The effects of d-amphetamine, methylphenidate, sydnocarb, and caffeine on prepulse inhibition of the startle reflex in DBA/2 mice

Effects of acute and chronic methylphenidate on prepulse inhibition: A sex difference study in Wistar rats

BACKGROUND

The utilization of methylphenidate (MPH) is experiencing a notable surge within the adult population. This growth can be attributed to two key factors: its recreational and cognitive enhancement purposes, as well as the rising prevalence of ADHD diagnoses within this population. This study examined acute and chronic oral MPH effects on attention in male and female Wistar rats. To this end, we used a prepulse inhibition (PPI) task, which is widely used to assess psychoactive drug effects in both humans and rodents. This task allowed us to evaluate changes in attention by analyzing sensorimotor gating associated with stimulus selection process.

METHODS

Animals were administered a clinically relevant dose of MPH (5 mg/kg) daily for seven days. The estrous cycle phases of the female rats were measured during behavioral sessions. The PPI task was conducted 20 min after drug administration on day 1 (acute), day 7 (chronic), and 48 h post-treatment.

RESULTS

Results indicated that both acute and chronic MPH treatment impaired PPI expression in male rats, but not in female rats, regardless of their estrous cycle phase. Furthermore, a differential effect of chronic MPH treatment on the PPI task was found in male rats. Specifically, on the seventh treatment day, the PPI effect was observed when animals undertook the PPI task for the first time but was impaired in those animals in which the initial PPI session occurred under the acute influence of the drug (day 1).

CONCLUSIONS

These findings suggest that the impact of MPH on sensorimotor gating responses may vary based on sex and task experience, possibly leading to state-dependent effects in healthy individuals.

Cannabidiol effects in the prepulse inhibition disruption induced by amphetamine

RATIONALE

The information processing appears to be deficient in schizophrenia. Prepulse inhibition (PPI), which measures the inhibition of a motor response by a weak sensory event, is considered particularly useful to understand the biology of information processing in schizophrenia patients. Drugs that facilitate dopaminergic neurotransmission such as amphetamine induce PPI disruption in human and rodents. Clinical and neurobiological findings suggest that the endocannabinoid system and cannabinoids may be implicated in the pathophysiology and treatment of schizophrenia. Cannabidiol (CBD), a non-psychotomimetic constituent of the Cannabis sativa plant, has also been reported to have potential as an antipsychotic.

OBJECTIVE

Our aim was to investigate if CBD pretreatment was able to prevent PPI disruption induced by amphetamine. Since one possible mechanism of CBD action is the facilitation of endocannabinoid-mediated neurotransmission through anandamide, we tested the effects of an anandamide hydrolysis inhibitor (URB597) in the amphetamine-induced PPI disruption.

METHODS

Male Swiss mice were treated with CBD systemic or intra-accumbens, or URB597 (systemic) prior to amphetamine and were exposed to PPI test.

RESULTS

Amphetamine (10 mg/kg) disrupted PPI while CBD (15-60 mg/kg) or URB597 (0.1-1 mg/kg) administered alone had no effect. Pretreatment with CBD attenuated the amphetamine-disruptive effects on PPI test after systemic or intra-accumbens administration. Similar effects were also found with the inhibitor of anandamide hydrolysis.

CONCLUSION

These results corroborate findings indicating that CBD induces antipsychotic-like effects. In addition, they pointed to the nucleus accumbens as a possible site of these effects. The increase of anandamide availability may be enrolled in the CBD effects.

Effects of selective estrogen receptor alpha and beta modulators on prepulse inhibition in male mice

RATIONALE

Multiple lines of evidence suggest that the sex steroid hormone 17-β estradiol (E2) plays a protective role in schizophrenia. Systemic E2 enhances prepulse inhibition (PPI) of the acoustic startle reflex, an operational measure of sensorimotor gating known to be impaired in schizophrenia and related disorders. However, the relative contribution of different estrogen-receptor (ER) isoforms in these associations still awaits examination.

OBJECTIVES

The present study explored the effects of ER-α and ER-β stimulation or blockade on PPI and their functional relevance in an amphetamine-induced PPI deficiency model in male mice.

METHODS

Prior to the assessment of PPI, C57BL/6N male mice were injected with the ER-α agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT), the ER-α antagonist 1,3-bis (4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy) phenol]-1N-pyrozole dihydrochloride (MPP), the ER-β agonist 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN), or the ER-β antagonist 4-[2-phenyl-5,7-bis (trifluoromethyl) pyrazolo [1,5-a] pyrimidin-3-yl] phenol (PHTPP), with or without concomitant amphetamine treatment.

RESULTS

Acute pharmacological stimulation and blockade of ER-α, respectively, led to a dose-dependent increase and decrease in basal PPI. In contrast, acute treatment with preferential ER-β modulators spared PPI under basal conditions. Pretreatment with either ER-α or ER-β agonist was, however, effective in blocking amphetamine-induced PPI disruption.

CONCLUSIONS

Our study demonstrates that activation of either ER isoform is capable of modulating dopamine-dependent PPI levels. At the same time, our results suggest that endogenous ER-α signaling may be more relevant than ER-β in the regulation of sensorimotor gating under basal conditions.

Sensorimotor gating is disrupted by acute but not chronic systemic exposure to caffeine in mice

RATIONALE

Caffeine is a psychostimulant drug that blocks adenosine A₁ and A₂A receptors (A₁Rs and A₂ARs). However, its ability to disrupt early sensory gating as indexed by prepulse inhibition (PPI), which is consistently disrupted by other psychostimulant agents, has never been convincingly demonstrated.

OBJECTIVES

To compare the impact of caffeine on PPI expression in C57BL/6 mice by two dose-response experiments differing in terms of chronicity, regimen, and route of administration. To study separately the acute effect of selective antagonists against A₁R or A₂AR.

METHODS

Caffeine (10, 30, 100 mg/kg, intraperitoneal (i.p.)) was either administered shortly before testing or via caffeinated drinking water (0.3, 1.0, 2 g/l) in home cages over 3 weeks. Two separate dose-response studies tested the acute effect of the selective A₁R antagonist, 1,3 dipropyl-8 cyclopentyl xanthine (DPCPX), and the selective A₂AR antagonist, 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c] (SCH 58261) (0.2, 1.0, 5.0 mg/kg, i.p.). The two drugs were combined in a final experiment to identify their potential synergistic interaction.

RESULTS

While the two lower acute doses of caffeine attenuated PPI, the highest dose potentiated PPI. By contrast, chronic caffeine exposure did not affect PPI. Neither DPCPX nor SCH 58261 altered PPI, and no synergism was observed when the two drugs were combined.

CONCLUSIONS

This is the first demonstration that acute caffeine disrupts PPI, but the relative contribution of A₁R and A₂AR blockade remains unclear, and possible non-adenosinergic mechanisms cannot be ruled out. The null effect under chronic caffeine exposure might involve the development of tolerance, but the precise receptor subtypes involved also warrant further investigation.

Examination of methylphenidate-mediated behavior regulation by glycogen synthase kinase-3 in mice

Abnormalities in dopaminergic activity have been implicated in psychiatric diseases, such as attention deficit hyperactivity disorder (ADHD), and are treated with therapeutic stimulants, commonly methylphenidate or amphetamine. Amphetamine administration increases glycogen synthase kinase-3 (GSK3) activation, which is necessary for certain acute behavioral responses to amphetamine, including increased locomotor activity and impaired sensorimotor gating. Here, we tested if modulating GSK3 by administration of the GSK3 inhibitor lithium or expression of constitutively active GSK3 altered behavioral responses to methylphenidate administered to mice acutely or daily for 8 days. Methylphenidate or amphetamine was administered to mice intraperitoneally for 1 or 8 days. Open-field activity and pre-pulse inhibition (PPI) were measured. In contrast to lithium's blockade of acute amphetamine-induced locomotor hyperactivity, lithium treatment did not significantly reduce methylphenidate-induced locomotor hyperactivity in wild-type mice after acute or 8 days of repeated methylphenidate administration. Lithium treatment significantly increased the impairment in PPI caused by methylphenidate, but significantly reduced the amphetamine-induced PPI deficit. In GSK3 knockin mice, expression of constitutively active GSK3β, but not GSK3α, significantly increased locomotor hyperactivity after acute methylphenidate treatment, and significantly impaired PPI, preventing further methylphenidate-induced impairment of PPI that was evident in wild-type mice and GSK3α knockin mice. Lithium does not counteract locomotor activity and PPI responses to methylphenidate as it does these responses to amphetamine, indicating that different mechanisms mediate these behavioral responses to methylphenidate and amphetamine. Only active GSK3β, not GSK3α, modulates behavioral responses to MPH, indicating selectivity in the actions of GSK3 isoforms.

The effect of thiamin tetrahydrofurfuryl disulfide on behavior of juvenile DBA/2J mice

Due to genetic defects or illness some individuals require higher amounts of thiamin than are typically provided by the diet. Lipid-soluble thiamin precursors can achieve high blood levels of thiamin and result in increased concentrations in the central nervous system. High intakes of thiamin have been reported as beneficial in children with autism and attention deficit/hyperactivity disorder. The current study examined the effect of thiamin tetrahydrofurfuryl disulfide (TTFD), a lipophilic precursor, on behavior in the juvenile male DBA/2J mouse. Mice given by oral gavage deionized water or deionized water providing 100 mg or 340 mg TTFD/kg body weight daily for 17 d, starting at postnatal day 18, were tested for effects on operant learning, social interaction, general activity level, and prepulse inhibition of acoustic startle, as well as effects on growth and select organ weights. Results indicate lower activity and altered social interaction at both treatment levels and decreased acoustic startle at the 100 mg/kg level. Compared to controls, percent weight gain was lower in the TTFD-treatment groups, but percent body length increase was not affected by TTFD treatment. TTFD treatment did not influence percent organ weights as percentage of body weights. TTFD treatment resulted in increased whole brain thiamin concentrations. These results support the concept that lipophilic thiamin precursors provided during early development can affect a number of behavioral parameters. In clinical trials with children with behavior disorders, attention should be given to preventing possible adverse gastrointestinal irritant effects associated with TTFD therapy.

Activation of dopamine neurons is critical for aversive conditioning and prevention of generalized anxiety

Generalized anxiety is thought to result, in part, from impairments in contingency awareness during conditioning to cues that predict aversive or fearful outcomes. Dopamine neurons of the ventral midbrain exhibit heterogeneous responses to aversive stimuli that are thought to provide a critical modulatory signal to facilitate orienting to environmental changes and assignment of motivational value to unexpected events. Here, we describe a mouse model in which activation of dopamine neurons in response to an aversive stimulus is attenuated by conditional genetic inactivation of functional N–methyl–D–aspartate–type glutamate receptors (NMDARs) on dopamine neurons. We discovered that altering the magnitude of excitatory responses by dopamine neurons in response to an aversive stimulus is associated with impaired conditioning to a cue that predicts an aversive outcome. Impaired conditioning by these mice is associated with development of a persistent, generalized anxiety–like phenotype. These data are consistent with a role for dopamine in facilitating contingency awareness that is critical for the prevention of generalized anxiety.