Optogenetic stimulation: Understanding memory and treating deficits.

Technology allowing genetically targeted cells to be modulated by light has revolutionized neuroscience in the past decade, and given rise to the field of optogenetic stimulation. For this, non-native, light activated proteins (e.g., channelrhodopsin) are expressed in a specific cell phenotype (e.g., glutamatergic neurons) in a subset of central nervous system nuclei, and short pulses of light of a narrow wavelength (e.g., blue, 473 nm) are used to modulate cell activity. Cell activity can be increased or decreased depending on which light activated protein is used. We review how the greater precision provided by optogenetics has transformed the study of neural circuits, in terms of cognition and behavior, with a focus on learning and memory. We also explain how optogenetic modulation is facilitating a better understanding of the mechanistic underpinnings of some neurological and psychiatric conditions. Based on this research, we suggest that optogenetics may provide tools to improve memory in neurological conditions, particularly diencephalic amnesia and Alzheimer's disease.

C-type natriuretic peptide in Parkinson's disease: reduced secretion and response to deprenyl.

C-type natriuretic peptide (CNP) is a neurotrophic factor widely expressed in the central nervous system including the basal ganglia, limbic system and hypothalamus. Nothing is known of CNP's role in the human brain but in rodents CNP promotes axon growth and branching, and interacts with dopaminergic function in models of addiction. Because preliminary evidence showed reduced levels in Parkinson's disease (PD), we examined concentrations of CNP peptides in cerebrospinal fluid (CSF) in 146 PD patients from the DATATOP study to determine changes over time in relation to medication status and cognitive function. CNP and an aminoterminal product of proCNP (NTproCNP) were measured in extracts from stored CSF by radioimmunoassay. CSF samples were obtained twice-at enrolment and at the study's endpoint (requirement for levodopa treatment) after treatment with placebo or deprenyl. At enrolment, median baseline concentration of CSF NTproCNP (776 pmol/L, n = 146) was significantly lower than that in a reference group without neurological disorder (1,010 pmol/L, p < 0.001). Concentrations declined significantly during placebo (p = 0.02) and lower values at enrolment were associated with more rapid functional decline (p < 0.01). In contrast, deprenyl-a treatment which delayed the need for levodopa-nullified the time-dependent decline in CSF NTproCNP. In conclusion subnormal CSF NTproCNP which declines with time and associates with increasing functional disability implicates CNP in PD. Concordant clinical and peptide responses to deprenyl suggest that some of the benefits of monoamine oxidase inhibitors in PD are mediated by preserving tissue CNP activity.

Anterior thalamic nuclei neurons sustain memory.

A hippocampal-diencephalic-cortical network supports memory function. The anterior thalamic nuclei (ATN) form a key anatomical hub within this system. Consistent with this, injury to the mammillary body-ATN axis is associated with examples of clinical amnesia. However, there is only limited and indirect support that the output of ATN neurons actively enhances memory. Here, in rats, we first showed that mammillothalamic tract (MTT) lesions caused a persistent impairment in spatial working memory. MTT lesions also reduced rhythmic electrical activity across the memory system. Next, we introduced 8.5 Hz optogenetic theta-burst stimulation of the ATN glutamatergic neurons. The exogenously-triggered, regular pattern of stimulation produced an acute and substantial improvement of spatial working memory in rats with MTT lesions and enhanced rhythmic electrical activity. Neither behaviour nor rhythmic activity was affected by endogenous stimulation derived from the dorsal hippocampus. Analysis of immediate early gene activity, after the rats foraged for food in an open field, showed that exogenously-triggered ATN stimulation also increased Zif268 expression across memory-related structures. These findings provide clear evidence that increased ATN neuronal activity supports memory. They suggest that ATN-focused gene therapy may be feasible to counter clinical amnesia associated with dysfunction in the mammillary body-ATN axis.

Nanopore sequencing of the glucocerebrosidase (GBA) gene in a New Zealand Parkinson's disease cohort.

INTRODUCTION: Bi-allelic mutations in the gene for glucocerebrosidase (GBA) cause Gaucher disease, an autosomal recessive lysosomal storage disorder. Gaucher disease causing GBA mutations in the heterozygous state are also high risk factors for Parkinson's disease (PD). GBA analysis is challenging due to a related pseudogene and structural variations (SVs) that can occur at this locus. We have applied and refined a recently developed nanopore DNA sequencing method to analyze GBA variants in a clinically assessed New Zealand longitudinal cohort of PD. METHOD: We examined amplicons encompassing the coding region of GBA (8.9 kb) from 229 PD cases and 50 healthy controls using the GridION nanopore sequencing platform, and Sanger validation. RESULTS: We detected 23 variants in 21 PD cases (9.2% of patients). We detected modest PD risk variant p.N409S (rs76763715) in one case, p.E365K (rs2230288) in 12 cases, and p.T408 M (rs75548401) in seven cases, one of whom also had p.E365K. We additionally detected the possible risk variants p.R78C (rs146774384) in one case, p.D179H (rs147138516) in one case which occurred on the same haplotype as p.E365K, and one novel variant c.335C > T or p.(L335 = ), that potentially impacts splicing of GBA transcripts. Additionally, we found a higher prevalence of dementia among patients with GBA variants. CONCLUSION: This work confirmed the utility of nanopore sequencing as a high-throughput method to identify known and novel GBA variants, and to assign precise haplotypes. Our observations may contribute to improved understanding of the effects of variants on disease pathogenesis, and to the development of more targeted treatments.

Cognitive characteristics associated with mild cognitive impairment in Parkinson's disease.

BACKGROUND: Cognitive deficits are common in Parkinson's disease (PD), but the range of deficits is variable. The aim of this study was to identify different cognitive subgroups associated with PD. METHODS: A broad range of neuropsychological measures and cognitive domains were used in a cluster analysis to identify subgroups of patients. RESULTS: Three subgroups of patients were identified. Compared to controls, one PD subgroup showed no or minimal cognitive impairment (PD-NCI), a second group showed a variable or uncertain pattern of mild to severe cognitive impairments (PD-UCI), and a third group had evidence of severe cognitive impairment across most cognitive domains (mild cognitive impairment; PD-MCI). The subgroups did not differ with regard to age, motor impairment, or disease duration. CONCLUSIONS: Patients with PD are heterogeneous with regard to cognitive presentation and it may be possible to identify patients in the preclinical stage of dementia. The identification of preclinical dementia in PD patients (PD-MCI) provides an opportunity to understand cognitive decline in PD and its progression to dementia.

Planning in Parkinson's disease: a matter of problem structure?

Although the Tower of London (TOL) has been extensively used to assess planning ability in patients with Parkinson's disease (PD), the reported presence or extent of any planning deficits has been inconsistent. This may partly be due to the heterogeneity of the TOL tasks used and a failure to consider how structural problem parameters may affect task complexity. In the present study, planning in PD patients was assessed by systematically manipulating TOL problem structure. Results clearly disprove the identity assumption of problems with an equal number of minimum moves. Instead, substantial parts of planning performance were related to more subtle aspects of problem structure, such as subgoaling patterns and goal hierarchy. Planning in PD patients was not impaired in general but was affected when the information provided by the problem states was ambiguous in terms of the sequential order of subgoals, but not by increases in search depth.

A profile of neuropsychiatric problems and their relationship to quality of life for Parkinson's disease patients without dementia.

Neuropsychiatric problems are common in Parkinson's disease (PD) but there is little information regarding how they impact on quality of life. PD patients without dementia (49) were assessed for low mood/depression, fatigue, apathy, sleep problems and hallucinations. Measures of quality of life and motor function were also obtained. Over 77% of the patients reported symptoms consistent with one or more neuropsychiatric problems. Low mood/depression, anxiety and the presence of hallucinations predicted poorer quality of life after controlling for motor symptoms. Additional to the motor symptoms, we found that specific neuropsychiatric problems may impact on quality of life for PD patients.

Parkinson's in the oldest old: Impact on estimates of future disease burden.

BACKGROUND: Traditionally the risk of Parkinson's has been considered to increase monotonically with age, although there is evidence that prevalence and incidence may decrease in the oldest old. To examine this further we estimated the national prevalence and incidence of Parkinson's in New Zealand, using drug-tracing methods, to examine the relationship of Parkinson's with sex and age up to 100+. METHODS: Information on Parkinson's-related medications was extracted from the national pharmaceutical database of community-dispensed medications from 2005 to 2014. Diagnoses for a large subset of individuals were independently determined through national mortality and hospital admissions datasets. We used a Bayesian model, accommodating diagnostic uncertainty and bias, to estimate the number of people with Parkinson's. RESULTS: The 2013 prevalence of Parkinson's in New Zealand was 210 per 100 000 population (95% uncertainty interval 208-212) with age-standardized prevalence rates higher for males (ratio 1.6:1). Incidence was 31 per 100 000 person-years (95% uncertainty interval 30-32), also higher in males (ratio 1.8:1). Incidence and prevalence by age increased exponentially until 75 years, peaked at 85 years, and then dropped sharply. CONCLUSIONS: The prevalence of Parkinson's in New Zealand is expected to double over a 25-year period but then increase at a slower rate due to the drop-off in prevalence and incidence in the oldest old. The findings suggest that Parkinson's disease is not an aging-dependent but an age-dependent disorder.

Both anteromedial and anteroventral thalamic lesions impair radial-maze learning in rats.

Disruption to the anterior thalamus (AT) may be an important factor in diencephalic amnesia. Rats with small lesions of the anteromedial (AM) or anteroventral (AV) nucleus showed persistent working-memory and reference-memory deficits in a 12-arm radial maze, although they were comparable to controls during the early part of training. The only activity difference in the maze was that lesioned rats failed to run more slowly when revisiting a baited arm. For all groups, both working and reference memory were impaired after extramaze cues were removed; removal of intramaze cues further impaired performance relative to the original conditions. These findings suggest the AT makes a distinct contribution to mnemonic functions, probably as part of an integrated system involving limbic cortex and the hippocampal formation, and that AT lesions produce a general rather than a specific deficit in spatial or working memory.

Preoperative differential housing and dorsal hippocampal lesions in rats.

Rats housed in impoverished environments often show greater behavioral deficits after receiving brain lesions than to rats housed in standard or enriched environments. However, the resemblance between the effects of social isolation and those of hippocampal lesions in rats prompted the suggestion that rats socially isolated at weaning rather than grouped counterparts may show less behavioral change after sustaining dorsal hippocampal lesions when adult. In socially reared rats, hippocampal lesions produced increased ambulation and object contact in an open field, reduced passive avoidance in a runway task, and produced faster acquisition of active avoidance in a shuttle box, but there were no such differences in isolation-reared rats. Ambulation and object contact in isolates were intermediate to those of rats with lesions and intact group-housed rats, and the behavior of isolates during passive and active avoidance training was generally similar to that of grouped rats with lesions. The introduction of a distractor during approach training in an alley reduced running speeds more in rats with lesions than in controls. The several significant interactions between housing state and lesion state suggest that neural pathways associated with the hippocampal formation may mediate some behavioral effects of differential housing.

Effects of lesions to the cerebellar vermis and hemispheres on timing and counting in rats.

The effects of lesions to the cerebellum on numerical and temporal discrimination were examined in rats using a psychophysical choice procedure. Lesions to the cerebellar hemispheres but not the cerebellar vermis produced performance deficits in a numerical discrimination task (2-8 events) and a milliseconds temporal discrimination task (0.2-0.8 s). However, temporal discriminations in the seconds range (2-8 s) were unaffected by either type of lesion. Using W. H. Meck and R. M. Church's (1983) mode-control model of timing and counting, these findings suggest that damage to the cerebellar hemispheres influences a source of constant variability (e.g., switch processes) because constant variability is a prominent source of error during both milliseconds timing and counting but is masked by other sources of variability when timing longer durations (>2 s).

Forgetting in rats following medial septum or mammillary body damage.

This study examined the effects of medial septal (MS) and mammillary body (MB) radio-frequency lesions in an automated delayed-matching-to-sample (DMTS) procedure using lever-position stimuli and rats. Memory performance pre- and postsurgery was assessed with a negative exponential decay function fitted to bias-free measures of recognition. Part 1 showed that MS, but not MB or sham-control surgery, impaired DMTS performance. This impairment in the MS group was best characterized as an increase in the rate of forgetting. Part 2 examined the interaction between MS and MB lesion effects and proactive interference arising from responses made on the previous DMTS trial. The results indicated that proactive interference effects were similar for all groups. These results provide further support for the critical role of the MS region in memory function but indicate that damage to this brain region does not disrupt memory function through a heightened sensitivity to proactive interference.

Comparison in the mouse of the effect of the opiate delta receptor antagonist ICI 154129 and naloxone in tests of extinction, passive avoidance and food intake.

The effects of 30 and 80 mg/kg ICI 154,129, an opiate delta receptor antagonist, were compared with those of 0.1 and 10 mg/kg naloxone using tests of food-intake, passive avoidance and extinction in mice. Whereas naloxone depressed food intake and facilitated extinction, ICI 154,129 failed to affect food intake, passive avoidance or extinction although the mice reared significantly more during the test of food intake.

Production of a serial position effect in rats using a 12-arm radial maze.

The effects of item position (the serial position effect: SPE) on the recognition of a list of arms presented in an 8-arm radial maze have not been shown to be robust across studies which differ in numbers of subjects, amount of training and task difficulty. The present study examined whether more robust SPEs could be obtained in rats with a 12-arm radial maze using a matching-to-sample serial probe recognition (SPR) procedure. In Part 1, 23 rats received extensive training on recognition of list of arms from a 5-arm list and, in Part 2, 20 rats received training with a 7-arm list. Both Parts 1 and 2 showed that a reliable and persistent SPE emerged due to superior recognition of items at the first and last serial positions compared with the middle positions. However, the SPE was more pronounced with the 7-arm than 5-arm list. It is argued that adequate task difficulty along with sufficient subject and trial numbers is necessary to produce a clear SPE. In Part 3, an alternative means of assessing accuracy derived from signal-detection theory is examined, and the procedural requirements for its use are identified. Although this measure did not alter the conclusions reached using percent correct, it is proposed that the bias-free measure, log d, is superior to traditional indices of memory performance which may obscure the presence of, or changes in, the SPE. The procedures used here provide a valuable means to produce clear, reliable and persistent SPEs. Such procedures are essential if researchers are to be confident about the effects of lesions or drugs upon list memory in their attempts to explore the neurological bases of memory and model human neurological disorders.

Housing conditions modulate the effects of intracerebral grafts in rats with brain lesions.

The aim of this study was to examine whether the behavioural effects of intracerebral grafts in rats with brain lesions can be modulated by postoperative housing conditions. Sixty-six young adult female rats were used. Twenty-two rats were sham-operated (S) and 44 rats sustained a complete aspirative lesion (L) of the fimbria-fornix and overlying tissue. The cavity was used in half the rats as the implantation site for solid fetal septal transplants (LT). Two days later, half the rats of each group were housed in an 'enriched' condition (S.EC, L.EC and LT.EC); the other half remained in standard condition (S.SC, L.SC and LT.SC). Two and 10 months later, the rats were tested in a Hebb-Williams maze. Two months after surgery, there was a highly significant lesion effect, no graft effect and no environmental effect except in S rats, S.EC rats making fewer initial errors than S.SC rats. Ten months after surgery, L rats still made more errors than S rats and S.EC rats made fewer initial errors than S.SC rats; however, the lesion-induced deficits were significantly attenuated in LT.EC rats, but not in LT.SC rats. These data show that both the enriched environment and the implant were unable alone to promote behavioural recovery but, applied together, they reduced the lesion-induced deficits. Dorsal hippocampus acetylcholinesterase (AChE)-staining intensity was reduced by the lesions, but this reduction was partially compensated for by the grafts; however, environmental conditions did not affect AChE-staining significantly. This latter observation suggests that the graft-derived partial cholinergic reinnervation of the hippocampus probably does not underly the behavioural improvement observed only in LT.EC rats.

Behavioral effects of basal forebrain grafts after dorsal septo-hippocampal pathway lesions.

There are many reports that basal forebrain grafts ameliorate behavioral impairments produced by dorsal septo-hippocampal pathway lesions, but several studies have either found that this recovery may be unrelated to concomitant restitution of cholinergic markers, may be modest and depend on certain experimental conditions or instead that grafts may actually exacerbate lesion-induced impairments. In this study, rats received one of three lesions of the dorsal septo-hippocampal pathways or a sham lesion, at 32 days of age, and intrahippocampal basal forebrain grafts or the vehicle control 10 days later. In grafted rats with total aspirative lesion of the fimbria-fornix, there was a substantial AChE-positive hippocampal reinnervation but no improvement of the severe lesion-induced spatial learning deficits, either reference memory or working memory, whether tested at 1 or 5 months post-grafting. In rats with bilateral medial fimbria lesions, grafts were successful, normal in appearance and produced substantial hippocampal cholinergic reinnervation; relative to non-grafted counterparts, however, grafted medial fimbria rats showed an early reference memory impairment and a persistent exacerbation of a working memory deficit. Exacerbation of learning impairments was also apparent in grafted rats with partial hippocampal denervation due to lesion of the cingulate and adjacent cortex above the fimbria-fornix. Nonetheless, basal forebrain grafts normalised general activity in these lesion groups, irrespective of whether the lesion-induced change was an increase or a decrease relative to controls. Graft-derived lesion groups, irrespective of whether the lesion-induced change was an increase or a decrease relative to controls. Graft-derived AChE-positive innervation was more marked than expected in both grafted cingulate-lesioned rats and grafted sham-lesioned rats, while control grafts of fetal cortex (above the septum) produced little or no AChE-positive innervation. Size of basal forebrain grafts, originally 3 microliters at two dorsal sites per hippocampus, increased markedly from rostral to caudal dorsal hippocampus in all groups but did not differ significantly across grafted groups, even with respect to non-lesioned rats. This study adds further evidence that basal forebrain grafts, successful with respect to cholinergic reinnervation, do not always enhance cognitive functions in rat hippocampal lesion models, and confirms that these grafts may have adverse effects after partial septo-hippocampal system lesions. It is important to attend to both the potential negative and positive effects of neural grafts.

Timing ability and numerical competence in rats.

Counting and timing ability in Wistar rats was tested in 4 psychophysical choice experiments. After training naive rats with discrete sound sequences that confounded time and number, only time gained control of behavior; control by time was stronger and acquired more rapidly after training with separate time- and number-relevant signals. Two nonnumeric cues associated with periodic sequences, temporal ratio and sequence pattern, did not appear to provide the basis for numerical discrimination, as performance was unaffected by a sudden change from periodic signals to signals with unique temporal patterns. Even after highly accurate performance with number, time showed exclusive control of behavior for signals with conflicting time and number cues. This study provides an unequivocal demonstration that rats can count, but they do so according to H. Davis and J. Memmott's (1983) "last resort" hypothesis.

List item memory in rats: effects of delay and delay task.

The Serial Position Effect (SPE) was studied in rats using 2 manipulations analogous to those that have been shown to decrease the recency effect but leave the primacy effect intact in human Ss. In Part 1, delays (5 s to 60 s) were imposed between exposure to a sequence of arms presented in a 12-arm radial maze and a subsequent test phase. In Part 2, the effect of free access to food in a short (10-s) delay was examined. The results from Parts 1 and 2 showed that the primacy and recency effects were differentially sensitive to the delay and events within it. In particular the recency effect was found to be more sensitive to disruption from these sources. The present demonstration of a reduction in recency with procedures analogous to those used with humans extends the evidence, suggesting that the SPE obtained in rats and humans is a similar phenomenon.

Effects of selegiline (deprenyl) on cognition in early Parkinson's disease.

The influence of selegiline (5 mg b.i.d.) on cognition of 20 levodopanaive patients with early Parkinson's disease (PD) was examined in an 8-week, randomized, placebo-controlled, double-blind trial. Clinical evaluations and cognitive tests were administered at baseline and at 8 weeks; patients with PD who received placebo were also examined 8 weeks after subsequent selegiline treatment. By comparison with non-PD controls, patients with PD were impaired on the Wisconsin card sorting task and on the advanced progressive matrices test, but not in terms of their performance on the Rivermead behavioral memory test or on the rod (spatial) orientation test. Selegiline improved scores on the mentation/mood part and the activities of daily living part of the Unified Parkinson's Disease Rating Scale, but it did not improve motor scores on this test, nor did it have clear effects on the specific neuropsychological measures that were examined.

The effect of social isolation of the rat on open field activity and emergence.

It has been suggested that naive isolated rats show more "fear responses" than group-housed controls. However, in contrast to previous studies, dark conditions and low noise levels were used to evaluate the latency to emerge from a small chamber into an open field and the subsequent ambulation and rearing behaviour of isolated and group-housed rats. The prediction that these conditions would be conducive to the rapid development of hyperactivity in isolates was confirmed, but there were no significant differences in emergence latency.