Kevin C.F. Fone

Behavioural and neurochemical effects of post-weaning social isolation in rodents—Relevance to developmental neuropsychiatric disorders

Exposing mammals to early-life adverse events, including maternal separation or social isolation, profoundly affects brain development and adult behaviour and may contribute to the occurrence of psychiatric disorders, such as depression and schizophrenia in genetically predisposed humans. The molecular mechanisms underlying these environmentally induced developmental adaptations are unclear and best evaluated in animal paradigms with translational salience. Rearing rat pups from weaning in isolation, to prevent social contact with conspecifics, produces reproducible, long-term changes including; neophobia, impaired sensorimotor gating, aggression, cognitive rigidity, reduced prefrontal cortical volume and decreased cortical and hippocampal synaptic plasticity. These alterations are associated with hyperfunction of mesolimbic dopaminergic systems, enhanced presynaptic dopamine (DA) and serotonergic (5-HT) function in the nucleus accumbens (NAcc), hypofunction of mesocortical DA and attenuated 5-HT function in the prefrontal cortex and hippocampus. These behavioural, morphological and neurochemical abnormalities, as reviewed herein, strongly resemble core features of schizophrenia. Therefore unravelling the mechanisms that trigger these sequelae will improve our knowledge of the aetiology of neurodevelopmental psychiatric disorders, enable identification of longitudinal biomarkers of dysfunction and permit predictive screening for novel compounds with potential antipsychotic efficacy.

Immunohistochemical localisation of the 5-HT2C receptor protein in the rat CNS

5-HT2C receptor mRNA has a widespread distribution in the human and rat CNS but the absence of a specific high affinity ligand has made autoradiographic localisation of the receptor difficult. By raising polyclonal antibodies against the rat 5-HT2C receptor protein this study reports the immunohistochemical distribution of this receptor in the rat CNS. A sephadex purified 5-HT2C antiserum visualised a single immunopositive band (54 kDa) in Western blots of membranes prepared from several rat brain regions and caused intense membrane immunofluorescence in HEK 293 cells transfected with h5-HT2C cDNA, which were both attenuated by incubation with the antigenic peptide sequence (200-300 microM). 5-HT2C-like immunoreactivity was located on neurones throughout the CNS. The most abundant 5-HT2C-like immunoreactive cell bodies were in the anterior olfactory nucleus, medial and intercalated amygdaloid nuclei, hippocampus layers CA1 to CA3, laterodorsal and lateral geniculate thalamic nuclei, caudate-putamen and several areas of the cortex (including piriform and frontal), consistent with this receptor being located postsynaptic to serotonergic neurones. Immunopositive neurones were also found in the dorsal raphé, suggesting that 5-HT2C receptors may be on some serotonergic neurones. The overall distribution of 5-HT2C-like immunoreactivity complements previous findings with conventional radioligands and agrees well with reported levels of 5-HT2C receptor mRNA.

5-ht6 receptors.

The 5-hydroxytryptamine(6) (5-ht(6)) was one of the most recent additions to the 5-HT receptor family, selective antagonists have recently been developed and potential functional roles are now becoming apparent. The high affinity of a wide range of psychiatric drugs for the 5-ht(6)receptor, together with its almost exclusive expression in the CNS, being abundant in limbic and cortical regions, has stimulated significant research interest. The 5-ht(6)receptor appears to regulate glutamatergic and cholinergic neuronal activity, and increasing evidence suggests that it may be involved in the regulation of cognition, feeding and, possibly, affective state and seizures. The current article will review all aspects of the discovery, genetics, distribution, pharmacology and function of the 5-ht(6)receptor. Taken together, this wealth of information warrants the use of the upper case nomenclature for the 5-ht(6) receptor to be approved and its true status recognised.

Depletion of 26S Proteasomes in Mouse Brain Neurons Causes Neurodegeneration and Lewy-Like Inclusions Resembling Human Pale Bodies

Ubiquitin-positive intraneuronal inclusions are a consistent feature of the major human neurodegenerative diseases, suggesting that dysfunction of the ubiquitin proteasome system is central to disease etiology. Research using inhibitors of the 20S proteasome to model Parkinsons disease is controversial. We report for the first time that specifically 26S proteasomal dysfunction is sufficient to trigger neurodegenerative disease. Here, we describe novel conditional genetic mouse models using the Cre/loxP system to spatially restrict inactivation of Psmc1 (Rpt2/S4) to neurons of either the substantia nigra or forebrain (e.g., cortex, hippocampus, and striatum). PSMC1 is an essential subunit of the 26S proteasome and Psmc1 conditional knock-out mice display 26S proteasome depletion in targeted neurons, in which the 20S proteasome is not affected. Impairment of specifically ubiquitin-mediated protein degradation caused intraneuronal Lewy-like inclusions and extensive neurodegeneration in the nigrostriatal pathway and forebrain regions. Ubiquitin and α-synuclein neuropathology was evident, similar to human Lewy bodies, but interestingly, inclusion bodies contained mitochondria. We support this observation by demonstrating mitochondria in an early form of Lewy body (pale body) from Parkinsons disease patients. The results directly confirm that 26S dysfunction in neurons is involved in the pathology of neurodegenerative disease. The model demonstrates that 26S proteasomes are necessary for normal neuronal homeostasis and that 20S proteasome activity is insufficient for neuronal survival. Finally, we are providing the first reproducible genetic platform for identifying new therapeutic targets to slow or prevent neurodegeneration.

5-HT6 receptor antagonists reverse delay-dependent deficits in novel object discrimination by enhancing consolidation—an effect sensitive to NMDA receptor antagonism

5-HT(6) receptors are expressed in brain regions associated with learning and memory, and blockade of their function increases central cholinergic and glutamatergic neurotransmission and enhances cognitive processes. This study examined the effects of acute systemic administration of two selective 5-HT(6) receptor antagonists Ro 04-6790 and SB-271046 (10 mg kg(-1) i.p.) on acquisition, consolidation, and retrieval in the novel object discrimination (NOD) task, a two-trial test of recognition memory in which rats exposed to two identical objects during a familiarisation trial can discriminate a novel from a familiar object during the subsequent choice trial, following inter-trial delays of up to 3 h. 5-HT(6) receptor antagonist administration 20 min prior to or immediately after the familiarisation trial, but not 20 min prior to the choice trial reversed the deficit in object discrimination produced by a 4 h inter-trial interval. The nootropic effects of the 5-HT(6) receptor antagonists in this task thus appear to involve enhanced consolidation. Pre-treatment with the non-competitive NMDA receptor antagonist MK-801 (0.05 mg kg(-1) i.p.) prevented the effect of Ro 04-6790 on delay-induced deficits in object discrimination. This suggests that the 5-HT(6) receptor antagonist-induced enhancement of consolidation involves increased central glutamatergic neurotransmission.

Evidence-based guidelines for management of attention-deficit/hyperactivity disorder in adolescents in transition to adult services and in adults: recommendations from the British Association for Psychopharmacology.

Attention-deficit/hyperactivity disorder (ADHD) is an established diagnosis in children, associated with a large body of evidence on the benefits of treatment. Adolescents with ADHD are now leaving children’s services often with no readily identifiable adult service to support them, which presents problems as local pharmacy regulations often preclude the prescription of stimulant drugs by general practitioners (GPs). In addition, adults with ADHD symptoms are now starting to present to primary care and psychiatry services requesting assessment and treatment. For these reasons, the British Association for Psychopharmacology (BAP) thought it timely to hold a consensus conference to review the body of evidence on childhood ADHD and the growing literature on ADHD in older age groups. Much of this initial guidance on managing ADHD in adolescents in transition and in adults is based on expert opinion derived from childhood evidence. We hope that, by the time these guidelines are updated, much evidence will be available to address the many directions for future research that are detailed here.

A role for 5-ht6 receptors in retention of spatial learning in the Morris water maze

This study investigates the effect of intracerebroventricular administration of a 5-ht6 antisense oligonucleotide (AO) complementary to bases 1-18 of the rat 5-ht6 cDNA initiation sequence (Mol. Pharmacol. 43 (1993) 320) (1.5 microg twice daily for six days) and i.p. injection of a selective 5-ht6 receptor antagonist Ro 04-6790 (10 or 30 mg/kg once daily for three days) on acquisition and retention in the Morris water maze. Neither the 5-ht6 AO (which reduced cortical [3H]-LSD binding sites by 10-16%) nor Ro 04-6790 affected acquisition, but both enhanced retention of the learned platform position such that rats spent significantly longer searching the trained platform position than any other area during the probe tests. Furthermore, neither AO nor Ro 04-6790 had any effect on the time taken to reach a raised visible platform, indicating that visual acuity was unimpaired. In addition, AO reduced both food consumption and body weight and the later effect was also seen following Ro 04-6790, suggesting a role for the 5-ht6 receptor in the regulation of feeding. Hence, while the underlying mechanism remains unclear, enhanced retention of spatial learning following both AO and 5-ht6 antagonist administration strongly indicate a role for this receptor in memory processes.

Genetic knockout and pharmacological blockade studies of the 5-HT7 receptor suggest therapeutic potential in depression

The affinity of several antidepressant and antipsychotic drugs for the 5-HT7 receptor and its CNS distribution suggest potential in the treatment of psychiatric diseases. However, there is little direct evidence of receptor function in vivo to support this. We therefore evaluated 5-HT7 receptors as a potential drug target by generating and assessing a 5-HT7 receptor knockout mouse. No difference in assays sensitive to potential psychotic or anxiety states was observed between the 5-HT7 receptor knockout mice and wild type controls. However, in the Porsolt swim test, 5-HT7 receptor knockout mice showed a significant decrease in immobility compared to controls, a phenotype similar to antidepressant treated mice. Intriguingly, treatment of wild types with SB-258719, a selective 5-HT7 receptor antagonist, did not produce a significant decrease in immobility unless animals were tested in the dark (or active) cycle, rather than the light, adding to the body of evidence suggesting a circadian influence on receptor function. Extracellular recordings from hypothalamic slices showed that circadian rhythm phase shifts to 8-OH-DPAT are attenuated in the 5-HT7 receptor KO mice also indicating a role for the receptor in the regulation of circadian rhythms. These pharmacological and genetic knockout studies provide the first direct evidence that 5-HT7 receptor antagonists should be investigated for efficacy in the treatment of depression.

Evidence for expression of the 5-hydroxytryptamine-2B receptor protein in the rat central nervous system

The 5-hydroxytryptamine-2B receptor is the most recent addition to the 5-hydroxytryptamine-2 family of G-protein-coupled receptors. In the rat stomach fundus, 5-hydroxytryptamine-2B receptor activation causes contraction; however, its distribution and function in the rat CNS are unclear. By performing immunohistochemistry with an antiserum raised against the N-terminus of the 5-hydroxytryptamine-2B receptor protein, this study identifies receptor expression in longitudinal and circular smooth muscle in the rat stomach fundus and in neurons in discrete nuclei in the cerebellum, lateral septum, dorsal hypothalamus and medial amygdala. The potential function of this receptor in the CNS is discussed.

Long-lasting changes in behavioural and neuroendocrine indices in the rat following neonatal maternal separation : Gender-dependent effects

Neonatal maternal separation (MS) has been used to model long-term changes in neurochemistry and behaviour associated with exposure to early-life stress. This study characterises changes in behavioural and neuroendocrine parameters following MS. On postnatal days (PND) 3-15, male and female Long-Evans rats underwent 3 h daily MS. Non-handled (NH) control offspring remained with the dams. Starting at PND 90, behaviour was assessed at weekly intervals in the elevated plus-maze, elevated T-maze, and locomotor activity boxes, and body weight monitored throughout. At the end of the study, adrenals were weighed and blood collected for analysis of plasma corticosterone and adrenocorticotropic hormone (ACTH) under basal conditions and following restraint stress. As adults, MS weighed more than NH animals. Activity on the open arms of the plus-maze was similar between MS and NH animals. In the T-maze, MS males had shorter emergence latencies than their NH counterparts. Spontaneous ambulation in a novel environment was significantly higher in MS than in NH animals, and males exhibited overall lower activity than females. Basal plasma corticosterone was lower in MS than in NH females, but no rearing condition difference was observed following restraint stress. Females had higher corticosterone and ACTH levels than males, whereas adrenal glands of MS animals weighed less than those of NH controls. The MS paradigm caused long-term gender dependent effects on behaviour and HPA axis status. The consistent gender differences confirm and expand existing results showing altered anxiety and stress reactivity in male and female rats.