Alexander Campbell

Localization of ionotropic glutamate receptors in caudate‐putamen and nucleus accumbens septi of rat brain: Comparison of NMDA, AMPA, and kainate receptors

Changes in binding of selective radioligands at NMDA ([3H]MK‐801), AMPA ([3H]CNQX), and kainate ([3H]kainic acid) glutamate (GLU) ionotropic receptors in rat caudate‐putamen (CPu) and nucleus accumbens (NAc) were examined by quantitative autoradiography following: 1) unilateral surgical ablation of frontal cerebral cortex to remove descending corticostriatal GLU projections, 2) unilateral injection of kainic acid (KA) into CPu or NAc to degenerate local intrinsic neurons, or 3) unilateral injections of 6‐hydroxydopamine (6‐OH‐DA) into substantia nigra to degenerate ascending nigrostriatal dopamine (DA) projections. Cortical ablation significantly decreased NMDA receptor binding in ipsilateral medial CPu (20%), and NAc (16%), similar to previously reported losses of DA D4 receptors. KA lesions produced large losses of NMDA receptor labeling in CPu and NAc (both by 52%), AMPA (41% and 45%, respectively), and kainate receptors (40% and 45%, respectively) that were similar to the loss of D2 receptors in CPu and NAc after KA injections. Nigral 6‐OH‐DA lesions yielded smaller but significant losses in NMDA (17%), AMPA (12%), and kainate (11%) receptor binding in CPu. The results indicate that most NMDA, AMPA, and kainate receptors in rat CPu and NAc occur on intrinsic postsynaptic neurons. Also, some NMDA, but not AMPA or kainate, receptors are also found on corticostriatal projections in association with D4 receptors; these may, respectively, represent excitatory presynaptic NMDA autoreceptors and inhibitory D4 heteroceptors that regulate GLU release from corticostriatal axons in medial CPu and NAc. Conversely, the loss of all three GLU receptor subtypes after lesioning DA neurons supports their role as excitatory heteroceptors promoting DA release from nigrostriatal neurons. Synapse 30:227–235, 1998.

Developmental Differences in Acute Nigrostriatal and Mesocorticolimbic System Response to Haloperidol

Dose-dependent effects of haloperidol (2.66 nmol/kg to 79.8 mmol/kg, IP) on levels of dopamine, homovanillic and (HVA) and dihydroxyphenylacetic acid (DOPAC) were assessed in the corpus striatum, nucleus accumbens, and medial prefrontal cortex (PFCTX) of 18-, 30-, and 110-day-old rats. Eighteen-day-old rats were 35% and 63% more sensitive than adults to the effects of haloperidol on striatal and accumbens turnover and had steeper dose-response curves. The dose-response function in the PFCTX was similar to striatum at 18 days, but became shallower and nonsigmoidal with age. Maximally effective doses of haloperidol produced, at all ages, a comparable percent rise in DOPAC levels in all regions. With maturation, the percent rise in HVA progressively outstripped DOPAC response in nucleus accumbens and striatum. Overall, prominent developmental differences emerged in these regions in their sensitivity and response to haloperidol, which are consistent with previously reported differences in behavioral sensitivity.

Differences between antipsychotic drugs in persistence of brain levels and behavioral effects

After a single dose of the butyrophenone neuroleptic haloperidol, behavioral effects and detectable drug levels in rat brain can last for several weeks. To determine if such persistence is a general property of neuroleptics, we compared drug levels and effects after IP administration of two butyrophenones (haloperidol and bromperidol), a high potency (fluphenazine) and a low potency (chlorpromazine) phenothiazine. Drug levels in brain tissue were measured by high pressure liquid chromatography and behavioral effects monitored as inhibition of apomorphine-induced stereotypy. Estimated near terminal elimination half-lives (t1/2) from brain for acutely administered chlorpromazine (20 mg/kg) and fluphenazine (1 mg/kg) were 0.41 and 0.62 days, respectively, and neither drug was detectable after 4 days. Fluphenazine given daily for 5 days showed an only slightly slower elimination (t1/2=1.1 days). In contrast, near-terminal elimination half-lives from brain for haloperidol and bromperidol (both at 1 mg/kg, IP) were much longer (6.6 and 5.8 days, respectively), and each was detectable for 21 days after dosing. Inhibition of apomorphine-induced stereotypy correlated highly (r=0.95) with brain levels of haloperidol. For fluphenazine, given once or repeatedly, early inhibition was replaced within 1 week by supersensitivity to apomorphine which persisted for up to 3 weeks. These findings, indicating marked differences in clearance and recovery times after dosing with butyrophenones and phenothiazines, have clear implications for studies of the effects of neuroleptic drugs in rats. While there are limits to the extrapolation of these findings to other species, our results and those from studies in human subjects suggest similarly persistent drug levels and effects may be seen when patients are withdrawn from neuroleptic drugs.

Tolerance to behavioral effects of haloperidol.

Abstract Haloperidol was given daily (3 mg/kg, i.p.) for 5 months. Catalepsy and ptosis in response to a single dose of the neuroleptic were measured weekly. Total scores of both responses gradually decreased, indicating the development of tolerance, but with different time courses. Ptosis and catalepsy responses became half of their initial values by approximately 5 and 10 weeks, respectively. In contrast, the onset of these behavioral responses gradually became more rapid after each dose of haloperidol over the first 3 to 4 months.

Receptor mechanisms in increased sensitivity to serotonin agonists after dihydroxytryptamine shown by electronic monitoring of muscle twitches in the rat.

Muscle twitches and autonomic changes were induced by systemic injections of L-5-hydroxytryptophan (5-HTP) or the serotonin agonist 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) in rats previously lesioned with intracranial 5,7-dihydroxytryptamine (5,7-DHT) after desmethylimipramine. Movements were recorded sensitively and continuously by an electronic activity monitor. Spontaneous locomotor activity was strongly reduced after 5-HTP in both intact and lesioned rats, so that electronically recorded activity correlated very closely with disordered jerking movements scored by a behavioral rating scale. This myoclonus was dependent on the doses of 5-HTP and of 5,7-DHT and was strongly inhibited by serotonin antagonists. In lesioned rats, myoclonus occurred with unaltered activity of monoamine oxidase (MAO) and after only small increases in serotonin levels after 5-HTP, but even large increases in availability of serotonin in intact rats, or strong inhibition of serotonin uptake failed to induce myoclonus unless MAO was first inhibited. The response to 5-HTP in lesioned rats was attenuated by repeated injections of 5-HTP or 5-MeO-DMT. This decreased response was in turn blocked by repeated doses of a serotonin antagonist, but appeared not to be due to altered metabolism of 5-HTP or of serotonin; repeated pretreatment with cyproheptadine potentiated the myoclonic response to 5-HTP after DHT. Changes in postsynaptic receptors may be important in the behavioral supersentivity following 5,7-DHT, and restitution of serotonin or stimulation of its receptors after presynaptic denervation may suppress an evolving supersensitivity at receptive postsynaptic membranes.

Prolonged antidopaminergic actions of single doses of butyrophenones in the rat

Rats were treated once with doses of haloperidol or of droperidol below and above the acute ID50 vs the dopamine agonist apomorphine; they were later challenged with an acute dose of apomorphine (0.3mg/kg, SC) and rated for stereotyped behavioral responses. The two neuroleptics were similar in acute anti-apomorphine potency (ID50=0.12 and 0.18mg/kg for haloperidol and droperidol, respectively). The antidopaminergic effects of droperidol persisted for nearly 1 week and those of haloperidol lasted for 20–40 days, depending on the dose given. The computed half-time of disappearance of their antidopaminergic effects was 7.6±1.0 days and 0.59±0.17 days for haloperidol and droperidol, respectively, following a dose of 0.3 mg/kg, and these indices of duration of action did not vary significantly at doses between 0.1 and 1.0mg/kg. Haloperidol reduced the acute entry of 3H-apomorphine into brain by 21.5% 1 week later. Treatment with apomorphine alone just prior to haloperidol (both at 0.3 mg/kg) prevented the prolonged antidopaminergic effects of the neuroleptic evaluated 1 week later. These results indicate that some neuroleptics may have very prolonged activity or retention in tissue at sites of action, even after moderate, single doses. Caution is recommended in the interpretation of studies which assume “neuroleptic-free” conditions of subjects previously exposed to a neuroleptic agent.

Changes in cortical and subcortical levels of monoamines and their metabolites following unilateral ventrolateral cortical lesions in the rat

Suction lesions were made in the anterior, posterior or both halves of the right ventrolateral cortex in rats. Six days later, levels of the monoamine neurotransmitters, norepinephrine (NE), dopamine (DA) and serotonin (5-HT), and their metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in cortical and subcortical regions of lesioned rats and compared to values in sham-operated animals. NE and 5-HT were decreased in sections of ipsilateral (right) cortex including, and posterior to lesions, while 5-HIAA was increased throughout the ipsilateral cortex. Decreases in monoamines and increases in metabolites and metabolite:monoamine ratios (especially 5-HIAA:5-HT) were found in ipsilateral subcortical structures, including striatum, nucleus accumbens, hippocampus, hypothalamus, midbrain and brainstem, depending on the type of lesion. Subacutely, focal ventrolateral cortical lesions may profoundly alter the levels and utilization rates of monoamine neurotransmitters in widespread regions of the ipsilateral hemisphere.

Effects of maturation and aging on behavioral responses to haloperidol in the rat

Male Sprague-Dawley rats were evaluated between ages 18 and 825 days for responses to doses of haloperidol (0 and 0.05–10 mg/kg, IP). Catalepsy, ptosis, and inhibition of general motor activity showed steady decreases in sensitivity to the drug with age during the first 1.5 years of maturation, while rats older than 1.5 years had strikingly increased sensitivity to the activity-inhibiting and cataleptic effects of the drug. The efficacy of haloperidol on all tests in 110-day old rats was indistinguishable whether food was available continuously, or restricted to reduce body weight by 55%, indicating that the effects of maturation are due to aging and not to increasing body weight. The effects may be due to altered drug metabolism or altered sensitivity of the central nervous system to neuroleptic agents. Clinical impressions too, indicate that immature and elderly patients are more sensitive to these and other psychotropic drugs than are young adults.

Mapping of locomotor behavioral arousal induced by microinjections of dopamine within nucleus accumbens septi of rat forebrain

Dopamine (DA) at ca. ED50 (16 microg) or saline was stereotaxically microinjected unilaterally 2 h after pretreatment with an MAO inhibitor into left or right nucleus accumbens septi of 697 freely moving rats (1394 injections) to define subregions involved in DA-induced behavioral arousal throughout the anatomical extent of the accumbens. Locomotion was quantified electronically and behavioral responses were assigned to histologically verified injection sites; postural or stereotyped behaviors characteristic of DA injections in caudate-putamen did not occur. Screening with 60 injections across mid-accumbens (2.2-3.2 mm rostral to bregma) indicated that locomotion was elicited non-homogeneously, and was particularly intense dorsomedially. Sites yielding intense arousal and their inactive surround were mapped along the rostrocaudal axis (1.4-4.2 mm anterior to bregma) in coronal sections. Responses to DA showed lateral symmetry and were similar across rostrocaudal levels, with intense responses in dorsomedial accumbens along its border with the caudate-putamen. This functional localization does not coincide closely with reported distributions of DA or its receptors, nor with histologically or histochemically defined core-shell regions of this limbic structure. Nucleus accumbens in rat brain thus appears to be organized functionally into distinct subregions differing markedly in ability to produce locomotor hyperactivity in response to exogenous DA.

Tissue levels of haloperidol by radioreceptor assay and behavioral effects of haloperidol in the rat

Abstract A radioreceptor assay verified by independent biochemical methods was used to evaluate tissue levels of neuroleptic activity in serum and brain extracts after injections of haloperidol in the rat. The assay detected activity between doses of 0.1 and 10 mg/kg at times between 0.25 and 12 hrs. Tissue levels in blood and brain were highly correlated and corresponded well with a behavioral test of catalepsy at one hour after drug administration. This relationship between brain levels and behavior persisted but changed quantitatively over time.