Drug Delivery: Enabling Technology for Drug Discovery and Development. iPRECIO Micro Infusion Pump: Programmable, Refillable, and Implantable

Early Stage Preclinical Formulation Strategies to Alter the Pharmacokinetic Profile of Two Small Molecule Therapeutics

Early stage chemical development presents numerous challenges, and achieving a functional balance is a major hurdle, with many early compounds not meeting the clinical requirements for advancement benchmarks due to issues like poor oral bioavailability. There is a need to develop strategies for achieving the desired systemic concentration for these compounds. This will enable further evaluation of the biological response upon a compound-target interaction, providing deeper insight into the postulated biological pathways. Our study elucidates alternative drug delivery paradigms by comparing formulation strategies across oral (PO), intraperitoneal (IP), subcutaneous (SC), and intravenous (IV) routes. While each modality boasts its own set of merits and constraints, it is the drug's formulation that crucially influences its pharmacokinetic (PK) trajectory and the maintenance of its therapeutic levels. Our examination of model compounds G7883 and G6893 highlighted their distinct physio-chemical attributes. By harnessing varied formulation methods, we sought to fine-tune their PK profiles. PK studies showcased G7883's extended half-life using an SC oil formulation, resulting in a 4.5-fold and 2.5-fold enhancement compared with the IP and PO routes, respectively. In contrast, with G6893, we achieved a prolonged systemic coverage time above the desired target concentration through a different approach using an IV infusion pump. These outcomes underscore the need for tailored formulation strategies, which are dictated by the compound's innate properties, to reach the optimal in vivo systemic concentrations. Prioritizing formulation and delivery optimization early on is pivotal for effective systemic uptake, thereby facilitating a deeper understanding of biological pathways and expediting the overall clinical drug development timeline.

Implantable magnetically-actuated capsule for on-demand delivery

Many implantable drug delivery systems (IDDS) have been developed for long-term, pulsatile drug release. However, they are often limited by bulky size, complex electronic components, unpredictable drug delivery, as well as the need for battery replacement and consequent replacement surgery. Here, we develop an implantable magnetically-actuated capsule (IMAC) and its portable magnetic actuator (MA) for on-demand and robust drug delivery in a tether-free and battery-free manner. IMAC utilizes the bistable mechanism of two magnetic balls inside IMAC to trigger drug delivery under a strong magnetic field (|Ba| > 90 mT), ensuring precise and reproducible drug delivery (9.9 ± 0.17 μg per actuation, maximum actuation number: 180) and excellent anti-magnetic capability (critical trigger field intensity: ∼90 mT). IMAC as a tetherless robot can navigate to and anchor at the lesion sites driven by a gradient magnetic field (∇ Bg = 3 T/m, |Bg| < 60 mT), and on-demand release drug actuated by a uniform magnetic field (|Ba| = ∼100 mT) within the gastrointestinal tract. During a 15-day insulin administration in vivo, the diabetic rats treated with IMAC exhibited highly similar pharmacokinetic and pharmacodynamic profiles to those administrated via subcutaneous injection, demonstrating its robust and on-demand drug release performance. Moreover, IMAC is biocompatible, batter-free, refillable, miniature (only Φ 6.3 × 12.3 mm3), and lightweight (just 0.8 g), making it an ideal alternative for precise implantable drug delivery and friendly patient-centered drug administration.

Effort-related effects of chronic administration of the DA D2 receptor antagonist haloperidol via subcutaneous programmable minipumps: Reversal by co-administration of the adenosine A2A antagonist istradefylline

RATIONALE

Long-acting antipsychotics such as haloperidol decanoate are becoming more commonly used. Long-acting depot formulations have several advantages, but secondary negative effects of prolonged delivery, including motivational dysfunctions, could have debilitating effects. Assessing the behavioral changes that emerge during chronic antipsychotic administration in rats could provide insight regarding the development of motivational dysfunctions and drug tolerance.

OBJECTIVES

Acute administration of dopamine D2 antagonists such as haloperidol induce motivational deficits in rats, as marked by a shift towards a low-effort bias during effort-based choice tasks. In the present studies, programmable subcutaneous infusion pumps provided continuous and controlled drug delivery of haloperidol. Animals were assessed using a fixed ratio (FR) 5 lever pressing schedule and the FR5/chow feeding test of effort-based choice. The adenosine A2A antagonist istradefylline was studied for its ability to reverse the effects of chronic haloperidol.

RESULTS

Continuous chronic infusions of haloperidol produced significant reductions in FR5 performance and a shift from lever pressing to chow intake in rats tested on FR5/chow feeding choice, with no evidence of tolerance over the 4-week infusion period. Behavior returned to baseline during the vehicle-infusion washout period. Istradefylline significantly reversed the effects of haloperidol, increasing lever pressing and decreasing chow intake in haloperidol-treated rats.

CONCLUSIONS

These studies provide an important behavioral characterization of the effects of chronically infused haloperidol, and demonstrate that A2A antagonism reverses the effects of chronic haloperidol. This research could contribute to the understanding and treatment of motivational dysfunctions seen in schizophrenia, Parkinson's disease, and other disorders involving dopamine.

In Vivo Injection of Anti-LGI1 Antibodies into the Rodent M1 Cortex and Hippocampus Is Ineffective in Inducing Seizures

Autoimmune encephalitis (AIE) associated with antibodies directed against the leucine-rich glioma inactivated 1 (LGI1) protein is the second most common AIE and is responsible for deleterious neocortical and limbic epileptic seizures. Previous studies demonstrated a pathogenic role of anti-LGI1 antibodies via alterations in the expression and function of Kv1 channels and AMPA receptors. However, the causal link between antibodies and epileptic seizures has never been demonstrated. Here, we attempted to determine the role of human anti-LGI1 autoantibodies in the genesis of seizures by analyzing the impact of their intracerebral injection in rodents. Acute and chronic injections were performed in rats and mice in the hippocampus and primary motor cortex, the two main brain regions affected by the disease. Acute infusion of CSF or serum IgG of anti-LGI1 AIE patients did not lead to the emergence of epileptic activities, as assessed by multisite electrophysiological recordings over a 10 h period after injection. A chronic 14 d injection, coupled with continuous video-EEG monitoring, was not more effective. Overall, these results demonstrate that acute and chronic injections of CSF or purified IgG from LGI1 patients are not able to generate epileptic activity by themselves in the different animal models tested.

A brief morning rest period benefits cardiac repair in pressure overload hypertrophy and postmyocardial infarction

Rest has long been considered beneficial to patient healing; however, remarkably, there are no evidence-based experimental models determining how it benefits disease outcomes. Here, we created an experimental rest model in mice that briefly extends the morning rest period. We found in 2 major cardiovascular disease conditions (cardiac hypertrophy, myocardial infarction) that imposing a short, extended period of morning rest each day limited cardiac remodeling compared with controls. Mechanistically, rest mitigates autonomic-mediated hemodynamic stress on the cardiovascular system, relaxes myofilament contractility, and attenuates cardiac remodeling genes, consistent with the benefits on cardiac structure and function. These same rest-responsive gene pathways underlie the pathophysiology of many major human cardiovascular conditions, as demonstrated by interrogating open-source transcriptomic data; thus, patients with other conditions may also benefit from a morning rest period in a similar manner. Our findings implicate rest as a key driver of physiology, creating a potentially new field - as broad and important as diet, sleep, or exercise - and provide a strong rationale for investigation of rest-based therapy for major clinical diseases.

Future Opportunities for Research in Rescue Treatments

Clinical studies of rescue medications for seizure clusters are limited and are designed to satisfy regulatory requirements, which may not fully consider the needs of the diverse patient population that experiences seizure clusters or utilize rescue medication. The purpose of this narrative review is to examine the factors that contribute to, or may influence the quality of, seizure cluster research with a goal of improving clinical practice. We address five areas of unmet needs and provide advice for how they could enhance future trials of seizure cluster treatments. The topics addressed in this article are: (1) unaddressed end points to pursue in future studies, (2) roles for devices to enhance rescue medication clinical development programs, (3) tools to study seizure cluster prediction and prevention, (4) the value of other designs for seizure cluster studies, and (5) unique challenges of future trial paradigms for seizure clusters. By focusing on novel end points and technologies with value to patients, caregivers, and clinicians, data obtained from future studies can benefit the diverse patient population that experiences seizure clusters, providing more effective, appropriate care as well as alleviating demands on health care resources.

Magnetically actuating implantable pump for the on-demand and needle-free administration of human growth hormone

A bolus of human growth hormone (hGH) is often prescribed for the treatment of growth hormone deficiency, which requires frequent injections in current clinical settings. This painful needle-involved delivery often results in poor patient compliance, leading to low medication adherence and poor clinical outcomes. Therefore, we propose a magnetically actuating implantable pump (MAP) that can infuse an accurate dose of hGH only at the time of non-invasive magnet application from the skin. The MAP herein could reproducibly infuse 20.6 ± 0.9 μg hGH per actuation without any leak at times without actuation. The infused amount increased proportionally with an increase in the number of actuations. When the MAP was implanted and actuated with a magnet in animals with growth hormone deficiency for 21 days, the profiles of plasma hGH concentration and insulin-like growth factor (IGF)-1, as well as changes in body weight, were similar to those observed in animals treated with conventional subcutaneous hGH injections. Therefore, we anticipate that the MAP fabricated in this study can be a non-invasive alternative to administer hGH without repeated and frequent needle injections.

Implantable device actuated by manual button clicks for noninvasive self-drug administration

Self-injectable therapy has several advantages in the treatment of metabolic disorders. However, frequent injections with needles impair patient compliance and medication adherence. Therefore, we develop a fully implantable device capable of on-demand administration of self-injection drugs via noninvasive manual button clicks on the outer skin. The device is designed to infuse the drug only at the moment of click actuation, which allows for an accurate and reproducible drug infusion, and also prevents unwanted drug leakage. Using a mechanical means of drug infusion, this implantable device does not contain any electronic compartments or batteries, making it compact, and semi-permanent. When tested in animals, the device can achieve subcutaneous injection-like pharmacokinetic and pharmacodynamic effects for self-injection drugs such as exenatide, insulin, and glucagon.

Telemetric data collection should be standard in modern experimental cardiovascular research

Cardiovascular (CV) health is often expressed by changes in heart rate and blood pressure, the physiological record of which may be affected by moving, anaesthesia, handling, time of day and many other factors in rodents. Telemetry measurement minimises these modulations and enables more accurate physiological recording of heart rate and blood pressure than non-invasive methods. Measurement of arterial blood pressure by telemetry requires implanting a catheter tip into the artery. Telemetry enables us to sample physiological parameters with a high frequency continuously for several months. By measuring the pressure in the artery using telemetry, we can visualize pressure changes over a heart cycle as the pressure wave. From the pressure wave, we can subtract systolic, diastolic, mean and pulse pressure. From the beat-to-beat interval (pressure wave) and the RR' interval (electrocardiogram), we can derive the heart rate. From beat-to-beat variability, we can evaluate the autonomic nervous system's activity and spontaneous baroreflex sensitivity and their impact on CV activity. On a long-term scale, circadian variability of CV parameters is evident. Circadian variability is the result of the circadian system's activity, which synchronises and organises many activities in the body, such as autonomic and reflex modulation of the CV system and its response to load over the day. In the presented review, we aimed to discuss telemetry devices, their types, implantation, set-up, limitations, short-term and long-term variability of heart rate and blood pressure in CV research. Data collection by telemetry should be, despite some limitations, standard in modern experimental CV research.

Implantable system for chronotherapy

Diurnal variation in enzymes, hormones, and other biological mediators has long been recognized in mammalian physiology. Developments in pharmacobiology over the past few decades have shown that timing drug delivery can enhance drug efficacy. Here, we report the development of a battery-free, refillable, subcutaneous, and trocar-compatible implantable system that facilitates chronotherapy by enabling tight control over the timing of drug administration in response to external mechanical actuation. The external wearable system is coupled to a mobile app to facilitate control over dosing time. Using this system, we show the efficacy of bromocriptine on glycemic control in a diabetic rat model. We also demonstrate that antihypertensives can be delivered through this device, which could have clinical applications given the recognized diurnal variation of hypertension-related complications. We anticipate that implants capable of chronotherapy will have a substantial impact on our capacity to enhance treatment effectiveness for a broad range of chronic conditions.

Metal‐HisTag Coordination for Remote Loading of Very Small Quantities of Biomacromolecules into PLGA Microspheres

Challenges to discovery and preclinical development of long‐acting release systems for protein therapeutics include protein instability, use of organic solvents during encapsulation, specialized equipment and personnel, and high costs of proteins. We sought to overcome these issues by combining remote‐loading self‐healing encapsulation with binding HisTag protein to transition metal ions. Porous, drug‐free self‐healing microspheres of copolymers of lactic and glycolic acids with high molecular weight dextran sulfate and immobilized divalent transition metal (M²⁺) ions were placed in the presence of proteins with or without HisTags to bind the protein in the pores of the polymer before healing the surface pores with modest temperature. Using human serum albumin, insulin‐like growth factor 1, and granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), encapsulated efficiencies of immunoreactive protein relative to nonencapsulation protein solutions increased from ~41%, ~23%, and ~9%, respectively, without Zn²⁺ and HisTags to ~100%, ~83%, and ~75% with Zn²⁺ and HisTags. These three proteins were continuously released in immunoreactive form over seven to ten weeks to 73%–100% complete release, and GM‐CSF showed bioactivity >95% relative to immunoreactive protein throughout the release interval. Increased encapsulation efficiencies were also found with other divalent transition metals ions (Co²⁺, Cu²⁺, Ni²⁺, and Zn²⁺), but not with Ca²⁺. Ethylenediaminetetraacetic acid was found to interfere with this process, reverting encapsulation efficiency back to Zn²⁺‐free levels. These results indicate that M²⁺‐immobilized self‐healing microspheres can be prepared for simple and efficient encapsulation by simple mixing in aqueous solutions. These formulations provide slow and continuous release of immunoreactive proteins of diverse types by using a amount of protein (e.g., <10 μg), which may be highly useful in the discovery and early preclinical development phase of new protein active pharmaceutical ingredients, allowing for improved translation to further development of potent proteins for local delivery.

Experimental design, development and evaluation of extended release subcutaneous thermo-responsive in situ gels for small molecules in drug discovery

The objective of this work is to develop extended release subcutaneous thermo-responsive in situ gel-forming delivery systems using the following commercially available triblock polymers: poly (lactic-co-glycolic acid)-poly (ethylene glycol)-poly (lactic-co-glycolic acid) (PLGA-PEG-PLGA, copolymer A & B) and poly (lactide-co-caprolactone)-poly (ethylene glycol)-poly (lactide-co-caprolactone) (PLCL-PEG-PLCL, copolymer C). Performance of two optimized formulations containing ketoprofen as a model compound, was assessed by comparing in vitro drug release profiles with in vivo performance following subcutaneous administration in rats. This work employs a Design of Experiment (DoE) approach to explore first, the relationship between copolymer composition, concentration, and gelation temperature (GT), and second, to identify the optimal copolymer composition and drug loading in the thermo-responsive formulation. Furthermore, this work discusses the disconnect observed between in vitro drug release and in vivo pharmacokinetic (PK) profiles. In vitro, both formulations showed extended-release profiles for 5-9 days, while PK parameters and plasma profiles were similar in vivo without extended release observed. In conclusion, a clear disconnection is observed between in vitro ketoprofen drug release and in vivo performance from the two thermogel formulations tested. This finding highlights a remaining challenge for thermogel formulation development, that is, being able to accurately predict in vivo behavior from in vitro results.

5-HT7 Receptor Restrains 5-HT-induced 5-HT2A Mediated Contraction in the Isolated Abdominal Vena Cava

ABSTRACT

Although discovered as a vasoconstrictor, 5-hydroxytryptamine (5-HT, serotonin) infused into man and rodent reduces blood pressure. This occurs primarily through activation of 5-HT7 receptors and, at least in part, venodilation. Vascular mechanisms by which this could occur include direct receptor activation leading to vasodilation and/or suppression of contractile 5-HT receptor activation. This study tests the hypothesis that the 5-HT7 receptor restrains activation of the 5-HT2A receptor. A subhypothesis is whether agonist-induced activation-independent of constitutive activity-of the 5-HT7 receptor is necessary for this restraint. The isolated abdominal aorta and vena cava from the normal male Sprague-Dawley rat was our model. Studies used real-time PCR and a pharmacological approach in the isolated tissue bath for measurement of isometric tone. Although 5-HT2A receptor mRNA expression in both aorta and vena cava was significantly larger than that of the 5-HT7 receptor mRNA, the 5-HT7/5-HT2A receptor mRNA ratio was greater in the vena cava (0.30) than in the aorta (0.067). 5-HT7 receptor antagonism by SB266970 and DR 4458 increased maximum contraction to 5-HT in the isolated vein by over 50% versus control. The 5-HT2A receptor agonists TCB-2 and NBOH were more potent in the aorta compared with 5-HT but less efficacious, serving as partial agonists. By contrast, these same three agonists caused no contraction in the vena cava isolated from the same rats up to 10 μM agonist. Antagonism of the 5-HT7 receptor by SB269970 did not increase either the potency or efficacy of TCB-2 or NBOH. These data support that the 5-HT7 receptor itself needs to be stimulated to reduce contraction and suggest there is little constitutive activity of the 5-HT7 receptor in the isolate abdominal vena cava.

A review of peristaltic micropumps

This report presents a review of progress on peristaltic micropumps since their emergence, which have been widely used in many research fields from biology to aeronautics. This paper summarizes different techniques that have been used to mimic this elegant physiological transport mechanism that is commonly found in nature. The analysis provides definitions of peristaltic micropumps and their different features, distinguishing them from other mechanical micropumps. Important parameters in peristalsis are presented, such as the operating frequency, stroke volume, and various actuation sequences, along with introducing design rules and analysis for optimizing actuation sequences. Actuation methods such as piezoelectric, motor, pneumatic, electrostatic, and thermal are discussed with their advantages and disadvantages for application in peristaltic micropumps. This review evaluates research efforts over the past 30 years with comparison of key features and outputs, and suggestions for future development. The analysis provides a starting point for researchers designing peristaltic micropumps for a broad range of applications.

Magnetically-driven implantable pump for on-demand bolus infusion of short-acting glucagon-like peptide-1 receptor agonist

For type 2 diabetic patients, short acting glucagon-like peptide-1 receptor agonist (GLP-1 RA) is often prescribed with frequent needled injections. Long-acting GLP-1 RA for less frequent injections do not mimic physiologic secretion of GLP-1. Therefore, an implantable pump is proposed in this work, which can deliver a short-acting GLP-1 RA, exenatide, without needles and batteries. The implanted pump can infuse an accurate amount of exenatide bolus only when a noninvasive magnetic force is applied from outside the body. The pump includes a safety feature of patterned magnets for actuation to prevent accidental infusion possibly caused by a general household magnet. The reservoir for exenatide is made of a flexible biomaterial and thus, a negative pressure build-up in the reservoir can be prevented even after multiple actuations and almost all drug consumption (~ 94%). This allows a reproducible drug dose for a longer period after implantation, hence less frequent replenishment procedures. The pump is also equipped with an intermediate container with two distinct check-valves and thus, the reservoir of exenatide can be further separated and better prevented from infiltration of the bodily fluid surrounding the implanted pump. When tested in Goto-Kakizaki rats, the pump demonstrates the efficacy of exenatide similar to conventional subcutaneous injections. Therefore, the pump can be promising for patient-friendly, optimal delivery of short-acting GLP-1 RA that better follows the physiologic secretion profile of GLP-1.

Rehabilitation Decreases Spasticity by Restoring Chloride Homeostasis through the Brain-Derived Neurotrophic Factor-KCC2 Pathway after Spinal Cord Injury

Activity-based therapy is routinely integrated in rehabilitation programs to facilitate functional recovery after spinal cord injury (SCI). Among its beneficial effects is a reduction of hyperreflexia and spasticity, which affects ∼75% of the SCI population. Unlike current anti-spastic pharmacological treatments, rehabilitation attenuates spastic symptoms without causing an active depression in spinal excitability, thus avoiding further interference with motor recovery. Understanding how activity-based therapies contribute to decrease spasticity is critical to identifying new pharmacological targets and to optimize rehabilitation programs. It was recently demonstrated that a decrease in the expression of KCC2, a neuronal Cl- extruder, contributes to the development spasticity in SCI rats. Although exercise can decrease spinal hyperexcitability and increase KCC2 expression on lumbar motoneurons after SCI, a causal effect remains to be established. Activity-dependent processes include an increase in brain-derived neurotrophic factor (BDNF) expression. Interestingly, BDNF is a regulator of KCC2 but also a potent modulator of spinal excitability. Therefore, we hypothesized that after SCI, the activity-dependent increase in KCC2 expression: 1) functionally contributes to reduce hyperreflexia, and 2) is regulated by BDNF. SCI rats chronically received VU0240551 (KCC2 blocker) or TrkB-IgG (BDNF scavenger) during the daily rehabilitation sessions and the frequency-dependent depression of the H-reflex, a monitor of hyperreflexia, was recorded 4 weeks post-injury. Our results suggest that the activity-dependent increase in KCC2 functionally contributes to H-reflex recovery and critically depends on BDNF activity. This study provides a new perspective in understanding how exercise impacts hyperreflexia by identifying the biological basis of the recovery of function.

A smart approach to enable preclinical studies in pharmaceutical industry: PLGA-based extended release formulation platform for subcutaneous applications

Objective: Validation of a prospective new therapeutic concept in a proof of concept study is costly and time-consuming. In particular, pharmacologically active tool compounds often lack suitable pharmacokinetic (PK) properties for subsequent studies. The current work describes a PLGA-based formulation platform, encapsulating different preclinical research compounds into extended release microparticles, to optimize their PK properties after subcutaneous administration.Significance: Developing a PLGA-based formulation platform offers the advantage of enabling early proof of concept studies in pharmaceutical research for a variety of preclinical compounds by providing a tailor-made PK profile.Methods: Different model compounds were encapsulated into PLGA microparticles, utilizing emulsification solvent evaporation or spray drying techniques. Formulations aiming different release rates were manufactured and characterized. Optimized formulations were assessed in in vivo studies to determine their PK properties, with the mean residence time (MRT) as one key PK parameter.Results: Utilizing both manufacturing methods, tested tool compounds were encapsulated successfully, with a drug load between 5% and 40% w/w, and an extended release time up to 250 h. In the following PK studies, the MRT was extended by a factor of 90, resulting in prolonged coverage of the required target through level. This approach was confirmed to be equally successful for additional internal compounds, verifying a general applicability of the platform.Conclusion: For different active pharmaceutical ingredients (API), an optimized, tailor-made PK profile was obtained utilizing the described formulation platform. This approach is applicable for a variety of pharmacologically active tool compounds, reducing timelines and costs in preclinical research.

Miniaturized peristaltic rotary pump for non-continuous drug dosing

Micro dosing pumps are the beating heart of infusion systems. Among many technologies to inject micro quantities of fluids, peristaltic pumps show high precision and the possibility to not alter the fluid properties. However, in real drug delivery applications, the continuous release behavior of typical peristaltic pumps is not favorable. In this paper, we investigate the intermittent performance of two prototypes of peristaltic pumps, based on four and five rollers, used to occlude the tube. The pump performances are reported for different rotation speeds and lag times between consecutive infusions. The proposed pumps showed a good volumetric precision (2.88 μL for the five rollers pump and 4.11 μL for the four rollers pump) without any dependency on rotation speed and lag time.

Intrastriatal Memantine Infusion Dampens Levodopa-Induced Dyskinesia and Motor Deficits in a Mouse Model of Hemiparkinsonism

Although the administration of dopamine precursor levodopa remains as the mainstay for the treatment of Parkinson's disease, long-term exposure to levodopa often causes a disabling complication, referred to as levodopa-induced dyskinesias. Therefore, the development of new therapeutic interventions to dampen levodopa-induced dyskinesias and parkinsonian motor deficits is needed in the treatment of Parkinson's disease. Intracerebral brain infusion has the merit of being able to specifically deliver any drug into any brain part. By using an intracerebral infusion system equipped with implantable, programmable, and refillable pumps, we show herein that continuous intrastriatal administration of memantine (MMT), which is a non-competitive N-methyl-D-aspartate receptor antagonist, attenuates levodopa-induced dyskinesias and parkinsonian signs in 6-hydroxydopamine-lesioned hemiparkinsonian mice that received daily levodopa treatment. Corroborating the general thought that overactivation of the striatal N-methyl-D-aspartate receptor function might generate levodopa-induced dyskinesias and parkinsonism, our results suggest that a continuous intrastriatal MMT infusion can be beneficial for the management of Parkinson's disease with levodopa-induced dyskinesias. Our study also provides indications for the prototypic use of pharmacological deep-brain modulation through intracerebral infusion systems for treating medically intractable movement disorders.

5-HT does not lower blood pressure in the 5-HT7 knockout rat

The fall in mean arterial pressure (MAP) after 24 h of 5-HT infusion is associated with a dilation of the portal vein (PV) and abdominal inferior vena cava (Ab IVC); all events were blocked by the selective 5-HT₇ receptor antagonist SB269970. Few studies have investigated the contribution of the 5-HT₇ receptor in long-term cardiovascular control, and this requires an understanding of the chronic activation of the receptor. Using the newly created 5-HT₇ receptor knockout (KO) rat, we presently test the hypothesis that continuous activation of the 5-HT₇ receptor by 5-HT is necessary for the chronic (1 wk) depressor response and splanchnic venodilation. We also address if the 5-HT₇ receptor contributes to endogenous cardiovascular regulation. Conscious MAP (radiotelemeter), splanchnic vessel diameter (ultrasound), and cardiac function (echocardiogram) were measured in ambulatory rats during multiday 5-HT infusion (25 μg·kg^-1·min^-1 via minipump) and after pump removal. 5-HT infusion reduced MAP and caused splanchnic venodilation of wild-type (WT) but not KO rats at any time point. The efficacy of 5-HT-induced contraction was elevated in the isolated abdominal inferior vena cava from the KO compared with WT rats, supporting loss of a relaxant receptor. Similarly, the efficacy of 5-HT causing an acute pressor response to higher doses of 5-HT in vivo was also increased in the KO vs. WT rat. Our work supports a novel mechanism for the cardiovascular effects of 5-HT, activation of 5-HT₇ receptors mediating venodilation in the splanchnic circulation, which could prove useful in the treatment of cardiovascular disease.

Implantable multireservoir device with stimulus-responsive membrane for on-demand and pulsatile delivery of growth hormone

Implantable devices for on-demand and pulsatile drug delivery have attracted considerable attention; however, many devices in clinical use are embedded with the electronic units and battery inside, hence making them large and heavy for implantation. Therefore, we propose an implantable device with multiple drug reservoirs capped with a stimulus-responsive membrane (SRM) for on-demand and pulsatile drug delivery. The SRM is made of thermosensitive POSS(MEO₂MA-co-OEGMA) and photothermal nanoparticles of reduced graphene oxide (rGO), and each of the drug reservoirs is filled with the same amount of human growth hormone (hGH). Therefore, with noninvasive near-infrared (NIR) irradiation from the outside skin, the rGO nanoparticles generate heat to rupture the SRM in the implanted device, which can open a single selected drug reservoir to release hGH. Therefore, the device herein is shown to release hGH reproducibly only at the times of NIR irradiation without drug leakage during no irradiation. When implanted in rats with growth hormone deficiency and irradiated with an NIR light from the outside skin, the device exhibits profiles of hGH and IGF1 plasma concentrations, as well as body weight change, similar to those in animals treated with conventional s.c. hGH injections.

Wirelessly Controlled Implantable System for On-demand and Pulsatile Insulin Administration

We propose a wirelessly controlled implantable system for on-demand and pulsatile insulin delivery with a more convenient and safer strategy than currently available strategies. The system is a combined entity of a magnetically driven pump (i.e., an MDP), external control device (i.e., an ECD) and mobile app. The MDP for implantation consists of a plunger, barrel and drug reservoir, where an accurate amount of insulin can be infused in a pulsatile manner only at the time when a magnetic force is applied to actuate the plunger in the barrel. The ECD at the outside body can modulate the MDP actuation with an electromagnet and its control circuit, and this modulation can be wirelessly controlled by the mobile app. As a safety feature, the mobile app is programmed to pre-set the restrictions for the insulin dose and administration schedule to avoid overdose. The system is shown to infuse insulin in a highly reproducible manner, but it does not allow for insulin infusion when the pre-set restrictions are violated. When tested with diabetic rats, the profiles of insulin plasma concentration and blood glucose level are similar to those of animals treated with a subcutaneous injection of the same dose of insulin.

Melatonin Administration Methods for Research in Mammals and Birds

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Drug delivery across length scales

Over the last century, there has been a dramatic change in the nature of therapeutic, biologically active molecules available to treat disease. Therapies have evolved from extracted natural products towards rationally designed biomolecules, including small molecules, engineered proteins and nucleic acids. The use of potent drugs which target specific organs, cells or biochemical pathways, necessitates new tools which can enable controlled delivery and dosing of these therapeutics to their biological targets. Here, we review the miniaturisation of drug delivery systems from the macro to nano-scale, focussing on controlled dosing and controlled targeting as two key parameters in drug delivery device design. We describe how the miniaturisation of these devices enables the move from repeated, systemic dosing, to on-demand, targeted delivery of therapeutic drugs and highlight areas of focus for the future.

Modulation of sympathetic vasoconstriction is critical for the effects of sleep on arterial pressure in mice

KEY POINTS

While values of arterial pressure during sleep are predictive of cardiovascular risk, the autonomic mechanisms underlying the cardiovascular effects of sleep remain poorly understood. Here, we assess the autonomic mechanisms of the cardiovascular effects of sleep in C57Bl/6J mice, taking advantage of a novel technique for continuous intraperitoneal infusion of autonomic blockers. Our results indicate that non-REM sleep decreases arterial pressure by decreasing sympathetic vasoconstriction, decreases heart rate by balancing parasympathetic activation and sympathetic withdrawal, and increases cardiac baroreflex sensitivity mainly by increasing fluctuations in parasympathetic activity. Our results also indicate that REM sleep increases arterial pressure by increasing sympathetic activity to the heart and blood vessels, and increases heart rate, at least in part, by increasing cardiac sympathetic activity. These results provide a framework for generating and testing hypotheses on cardiovascular derangements during sleep in mouse models and human patients.

ABSTRACT

The values of arterial pressure (AP) during sleep predict cardiovascular risk. Sleep exerts similar effects on cardiovascular control in human subjects and mice. We aimed to determine the underlying autonomic mechanisms in 12 C57Bl/6J mice with a novel technique of intraperitoneal infusion of autonomic blockers, while monitoring the electroencephalogram, electromyogram, AP and heart period (HP, i.e. 1/heart rate). In different sessions, we administered atropine methyl nitrate, atenolol and prazosin to block muscarinic cholinergic, β₁ -adrenergic and α₁ -adrenergic receptors, respectively, and compared each drug infusion with a matched vehicle infusion. The decrease in AP from wakefulness to non-rapid-eye-movement sleep (N) was abolished by prazosin but was not significantly affected by atropine and atenolol, which, however, blunted the accompanying increase in HP to a similar extent. On passing from N to rapid-eye-movement sleep (R), the increase in AP was significantly blunted by prazosin and atenolol, whereas the accompanying decrease in HP was blunted by atropine and abolished by atenolol. Cardiac baroreflex sensitivity (cBRS, sequence technique) was dramatically decreased by atropine and slightly increased by prazosin. These data indicate that in C57Bl/6J mice, N decreases mean AP by decreasing sympathetic vasoconstriction, increases HP by balancing parasympathetic activation and sympathetic withdrawal, and increases cBRS mainly by increasing fluctuations in parasympathetic activity. R increases mean AP by increasing sympathetic vasoconstriction and cardiac sympathetic activity, which also explains, at least in part, the concomitant decrease in HP. These data represent the first comprehensive assessment of the autonomic mechanisms of cardiovascular control during sleep in mice.

Effect of Scopolamine on Mice Motor Activity, Lick Behavior and Reversal Learning in the IntelliCage

Automated homecage monitoring systems are now widely recognized and used tools in cognitive neuroscience. However, few of these studies cover pharmacological interventions. Scopolamine, an anticholinergic memory disrupting agent is frequently used to study learning behavior. We studied the impact of scopolamine treatment in a relevant dose-range on activity, drinking behavior and reversal learning of C57BL/DJ mice in a homecage-like, social environment, using the IntelliCage. Naïve mice were first habituated to the IntelliCage, where they learned to nosepoke in any of the four corners in order to gain access to the water reward. Visits, nosepokes, lick numbers and durations were recorded. Mice were then trained to distinguish between a rewarded correct corner and punished, incorrect corners. Later, in the reversal learning phase, the assigned correct corner was rotated clockwise every 24 h. Upon s.c. administration of scopolamine general activity represented by visit and nosepoke numbers increased, but their durations were shorter. Surprisingly, general activity and lick behavior were drastically altered. Scopolamine also significantly reduced the ability to perform a reversal learning task. We not only found significant decline in reversal learning due to scopolamine treatment, but studied the method specific underlying behaviors: the general activity and lick behavior as well.

5-HT causes splanchnic venodilation

Serotonin [5-hydroxytryptamine (5-HT)] causes relaxation of the isolated superior mesenteric vein, a splanchnic blood vessel, through activation of the 5-HT₇ receptor. As part of studies designed to identify the mechanism(s) through which chronic (≥24 h) infusion of 5-HT lowers blood pressure, we tested the hypothesis that 5-HT causes in vitro and in vivo splanchnic venodilation that is 5-HT₇ receptor dependent. In tissue baths for measurement of isometric contraction, the portal vein and abdominal inferior vena cava relaxed to 5-HT and the 5-HT_1/7 receptor agonist 5-carboxamidotryptamine; relaxation was abolished by the 5-HT₇ receptor antagonist SB-269970. Western blot analyses showed that the abdominal inferior vena cava and portal vein express 5-HT₇ receptor protein. In contrast, the thoracic vena cava, outside the splanchnic circulation, did not relax to serotonergic agonists and exhibited minimal expression of the 5-HT₇ receptor. Male Sprague-Dawley rats with chronically implanted radiotelemetry transmitters underwent repeated ultrasound imaging of abdominal vessels. After baseline imaging, minipumps containing vehicle (saline) or 5-HT (25 μg·kg^-1·min^-1) were implanted. Twenty-four hours later, venous diameters were increased in rats with 5-HT-infusion (percent increase from baseline: superior mesenteric vein, 17.5 ± 1.9; portal vein, 17.7 ± 1.8; and abdominal inferior vena cava, 46.9 ± 8.0) while arterial pressure was decreased (~13 mmHg). Measures returned to baseline after infusion termination. In a separate group of animals, treatment with SB-269970 (3 mg/kg iv) prevented the splanchnic venodilation and fall in blood pressure during 24 h of 5-HT infusion. Thus, 5-HT causes 5-HT₇ receptor-dependent splanchnic venous dilation associated with a fall in blood pressure.NEW & NOTEWORTHY This research is noteworthy because it combines and links, through the 5-HT₇ receptor, an in vitro observation (venorelaxation) with in vivo events (venodilation and fall in blood pressure). This supports the idea that splanchnic venodilation plays a role in blood pressure regulation.

Implantable batteryless device for on-demand and pulsatile insulin administration

Many implantable systems have been designed for long-term, pulsatile delivery of insulin, but the lifetime of these devices is limited by the need for battery replacement and consequent replacement surgery. Here we propose a batteryless, fully implantable insulin pump that can be actuated by a magnetic field. The pump is prepared by simple-assembly of magnets and constituent units and comprises a drug reservoir and actuator equipped with a plunger and barrel, each assembled with a magnet. The plunger moves to noninvasively infuse insulin only when a magnetic field is applied on the exterior surface of the body. Here we show that the dose is easily controlled by varying the number of magnet applications. Also, pump implantation in diabetic rats results in profiles of insulin concentration and decreased blood glucose levels similar to those observed in rats treated with conventional subcutaneous insulin injections.

A users guide to HPA axis research

Glucocorticoid hormones (cortisol and corticosterone - CORT) are the effector hormones of the hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine system. CORT is a systemic intercellular signal whose level predictably varies with time of day and dynamically increases with environmental and psychological stressors. This hormonal signal is utilized by virtually every cell and physiological system of the body to optimize performance according to circadian, environmental and physiological demands. Disturbances in normal HPA axis activity profiles are associated with a wide variety of physiological and mental health disorders. Despite numerous studies to date that have identified molecular, cellular and systems-level glucocorticoid actions, new glucocorticoid actions and clinical status associations continue to be revealed at a brisk pace in the scientific literature. However, the breadth of investigators working in this area poses distinct challenges in ensuring common practices across investigators, and a full appreciation for the complexity of a system that is often reduced to a single dependent measure. This Users Guide is intended to provide a fundamental overview of conceptual, technical and practical knowledge that will assist individuals who engage in and evaluate HPA axis research. We begin with examination of the anatomical and hormonal components of the HPA axis and their physiological range of operation. We then examine strategies and best practices for systematic manipulation and accurate measurement of HPA axis activity. We feature use of experimental methods that will assist with better understanding of CORT's physiological actions, especially as those actions impact subsequent brain function. This research approach is instrumental for determining the mechanisms by which alterations of HPA axis function may contribute to pathophysiology.

Oh, the places you'll go! My many colored serotonin (apologies to Dr. Seuss)

Serotonin [5-hydroxytryptamine (5-HT)] has a truly fascinating history in the cardiovascular world. Discovered in the blood, 5-HT has long been appropriately regarded as a vasoconstrictor. A multitude of in vitro studies of isolated vessels support that addition of 5-HT causes vascular contraction. In only a few cases was 5-HT a vasodilator. Moreover, the potency and threshold of 5-HT causing contraction is increased in arteries from hypertensive vs. normotensive subjects, both animal and human. As such, we and others have hypothesized that 5-HT would contribute to hypertension by elevating arterial tone. In stark contrast to these decades of findings, we observed that a chronic infusion of 5-HT into conscious rats caused a reduction in blood pressure and nearly normalized blood pressure of experimentally hypertensive rats. Going back to the early work of Irvine Page, one of the scientists who discovered 5-HT, reveals an early recognized but never understood ability of 5-HT to reduce systemic blood pressure. Our laboratory, in collaboration with colleagues around the world, has dedicated itself to understanding the mechanisms of 5-HT-induced reduction in blood pressure. This manuscript takes you through a brief history of the discovery of 5-HT, in vitro serotonergic pharmacology of blood vessels, in vivo work with 5-HT and our studies that suggests the venous vasculature, potentially in combination with small arterioles, may be important to the actions of 5-HT in reducing blood pressure. 5-HT has certainly ended up in a place I never expected it to go.

Assessment of implantable infusion pumps for continuous infusion of human insulin in rats: potential for group housing

Group housing is considered to be important for rats, which are highly sociable animals. Single housing may impact behaviour and levels of circulating stress hormones. Rats are typically used in the toxicological evaluation of insulin analogues. Human insulin (HI) is frequently used as a reference compound in these studies, and a comparator model of persistent exposure by HI infusion from external pumps has recently been developed to support toxicological evaluation of long-acting insulin analogues. However, this model requires single housing of the animals. Developing an insulin-infusion model which allows group housing would therefore greatly improve animal welfare. The aim of the present study was to investigate the suitability of implantable infusion pumps for HI infusion in group-housed rats. Group housing of rats implanted with a battery-driven pump proved to be possible. Intravenous infusion of HI lowered blood glucose levels persistently for two weeks, providing a comparator model for use in two-week repeated-dose toxicity studies with new long-acting insulin analogues, which allows group housing, and thereby increasing animal welfare compared with an external infusion model.

In vivo organ specific drug delivery with implantable peristaltic pumps

Classic methods for delivery of agents to specific organs are technically challenging and causes superfluous stress. The current study describes a method using programmable, implantable peristaltic pumps to chronically deliver drugs in vivo, while allowing animals to remain undisturbed for accurate physiological measurements. In this study, two protocols were used to demonstrate accurate drug delivery to the renal medulla. First, the vasopressin receptor-2 agonist, dDAVP, was delivered to the renal medulla resulting in a significant increase in water retention, urine osmolality and aquaporin-2 expression and phosphorylation. Second, in a separate group of rats, the histone deacetylase (HDAC) inhibitor, MS275, was delivered to the renal medulla. HDAC inhibition resulted in a significant increase in histone H3-acetylation, the hallmark for histone deacetylase inhibition. However, this was confined to the medulla, as the histone H3-acetylation was similar in the cortex of vehicle and MS275 infused rats, suggesting targeted drug delivery without systemic spillover. Thus, implantable, peristaltic pumps provide a number of benefits compared to externalized chronic catheters and confer specific delivery to target organs.

Miniaturized Technologies for Enhancement of Motor Plasticity

The idea that the damaged brain can functionally reorganize itself – so when one part fails, there lies the possibility for another to substitute – is an exciting discovery of the twentieth century. We now know that motor circuits once presumed to be hardwired are not, and motor-skill learning, exercise, and even mental rehearsal of motor tasks can turn genes on or off to shape brain architecture, function, and, consequently, behavior. This is a very significant alteration from our previously static view of the brain and has profound implications for the rescue of function after a motor injury. Presentation of the right cues, applied in relevant spatiotemporal geometries, is required to awaken the dormant plastic forces essential for repair. The focus of this review is to highlight some of the recent progress in neural interfaces designed to harness motor plasticity, and the role of miniaturization in development of strategies that engage diverse elements of the neuronal machinery to synergistically facilitate recovery of function after motor damage.

5-HT is a potent relaxant in rat superior mesenteric veins

Serotonin (5-HT, 5-hydroxytryptamine) reduces blood pressure of the conscious rat when administered chronically (1 week). 5-HT does not directly relax isolated arteries, and microsphere experiments in 5-HT-infused rats suggested that 5-HT increased flow to the splanchnic bed. We hypothesized that 5-HT increased splanchnic flow because of direct venous relaxation; our focus was thus on the superior mesenteric vein (SMV) as an important vein in splanchnic circulation. Real-time RT-PCR, immunohistochemistry and Western analyses supported the predominant expression of the 5-HT_2B and 5-HT₇ receptor in the SMV. The SMV was mounted in tissue baths for measurement of isometric contraction. 5-HT caused a concentration-dependent relaxation of the endothelin-1 (ET-1)-contracted vein. The threshold of 5-HT-induced venous relaxation was significantly lower than for 5-HT-induced venous contraction (∼2 vs. 700 nmol/L, respectively). A series of serotonergic agonists established in their use of receptor characterization was tested, and the following rank order of potency found for agonist-induced relaxation (receptor selectivity): 5-CT (5-HT₁/5-HT₇)>5-HT = LP-44 (5-HT₇)>PNU109291 (5-HT_1D) = BW723C86 (5-HT_2B). 8-OH-DPAT (5-HT_1A/7), CP93129 (5-HT_1B), mCPBG (5-HT_3/4), AS19 (5-HT₇) and TCB-2 (5-HT_2A) did not relax the isolated vein. Consistent with these findings, two different 5-HT₇ receptor antagonists SB 269970 and LY215840 but not the 5-HT_2B receptor antagonist LY272015 nor the nitric oxide synthase inhibitor LNNA abolished 5-CT-induced relaxation of the isolated SMV. 5-CT (1 μg kg⁻¹ min⁻¹, sc) also reduced blood pressure over 7 days. These findings suggest that 5-HT directly relaxes the SMV primarily through activation of the 5-HT₇ receptor.

Comparison of arterial pressure and plasma ANG II responses to three methods of subcutaneous ANG II administration

Angiotensin II (ANG II)-induced hypertension is a commonly studied model of experimental hypertension, particularly in rodents, and is often generated by subcutaneous delivery of ANG II using Alzet osmotic minipumps chronically implanted under the skin. We have observed that, in a subset of animals subjected to this protocol, mean arterial pressure (MAP) begins to decline gradually starting the second week of ANG II infusion, resulting in a blunting of the slow pressor response and reduced final MAP. We hypothesized that this variability in the slow pressor response to ANG II was mainly due to factors unique to Alzet pumps. To test this, we compared the pressure profile and changes in plasma ANG II levels during subcutaneous ANG II administration (150 ng·kg(-1)·min(-1)) using either Alzet minipumps, iPrecio implantable pumps, or a Harvard external infusion pump. At the end of 14 days of ANG II, MAP was highest in the iPrecio group (156 ± 3 mmHg) followed by Harvard (140 ± 3 mmHg) and Alzet (122 ± 3 mmHg) groups. The rate of the slow pressor response, measured as daily increases in pressure averaged over days 2-14 of ANG II, was similar between iPrecio and Harvard groups (2.7 ± 0.4 and 2.2 ± 0.4 mmHg/day) but was significantly blunted in the Alzet group (0.4 ± 0.4 mmHg/day) due to a gradual decline in MAP in a subset of rats. We also found differences in the temporal profile of plasma ANG II between infusion groups. We conclude that the gradual decline in MAP observed in a subset of rats during ANG II infusion using Alzet pumps is mainly due to pump-dependent factors when applied in this particular context.

Replenishable dendrimer-nanoparticle hybrid membranes for sustained release of therapeutics

We report a versatile hybrid membrane for sustained release therapeutic delivery systems. Chemically-directed assembly of a hybrid membrane of nanoparticles and dendrimers was integrated with a fluidic delivery device and a refillable drug reservoir, providing continuous sustained release.

Micro- and nano-fabricated implantable drug-delivery systems

Implantable drug-delivery systems provide new means for achieving therapeutic drug concentrations over entire treatment durations in order to optimize drug action. This article focuses on new drug administration modalities achieved using implantable drug-delivery systems that are enabled by micro- and nano-fabrication technologies, and microfluidics. Recent advances in drug administration technologies are discussed and remaining challenges are highlighted.

One-month serotonin infusion results in a prolonged fall in blood pressure in the deoxycorticosterone acetate (DOCA) salt hypertensive rat

A 7-day infusion of serotonin (5-hydroxytryptamine, 5-HT) causes a sustained fall in elevated blood pressure in the male deoxycorticosterone acetate (DOCA)-salt rat. As hypertension is a long-term disease, we presently test the hypothesis that a longer (30 day) 5-HT infusion could cause a sustained fall in blood pressure in the established hypertensive DOCA-salt rat. This time period (∼4 weeks) was also sufficient to test whether 5-HT could attenuate the development of DOCA-salt hypertension. 5-HT (25 μg/kg/min; sc) or vehicle (Veh) was delivered via osmotic pump to (1) established DOCA-salt rats for one month, (2) Sprague-Dawley rats prior to DOCA-salt administration for one month, and blood pressure and heart rate measured telemetrically. On the final day of 5-HT infusion, free platelet poor plasma 5-HT concentrations were significantly higher in 5-HT versus Veh-infused rats, and mean arterial pressure was significantly lower in 5-HT-infused (135 ± 4 mmHg vs Veh-infused 151 ± 7 mmHg) established DOCA-salt rats. By contrast, 5-HT-infusion did not prevent the development of DOCA-salt hypertension (144 ± 7 mmHg vs Veh = 156 ± 6 mmHg). Isometric contraction of aortic strips was measured, and neither the potency nor maximum contraction to the alpha adrenergic receptor agonist phenylephrine (PE) or 5-HT were modified by infusion of 5-HT (established or preventative infusion), and maximum aortic relaxation to acetylcholine (ACh) was modestly but not significantly enhanced (∼15% improvement). This study demonstrates 5-HT is capable of lowering blood pressure in established DOCA-salt hypertensive rats over the course of one month in a mechanism that does not significantly modify or is dependent on modified vascular responsiveness. This finding opens the possibility that elevation of 5-HT levels could be useful in the treatment of hypertension.

Serotonin and blood pressure regulation

5-Hydroxytryptamine (5-HT; serotonin) was discovered more than 60 years ago as a substance isolated from blood. The neural effects of 5-HT have been well investigated and understood, thanks in part to the pharmacological tools available to dissect the serotonergic system and the development of the frequently prescribed selective serotonin-reuptake inhibitors. By contrast, our understanding of the role of 5-HT in the control and modification of blood pressure pales in comparison. Here we focus on the role of 5-HT in systemic blood pressure control. This review provides an in-depth study of the function and pharmacology of 5-HT in those tissues that can modify blood pressure (blood, vasculature, heart, adrenal gland, kidney, brain), with a focus on the autonomic nervous system that includes mechanisms of action and pharmacology of 5-HT within each system. We compare the change in blood pressure produced in different species by short- and long-term administration of 5-HT or selective serotonin receptor agonists. To further our understanding of the mechanisms through which 5-HT modifies blood pressure, we also describe the blood pressure effects of commonly used drugs that modify the actions of 5-HT. The pharmacology and physiological actions of 5-HT in modifying blood pressure are important, given its involvement in circulatory shock, orthostatic hypotension, serotonin syndrome and hypertension.