Some observations on the biology of two rarely seen deep-sea chimaerids, Chimaera carophila and Hydrolagus homonycteris.

Chimaera carophila (n = 45) and Hydrolagus homonycteris (n = 11), two deep-sea chimaerids rarely caught in the waters off New Zealand, were collected from research trawl catches and commercial fishery catches around New Zealand at depths between 400 and 1300 m, between 2014 and 2016. Additional preserved specimens of both species (n = 58) from museum collections were analysed for size, sex and maturity. External assessment of male claspers and a combination of internal assessments of female gonad mass and oviducal gland width, were used to determine maturity. For both species, length at first maturity was 0·70-0·82 of their maximum observed chimaera length (LC ), with females maturing at a larger size. Length at maturity for C. carophila (LC range: 28·7-103·9 cm) was estimated at 72·5 cm LC for males (n = 163) and 82·5 LC for females (n = 58). In H. homonycteris, length at maturity (length range: 78·6-99·8 cm LC ) was estimated at 79·1 cm LC for males (n = 51) and 80·1 cm LC for females (n = 17). Ovarian fecundity was up to 31 for C. carophila and sperm storage was confirmed in the oviducal gland of this species. Both species preyed on benthic invertebrates. Some C. carophila and H. homonycteris inhabit depths beyond most current fisheries, but both species appear to be relatively rare and have reproductive parameters characteristic of low productivity, which may make these species vulnerable to population decline if mortality was to increase in the future.

Reproductive biology and feeding habits of the prickly dogfish Oxynotus bruniensis.

The reproductive biology and diet of prickly dogfish Oxynotus bruniensis, a deep-sea elasmobranch, endemic to the outer continental and insular shelves of southern Australia and New Zealand, and caught as by-catch in demersal fisheries, are described from specimens caught in New Zealand waters. A total of 53 specimens were obtained from research surveys and commercial fisheries, including juveniles and adults ranging in size from 33·5 to 75·6 cm total length (LT ). Estimated size-at-maturity was 54·7 cm LT in males and 64·0 cm LT in females. Three gravid females (65·0, 67·5 and 71·2 cm LT ) were observed, all with eight embryos. Size-at-birth was estimated to be 25-27 cm LT . Vitellogenesis was not concurrent with embryo development. Analysis of diet from stomach contents, including DNA identification of prey using the mitochondrial genes cox1 and nadh2, revealed that O. bruniensis preys exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans. Based on spatial overlap with deep-sea fisheries, a highly specialized diet, and reproductive characteristics representative of a low productivity fish, the commercial fisheries by-catch of O. bruniensis may put this species at relatively high risk of overfishing.

Altered expression of glutamate signaling, growth factor, and glia genes in the locus coeruleus of patients with major depression.

Several studies have proposed that brain glutamate signaling abnormalities and glial pathology have a role in the etiology of major depressive disorder (MDD). These conclusions were primarily drawn from post-mortem studies in which forebrain brain regions were examined. The locus coeruleus (LC) is the primary source of extensive noradrenergic innervation of the forebrain and as such exerts a powerful regulatory role over cognitive and affective functions, which are dysregulated in MDD. Furthermore, altered noradrenergic neurotransmission is associated with depressive symptoms and is thought to have a role in the pathophysiology of MDD. In the present study we used laser-capture microdissection (LCM) to selectively harvest LC tissue from post-mortem brains of MDD patients, patients with bipolar disorder (BPD) and from psychiatrically normal subjects. Using microarray technology we examined global patterns of gene expression. Differential mRNA expression of select candidate genes was then interrogated using quantitative real-time PCR (qPCR) and in situ hybridization (ISH). Our findings reveal multiple signaling pathway alterations in the LC of MDD but not BPD subjects. These include glutamate signaling genes, SLC1A2, SLC1A3 and GLUL, growth factor genes FGFR3 and TrkB, and several genes exclusively expressed in astroglia. Our data extend previous findings of altered glutamate, astroglial and growth factor functions in MDD for the first time to the brainstem. These findings indicate that such alterations: (1) are unique to MDD and distinguishable from BPD, and (2) affect multiple brain regions, suggesting a whole-brain dysregulation of such functions.

Diet and feeding niches of juvenile Gadus morhua, Melanogrammus aeglefinus and Merlangius merlangus during the settlement transition in the northern North Sea.

A study on the feeding ecology of juvenile cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus during the pelagic to demersal transition was carried out on fishes sampled throughout their settlement season at a local nursery ground in the north-western North Sea, off the Scottish east coast. A comprehensive quantitative taxonomic analysis of the diets, as described in the paper, showed the emergence of distinctive feeding niches, minimizing the potential for competition between species and size categories. The diet of the juveniles changed with fish size, water depth, time of year and distance offshore. Small G. morhua were present in the study area earlier in the season, settled further inshore and ate a higher proportion of pelagic prey (copepods) and as size increased they moved into deeper waters and targeted larger, more benthic prey. As M. aeglefinus grew larger and moved into deeper waters, a diet of largely copepods, amphipods, pelagic Ammodytes spp., cyprids and pelagic gastropods evolved to one dominated predominantly by fishes and benthic invertebrates. In the case of M. merlangus, widespread ages and sizes throughout the sampling season, a consequence of their more protracted spawning season, resulted in dietary changes which were more likely to be influenced by seasonal changes in the prey field, in addition to developmental (size) changes, than the diets of the other two species.

Commissural and cortico-cortical "columns" in the somatic sensory cortex of primates.

Anatomical experiments demonstrate that commissural and cortico-cortical fibers arising and terminating in the somatic sensor- cortex of monkeys terminate in layers I through IV in a mosaic of precisely ordered vertical bands. The cells of origin of these fibers, found predominantly in layer III, are also arranged in vertical aggregations.

Thalamic and brainstem contributions to large-scale plasticity of primate somatosensory cortex.

After long-term denervation of an upper limb in macaque monkeys, the representation of the face in somatosensory cortex expands over many millimeters into the silenced representation of the hand. Various brainstem and cortical mechanisms have been proposed to explain this phenomenon. Reorganization in the thalamus has been largely ignored. In monkeys with deafferented upper limbs for 12 to 20 years, it was found that the brainstem cuneate and the thalamic ventral posterior nuclei had undergone severe transneuronal atrophy, and physiological mapping in the thalamus revealed that the face and trunk representations were adjoined while the normally small representation of the lower face had expanded comparable to the expansion in cortex. Reorganization of brainstem and thalamic nuclei associated with slow transneuronal atrophy is likely to be a progressive process. When coupled with divergence of ascending connections, it is likely to make a substantial contribution to representational changes in cortex.

Activity-dependent regulation of GABA expression in the visual cortex of adult monkeys.

Levels of the inhibitory transmitter, GABA, and its synthesizing enzyme, GAD, appear to be regulated in the visual cortex of young adult monkeys in an activity-dependent manner. In monkeys subjected to monocular deprivation by eye removal, tetrodotoxin injection, or eyelide suture, the number of GABA and GAD immunoreactive neurons in deprived-eye columns of the cortex is reduced by up to 50%. This effect is unaccompanied by cell death and is reversible. After cessation of TTX injection or reopening of the eyes, the number of immunostained cells returns to normal. The effect appears after 4-5 days of eye removal or tetrodotoxin injection, but only after 7-16 weeks of eyelid suture. In the latter case, it is more severe in the younger monkeys. The reversible reduction in GABA and GAD immunostaining extends out of layer IVC into lay IVA and to neurons around but not in cytochrome oxidase periodicities of layer III. This may indicate selective vulnerability of GABA cells sensitive to high spatial frequency.

The fibroblast growth factor family and mood disorders.

While there has been a great deal of interest in the role of brain-derived neurotrophic factor (BDNF) in mood disorders and/or the mode of action of antidepressants, less is known about the role of other growth factors. This paper is focused on a group of growth factors, the fibroblast growth factor (FGF) family and their potential role in mood disorders.

Methodological considerations for gene expression profiling of human brain.

Gene expression profiles of postmortem brain tissue represent important resources for understanding neuropsychiatric illnesses. The impact(s) of quality covariables on the analysis and results of gene expression studies are important questions. This paper addressed critical variables which might affect gene expression in two brain regions. Four broad groups of quality indicators in gene expression profiling studies (clinical, tissue, RNA, and microarray quality) were identified. These quality control indicators were significantly correlated, however one quality variable did not account for the total variance in microarray gene expression. The data showed that agonal factors and low pH correlated with decreased integrity of extracted RNA in two brain regions. These three parameters also modulated the significance of alterations in mitochondrial-related genes. The average F-ratio summaries across all transcripts showed that RNA degradation from the AffyRNAdeg program accounted for higher variation than all other quality factors. Taken together, these findings confirmed prior studies, which indicated that quality parameters including RNA integrity, agonal factors, and pH are related to differences in gene expression profiles in postmortem brain. Individual candidate genes can be evaluated with these quality parameters in post hoc analysis to help strengthen the relevance to psychiatric disorders. We find that clinical, tissue, RNA, and microarray quality are all useful variables for collection and consideration in study design, analysis, and interpretation of gene expression results in human postmortem studies.

The thalamic matrix and thalamocortical synchrony.

High-frequency synchronous activity of neurons in the cerebral cortex and thalamus is a concomitant of discrete conscious events. In the primate thalamus, a newly identified population of neurons provides a basis for this synchronization. A matrix of calbindin-immunoreactive neurons extends throughout the thalamus and projects to superficial layers of cortex over wide areas, unconstrained by boundaries between areas. In some nuclei, a core of parvalbumin-immunoreactive neurons is superimposed upon the matrix. Core neurons project in a topographically ordered fashion to middle layers of the cortex in an area-specific manner. Matrix neurons, recruited by corticothalamic connections, can disperse activity across cortical areas and thalamic nuclei. Their superficial terminations can synchronize specific and nonspecific elements of the thalamocortical network in coherent activity that underlies cognitive events.

Santiago Ramón y Cajal and methods in neurohistology.

Controversy, misunderstanding or uninformed opinion abound over the extent to which the great Spanish neurohistologist, Santiago Ramón y Cajal, specified his staining methods in his analytical papers, the methods by which he analysed and presented his data, and the microscopes available to him. In this paper, we have attempted to outline the information on these points that we have been able to obtain from a detailed examination of his writings and a study of the evidence remaining in the Cajal Museum in Madrid.

Progressive transneuronal changes in the brainstem and thalamus after long-term dorsal rhizotomies in adult macaque monkeys.

This study deals with a potential brainstem and thalamic substrate for the extensive reorganization of somatosensory cortical maps that occurs after chronic, large-scale loss of peripheral input. Transneuronal atrophy occurred in neurons of the dorsal column (DCN) and ventral posterior lateral thalamic (VPL) nuclei in monkeys subjected to cervical and upper thoracic dorsal rhizotomies for 13-21 years and that had shown extensive representational plasticity in somatosensory cortex and thalamus in other experiments. Volumes of DCN and VPL, number and sizes of neurons, and neuronal packing density were measured by unbiased stereological techniques. When compared with the opposite, unaffected, side, the ipsilateral cuneate nucleus (CN), external cuneate nucleus (ECN), and contralateral VPL showed reductions in volume: 44-51% in CN, 37-48% in ECN, and 32-38% in VPL. In the affected nuclei, neurons were progressively shrunken with increasing survival time, and their packing density increased, but there was relatively little loss of neurons (10-16%). There was evidence for loss of axons of atrophic CN cells in the medial lemniscus and in the thalamus, with accompanying severe disorganization of the parts of the ventral posterior nuclei representing the normally innervated face and the deafferented upper limb. Secondary transneuronal atrophy in VPL, associated with retraction of axons of CN neurons undergoing primary transneuronal atrophy, is likely to be associated with similar withdrawal of axons from the cerebral cortex and should be a powerful influence on reorganization of somatotopic maps in the somatosensory cortex.

Comparison of vector space model methodologies to reconcile cross-species neuroanatomical concepts.

Generating informational thesauri that classify, cross-reference, and retrieve diverse and highly detailed neuroscientific information requires identifying related neuroanatomical terms and acronyms within and between species (Gorin et al., 2001) Manual construction of such informational thesauri is laborious, and we describe implementing and evaluating a neuroanatomical term and acronym reconciliation (NTAR) system to assist domain experts with this task. NTAR is composed of two modules. The neuroanatomical term extraction (NTE) module employs a hidden Markov model (HMM) in conjunction with lexical rules to extract neuroanatomical terms (NT) and acronyms (NA) from textual material. The output of the NTE is formatted into collections of term- or acronym-indexed documents composed of sentences and word phrases extracted from textual material. The second information retrieval (IR) module utilizes a vector space model (VSM) and includes a novel, automated relevance feedback algorithm. The IR module retrieves statistically related neuroanatomical terms and acronyms in response to queried neuroanatomical terms and acronyms. Neuroanatomical terms and acronyms retrieval obtained from term-based inquiries were compared with (1) term retrieval obtained by including automated relevance feedback and with (2) term retrieval using "document-to-document" comparisons (context-based VSM). The retrieval of synonymous and similar primate and macaque thalamic terms and acronyms in response to a query list of human thalamic terminology by these three IR approaches was compared against a previously published, manually constructed concordance table of homologous cross-species terms and acronyms. Term-based VSM with automated relevance feedback retrieved 70% and 80% of these primate and macaque terms and acronyms, respectively, listed in the concordance table. Automated feedback algorithm correctly identified 87% of the macaque terms and acronyms that were independently selected by a domain expert as being appropriate for manual relevance feedback. Context-based VSM correctly retrieved 97% and 98% of the primate and macaque terms and acronyms listed in the term homology table. These results indicate that the NTAR system could assist neuroscientists with thesauri creation for closely related, highly detailed neuroanatomical domains.

Maldistribution of interstitial neurons in prefrontal white matter of the brains of schizophrenic patients.

BACKGROUND: The cortical subplate is a transitory structure involved in the formation of connections in developing cerebral cortex. Interstitial neurons, normally present in subcortical white matter (WM) of the adult brain, have escaped the programmed cell death that eliminates most subplate neurons. Previous investigations indicated a maldistribution of one population of interstitial neurons in the WM of brains of schizophrenic patients, suggesting a defect of the subplate during brain development. METHODS: Three histochemically or immunocytochemically defined neuronal populations were studied in WM beneath the middle frontal gyrus of 20 schizophrenic patients and 20 matched control subjects. RESULTS: Brains of schizophrenic patients showed significant changes in the distribution of the three neuronal populations: microtubule-associated protein 2 and nonphosphorylated neurofilament-immunoreactive neurons showed a decreased density in superficial WM and an increased density in deeper WM. Nicotinamide adenine dinucleotide phosphate-diaphorase neurons were reduced in superficial WM and showed variable densities in deeper WM. Thirty-five percent of the brains of schizophrenic patients but no brains of the control subjects showed a maldistribution of neurons toward deeper WM with at least two of the three markers. Changes in neuronal distribution were not linked to age, gender, autolysis time, or subtype of schizophrenia. CONCLUSIONS: Selective displacement of interstitial WM neurons in the frontal lobe of brains of schizophrenic patients may indicate alteration in the migration of subplate neurons or in the pattern of programmed cell death. Both could lead to defective cortical circuitry in the brains of schizophrenic patients.

Distorted distribution of nicotinamide-adenine dinucleotide phosphate-diaphorase neurons in temporal lobe of schizophrenics implies anomalous cortical development.

The distribution of neurons expressing the enzyme nicotinamide-adenine dinucleotide phosphate-diaphorase (NADPH-d) in the lateral and medial temporal lobes of schizophrenic and matched control brains was investigated in a systematic blind analysis. Schizophrenics had significantly lower numbers of NADPH-d neurons in the hippocampal formation and in the neocortex of the lateral temporal lobe but significantly greater numbers of NADPH-d neurons in the white matter of the lateral temporal lobe and a tendency toward greater numbers in parts of the parahippocampal white matter. The distorted distribution of NADPH-d neurons in the lateral temporal lobe, which may be explained by developmental disturbances, such as impaired neuronal migration or an alteration in the death cycle of transitory subcortical neurons, is similar to that found in the prefrontal cortex of schizophrenics. Alterations of cortical ontogenesis, as reflected in the distribution of NADPH-d neurons, appear to be widespread among neocortical association fields in schizophrenics and may provide a clue to the cause of the disease.

Gene expression for glutamic acid decarboxylase is reduced without loss of neurons in prefrontal cortex of schizophrenics.

BACKGROUND: Up-regulation of gamma-aminobutyric acidA (GABAA) receptors and decreased GABA uptake in the cerebral cortex of schizophrenics suggest altered GABAergic transmission, which could be caused by primary disturbance of GABA synapses or by decreased production of the transmitter. Decreased production could be due to a shutdown in GABA production or to loss of GABA neurons caused by cell death or their failure to migrate to the cortex during brain development. METHODS: To discriminate between these possibilities, we quantified levels of messenger RNA (mRNA) for the 67-kd isoform of glutamic acid decarboxylase (GAD), the key enzyme in GABA synthesis, and the number and laminar distribution of GAD mRNA--expressing neurons in the dorsolateral prefrontal cortex (DLPFC) of schizophrenics and matched controls, using in situ hybridization-histochemistry, densitometry, and cell-counting methods. These data were compared with the total number of neurons, the number of small, round or ovoid neurons 8 to 15 microns in diameter, and overall frontal lobe volume. As a control, mRNA levels for type II calcium-calmodulin-dependent protein kinase (CamIIK) were quantified. RESULTS: Schizophrenics showed a pronounced decrease in GAD mRNA levels in neurons of layer I (40%) and layer II (48%) and an overall 30% decrease in layers III to VI. There were also strong overall reductions in GAD mRNA levels. The CamIIK mRNA levels showed no significant differences between samples. No differences were found in the total number of neurons nor in small, round or ovoid neurons, which should include a majority of the GABA cells. Prefrontal gray and white matter volume did not differ significantly between controls and schizophrenics. CONCLUSIONS: The prefrontal cortex of schizophrenics shows reduced expression for GAD in the absence of significant cell loss. This may be brought about by an activity-dependent down-regulation associated with the functional hypoactivity of the DLPFC. The lack of significant alterations in cell numbers in the DLPFC and frontal lobe volume in schizophrenics also implies that overall cortical neuronal migration had not been compromised in development. Previous reports of altered neuronal distribution in the subcortical white matter of schizophrenic brains in comparison with that of controls may indicate disturbances of migration or programmed cell death in the cortical subplate, leading to altered connection formation in the overlying cortex of schizophrenics and activity-dependent down-regulation of neurotransmitter-related gene expression.

Altered distribution of nicotinamide-adenine dinucleotide phosphate-diaphorase cells in frontal lobe of schizophrenics implies disturbances of cortical development.

Epidemiological and anatomical studies support the theory that disturbances of brain development may play a contributory role in the etiology of schizophrenia. Anatomical findings suggest that the normal pattern of neuronal migration during development of the cerebral cortex may be affected in the brains of schizophrenics, with the implication that cortical connectivity and associative function will be disrupted. In the present investigation in matched schizophrenic and control brains, we examined a particular population of neurons found in the prefrontal cortex and underlying white matter and characterized by histochemical staining for the enzyme nicotinamide-adenine dinucleotide phosphate-diaphorase. In normal brains, these neurons are found in highest numbers in the white matter immediately deep to layer VI of the cortex where they remain from the subplate, an early formed, but transitory structure that plays a key role in cortical development and connection formation. The dorsolateral prefrontal area of schizophrenics showed a significant decline in nicotinamide-adenine dinucleotide phosphate-diaphorase neurons in the superficial white matter and in the overlying cortex but a significant increase in these neurons in white matter deeper than 3 mm from the cortex. These findings are consistent with a disturbance of the subplate during development in which the normal pattern of programmed cell death is compromised and accompanied by a defect in the normal orderly migration of neurons toward the cortical plate. These are likely to have serious consequences for the establishment of a normal pattern of cortical connections leading to a potential breakdown of frontal lobe function in schizophrenics.

Simultaneous Demonstration of Serotonin-immunoreactive Terminals and GABAergic Neurons in the VPL Nucleus of the Cat Thalamus.

Pre-embedding immunoperoxidase (for serotonin) and postembedding immunogold (for gamma-aminobutyric acid; GABA) labelling were combined at light and electron microscopic levels to demonstrate the neuronal targets of serotonin (5-HT) afferents in the ventral posterior lateral nucleus (VPL) of the cat thalamus. 5-HT-immunoreactive fibres and terminal varicosities were found in close proximity to GABA-immunoreactive interneurons and non-GABAergic relay neurons. Ultrastructurally, the vast majority of 5-HT terminals made close membrane contacts without overt membrane specializations with GABAergic axon terminals, GABAergic presynaptic dendrites and GABAergic somata. A very small number of 5-HT terminals formed typical asymmetrical synapses with GABAergic presynaptic dendrites and with dendritic shafts of relay cells. Some 5-HT terminals participated with the presynaptic dendrites in triadic synaptic arrangements. These findings suggest a dual innervation pattern by 5-HT afferents in VPL and the release of 5-HT in large part at sites not associated with morphologically detectable synapses.

High-Resolution Light and Electron Microscopic Immunocytochemistry of Colocalized GABA and Calbindin D-28k in Somata and Double Bouquet Cell Axons of Monkey Somatosensory Cortex.

A simple method for high-resolution immunocytochemical colocalization of different antigens in semithin sections 1 - 3 microm thick was used to study the colocalization of the calcium binding protein calbindin D-28k (calbindin) with gamma-aminobutyric acid (GABA) in double bouquet cells of monkey (Macaca fuscata) somatosensory cortex. Double bouquet cells were first visualized in vibratome sections by pre-embedding immunocytochemical staining for calbindin. Sections containing calbindin-immunoreactive somata and double bouquet cell axons were then osmicated, embedded in Araldite, resectioned at 1 - 3 microm and stained for GABA by postembedding immunocytochemistry after elution of the bound anti-calbindin antibodies. Other semithin sections adjacent to those eluted and still containing calbindin immunoreactive somata and processes were resectioned at 60 - 70 nm for electron microscopy and stained immunocytochemically for GABA by the postembedding immunogold procedure. Calbindin-positive cells are most numerous in layer II and upper layer III, where they outnumber those in all other layers combined. In layers II and upper III, approximately 30% of the stained cells are pyramidal and do not colocalize GABA. Only approximately two-thirds of the calbindin-stained nonpyramidal cells in these layers colocalize GABA, but among these virtually all the calbindin-positive double bouquet cells and their axons are GABA-immunoreactive. In deeper layers all calbindin-positive cells are nonpyramidal and all colocalize GABA. At the electron microscopic level, however, significant numbers of calbindin-positive axon terminals making symmetrical synapses are not GABA-immunoreactive. These results suggest the calbindin cells of monkey somatosensory cortex are a heterogeneous population that includes GABAergic and non-GABAergic cell types.

Differential Calcium Binding Protein Immunoreactivity Distinguishes Classes of Relay Neurons in Monkey Thalamic Nuclei.

The distributions of neurons displaying immunoreactivity for two calcium binding proteins, parvalbumin and 28Kd calbindin, were studied in the thalamus of M. fascicularis. Colocalization experiments were carried out to determine the extent to which parvalbumin- and calbindin-like immunoreactivity was found in the same cells and the extent to which either was localized in GABAergic interneurons. Anterograde and retrograde tracing experiments involving the fluorescent tracer, fast blue, were also used to determine that cells expressing the calcium binding proteins projected upon the cerebral cortex. In the dorsal thalamus, nuclei are distinguished by different patterns of parvalbumin-like and calbindin-like immunoreactivity. In certain nuclei, for example the lateral dorsal and anterior pulvinar, neurons express immunoreactivity for only one of the calcium binding proteins. In others, neurons in different layers, for example the dorsal lateral geniculate nucleus, or in different compartments, for example the intralaminar nuclei, express immunoreactivity for either parvalbumin or calbindin; in other nuclei, for example the ventral group, neurons are mixed and immunoreactivity for parvalbumin and calbindin is commonly colocalized. In the ventral thalamus and epithalamus, similar patterns are observed. Colocalization of parvalbumin- and GABA-immunoreactivity is found in all cells of the reticular nucleus but only in certain cells in selected nuclei of the dorsal thalamus, namely the dorsal lateral geniculate and magnocellular medial geniculate. No calbindin-positive cells are also GABA-positive. Most parvalbumin and/or calbindin positive cells in the dorsal thalamus project to the cerebral cortex, as indicated by the retrograde tracing studies, and many parvalbumin positive fibres entering the cerebral cortex could also be shown to contain fast blue anterogradely transported from a thalamic injection. Most of the major sensory and motor pathways entering the dorsal thalamus express parvalbumin immunoreactivity. The optic tract also expresses calbindin immunoreactivity but most other calbindin positive fibres entering the thalamus ascend in the midbrain tegmentum. The differential distributions of parvalbumin and calbindin implied by these results suggest that thalamic cells belonging to different functional systems and projecting differentially upon the cerebral cortex can be distinguished by differential expression of these or closely related calcium binding proteins. This may yield clues to their differential responsivity to afferent driving.