological disorders, and can they be therapeutically targeted? Finally, the brain vasculature is now considered to be a major contributor of the neurogenic stem cell niche. Can this process be exploited for brain repair? Finding

an answer to these and other questions promises to be a scientifically exciting journey with great translational potential. Due to space limitations BMS-754807 datasheet the authors regret not being able to cite original publications, except when not covered in recent overview articles. The authors are supported by “Long-term structural Methusalem funding by the Flemish Government,” the Fund for Scientific Research-Flemish Government (G0125.00, G.0121.02, G.076.09N, G.0319.07N, G.0210.07), Concerted Research Activities K.U.Leuven (GOA/2006/11), ASFM1537, and the Belgian Science Policy (IUAP-P6/30). A.Q. is a fellow of the Fund for Scientific

Research (FWO), Flanders. C.L. receives a long-term postdoctoral fellowship from the European Molecular Biology Organization (EMBO). We thank Leen Notebaert, Agnes Truyens, and Evelien Vos for help secondly with the figures. P.C. is named as inventor on patent applications WO 01/76620 and WO 2005/117946, and applicable resulting patents, claiming subject matter related to the results described in this paper. The aforementioned patent application has been licensed, which may result in a royalty payment to P.C. “
“Throughout the visual system of vertebrates, neurons are tuned to respond to different features of a visual scene, such as the position, orientation, or direction of motion

of a given object. In the mammalian primary visual cortex, most neurons respond selectively to a preferred orientation of visual stimuli. Some of these neurons are also direction selective, in that they are significantly more activated by a preferred direction of stimulus motion than by any other direction (Hubel, 1959 and Hubel and Wiesel, 1959). Since the first recordings of visual responses in the cat primary visual cortex (Hubel, 1959 and Hubel and Wiesel, 1959), numerous studies have focused on the mechanisms underlying the development of selective properties of visual cortical neurons. These studies were mostly performed in carnivores, such as cats and ferrets, and in primates.

We generated long-tailed degree distributions using the power law

We generated long-tailed degree distributions using the power law with exponential cut-off described in Section 2, and found that the average distance to the empirical distributions was about 5.2 times zB. We then applied each of the rounding schemes described in Section 2. Scheme 1 (rounding all degrees up by 5) and Scheme 2 (by 10), reduced the factor from 5.2 to 2.7 and 2.3, respectively. Scheme 3 (adding 5 to every degree) increased the distance somewhat to 5.5. However, the more sophisticated FG-4592 mw Scheme 4 (rounding to the nearest 10 for k < 100 and to the nearest 100 for k > 100)

reduced the factor to 1.4; while Scheme 5, which is like Scheme 4 but also draws all degrees under 10 from the combined Bristol distributions, decreases this factor further still to 1.2, Table S3. In other words, these schemes produce distributions almost as close to the empirical ones as the two Bristol datasets are to each other. Note, however, that the level of interference involved in Schemes 4 and 5 should be seen as the minimum reporting error required to obtain realistic reported distributions from smooth underlying ones. If in fact it were the individuals with few contacts who nonetheless claimed to have hundreds while the

highly connected reported only a small number, this would not be evident in the data. The bias introduced by inaccuracies in reported degrees which we go on to analyse should therefore be regarded as a lower bound to the potential importance of this Florfenicol effect. Inaccuracy in reported degrees selleck kinase inhibitor had a large effect on the reliability of estimates of prevalence and incidence (Fig. 2). The top half of Fig. 2 shows estimates of prevalence from RDS surveys where degree was mis-reported by the 5 rounding schemes. The estimates were calculated using the Volz–Heckathorn estimator. Mis-reporting degrees caused all surveys to over-estimate prevalence (compare to the ‘Actual’ prevalence in the

whole network, top). However, if degrees were correctly reported (standard RDS) the average prevalence estimate from 100 surveys was accurate, but individual variation was large. Even with inaccurate degreees, the adjusted estimates (blue bars) were still closer to the true prevalence or incidence than the point estimate from the raw data (green bars). Two of our degree-biasing rounding schemes were based on degrees collected in Bristol, UK. Scheme 4 adjusted only those degrees larger than 10: the prevalence estimate is comparable with the estimate using correct degrees. However, the error increased when inaccuracies were added to the lower degrees (1 ≤ d ≤ 10) in Scheme 5. Those with low degree have a higher weighting in the estimator (Eq. (1)) than those with high degree; therefore mis-reporting these degrees had a larger effect on the estimate. The average prevalence for rounding Scheme 5 was 39.8% [31.1–51.4% 95% CI] compared to the actual average prevalence of 27.2% [26.1–28.4% 95% CI].

In contrast, others (Khalilov et al , 2002) have indicated a pote

In contrast, others (Khalilov et al., 2002) have indicated a potential for GluK1

agonists Venetoclax molecular weight as antieplieptic based on the overinhibition largely mediated by GluK1-containing receptors, which are enriched in hippocampal interneurons. The muscarinic agonist pilocarpine is used as a standard model to generate epileptiform activity in order to evaluate the potential of anticonvulsant drugs (cf. Smolders et al., 2002 and references therein). One of the advantages of this model is that it does not involve direct stimulation of KARs, thereby allowing the evaluation of the contribution of tonic KAR activation by ambient glutamate to the epileptic phenomena. It is likely that multiple mechanisms may account for the involvement of KARs in epilepsy. It is possible that the glutamate released due to circuit hyperactivity may provoke both tonic activation

of CA3 neurons and KAR-mediated depression of synaptic inhibition. These two actions NVP-BGJ398 research buy would be sufficient to generate a drastic imbalance between excitation and inhibition, leading to hippocampal seizures. A similar mechanism has been invoked in the amygdala to account for the therapeutic effects of topiramate (Braga et al., 2009), an approved antiepileptic medicine. A linkage study of 20 families found a significant excess of the Grik1 tetranucleotide polymorphism (nine “AGTA” repeats) in members of families affected by idiopathic juvenile absence epilepsy ( Sander et al., 1997). This allelic variant of Grik1 probably confers susceptibility to juvenile absence epilepsy, when superimposed on a background of strong polygenic effects. The tetranucleotide polymorphism maps to the noncoding region of the gene, close to regulatory sequences, and although it does not seem to affect receptor

structure ( Izzi et al., 2002), it could alter gene expression. However, as there is no evidence of this to date, this association may also be due to a hypothetical epilepsy gene in this region in linkage disequilibrium with Grik1 tetranucleotide repeats ( Lucarini et al., 2007). Despite all the evidence linking KARs to epilepsy, to our knowledge no antiepileptic drugs have been developed to date based on KAR antagonists. KARs are others expressed strongly in DRG cells and dorsal horn neurons, pointing to a specific role for these receptors in sensory transmission and pain. Indeed, KARs were targeted as potential elements involved in pain transmission and kainate was demonstrated to depolarize primary afferents (Agrawal and Evans, 1986). Moreover, a pure population of KARs was initially isolated from DRG neurons that are likely to be C fiber nociceptors (Huettner, 1990). Molecular and electrophysiological characterization of these neurons led us to conclude that these DRG KARs are made up of heteromeric GluK1 and GluK5 subunits (Sommer et al., 1992, Bahn et al., 1994 and Rozas et al.

05; p < 0 05), as well as a subtle and not


05; p < 0.05), as well as a subtle and not

statistically significant increase in the global levels of 5mC (p > 0.05) (Figure 1A). These relatively small overall changes in the global genomic levels of 5hmC and 5mC in the Tet1KO brains are likely to reflect compensatory functions from Tet2 and Tet3, which are also expressed in the brain (Figure S1B). Anatomical and morphological characterization of the Tet1KO brains did not reveal any significant abnormalities. The number of neurons see more in different brain areas including the cingulate cortex and hippocampus (Figures 1C, 1D, and data not shown) and the average brain weight (Figure 1E) were unaffected by Tet1 ablation, suggesting that Tet1 is dispensable for normal brain development and/or that Tet2 and Tet3 compensate for the loss Perifosine of Tet1. In order to examine more specifically synaptic connectivity in Tet1KO brains, we performed morphological analysis of various brain areas in control and Tet1KO littermate mice (3 + 3 animals, 3 months old) using Synapsin I as a marker of synaptic abundance. As no significant differences in amount or distribution of Synapsin I were found in the cortex and hippocampus of Tet1KO and Tet1+/+ mice (p > 0.05; p > 0.05; Figure S1C), we conclude that synaptic development remains largely unperturbed by the

loss of Tet1. To evaluate potential effects of Tet1 ablation upon behavior of adult mice, we performed a general battery of behavioral tests using 4-month-old Tet1KO and Tet1+/+ male littermate mice (8 to 12 animals per group). None of the animals used in these tests had any overt anatomical or developmental abnormalities (data not shown). We observed normal locomotor behavior in the Tet1KO mice in the open field across all parameters

measured (p > 0.05; Figure S2A). In addition, parameters characterizing anxiety did not differ significantly between the mutant and control groups (p > 0.05; Figure S2B). Tet1KO mice were also indistinguishable from their Tet1+/+ littermates in another common test for anxiety-like behavior in rodents, next the elevated-plus maze (Dawson and Tricklebank, 1995) (Figure S2C). Using the Porsolt forced swim test (Petit-Demouliere et al., 2005), a measure of depressive-like behavior in the rodents, we also observed no significant differences between the Tet1KO and Tet1+/+ animals (p > 0.05; Figure S2D). As DNA (de)methylation in the brain appears to be important for cognition (Miller et al., 2008 and Miller et al., 2010), we wanted to examine hippocampus-dependent learning and memory in Tet1+/+ and Tet1KO animals. To do this, we performed a classical Pavlovian fear conditioning (Phillips and LeDoux, 1992). We observed no difference between the groups in contextual learning (p > 0.05; Figure 2A) as well as cued fear memory acquisition (p > 0.05; Figure 2B). Hot plate tests showed that there were no differences in nociception between the Tet1KO and Tet1+/+ animals (p > 0.05; Figure 2C).

This is further supported by our finding that the organization of

This is further supported by our finding that the organization of the ppk11/16 locus is conserved across multiple species of Drosophila ( Figure S2), representing approximately 30 million years of evolutionary divergence, selleck products suggesting that the

tandem placement of these genes is relevant to their regulation. Although the ppk11/16 locus is transcribed as a single RNA, we do not know whether these two could also be transcribed independently. This is important to consider when interpreting the results of transgenic RNAi. Specifically, this concerns whether UAS-ppk11-RNAi targets only the ppk11 gene or whether it will also affect expression of cotranscribed ppk16 and vice versa ( Figures 3 and 4). One further observation is worth considering in the trans-heterozygous data set. When mutations in ppk11 and ppk16 are placed selleck screening library in trans, synaptic homeostasis is blocked but baseline synaptic transmission (in the absence of PhTx) is not statistically different from

wild-type ( Figure 6G). The only significant change observed is a minor decrease in mEPSP amplitude in trans-heterozygous mutants. These data confirm, again, that homeostatic synaptic plasticity can be blocked by disruption of the ppk11/16 locus without a parallel change in baseline synaptic transmission. We hypothesize that PPK11/16-containing DEG/ENaC channels are inserted into the presynaptic plasma membrane to cause a homeostatic increase in presynaptic release and that these channels must be maintained on the plasma membrane in order to sustain the expression of synaptic homeostasis over several days. If this is correct, then pharmacological blockade of the PPK11/16 channel conductance should erase homeostatic potentiation that was previously induced by either PhTx application or by the presence of the GluRIIA mutation. This appears to be the case. DEG/ENaC channels are blocked by amiloride and its however derivatives (Kleyman and Cragoe, 1988). In Drosophila,

Benzamil has been shown to be a potent inhibitor of ENaC channel function ( Liu et al., 2003a). In our first set of experiments, wild-type NMJs were coincubated in 50 μM Benzamil and 10 μM PhTx. After a 10 min incubation, recordings were made in the presence of 50 μM Benzamil. Ten minutes is normally sufficient to induce potent homeostatic compensation ( Figure 7B). However, in the presence of 50 μM Benzamil, we saw a complete block in synaptic homeostasis ( Figures 7A and 7B). Next, we tested whether this effect could be washed out. Benzamil reversibly blocks DEG/ENaC channels, while PhTx irreversibly antagonizes Drosophila glutamate receptors ( Drummond et al., 1998 and Frank et al., 2006). Therefore, we were able to incubate larvae in PhTx and 50 μM Benzamil for 10 min and then wash out only Benzamil, limiting its action to the time when synaptic homeostasis was induced.

The probability distribution of stochastic R∗ lifetimes (τRstoch)

The probability distribution of stochastic R∗ lifetimes (τRstoch) predicts that the vast majority of R∗ lifetimes are less than 80 ms, with a mode of 33 ms (Figure 6E, inset). The c.v. of this distribution is 0.52

(Figure 6F, black checked bar), smaller than that of a first-order deactivation process (c.v. = 1) but significantly larger than the experimentally measured c.v. of WT and GCAPs−/− SPR amplitudes (Figure 6F, solid green and blue bars). To predict the Sirolimus research buy SPR amplitude c.v. associated with the multistep R∗ deactivation scheme, 100,000 stochastic R∗ trajectories were simulated (Figure S2) and each trajectory was used as the driving input for the spatiotemporal model under conditions with and without feedback to cGMP synthesis. The amplitude distributions of the two ensembles of simulated SPRs (Figure 6E, dark blue and dark green

dotted lines) have coefficients of variation that are close to the measured values for both WT and GCAPs−/− rods (hatched green and blue bars in Figure 6F). These simulated amplitude distributions were nearly identical to those obtained by simply transforming the τRstoch distribution by the compressive relations this website describing the stability data (Figure 4C), emphasizing that GCAPs-mediated feedback contributes to reproducibility in the same way that it confers amplitude stability (Figure 6E, solid blue and green curves). In addition to calculating the c.v. of these distributions, we also calculated the time-dependent mean and standard deviations of the ensembles of simulated SPRs. The theoretical mean SPRs and standard deviations agree both in magnitude and time course with the experimental population average SPR data of both

genotypes (black and red smooth curves in Figures 6C and 6D). Thus, even fairly noisy, stochastic deactivation of R∗ can yield SPRs with the experimentally observed degree of reproducibility, aminophylline owing to the compensatory effects of calcium feedback to cGMP synthesis. Notably, the c.v. of the SPR amplitudes produced by the very same ensemble of R∗ deactivation trajectories is predicted to be lower in WT than in GCAPs−/− rods. The analysis shows this lowered c.v. is achieved mainly by the ramping cGMP synthesis in WT rods (Figure 5B), which effectively removes variation that would otherwise arise from the occasionally slower stochastic R∗ deactivations of the ensemble. We have found that GCAPs-mediated feedback to cGMP synthesis helps to stabilize the SPR amplitude against variation in R∗ lifetime (Figure 4). Although this stabilization is clearly more potent for longer R∗ lifetimes, the “power” of the calcium feedback does not arise from a decline in calcium concentration disproportionate to R∗ lifetime, nor because the feedback has greater cooperativity than estimated in biochemical experiments, as previously suggested (Burns et al., 2002).