The dose of CNO was chosen based on a previous study reporting hi

The dose of CNO was chosen based on a previous study reporting high in vivo efficacy at doses between 1 and 5 mg/kg on locomotor activity and stereotypy in a transgenic mouse expressing the hM3Dq receptor within the forebrain (Alexander et al., 2009). CNO reduced the firing rate of a substantial portion

of the MD units (Figures 2B–2D). To quantify this effect, we first FK228 solubility dmso calculated the ratio of firing rates after saline and CNO for each unit; the distribution of ratios in the sample was significantly different than that expected by chance (p < 0.01, Wilcoxon signed-rank test) (Figure 2C). We next compared firing rates after saline and CNO injections for each neuron independently. CNO decreased firing rate significantly (p < 0.05 by paired t test) in 30 neurons (48%). In an additional 11 units (17%), CNO increased the firing rate. Using a more stringent Bonferroni correction (p < 0.0008) 16 (25%) and 6 (9.5%) units were inhibited or activated

by CNO, respectively. For both analyses neurons with decreased firing rate were overrepresented as a consequence of CNO treatment (Binomial test: p < 0.01, p < 0.05 for Bonferroni-corrected values). Importantly, CNO treatment did not completely silence MD neurons; the neurons with decreased firing rate showed an average decrease of 38.7% ± 5.3%. This decrease in firing rate was not related to changes in locomotor activity or to differences in the isolation of single units (Figures S2A–S2C). The CNO-mediated decrease in firing rate was not observed Protein Tyrosine Kinase inhibitor in wild-type mice that do not express hM4D, demonstrating its dependence on hM4D (Figure 2C, inset). While hyperpolarization of thalamic cells can induce a shift in the firing pattern from a tonic to a bursting mode due to the activation of T-type Ca2+ channels (Jahnsen and Llinás, 1984), we did not observe a significant change in the fraction of burst firing in vivo after CNO injection (Figure S2D). Due to the strong projections of the MD to the orbitofrontal cortex (OFC) (Figure 1D), we first tested whether decreasing MD activity affects reversal learning, a cognitive process of executive Parvulin function that is sensitive to orbitofrontal lesions (Schoenbaum et al., 2002). To address reversal

learning, we developed an operant-based reversal learning task for the mouse in which lever presses are rewarded in the presence of one visual cue (S+), but not in the presence of another visual cue (S−) (discrimination phase). After mice reached criterion the contingencies were reversed (reversal phase) (Figure 3A). The acquisition of the discrimination phase was not affected by decreasing MD activity (repeated ANOVA p = 0.17) though CNO-treated MDhM4D mice showed a tendency for a delay in learning during the first three days of acquisition (Figure 3B). In contrast, reversal learning was clearly impaired in CNO-treated MDhM4D mice when compared to the three control groups (repeated ANOVA followed by Bonferroni correction for group comparisons ∗p < 0.05, ∗∗p < 0.

One critical difference between current injection and a laser pul

One critical difference between current injection and a laser pulse is the number of neurons Dasatinib order activated: the laser beam will synchronously activate a population of ChIs and/or their axons owing to the extensive overlapping arborization of ChI axons and dendrites (Contant et al., 1996). These data therefore suggest that ChI-driven DA release occurs during synchronization of activity in ChIs. The requirement for synchronization was confirmed by showing that laser stimuli that minimize synchrony in ChIs did not evoke DA release. To achieve this, we recruited activity gradually in a population of ChIs by slowly ramping laser

intensity during continuous exposure until threshold for spiking was reached in a given recorded ChI. Using this protocol, outcome on activity in each ChI was variable (e.g., threshold intensity, see variation in spike frequency in Figure 2C, n = 6) and this protocol did not evoke DA release (Figure 2C, n = 6). Multiple spikes in a given ChI per se did not preclude DA release

since longer duration laser pulses above threshold that evoked burst firing in ChIs were accompanied by DA release (Figure 2D, n = 11). These data show that synchronous Androgen Receptor Antagonist solubility dmso recruitment of activity in a population of ChIs and/or axons evokes DA release. We also noted that multiple action potentials in a given ChI induced by long laser pulses did not evoke more DA release than a single action potential (compare Figures 2D and 2B), suggesting that ChI-driven DA release does not convey frequency information from individual ChIs. This weak relationship between frequency and DA release is also seen with striatal electrical stimulation when DA axons and ChIs are simultaneously depolarized (Rice and Cragg, 2004 and Zhang and Sulzer, 2004), but not with stimulation of medial forebrain bundle when DA axons are activated (Chergui et al., 1994). These observations suggest that ChI-driven DA release does not report frequency and isothipendyl moreover that it may limit how frequency information in ascending

DA axons is transduced into DA release. We therefore explored the relationships between frequency of activation and DA transmission during activation of ChIs only, DA axons only, or both in combination. Trains of four laser pulses at a range of frequencies in ChR2-expressing ChAT-Cre striatum reliably evoked four action potentials in ChIs at corresponding frequencies (Figure 3A), but the consequent DA release was invariant, reaching only DA levels seen with a single light pulse (and single action potentials) (Figures 3B and 3D, n = 8). This refractoriness (or depression) of rerelease after release by single synchronized spikes in ChIs was therefore not due to spike attenuation in ChIs (and was also not due to activation of mAChRs or D2 receptors causing ACh terminal inhibition, data not shown). These data show that ChI-driven DA release is not a direct readout of the frequency of activity in a given ChI.

There was a general consensus

that (if there was evidence

There was a general consensus

that (if there was evidence of effectiveness), the use of CM in principle might be a useful addition to the therapeutic armamentarium. This idea was most positively endorsed by those in the professional groups with greatest experience and training. BKM120 concentration However, there was a range of views expressed: from unequivocal benefit, through to a more cautious acceptance of it. Concerns were raised that in a system with limited resources it may be seen as a cost saving alternative, replacing established and more valued interventions (e.g., time with a member of staff) and therefore best kept as a ‘last resort’. Much of the discussions of aspects of treatment delivery are common to other aspects of health care where incentives are used as part of treatment. They were framed within the concepts of health economics and medical ethics and included the following five themes: practicalities of implementation; the opportunity costs of the intervention; the possibility of CM acting as a perverse incentive; issues of equity; and the potential impact on the therapeutic relationship (see Fig. 2 and Table 2.1). The practicalities and potential problems of implementation was a major theme across all but one

focus group (service users) and included PFT�� aspects that would be anticipated from any discussion about change management. However, concerns were also expressed that were more specific to implementing a behavioural intervention, where it is well recognised that the precise details are integral to the effectiveness of the implementation, and the possibility of unintended consequences. Regarding

however the implementation of CM within a publicly funded system, participants in four groups (3 professional groups and the ex-service user group) expressed concerns about the opportunity cost of such a change of focus. All nine groups expressed concerns about the feasibility of the level of urine testing (three times per week). However, whilst the professional teams viewed this as being resource heavy and had concerns about the potential opportunity costs of delivery (see Table 2.1), the service user groups felt strongly that such a regime acted as a disincentive that would outweigh any benefit from the financial incentive offered. Concerns about the notion of equity of access to interventions within the treatment system, and that CM might act to incentivise non-engagement (i.e., act as a perverse incentive) were discussed in 6/9 groups. Concerns about equity were primarily expressed in the professional groups. Service user groups felt it more appropriate for CM to be offered on an individual basis depending on the needs of the service user at a particular time, rather than being mandated to particular groups and certain points in their treatment journey.

Plasmid β-loop-TMD-Dendra2 consists of the cytoplasmic M3-M4 loop

Plasmid β-loop-TMD-Dendra2 consists of the cytoplasmic M3-M4 loop of mouse GlyRβ (residues N334–A454 excluding signal peptide, UniProt ID P48168) fused to a single transmembrane domain and extracellular Dendra2 (in analogy to βLwt-TMD-pHluorin; Specht et al., 2011). The fusion constructs were cloned in a eukaryotic expression vector derived from pEGFP-N1 (Clontech) with a partial deletion of the cytomegalovirus promoter. Spinal cord dissociated neuron cultures were prepared from Sprague-Dawley rats (at E14) and from homozygous mRFP-gephyrin KI mice (at E13) as described elsewhere (Calamai et al., 2009), in accordance with the guidelines of the French Ministry of Agriculture

and the Direction départamentale des services vétérinaires de Paris (Ecole Normale Supérieure, Animalerie des Rongeurs, license GSK1349572 in vitro B 75-05-20). Neurons were plated at a density of 6 × 104/cm2 on 18 mm coverslips (thickness, 0.13–0.16 mm); cultured in neurobasal medium containing B-27, 2 mM Crizotinib datasheet glutamine, 5 U/ml penicillin, and 5 μg/ml streptomycin at 36°C and 5% CO2; transfected with 0.5 μg plasmid DNA per coverslip using Lipofectamine 2000; and used for experiments on the following day (at 12–24 days in vitro [DIV]). COS-7 cells were grown on coverslips in Dulbecco’s modified Eagle’s medium containing 10% fetal calf serum, and cotransfected with β-loop-TMD-Dendra2 and mRFP-gephyrin in a stoichiometry of 1:4 on the day

prior to the experiments using FuGENE 6. Cell cultures were fixed for 10 min in 0.1 M sodium phosphate, pH 7.4, containing 4% paraformaldehyde (PFA) and 1% sucrose, rinsed, and imaged in PBS (pH crotamiton 7.4) (PALM and fluorophore counting). For PALM and STORM imaging, fiducial markers (TetraSpeck microspheres, 100 nm diameter, Invitrogen T7279) were attached to the coverslips after fixation. For immunolabeling, fixed neurons were permeabilized with 0.25% Triton X-100 where necessary and labeled in PBS containing 3% bovine serum albumin with antibodies against extracellular epitopes of GlyRα1 (Synaptic Systems, mAb2b, 146111, 1:200–400 dilution) and GABAARα2 (Synaptic Systems, 224103, 1:400),

the phosphorylated C domain of gephyrin (Synaptic Systems, mAb7a, 147011, 1:500; Kuhse et al., 2012), or the N terminus of bassoon (sap7f, 1:500; tom Dieck et al., 1998), followed by Alexa Fluor 647- or 488-tagged secondary antibodies (Invitrogen, 1:250–500). dSTORM was conducted in PBS (pH 7.4), containing 10% glucose, 50 mM β-mercaptoethylamine, 0.5 mg/ml glucose oxidase, and 40 μg/ml catalase, degassed with N2 (Izeddin et al., 2011). Spinal cord and cerebral cortex sections were prepared from mRFP-gephyrin KI mice. Male animals of 1 week to 6 months of age were perfused intracardially with 4% PFA and 0.1% glutaraldehyde in PBS (pH 7.4). Spinal cords (thoracic dorsal horn) and cortices (nonsuperficial layers of the frontal lobe) were dissected, postfixed with 4% PFA in PBS, cut into 1 mm segments, and incubated overnight in 2.3 M sucrose in PBS at 4°C.


“Advances in research for ectoparasitological control have


“Advances in research for ectoparasitological control have brought new therapeutic drugs forward for clinical usage (e.g., fipronil, imidacloprid and spinosad) (Beugnet and Franc, 2012). www.selleckchem.com/products/DAPT-GSI-IX.html Afoxolaner is a compound from a new structurally unique isoxazoline class which acts as a novel and specific blocker of insect ligand-gated chloride ion channels (Shoop et al., 2014). It was formulated in a unique soft, beef-flavored chew (Nexgard®, Merial). There are four

chew sizes, of respectively 0.5 g, 1.25 g, 3 g and 6 g, containing 11.3 mg, 28.3 mg, 68 mg and 136 mg of afoxolaner. They are intended for dogs weighing 2–4 kg, 4.1–10 kg, 10.1–25 kg and 25.1–50 kg, respectively. The weight bands of the various chew sizes can result in a minimum therapeutic dose of 2.5 mg/kg and a maximum exposure dose of 6.3 mg/kg body weight. The assessment of the safety of a compound in the target species is a prerequisite for registration of veterinary products. The guidelines for target animal safety studies now require that the compound be tested using the final commercial formulation at 1, 3, and 5 times the maximum exposure dose (VICH,

2008). Oral as well as topically applied antiparasitic drugs are usually manufactured so that one size tablet/chewable or pipette can be administered to animals within a specified weight range (Blagburn et al., 2010). KU-55933 purchase The dose received by the heaviest animal in the range is designated not as the minimum therapeutic dose. The dose received by the lightest animal in the range is designated the maximum

exposure dose. The maximum exposure dose must then be multiplied by 1, 3, and 5 times. The regulatory guidelines also determine the number of times a formulation must be administered during the study and in addition to the minimum age of animals to be tested. The formulation is recommended to be administered monthly for six treatments. If a product is designed for use in young animals, the age of the animal tested must be the minimum age for which the commercial product will be used. Establishment of safety for use in the target species and for animal at a minimum age is mandatory to get a registration as veterinary medicine. It is necessary to demonstrate to the veterinarians and the pet owners that no unexpected adverse event will occur in treated dogs. Therefore, the objective of this study was to determine the safety profile of afoxolaner administered in a soft chewable formulation to 8-week-old dogs at either 1×, 3× or 5× the maximum exposure dose (i.e., 6.3 mg/kg, 18.9 mg/kg and 31.5 mg/kg) at three, one-month-dose-intervals followed by three, 2-week-dose intervals.

, 2013) Numerous studies have shown that underlying early drug u

, 2013). Numerous studies have shown that underlying early drug use is a general, highly heritable predisposition to externalizing behaviors (Agrawal and Lynskey, 2006). At the same time, it has been suggested that although illicit drug use and dependence is associated with a

range of early life circumstances that put individuals at greater risk, the use of cannabis in late adolescence emerge as the strongest risk factor for later illicit drug use (Fergusson et al., 2008). This is supported by twin studies, reporting early-onset cannabis see more users to be at two to four times greater risk of use of drugs such as cocaine, hallucinogens, sedatives and opioids and twice as likely as their co-twins to meet criteria for dependence on hard drugs and alcohol (Agrawal and Lynskey, 2014 and Lynskey et al., 2003). In our study, 80% of the extensive cannabis users reported

having also used other drugs, unknown to what extent. Existing research indicates that individuals with poly-substance use experience greater social consequences and higher rates of dependence, when compared to individuals who use only one drug (Midanik et al., 2007, Pacek et al., 2013 and Stenbacka, 2003). Nevertheless, research on poly-substance use in relation to health and psychosocial functioning is scarce (Martin, 2008). Findings suggest psychiatric severity increases linearly because with increased poly-substance Vandetanib mw use (Fischer et al., 2010) and poly-drug users to be at increased risk of unemployment (Carter et al., 2013 and Quek et al., 2013). Our study did, however, focus on disability pension (i.e., a permanent exclusion from the labor market with a medical diagnosis). Also, important to highlight is the fact that when we controlled for use of other drugs the association between adolescent cannabis

use and DP still remained. We are not able to fully explain the mechanisms which underlie the observed associations between adolescent cannabis use and later DP. For example, there is reason to believe that the associations found in our study develop over a long period of time and are intertwined with problems in the both the labor market, in the social security system, and with the individual. For one thing, we know from previous studies that drug use and dependence are associated with many psychiatric disorders (Goldstein et al., 2012), which in turn represents a large proportion of the disability pensions in Sweden. When we adjusted for mental functions (e.g., psychiatric diagnosis, cognitive ability, emotional stability and social maturity) by the age of 18, the associations weakened considerably. We have, however, no knowledge of the later diagnoses leading to DP in our population.

While the 5% deviant responses were essentially as likely to be l

While the 5% deviant responses were essentially as likely to be larger or smaller in the Random compared

to the Periodic condition (66/138, 48%), the majority of the responses to 20% deviants were larger in the Random compared to the Periodic condition (103/156, 66%); furthermore, the average response to the 20% deviants was significantly larger in the Random than in the Periodic condition. The responses to standards followed the reverse tendencies: the differences between the responses in the Periodic and Random conditions became less prominent with increasing deviant probability (and decreasing standard probability). Thus, while the LFP responses to Periodic standards were overwhelmingly smaller than the responses to Random standards for 5% deviant probability (99/124, 80%), the imbalance in the standard response was substantially smaller when deviant probability see more 3-MA solubility dmso was 20% (85/147, 58%). It has been previously shown that SSA has several timescales, from hundreds of milliseconds to tens of seconds (Ulanovsky et al., 2004). In order to examine the time course of the effects shown above, we calculated the average responses

to the standards with different time resolutions along the sequence. Figure 5 shows the average LFP responses to standards (Figure 5A) and deviants (Figure 5B), as a function of the sequential position of the stimulus within the sequence for the 5% (left) and 20% (right) deviant probabilities. In Figure 5A, the blue and green bars represent the average response to the standard stimuli at four ranges of trials along the sequence (1–19, 20–80, 81–278, 279–475 for the 5% conditions; 1–4, 5–19, 20–59, 60–100 for the 20% conditions) in the Random and Periodic conditions, respectively. In Figure 5B, the red and yellow bars represent

the average response to the deviant stimuli in four ranges of trials (1:3, 4:6, 8:16, 17:25) in the Random and Periodic conditions, below respectively. We analyzed the data with a three-way ANOVA on time bin and sequence type, with recording site as a random factor. The main effects of time bin were significant for all conditions [5%: standards F(3,2032) = 46.01, p < < 0.01; deviants F(3,2508) = 3.22, p = 0.022; 20%: standards F(3,3076) = 47.57, p < < 0.01; deviants F(3,3172) = 4.85 p = 2.3∗10−3]. The main effect of sequence type (Periodic versus Random) was significant for the standards in the 5% conditions [F(1,2032) = 52.75, p < < 0.01] but not for the deviants [F(1,2508) = 0.16 p = 0.69]. In contrast, in the 20% conditions the main effect of sequence type was significant for the deviants [F(1,3172) = 14.5 p = 1∗10−4] but not for the standards [F(1,3076) = 0.29 p = 0.59].

However, whether postendocytotic trafficking

of MORs can

However, whether postendocytotic trafficking

of MORs can be modulated by DORs remains to be examined. Furthermore, if DORs and MORs were colocalized in sensory afferent fibers, it would be interesting to BAY 73-4506 supplier explore the physical interaction and functional correlation between these two types of opioid receptors in vivo. The aim of the present study was to investigate the postendocytotic process of the MOR/DOR complex after agonist stimulation and its correlation with the DOR-mediated negative regulation of MOR-mediated spinal analgesia. We found that the activation of DORs in the MOR/DOR complex could target MORs into the postendocytotic degradation pathway, resulting in MOR desensitization. Furthermore, morphine analgesia could be facilitated by disrupting the MOR/DOR interaction with an interfering peptide that corresponds to the first transmembrane domain (TM1)

of MOR fused with the TAT peptide, which is the cell membrane transduction domain of the human immunodeficiency virus and used as a cell-penetrating vector to deliver small cargos or large molecules (Schwarze et al., 1999). Therefore, physical disassociation of MORs from DORs could be a strategy to enhance MOR-mediated analgesia. To assess whether MOR trafficking could be modulated ZD1839 in vivo by activation of DORs, we examined the distribution and translocation of MORs and DORs first in human embryonic kidney 293 (HEK293) cells that were cotransfected with plasmids expressing MOR with an N-terminal hemagglutinin (HA) tag (HA-MOR) and DOR with an N-terminal Myc tag (Myc-DOR). Because HA and Myc were tagged at the N termini of MOR and DOR, respectively, and exposed to the extracellular space following insertion of the receptors into the plasma membrane, HA-MOR and Myc-DOR on the cell surface of living cells could be prelabeled using rabbit anti-HA and mouse anti-Myc antibodies. Under control conditions, the prelabeled DORs and MORs were mainly present on the surface of the double-transfected HEK293 cells (Figure 1A).

Interestingly, after a 30 min treatment with the selective DOR agonists deltorphin (Delt) I, Delt II, or (+)-4-[(αR)-α-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80) (1 μM), the prelabeled DORs and MORs were cointernalized and colocalized in the same vesicular structures (Figure 1A). When DAMGO (1 μM), a selective MOR agonist, was applied for 30 min, the cointernalization of prelabeled MORs and DORs was also observed in the double-transfected HEK293 cells (Figure 1A). The reaction induced by Delt I or DAMGO could be abolished using the DOR antagonist naltrindole (NTI) or the MOR antagonists naloxone and D-Phe-Cys-Tyr-D-Trp-Om-Thr-Pen-Thr-NH2 (CTOP) (Figure 1A), indicating that the receptor cointernalization is induced in a receptor-specific manner.

, 2004, Shen and Bargmann, 2003, Shen et al , 2004, Yamagata and

, 2004, Shen and Bargmann, 2003, Shen et al., 2004, Yamagata and Sanes, 2008 and Yamagata et al., 2002) and negative (Inaki et al., 2007, Klassen and Shen, 2007, Pecho-Vrieseling et al., 2009 and Tran et al., 2009) cues, is now fairly well established, and it appears that cadherin-mediated interactions may play a similar role in the generation of synaptic diversity. The SPO specificity assay reveals

that decreasing cadherin-9 expression in postsynaptic neurons in culture has two main effects. First, it reduces the number of DG synapses onto CA3 neurons, without affecting non-DG synapses, indicating that it is specifically required for DG-CA3 synapse formation. Second, PARP inhibitor LY2157299 the DG-CA3 synapses that do form onto neurons with reduced cadherin-9 expression are much smaller than controls, indicating that cadhein-9 signaling also regulates the growth of this unusually large synapse. Furthermore, it is intriguing that cadherin-9 also appears to play a role in the formation of the few DG-DG synapses that form in culture. This is most likely due to an interaction between axonal and dendritic cadherin-9 in DG neurons. In vivo, DG axons normally do not have access to DG dendrites due to the trajectory of axon growth in the mossy fiber pathway; however, DG-DG synapses do sometimes develop in response to seizure

activity through a process known as mossy fiber sprouting (Dudek and Sutula, 2007). It will be interesting to determine if cadherin-9 plays a role in this process and whether inhibiting cadherin-9 function can ameliorate the effects of generating a seizure-induced back-projecting DG circuit. Our results provide strong evidence in support of a role for cadherin-9 in regulating mossy fiber synapse formation in vivo. Cadherin-9 knockdown results in multiple-related phenotypes, suggesting that cadherin-9 may have a multifaceted role in target recognition,

synapse formation, ADP ribosylation factor and synapse maturation at the mossy fiber synapse. Because cadherin-9 is expressed specifically in DG and CA3 neurons, cadherin-9-mediated homophilic adhesion may provide a target recognition cue between DG and CA3 neurons. Support for this comes from the fact that reduction of cadherin-9 in CA3 neurons generates extremely long thin filopodia-like spines. Filopodia are thought to be precursors to mature spines. Their length and flexibility are thought to make them more motile so that they may sample the environment in search of potential synaptic partners. It is possible that without cadherin-9, CA3 dendrites are largely unable to recognize DG axons and, therefore, do not initiate maturation of TE spines. Despite the severe effects of cadherin-9 knockdown on mossy fiber synapse morphology in vivo, some DG-CA3 synapses are still made.

For example, might some of the excess innervation originate from

For example, might some of the excess innervation originate from axons that were sending long collateral branches to multiple muscles in the embryonic period, or, alternatively, might some of the branches originate from motor neurons that are at the tail end of the period of naturally

occurring motor neuron cell death and are destined to die? The idea of cell death was ruled out by finding that there were no activated caspase-3 or TUNEL-positive ventral horn cholinergic cells in the spinal cord at birth, even though CHIR-99021 purchase we could induce caspase-3 or TUNEL labeling in the sternomastoid muscle motor neurons by axotomy in the spinal accessory nerve of pups at P0 (Figure 6C). We also found no evidence of axons branching to more than one muscle at birth by examining both retrograde labeling of motor neurons projecting to different muscles and lipophilic axon tracing from different muscles (Figure 6B). This study shows extensive connectivity in the developing neuromuscular system that resolves over the first few postnatal days into the much simpler pattern that has been well described in previous studies. Motor axons innervate

roughly an order of magnitude more target cells, and target cells each receive input from an order of magnitude more axons at birth than 2 weeks later. The loss occurs precipitously because even by postnatal day 6, many of these muscle fibers are singly innervated (Keller-Peck et al., 2001), meaning that the postsynaptic cells must be losing innervation from more than buy MLN0128 an axon per day during the first postnatal week. This data also shows that the peak of the “exuberance” is just before birth, suggesting perhaps that postnatal life may be a critical impetus for this synapse elimination.

Although there are many possible reasons for a die off of axonal branches, the studies presented here indicate that neither late apoptosis of a subset of neurons (Landmesser Phosphatidylinositol diacylglycerol-lyase and Pilar, 1974), nor the pruning of long intermuscular axon collaterals that projected erroneously to multiple targets (Bunt and Lund, 1981, Innocenti, 1981 and Stanfield et al., 1982), nor the pruning of large intramuscular branches with many synaptic terminals explains the result. Rather, the results show that pruning of terminal synaptic branches explains the large reduction in axonal complexity beginning in the perinatal period. We have studied the excessive branching using light and electron microscopical anatomical methods. Light and electron microscopy were necessary because of technical limitations of electrophysiological and more traditional light microscopic assays when used in developing systems. We measured the size of neonatal motor units anatomically because the several physiological methods previously used are insensitive to subthreshold innervation. One approach measures the muscle tension elicited by individual motor axons and compares it with the total tension a muscle is capable of generating (Brown et al., 1976).