Roger Raymond

Antidepressant-like effects of medial prefrontal cortex deep brain stimulation in rats.

BACKGROUND Subcallosal cingulate gyrus (SCG) deep brain stimulation (DBS) is being investigated as a treatment for major depression. We report on the effects of ventromedial prefrontal cortex (vmPFC) DBS in rats, focusing on possible mechanisms involved in an antidepressant-like response in the forced swim test (FST). METHODS The outcome of vmPFC stimulation alone or combined with different types of lesions, including serotonin (5-HT) or norepineprhine (NE) depletion, was characterized in the FST. We also explored the effects of DBS on novelty-suppressed feeding, learned helplessness, and sucrose consumption in animals predisposed to helplessness. RESULTS Stimulation at parameters approximating those used in clinical practice induced a significant antidepressant-like response in the FST. Ventromedial PFC lesions or local muscimol injections did not lead to a similar outcome. However, animals treated with vmPFC ibotenic acid lesions still responded to DBS, suggesting that the modulation of fiber near the electrodes could play a role in the antidepressant-like effects of stimulation. Also important was the integrity of the serotonergic system, as the effects of DBS in the FST were completely abolished in animals bearing 5-HT, but not NE, depleting lesions. In addition, vmPFC stimulation induced a sustained increase in hippocampal 5-HT levels. Preliminary work with other models showed that DBS was also able to influence specific aspects of depressive-like states in rodents, including anxiety and anhedonia, but not helplessness. CONCLUSIONS Our study suggests that vmPFC DBS in rats may be useful to investigate mechanisms involved in the antidepressant effects of SCG DBS.

In vivo quantification of regional dopamine-D3 receptor binding potential of (+)-PHNO: Studies in non-human primates and transgenic mice.

Examination of dopamine‐D3 (D3) receptors with positron emission tomography (PET) have been hampered in the past by the lack of a PET ligand with sufficient selectivity for D3 over dopamine‐D2 (D2) receptors. The two types co‐localize in the brain, with D2 density significantly higher than D3, hence nonselective PET ligands inform on D2, rather than D3 status. [11C]‐(+)‐PHNO is a novel PET ligand with a preferential affinity for D3 over D2. We used the selective D3 antagonist, SB‐277011 to dissect regional fractions of the [11C]‐(+)‐PHNO signal attributable to D3 and D2 in primate brain. The results were compared with quantitative autoradiography with 3H‐(+)‐PHNO in wild‐type, D2‐knock‐out, and D3‐knock‐out mice examined at baseline and following administration of SB‐277011. Both sets of results converged to indicate a predominant D3‐related component to (+)‐PHNO binding in extra‐striatal regions, with binding in the midbrain being entirely attributable to D3. The midbrain is thus an excellent target region to examine D3 receptor occupancy with [11C]‐(+)‐PHNO PET in vivo. Synapse 63:782–793, 2009.

The Antipsychotics Olanzapine, Risperidone, Clozapine, and Haloperidol Are D2-Selective Ex Vivo but Not In Vitro

In a recent human [11C]-(+)-PHNO positron emission tomography study, olanzapine, clozapine, and risperidone occupied D2 receptors in striatum (STR), but, despite their similar in vitro D2 and D3 affinities, failed to occupy D3 receptors in globus pallidus. This study had two aims: (1) to characterize the regional D2/D3 pharmacology of in vitro and ex vivo [3H]-(+)-PHNO binding sites in rat brain and (2) to compare, using [3H]-(+)-PHNO autoradiography, the ex vivo and in vitro pharmacology of olanzapine, clozapine, risperidone, and haloperidol. Using the D3-selective drug SB277011, we found that ex vivo and in vitro [3H]-(+)-PHNO binding in STR is exclusively due to D2, whereas that in cerebellar lobes 9 and 10 is exclusively due to D3. Surprisingly, the D3 contribution to [3H]-(+)-PHNO binding in the islands of Calleja, ventral pallidum, substantia nigra, and nucleus accumbens was greater ex vivo than in vitro. Ex vivo, systemically administered olanzapine, risperidone, and haloperidol, at doses occupying ∼80% D2, did not occupy D3 receptors. Clozapine, which also occupied ∼80% of D2 receptors ex vivo, occupied a smaller percentage of D3 receptors than predicted by its in vitro pharmacology. Across brain regions, ex vivo occupancy by antipsychotics was inversely related to the D3 contribution to [3H]-(+)-PHNO binding. In contrast, in vitro occupancy was similar across brain regions, independent of the regional D3 contribution. These data indicate that at clinically relevant doses, olanzapine, clozapine, risperidone, and haloperidol are D2-selective ex vivo. This unforeseen finding suggests that their clinical effects cannot be attributed to D3 receptor blockade.

Long-term changes in regional brain cytochrome oxidase activity induced by electroconvulsive treatment in rats.

Quantitative cytochrome oxidase (CO) histochemistry was used to examine brain regional metabolic effects of electroconvulsive shock-induced seizures (ECS). Rats receive a course of either eight ECS or control treatments and were sacrificed either 24 h or 28 days after the last session. Regional CO activity (mumol/gT/min) was quantitated throughout the brain using internally calibrated standards. Twenty-four hours after the last ECS session there was no significant difference between ECS- and sham-treated brains in any of the 99 brain regions examined. In contrast, 28 days after the last session, ECS brains showed significant increases in CO activity in the interpeduncular nucleus (+20%), bed nucleus of the stria terminalis (+25%), dorsomedial hypothalamus (+20%), ventromedial hypothalamus (+12%), mammillary nucleus (+14%), pontine nucleus (+16%), basolateral amygdala (+14%), medial amygdala (+12%), piriform cortex (+12%) and ventromedial thalamus (+9%). These results suggest that ECS induces localized increases in brain CO activity which are long-lasting and may develop independently of additional stimulation. The fact that CO changes were predominantly in limbic areas suggests that they may be relevant to the antidepressant effects of ECS.

SLEEP DEPRIVATION DOES NOT AFFECT INDICES OF NECROSIS OR APOPTOSIS IN RAT BRAIN

Recent indications of oxidative stress in hypothalamus of sleep deprived rats prompted us to address the possibility that sleep deprivation may induce pathological cell loss changes in brain. Indices of necrosis and apoptosis were quantified after 96 h of sleep deprivation induced by the classical platform technique in rats. Binding of the peripheral-type benzodiazepine ligand [³H]PK 11195 to reactive astrocytes, a reliable and sensitive index of necrotic changes, was not altered in any of 14 brain regions examined. Likewise, no changes were found in mRNA levels of the apoptosis-related genes bcl-2 and bax in any of 24 brain regions examined. This was corroborated by quantitative TUNEL analyses in hypothalamus, amygdala, and cortex, which also revealed no effects in sleep deprived animals. These results are consistent with other recent evidence that sleep deprivation does not induce necrotic or apoptotic cell loss in brain. This suggests that recent findings of oxidative stress in sleep deprived brains do not result in cell loss. The possibility that sleep deprivation may result in functional deficits, or that structural changes may emerge after repeated episodes of sleep deprivation, remains to be addressed.

Acute stress increases thyroid hormone levels in rat brain

BACKGROUND In experimental animals, exposure to uncontrollable stress induces a number of behavioral and biochemical changes that resemble symptoms seen in human depression and other psychiatric conditions. The present study used a yoked design to examine the effects of uncontrollable footshock stress on brain thyroid hormones in male and female rats. METHODS Animals in one group received 15 trials where footshock could be terminated by pressing a lever (escapable shock). Rats in a second group received the same amount of shock, but had no control over shock termination (inescapable shock). Control rats received no shock. RESULTS No significant differences were found among the three groups, for either males or females, in whole brain levels of thyroxine (T4) 3 hours after the footshock session. In contrast, significant group differences in brain levels of triiodothyronine (T3) were found for both males and females. In males, brain T3 was elevated by 21% in the inescapable shock group when compared to controls (p < .012). In females, brain T3 increased by 19% in the escapable shock group when compared to controls (p < .026). Plasma levels of both T3 and T4 were at control levels for all groups. CONCLUSIONS These results provide the first demonstration that brain T3 levels change rapidly in response to acute stress. The data further suggest that the effects of stress controllability on brain T3 levels may be different for males and females.

Tyrosine hydroxylase immunoreactivity and [3H]WIN 35,428 binding to the dopamine transporter in a hamster model of idiopathic paroxysmal dystonia

Recent pharmacological studies and receptor analyses have suggested that dopamine neurotransmission is enhanced in mutant dystonic hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia which displays attacks of generalized dystonia in response to mild stress. In order to further characterize the nature of dopamine alterations, the present study investigated possible changes in the number of dopaminergic neurons, as defined by tyrosine hydroxylase immunohistochemistry, as well as binding to the dopamine transporter labelled with [3H]WIN 35,428 in dystonic hamsters. No differences in the number of tyrosine hydroxylase-immunoreactive neurons were found within the substantia nigra and ventral tegmental area of mutant hamsters compared to non-dystonic control hamsters. Similarly, under basal conditions, i.e. in the absence of a dystonic episode, no significant changes in [3H]WIN 35,428 binding were detected in dystonic brains. However, in animals killed during the expression of severe dystonia, significant decreases in dopamine transporter binding became evident in the nucleus accumbens and ventral tegmental area in comparison to controls exposed to the same external stimulation. Since stimulation tended to increase [3H]WIN 35,428 binding in control brains, the observed decrease in the ventral tegmental area appeared to be due primarily to the fact that binding was increased less in dystonic brains than in similarly stimulated control animals. This finding could reflect a diminished ability of the dopamine transporter to undergo adaptive changes in response to external stressful stimulation in mutant hamsters. The selective dopamine uptake inhibitor GBR 12909 (20 mg/kg) aggravated dystonia in mutant hamsters, further suggesting that acute alterations in dopamine transporter function during stimulation may be an important component of dystonia in this model.

Immediate increase in benzodiazepine binding in rat brain after a single brief experience in the plus maze: a paradoxical effect

A single drug-free experience in the elevated plus-maze is well documented to reduce the behavioral effects of benzodiazepines (BZs) in subsequent tests. To ascertain the possible role of altered BZ receptor binding to in this phenomenon, rats received a 5-min exposure to the elevated plus maze and were immediately sacrificed. Receptor autoradiography revealed that [3H]flunitrazepam binding was significantly elevated in several amygdaloid and hippocampal nuclei (range: 13-23%); [3H]muscimol binding in adjacent sections was not significantly altered. These results suggest that BZ receptors can change very rapidly in response to anxiogenic conditions. However, the unexpected finding that [3H]flunitrazepam binding is increased by maze exposure suggests that the subsequent loss of BZ anxiolytic effects in the plus-maze is probably unrelated to alterations in BZ binding in brain.

Development and characterization of a promising fluorine-18 labelled radiopharmaceutical for in vivo imaging of fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH), the enzyme responsible for terminating signaling by the endocannabinoid anandamide, plays an important role in the endocannabinoid system, and FAAH inhibitors are attractive drugs for pain, addiction, and neurological disorders. The synthesis, radiosynthesis, and evaluation, in vitro and ex vivo in rat, of an (18)F-radiotracer designed to image FAAH using positron emission tomography (PET) is described. Fluorine-18 labelled 3-(4,5-dihydrooxazol-2-yl)phenyl (5-fluoropentyl)carbamate, [(18)F]5, was synthesized at high specific activity in a one-pot three step reaction using a commercial module with a radiochemical yield of 17-22% (from [(18)F]fluoride). In vitro assay using rat brain homogenates showed that 5 inhibited FAAH in a time-dependent manner, with an IC50 value of 0.82nM after a preincubation of 60min. Ex vivo biodistribution studies and ex vivo autoradiography in rat brain demonstrated that [(18)F]5 had high brain penetration with standard uptake values of up to 4.6 and had a regional distribution which correlated with reported regional FAAH enzyme activity. Specificity of binding to FAAH with [(18)F]5 was high (>90%) as demonstrated by pharmacological challenges with potent and selective FAAH inhibitors and was irreversible as demonstrated by radioactivity measurements on homogenized brain tissue extracts. We infer from these results that [(18)F]5 is a highly promising candidate radiotracer with which to image FAAH in human subjects using PET and clinical studies are proceeding.

Changes in AMPA Receptor Binding in an Animal Model of Inborn Paroxysmal Dystonia

Previous pharmacological studies suggested that glutamatergic overactivity contributes to manifestation of dystonic attacks in mutant hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia in which episodes of dystonia occur in response to stress. In the present study, [(3)H]AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate) receptor binding was determined by autoradiographic analyses in 41 brain (sub)regions of dt(sz) hamsters under basal conditions, i.e., in the absence of dystonia, and in a group of mutant hamsters that exhibited severe stress-induced dystonic attacks immediately prior to sacrifice. In comparison to nondystonic control hamsters the basal [(3)H]AMPA binding was significantly higher in the ventromedial and ventrolateral caudate putamen, the anterior cingulate cortex, the hippocampus, and the lateral septum of dystonic brains. During dystonic attacks the [(3)H]AMPA binding was significantly lower in the dorsomedial, dorsolateral, and posterior caudate putamen; the ventromedial thalamus; and the frontal cortex of mutant hamsters compared with control animals that were exposed to the same external stimulation. The basal increase in AMPA receptor density within limbic structures may contribute to the susceptibility of stress-inducible dystonic episodes in mutant hamsters. Since AMPA receptor activation is known to cause a fast reduction of the affinity and an internalization of postsynaptic AMPA receptors, the latter finding could reflect a glutamatergic overactivity within the striato-thalamo-cortical circuit during the expression of dystonia, which is in line with previous neurochemical and pharmacological data in dt(sz) hamsters.