ß1-adrenoceptor expression on GABAergic interneurons in primate dorsolateral prefrontal cortex: potential role in stress-induced cognitive dysfunction.

Uncontrollable stress exposure impairs working memory and reduces the firing of dorsolateral prefrontal cortex (dlPFC) "Delay cells", involving high levels of norepinephrine and dopamine release. Previous work has focused on catecholamine actions on dlPFC pyramidal cells, but inhibitory interneurons may contribute as well. The current study combined immunohistochemistry and multi-scale microscopy with iontophoretic physiology and behavioral analyses to examine the effects of beta1-noradrenergic receptors (ß1-ARs) on inhibitory neurons in layer III dlPFC. We found ß1-AR robustly expressed on different classes of inhibitory neurons labeled by the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV). Immunoelectron microscopy confirmed ß1-AR expression on the plasma membrane of PV-expressing dendrites. PV interneurons can be identified as fast-spiking (FS) in physiological recordings, and thus were studied in macaques performing a working memory task. Iontophoresis of a ß1-AR agonist had a mixed effect, increasing the firing of a subset and decreasing the firing of others, likely reflecting loss of firing of the entire microcircuit. This loss of overall firing likely contributes to impaired working memory during stress, as pretreatment with the selective ß1-AR antagonist, nebivolol, prevented stress-induced working memory deficits. Thus, selective ß1-AR antagonists may be helpful in treating stress-related disorders.

mGluR2/3 mechanisms in primate dorsolateral prefrontal cortex: evidence for both presynaptic and postsynaptic actions.

Cognitive deficits in psychiatric and age-related disorders generally involve dysfunction of the dorsolateral prefrontal cortex (dlPFC), but there are few treatments for these debilitating symptoms. Group II metabotropic glutamate receptors (mGluR2/3), which couple to Gi/Go, have been a focus of therapeutics based on rodent research, where mGluR2/3 have been shown to reduce axonal glutamate release and increase glial glutamate uptake. However, this strategy has had mixed results in patients, and understanding mGluR2/3 mechanisms in primates will help guide therapeutic interventions. The current study examined mGluR2/3 localization and actions in the primate dlPFC layer III circuits underlying working memory, where the persistent firing of 'Delay cells' is mediated by N-methyl-d-aspartate receptors and weakened by cAMP-PKA-potassium channel signaling in dendritic spines. Immunoelectron microscopy identified postsynaptic mGluR2/3 in the spines, in addition to the traditional presynaptic and astrocytic locations. In vivo iontophoretic application of the mGluR2/3 agonists (2R, 4R)-APDC or LY379268 onto dlPFC Delay cells produced an inverted-U effect on working memory representation, with enhanced neuronal firing following low doses of mGluR2/3 agonists. The enhancing effects were reversed by an mGluR2/3 antagonist or by activating cAMP signaling, consistent with mGluR2/3 inhibiting postsynaptic cAMP signaling in spines. Systemic administration of these agonists to monkeys performing a working memory task also produced an inverted-U dose-response, where low doses improved performance but higher doses, similar to clinical trials, had mixed effects. Our data suggest that low doses of mGluR2/3 stimulation may have therapeutic effects through unexpected postsynaptic actions in dlPFC, strengthening synaptic connections and improving cognitive function.

Role of disrupted in schizophrenia 1 (DISC1) in stress-induced prefrontal cognitive dysfunction.

Recent genetic studies have linked mental illness to alterations in disrupted in schizophrenia 1 (DISC1), a multifunctional scaffolding protein that regulates cyclic adenosine monophosphate (cAMP) signaling via interactions with phosphodiesterase 4 (PDE4). High levels of cAMP during stress exposure impair function of the prefrontal cortex (PFC), a region gravely afflicted in mental illness. As stress can aggravate mental illness, genetic insults to DISC1 may worsen symptoms by increasing cAMP levels. The current study examined whether viral knockdown (KD) of the Disc1 gene in rat PFC increases susceptibility to stress-induced PFC dysfunction. Rats were trained in a spatial working memory task before receiving infusions of (a) an active viral construct that knocked down Disc1 in PFC (DISC1 KD group), (b) a 'scrambled' construct that had no effect on Disc1 (Scrambled group), or (c) an active construct that reduced DISC1 expression dorsal to PFC (Anatomical Control group). Data were compared with an unoperated Control group. Cognitive performance was assessed following mild restraint stress that had no effect on normal animals. DISC1 KD rats were impaired by 1 h restraint stress, whereas Scrambled, Control, and Anatomical Control groups were unaffected. Thus, knocking down Disc1 in PFC reduced the threshold for stress-induced cognitive dysfunction, possibly through disinhibited cAMP signaling at neuronal network synapses. These findings may explain why patients with DISC1 mutations may be especially vulnerable to the effects of stress.

The neuropsychopharmacology of fronto-executive function: monoaminergic modulation.

We review the modulatory effects of the catecholamine neurotransmitters noradrenaline and dopamine on prefrontal cortical function. The effects of pharmacologic manipulations of these systems, sometimes in comparison with the indoleamine serotonin (5-HT), on performance on a variety of tasks that tap working memory, attentional-set formation and shifting, reversal learning, and response inhibition are compared in rodents, nonhuman primates, and humans using, in a behavioral context, several techniques ranging from microiontophoresis and single-cell electrophysiological recording to pharmacologic functional magnetic resonance imaging. Dissociable effects of drugs and neurotoxins affecting these monoamine systems suggest new ways of conceptualizing state-dependent fronto-executive functions, with implications for understanding the molecular genetic basis of mental illness and its treatment.

Ameliorating prefrontal cortical dysfunction in mental illness: inhibition of phosphotidyl inositol-protein kinase C signaling.

BACKGROUND: Bipolar disorder and schizophrenia are associated with profound dysfunction of the prefrontal cortex (PFC), with bipolar disorder most associated with changes in ventromedial PFC and schizophrenia more associated with changes in dorsolateral PFC. DISCUSSION: Recent genetic and biochemical studies have also linked these illnesses to disinhibition of phosphotidyl inositol-protein kinase C signaling. For example, DAG kinase eta, an enzyme that metabolizes DAG and thus reduces protein kinase C activity, is the gene most altered in bipolar disorder. Similarly, regulator of G protein signaling 4 is the molecule most altered in the PFC of patients with schizophrenia, and this molecule normally serves to inhibit Gq signaling. Animal studies have shown that high levels of phosphotidyl inositol-protein kinase C signaling in the PFC markedly impair PFC function at the behavioral and cellular levels. Most importantly, many effective medications for bipolar disorder and schizophrenia inhibit phosphotidyl inositol-protein kinase C signaling, either through intracellular actions (lithium, valproate) or through extracellular blockade of receptors coupled to this pathway (5HT2 receptors and alpha-1 adrenoceptors). Recent data suggest that lithium and valproate can protect gray matter in patients with bipolar disorder. These findings encourage the development of protein kinase C inhibitors for the treatment of mental illness.

Estrogen prevents norepinephrine alpha-2a receptor reversal of stress-induced working memory impairment.

Understanding effects of estrogen on the medial prefrontal cortex (PFC) may help to elucidate the increased prevalence of depression and post-traumatic stress disorder in women of ovarian cycling age. Estrogen replacement in ovariectomized (OVX) young rats amplifies the detrimental effects of stress on working memory (a PFC-mediated task), but the mechanisms by which this occurs have yet to be identified. In male rats, stimulation of norepinephrine alpha-2 adrenoceptors protects working memory from stress-induced impairments. However, this effect has not been studied in females, and has not been examined for sensitivity to estrogen. The current study asked whether OVX females with estrogen replacement (OVX+Est) and without replacement (OVX+Veh) responded differently to stimulation of alpha-2 adrenoceptors after administration of the benzodiazepine inverse agonist FG7142, a pharmacological stressor. The alpha-2 agonist, guanfacine, protected working memory from the impairing effects of FG7142 in OVX+Veh, but not in OVX+Est rats. Western Blot analysis for alpha-2 receptors was performed on PFC tissue from each group, but no changes in expression were found, indicating that the behavioral effects observed were likely not due to changes in receptor expression. These findings point to possible mechanisms by which estrogen may enhance the stress response, and hold implications for the gender discrepancy in the prevalence of stress-related mental illness.

Protein kinase C overactivity impairs prefrontal cortical regulation of working memory.

The prefrontal cortex is a higher brain region that regulates thought, behavior, and emotion using representational knowledge, operations often referred to as working memory. We tested the influence of protein kinase C (PKC) intracellular signaling on prefrontal cortical cognitive function and showed that high levels of PKC activity in prefrontal cortex, as seen for example during stress exposure, markedly impair behavioral and electrophysiological measures of working memory. These data suggest that excessive PKC activation can disrupt prefrontal cortical regulation of behavior and thought, possibly contributing to signs of prefrontal cortical dysfunction such as distractibility, impaired judgment, impulsivity, and thought disorder.

Estrogen mediates sex differences in stress-induced prefrontal cortex dysfunction.

Many anxiety disorders, as well as major depressive disorder (MDD), are at least twice as prevalent in women as in men, but the neurobiological basis of this discrepancy has not been well studied. MDD is often precipitated by exposure to uncontrollable stress, and is frequently characterized by abnormal or disrupted prefrontal cortex (PFC) function. In animals, exposure to stress has been shown to cause PFC dysfunction, but sex differences in this effect have not been investigated. The present study tested male and female rats on a PFC-dependent working memory task after administration of FG7142, a benzodiazepine inverse agonist that activates stress systems in the brain. Female rats were impaired by lower doses than males during proestrus (high estrogen), but not during estrus (low estrogen). Similarly, ovariectomized females showed increased stress sensitivity only after estrogen replacement. These results suggest that estrogen amplifies the stress response in PFC, which may increase susceptibility to stress-related disorders.

A placebo-controlled study of guanfacine in the treatment of children with tic disorders and attention deficit hyperactivity disorder.

OBJECTIVE: This study evaluated the efficacy and safety of guanfacine in treating children with tic disorders and attention deficit hyperactivity disorder (ADHD). METHOD: Subjects from a specialty tic disorders clinic were randomly assigned to receive 8 weeks of treatment with guanfacine or placebo under double-blind conditions. Follow-up visits occurred every 2 weeks for safety monitoring and dose adjustment. RESULTS: Thirty-four medication-free subjects (31 boys and three girls with a mean age of 10.4 years) with ADHD, combined type, and a tic disorder participated. After 8 weeks of treatment, guanfacine was associated with a mean improvement of 37% in the total score on the teacher-rated ADHD Rating Scale, compared to 8% improvement for placebo. Nine of 17 subjects who received guanfacine were blindly rated on the Clinical Global Improvement scale as either much improved or very much improved, compared with none of 17 subjects who received placebo. The mean score on the parent-rated hyperactivity index improved by 27% in the guanfacine group and 21% in the placebo group, not a significant difference. On the Continuous Performance Test, commission errors decreased by 22% and omission errors by 17% in the guanfacine group, compared with increases of 29% in commission errors and of 31% in omission errors in the placebo group. Tic severity decreased by 31% in the guanfacine group, compared to 0% in the placebo group. One guanfacine subject with sedation withdrew at week 4. Guanfacine was associated with insignificant decreases in blood pressure and pulse. CONCLUSIONS: Guanfacine appears to be a safe and effective treatment for children with tic disorders and ADHD.

Use of guanfacine to control self-injurious behavior in two rhesus macaques (Macaca mulatta) and one baboon (Papio anubis).

BACKGROUND AND PURPOSE: Self-injurious behavior (SIB) affects 0.8 to 10% of individually housed non-human primates, and is a substantial threat to their health and well being. The potential for SIB to involve multiple neurotransmitters and the complex variations in response to external stressors complicate case management. Modulation of the adrenergic system by use of guanfacine, an alpha2A-adrenergic receptor agonist, was assessed as a novel therapeutic strategy for SIB. METHODS: The efficacy of guanfacine against SIB was evaluated in 11 self-biting episodes among two rhesus macaques (Macaca mulatta) and one baboon (Papio cynocephalus anubis). Affected animals were given guanfacine IM or PO at 0.5 mg/kg of body weight twice daily (rhesus) or 0.3 mg/kg (baboon) for 5 to 10 days, followed by gradual reduction of the dose to 0.25 mg/kg (rhesus) or 0.15 mg/kg (baboon) once daily over an average of 33 days. RESULTS: The 0.5 mg/kg twice daily regimen of guanfacine halted all self-biting, whereas reducing the dose to 0.25 mg/kg given twice daily or 0.5 mg/kg given once daily resulted in reversion to self-biting in four of the 11 episodes. Recurrence was controlled by returning to twice daily 0.5 mg/kg dosing for one aggressive episode, and resolved in the three milder episodes without dose or frequency being increased. Self-biting after discontinuation of therapy recurred six times over five years in case 1, three times over 1.5 years in case 2, and three times over one year in case 3. Clinical assessment suggested that guanfacine therapy decreased agitation without overt side effects associated with alpha2-agonists, such as profound sedation. CONCLUSION: The mechanism for guanfacine inhibition of self-biting is unclear, but could result from strengthening of prefrontal cortex inhibitory functions. Guanfacine therapy provides an effective psychological stabilizing tool that alleviates self-biting, and provides time to assess and address external stressors and triggers.

The selective dopamine D4 receptor antagonist, PNU-101387G, prevents stress-induced cognitive deficits in monkeys.

Stress exposure impairs the cognitive functioning of the prefrontal cortex (PFC). Previous research has examined the dopamine (DA) D1 receptor mechanisms underlying this response. The current study performed a preliminary examination of the role of D4 receptor mechanisms by determining whether the selective D4 receptor antagonist, PNU-101387G, could prevent stress-induced working memory deficits in monkeys. Animals were tested on the delayed response task following treatment with PNU-101387G (0 or 0.1-0.8 mg/kg, 60-min pretreatment), and the pharmacological stressor, FG7142 (0 or 0.2 mg/kg, 30-min pretreatment). FG7142 significantly impaired delayed response performance relative to vehicle; PNU-101387G pretreatment produced a dose-related reversal of the FG7142 response. PNU-101387G had no significant effects on its own, but there were trends toward improvement at low doses and impairment at higher doses. Further studies in a larger number of animals appear warranted. These preliminary findings suggest that D4 receptor mechanisms contribute to stress-induced cognitive dysfunction.

The alpha-2A-adrenoceptor agonist, guanfacine, increases regional cerebral blood flow in dorsolateral prefrontal cortex of monkeys performing a spatial working memory task.

Research indicates that norepinephrine enhances the working memory functions of the prefrontal cortex (PFC) through actions at post-synaptic, alpha-2A adrenoceptors. The current study examined the effects of the alpha-2A adrenoreceptor agonist, guanfacine (0.7 mg/kg, i.m.), compared to saline on SPECT measures of regional cerebral blood flow (rCBF) in monkeys performing a spatial working memory task. Animals were infused with the SPECT blood flow tracer, Tcm-99m ECD, through an indwelling intravenous catheter while performing the working memory task. Guanfacine treatment significantly improved cognitive performance of the working memory task, and significantly increased rCBF values in the dorsolateral PFC, the brain region most tightly associated with performance of spatial working memory tasks. In contrast, guanfacine had no significant effect on rCBF in the superior temporal cortex, an auditory association area unrelated to task performance. These data are consistent with the hypothesis that alpha-2A adrenoceptor stimulation preferentially enhances functioning of the PFC.

Noradrenergic alpha-2 receptor agonists reverse working memory deficits induced by the anxiogenic drug, FG7142, in rats.

Performance on working memory tasks, a measure of prefrontal cortical function, is impaired by exposure to mild stress as well as the anxiogenic drug, FG7142. Previous studies have shown that like stress, FG7142 increases catecholamine release in the prefrontal cortex (PFC) and that high levels of dopamine (DA) D(1) and norepinephrine (NE) alpha-1 receptor stimulation underlie the FG7142-induced cognitive impairment. Both the FG7142-induced DA turnover and working memory deficit can be blocked by pretreatment with the nonselective NE alpha-2/imidazoline I1 receptor agonist, clonidine. The present study examined the alpha-2 adrenoceptor subtype underlying this reversal in FG7142-induced working memory deficits by comparing the efficacy of clonidine with the more selective alpha-2A adrenoceptor agonist, guanfacine. The anxiogenic drug, FG7142 (0, 10, 20, or 30 mg/kg), dose-dependently impaired delayed alternation performance. Clonidine pretreatment (0.1 mg/kg, 30 min prior to FG7142) partially reversed the FG7142-induced impairment while guanfacine pretreatment (0.11 mg/kg) completely blocked the FG7142-induced impairment. Neither clonidine nor guanfacine had any effect on performance when administered alone. This study suggests that stimulation of the NE alpha-2A receptor subtype is sufficient to ameliorate the cognitive deficit induced by FG7142. Clonidine's sedative and hypotensive side effects limit its therapeutic usefulness; however, selective alpha-2A receptor agonists may be effective in treating prefrontal cognitive deficits in stress-related neuropsychiatric disorders with fewer side effects.

Local infusion of an alpha-1 adrenergic agonist into the prefrontal cortex impairs spatial working memory performance in monkeys.

BACKGROUND: Stimulation of alpha-2 adrenoceptors in the monkey or rat prefrontal cortex (PFC) has been known to improve spatial working memory (SWM) and stimulation of alpha-1 adrenoceptors in the rat PFC has been reported to impair SWM. The present study attempted to replicate in monkey the rat experiments on alpha-1 adrenoceptor stimulation. METHODS: The alpha-1 adrenergic agonist phenylephrine or the alpha-2 adrenergic agonist guanfacine was infused into the dorsolateral prefrontal cortex (dlPFC) of monkeys performing the delayed-response (DR) task, a task of SWM, to see how the drugs affect SWM performance. RESULTS: Phenylephrine infusion in dlPFC significantly impaired DR performance, whereas guanfacine improved performance. The effects of both drugs were delay-dependent. Infusions outside dlPFC were ineffective. CONCLUSIONS: Stimulation of prefrontal cortical alpha-1 adrenoceptors impairs SWM function in monkeys, consistent with the parallel study in rats, whereas stimulation of alpha-2 adrenoceptors improves SWM, indicating that alpha-1 and alpha-2 adrenoceptors may have opposing roles in the PFC.

A role for norepinephrine in stress-induced cognitive deficits: alpha-1-adrenoceptor mediation in the prefrontal cortex.

BACKGROUND: Stress exacerbates many neuropsychiatric disorders associated with prefrontal cortical (PFC) dysfunction. Stress also impairs the working memory functions of the PFC. Although stress research has focused on dopaminergic mechanisms, stress also increases norepinephrine (NE) release in PFC, and intra-PFC infusions of NE alpha-1-adrenoceptor agonists impair working memory. The current study examined whether NE alpha-1-adrenoceptor actions in PFC contribute to stress-induced deficits in working memory performance. METHODS: Rats were treated with a pharmacological stressor, FG7142 (30 mg/kg) or vehicle 30 min before testing on a test of spatial working memory, delayed alternation. The alpha-1-adrenoceptor antagonist, urapidil (0.1 microgram/0.5 microL), or saline vehicle, was infused into the PFC 15 min before delayed alternation testing. RESULTS: As observed previously, FG7142 significantly impaired the accuracy of delayed alternation performance, and induced a perseverative pattern of responding consistent with PFC dysfunction. FG7142 also slowed motor response times. Infusion of urapidil into the PFC completely reversed the FG7142-induced impairment in delayed alternation performance, but did not alter the slowed motor responding. CONCLUSIONS: These findings indicate that alpha-1-adrenoceptor stimulation in the PFC contributes to stress-induced impairments in PFC cognitive functions. These neurochemical actions may contribute to symptoms of working memory impairment, poor attention regulation, or disinhibited behaviors in neuropsychiatric disorders sensitive to stress exposure.