Biomedical subjects

C M Leonard

Publications and source records attributed to C M Leonard.

At least 19 recordsLinked to original sources

PubMed1992

Altered precision grasping in stumptail macaques after fasciculus cuneatus lesions.

Patterns of precision grasp are described in stumptail macaques (Macaca arctoides) before and after lesions of the fasciculus cuneatus (FC). Three monkeys were videotaped while reaching for and grasping small food items. From these videotapes, records were made of the style and outcome of each grasp. Kinematic measurements were also made to describe grip formation and terminal grasp. During grip formation, grip aperture was measured as the distance between the tips of the index finger and the thumb. For terminal grasp, the joint angles of the index finger were measured. The majority of grasps by normal monkeys were of the precision type, in which the item was carried between the tips of the index finger and thumb. Each normal monkey approached objects with a highly consistent grip formation; that is, the fingertips formed a small grip aperture during the approach, and the aperture varied little on repeated grasps. To grasp an item, the forefinger moved in a multiarticular pattern, in which the proximal joint flexed and the distal joint extended. As a result of this combination of movements, the forefinger pad was placed directly onto the object. Following FC transection, the monkeys were studied for 10 months, beginning 1 month after the lesion, to allow for recovery from the acute effects of surgery. The monkeys could grasp the food items, but they rarely opposed the fingertips in precision grasp. Grip formation was altered and was characterized either by excessive grip aperture or by little to no finger opening. All of the monkeys used the table surface to help grasp items. Combined multiarticular patterns of flexion and extension were never observed postoperatively; they were replaced by flexion at all joints of the fingers. These results suggest that the FCs are more important for precision grasping than for other, less refined grasp forms (e.g., power grasps; Napier, 1956). The FCs provide critical proprioceptive feedback to cerebral areas involved in the planning and/or the execution of these movements.

Afferent Pathways↗

PubMed1992

Alterations of natural hand movements after interruption of fasciculus cuneatus in the macaque.

As part of a series of investigations on the control of fine finger movements in the macaque, spontaneous use of the hand in grooming, scratching, and manipulation was observed before and after interruption of fasciculus cuneatus (FC). Videotaped observations were made of four stumptail macaques (Macaca arctoides) living outdoors in social groups. The monkeys were followed for 1 to 3 years postoperatively. For the first 2 weeks following surgery, all monkeys neglected the affected hand and did not use it for support, locomotion, climbing, scratching, foraging, or grooming. Recovery of gross arm and hand movements occurred over a 1- to 3-month period. All the monkeys eventually used the hand for support, climbing, and object manipulation, but fine control of the fingers did not recover. Also, there was an apparent hypotonia of the fingers, imparting a "floppy" appearance to the hand. The animals coped with the loss of fine control by decreasing the frequency of some behaviors, eliminating others, and developing alternative strategies. Exploratory movements that were utilized for investigating the anogenital area or foraging for small food items were eliminated by FC interruption. There were obvious deficits in grip formation and grasp of small food objects (see Glendinning et al., this issue), but effects on similar movements during grooming only became obvious after repeated inspection of videotaped records. Self-scratching and sweeps of the hand in grooming were preserved but altered in form and frequency. The component movements in these behaviors were relatively uncoordinated, and the fingers were splayed (abducted). Often the hand was formed in a rigid posture throughout the sweeping motion, and the fingers did not stroke the skin individually. Frame-by-frame analysis of videotapes revealed that the morphology of the precision grip during grooming, in movements termed "plucks," was permanently altered. Preoperatively, the monkeys kept the index finger and thumb closely apposed and routinely made contact on the distal surfaces of the digits, as has been described for precision grip in humans. Postoperatively, this relationship was altered. The index finger frequently missed the thumb tip and made contact on the proximal part of the phalanx, or missed the thumb altogether. Thus, the dorsal column input is important for proprioceptive guidance of movements that achieve "tactile foveation," when objects or surfaces are actively contacted by the receptive areas of keenest sensitivity (on the fingertips).

Afferent Pathways↗

PubMed1991

Comparative neuroanatomy of the sexually dimorphic hypothalamus in monogamous and polygamous voles.

In the present work we evaluated the degree of sexual dimorphism in two cell groups of the medial preoptic-anterior hypothalamus (MPOA-AH) in monogamous and polygamous voles. Quantitative determinations were made of volume, cell number, and cell density for the anteroventral-periventricular nucleus (AVPV) and the sexually dimorphic nucleus of the preoptic area (SDN-POA). Polygamous montane voles (Microtus montanus) had a greater degree of sexual dimorphism in both cell groups than did monogamous prairie voles (M. ochrogaster). Most notable was the complete absence of the AVPV in male montane voles; male montane voles also had a significantly larger SDN-POA volume than did females. The only sexual dimorphism in prairie voles was a greater cell density in the female AVPV. In addition, prairie voles had larger relative brain size than did montane voles. Comparative behavioral studies have revealed a correlation between the degree of sexual dimorphism in external morphology and mating system, i.e., polygamous species display greater levels of dimorphism than do monogamous species. The present results indicate that the effects of sexual selection can also be seen in those brain regions, like the hypothalamus, that underlie social and reproductive behavior. Moreover, these results support the hypothesis that neuroanatomic dimorphisms in the MPOA-AH may be related to sex differences in behavior.

Animals↗

PubMed1991

Role of transforming growth factor-beta in chondrogenic pattern formation in the embryonic limb: stimulation of mesenchymal condensation and fibronectin gene expression by exogenenous TGF-beta and evidence for endogenous TGF-beta-like activity.

The possible role of TGF-beta-like molecules in skeletal pattern formation in the embryonic vertebrate limb was studied by analyzing the mechanism of enhancement of chondrogenesis in chick wing bud mesenchyme in vitro and testing for the presence and distribution of endogenous TGF-beta-like activity in this tissue. Transient exposure (3-6 hr) to TGF-beta 1 (1-2 ng/ml) on the day after plating resulted in a 1.5- to 2-fold enhancement of accumulation of Alcian blue (pH 1.0)-stainable extracellular matrix 5 days later. The enhancement of differentiation was preceded by an acceleration and an increase in the extent of precartilage condensation formation, visualized by Hoffman Modulation Contrast microscopy a day after TGF-beta treatment. In contrast, neither condensation nor subsequent chondrogenesis was stimulated by transient treatment with TGF-beta 1 on the day of plating. The effectiveness of a TGF-beta treatment regimen in enhancing chondrogenesis was correlated with its effectiveness in stimulating condensation formation. Exposures to the factor for 3-6 hr on the day after plating, which most consistently stimulated both condensation formation and chondrogenesis, also corresponded to a peak in the enhancement of the steady-state level of fibronectin mRNA (fourfold to eightfold over control levels) measured at the end of the treatment period. The elevation in fibronectin mRNA levels brought about by this treatment persisted throughout the period of condensation. Endogenous TGF-beta-like activity was detected in limb mesenchyme: extracts of freshly isolated and cultured limb tissues contained 6-25 pg TGF-beta-like activity per 1 x 10(6) cells by the Mv1Lu cell proliferation inhibition assay, and indirect immunofluorescence using a polyclonal antibody directed against a TGF-beta-related peptide indicated a patchy distribution of endogenous TGF-beta-like reactivity within a day after culture. These findings are discussed in relation to the "fibronectin prepattern" hypothesis for limb pattern formation.

Animals↗

PubMed1989

Abnormal ambient glucose levels inhibit proteoglycan core protein gene expression and reduce proteoglycan accumulation during chondrogenesis: possible mechanism for teratogenic effects of maternal diabetes.

Using a tissue culture system based on a nearly pure population of avian precartilage mesenchymal cells, we have found that ambient glucose levels as little as 50% lower, or 100% higher, than normally present in embryonic sera are deleterious to cartilage development, as measured by the accumulation of highly sulfated proteoglycan and the corresponding cartilage-specific chondroitin sulfate core protein mRNA. Abnormal glucose concentrations in the ranges studied did not selectively influence cell replication, and the effects on chondrogenesis were not due to differences in overall protein synthesis or glucose utilization in the treatment groups. Core protein gene expression was more severely affected than accumulation of extracellular product, suggesting the existence of posttranscriptional compensatory mechanisms. The sensitivity to ambient glucose levels of both expression of the cartilage-specific chondroitin sulfate core protein gene and the accumulation of the corresponding extracellular matrix macromolecules during chondrogenesis suggest a molecular mechanism for the well-known adverse effect of maternal diabetes on embryonic skeletogenesis. The results further suggest that hypoglycemia resulting from stringent control of diabetes may also be deleterious to skeletal development.

Aggrecans↗

PubMed1988

Metallothionein mRNA expression in mice homozygous for chromosomal deletions around the albino locus.

Deletions in chromosome 7 of the mouse affect the expression of the metallothionein gene Mt-1, which maps on chromosome 8, and steady-state levels of Mt-1 mRNA are reduced to 15-40% of normal in livers of newborn mice homozygous for either the c3H or c14CoS deletion. Glucocorticoids fail to induce hepatic Mt-1 mRNA levels in deletion homozygotes in contrast to normal littermates. However, zinc chloride is effective in inducing Mt-1 mRNA levels in livers of deletion homozygotes as well as of their normal littermates. Other tissues (e.g., kidney and intestine) of deletion homozygotes express basal levels of Mt-1 mRNA higher than those of normal littermates. In the intestine these are furthermore inducible by both hormonal and metal agents. Thus, loss of inducibility of the Mt-1 gene in deletion homozygotes concerns glucocorticoids only and is furthermore restricted to specific cell types (i.e., hepatocytes). The trans-acting factor(s) normally encoded in the deleted region of chromosome 7 appears to be instrumental in conferring on the metallothionein gene in hepatocytes the essential competence to respond to hormonal inducing signals.

Albinism↗

PubMed1988

Developmental regulation of constitutive and inducible expression of hepatocyte-specific genes in the mouse.

Deletions in chromosome 7 of the mouse have been shown to cause failure of expression of certain liver-specific enzymes in newborn deletion homozygotes. Among these enzymes are L-tyrosine:2-oxoglutarate aminotransferase (EC 2.6.1.5) and phosphoenolpyruvate carboxykinase (GTP) [GTP:oxaloacetate carboxy-lase (transphosphorylating); EC 4.1.1.32]. The studies reported here show that in fetal stages constitutive expression of the relevant genes on the level of steady-state mRNA is identical in the livers of homozygous deletion mutants and normal littermates. Furthermore, prenatally these enzymes are expressed also in cell types other than hepatocytes. Thus, the putative trans-acting regulatory factors encoded in the deleted region of chromosome 7 of the mouse appear to be concerned specifically with the regulation of cell type-specific inducible expression of various hepatocyte-specific genes, whereas constitutive expression of the same genes is not affected.

Animals↗

PubMed1987

Terminal nerve damage impairs the mating behavior of the male hamster.

We examined the effects of bilateral terminal nerve (TN) transections (TNx) on the sexual behavior of male hamsters. These lesions produced a decrease in mating frequency and/or an increase in the number of intromissions required to reach ejaculation. Damage to the olfactory bulbs or rostral forebrain did not account for these effects. No amelioration of the behavioral impairments occurred over the mating sessions. Basal testosterone levels in the blood of male hamsters were not altered by TN damage. Hamsters with TNx retained their ability to detect odors, but demonstrated reduced attraction to vaginal odors as compared with unoperated animals. The reduced attraction to vaginal odors was most pronounced in sporadically mating TNx animals. These data suggest that the TN may facilitate odor-induced sexual excitation in the male hamster.

Animals↗

PubMed1987

Nuclear events during early chondrogenesis: phosphorylation of the precartilage 35.5-kDa domain-specific chromatin protein and its regulation by cyclic AMP.

During chondrogenesis in vivo and in vitro, a family of nonhistone proteins (Mr 35,500), designated PCP 35.5, is lost from the nuclei of precartilage mesenchyme cells. A basic subcomponent of this family, designated PCP 35.5b, is phosphorylated during the first few hours of chondrogenesis in vitro by a phosphorylating system whose activity is enhanced 12- to 15-fold by exposure of differentiating precartilage cells to dibutyryl cyclic AMP. This phosphorylating system is present in isolated precartilage cell nuclei, where it retains its dependence on cyclic AMP and its specificity for PCP 35.5b. Assays for nuclear cyclic AMP inhibitable protein phosphatase activity capable of dephosphorylating PCP 35.5b were negative, indicating that the system responsible for phosphorylating this protein is a cyclic AMP-dependent protein kinase. Chromatin fractionation studies indicate that PCP 35.5b is localized at sites previously shown to be closely associated with DNase I-sensitive domains of precartilage cell chromatin. These studies define PCP 35.5b as a strategically located component of precartilage cell chromatin which is the major or sole chromatin target of cyclic AMP-dependent phosphorylation during chondrogenesis. This chromatin modification occurs prior to overt cartilage differentiation and may therefore play a regulatory role in the acquisition of the cartilage cell phenotype.

Animals↗

PubMed1987

Functional subdivisions of the temporal lobe neocortex.

In order to gather evidence on functional subdivisions of the temporal lobe neocortex of the primate, the activity of more than 2600 single neurons was recorded in 10 myelo- and cytoarchitecturally defined subdivisions of the cortex in the superior temporal sulcus (STS) and inferior temporal gyrus of the anterior part of the temporal lobe of 5 hemispheres of 3 macaque monkeys. First, convergence of different modalities into each area was investigated. Areas TS and TAa, in the upper part of this region, were found to receive visual as well as auditory inputs. Areas TPO, PGa, and IPa, in the depths of the STS, received visual, auditory, and somatosensory inputs. Areas TEa, TEm, TE3, TE2, and TE1, which extend from the ventral bank of the STS through the inferior temporal gyrus, were primarily unimodal visual areas. Second, of the cells with visual responses, it was found that some neurons in areas TS-IPa could be activated only by moving visual stimuli, whereas the great majority of neurons in areas TEa-TE1 could be activated by stationary visual stimuli. Third, it was found that there were few sharply discriminating visual neurons in areas TS and TAa; of the sharply discriminating visual neurons in other areas, however, neurons that responded primarily to faces were found predominantly in areas TPO, TEa, and TEm (in which they represented 20% of the neurons with visual responses); neurons that were tuned to relatively simple visual stimuli such as sine-wave gratings, color, or simple shapes were relatively common in areas TEa, TEm, and TE3; and neurons that responded only to complex visual stimuli were common in areas IPa, TEa, TEm, and TE3. These findings show inter alia that areas TPO, PGa, and IPa are multimodal, that the inferior temporal gyrus areas are primarily unimodal, that there are areas in the cortex in the anterior and dorsal part of the STS that are specialized for the analysis of moving visual stimuli, that neurons responsive primarily to faces are found predominantly in areas TPO, TEa, and TEm, and that architectural subdivisions of the temporal lobe cortex are related to neuronal response properties.

Action Potentials↗

PubMed1986

Developmental changes in the astrocytic response to lateral olfactory tract section.

When the lateral olfactory tract (LOT) of the golden hamster, Mesocricetus auratus, is transected in the first week of postnatal life, axons can grow back past the lesion and achieve functional reinnervation of caudal projection regions. In contrast, when the tract is sectioned after postnatal day 7 (P7), axons do not reinnervate regions caudal to the cut. The experiments reported here investigated whether regenerative failure after tract section in pups older than P7 is accompanied by developmental changes in the astrocytic response. LOT transections were performed at P3 and P9 and the glial reaction was observed at survival times ranging from 12 hr to 2 weeks. Immunocytochemistry with glial fibrillary acidic protein (GFAP) was employed for histological visualization of astrocytic reactivity. Staining for GFAP immunoreactivity showed an appreciable glial reaction after tract section at both P3 and P9, but the extent of astrocytic hypertrophy and proliferation of glial processes was considerably greater and more extensive after tract section at P9. Radial glial cells were observed 2 weeks after LOT transection at P3 but were absent after lesions made at P9. The results from this study suggest that the developmental loss of regenerative capacity after LOT transection may be related to maturational changes in the glial response. In particular, the presence of radial glial elements after P3 lesions could serve to establish a more favorable microenvironment for axonal elongation.

Animals↗

PubMed1986

The terminal nerve projects centrally in the hamster.

The projections of the peripheral and intracerebral portions of the hamster terminal nerve were examined with lesion and immunocytochemical techniques. After transection, proximal processes of the terminal nerve accumulate luteinizing hormone-releasing hormone-immunoreactive material, while the distal processes disintegrate and are no longer stained. It thus becomes possible to determine the direction of conduction of terminal nerve axons. The results of transection at the level of the cribriform plate, along the olfactory bulb, and in the ventral forebrain were all consistent in indicating a centripetal direction of conduction. Immunoreactive material collected distal to the lesion at each of these levels. All peripheral lesions eliminated processes coursing into and through the terminal ganglion at the base of the ventral forebrain. These lesions left intact, however, the terminal ganglion projections to the accessory olfactory bulb and ventral forebrain. These results indicate a centripetal projection from terminal neurons in the nasal cavity, along the olfactory bulbs and within the terminal ganglion to successively more caudal levels. This suggests that neural messages are conveyed from nasal cavity to the brain through this route. Because immunoreactive fibers were found within the sensory epithelium of the vomeronasal organ a sensory and/or sensory modulatory action is suggested.

Afferent Pathways↗

PubMed1986

Acetylcholinesterase and luteinizing hormone-releasing hormone distinguish separate populations of terminal nerve neurons.

The terminal nerve is composed of a morphologically heterogeneous population of unipolar, bipolar and multipolar neurons located in the nasal and intracranial cavities of vertebrates. The question has arisen as to whether these neurons are neurochemically heterogeneous and therefore possibly functionally different as well. Among the substances localized in the terminal nerve are acetylcholinesterase and luteinizing hormone-releasing hormone-like immunoreactive material. We have developed a double-label procedure, combining immunocytochemistry and enzyme histochemistry to determine whether these two substances are localized within different populations of terminal nerve neurons. Compatibility of the two procedures was accomplished by modifications of the fixative and primary antibody solutions. In the immunocytochemical step, the avidin-biotin-peroxidase complex coupled to a new chromogen, Chromo-red, produced a bright red reaction product in neurons containing luteinizing hormone-releasing hormone-like material. This reaction product was easily differentiated from the black silver-intensified acetylcholinesterase label. In both neonatal and adult preparations, a large population of terminal neurons contained the acetylcholinesterase label only, whereas a smaller population contained both acetylcholinesterase and luteinizing hormone-releasing hormone-like material. The acetylcholinesterase-containing population of neurons was concentrated peripherally and included multipolar neurons. In contrast neurons with the two substances co-localized were unipolar or bipolar and were concentrated centrally. The simultaneous visualization of acetylcholinesterase and luteinizing hormone-releasing hormone-like material in the same tissue section enable the differentiation of two separate neurochemically defined populations of terminal neurons. The distribution of these two neuronal types was the same in neonatal and adult animals. These data provide support for a functional diversity of terminal neurons.

Acetylcholinesterase↗

PubMed1985

Selectivity between faces in the responses of a population of neurons in the cortex in the superior temporal sulcus of the monkey.

There is a population of neurons in the cortex in the middle and anterior part of the superior temporal sulcus (STS) of the monkey with responses which are selective for faces. If, consistent with the effects of damage to the temporal lobe, these neurons are involved in face recognition or in making appropriate social responses to different individuals, then it might be expected that at least some of these neurons might respond differently to different faces. To investigate whether at least some of these neurons do respond differently to different faces, their responses were measured to a standard set of faces, presented in random sequence using a video framestore. It was found that a considerable proportion of the neurons with face-selective responses tested (34/44 or 77%) responded differently to different faces, as shown by analyses of variance. An index of the discriminability of the most and least effective face stimulus (d') ranged between 0.2 and 5.0 for the different neurons. Although these neurons often responded differently to different faces, they did not usually respond to only one of the faces in the set, so that information that a particular face had been shown was present across an ensemble of neurons, rather than in the responses of an individual neuron. These findings indicate that the responses of these neurons would be useful in providing information on which different behavioral responses made to different faces could be based. These neurons could thus be filters, the output of which could be used for recognition of different individuals and in emotional responses made to different individuals.

Animals↗

PubMed1985

Role of low and high spatial frequencies in the face-selective responses of neurons in the cortex in the superior temporal sulcus in the monkey.

There are neurons in the cortex in the anterior part of the superior temporal sulcus of the macaque monkey with visual responses selective for faces. One aim of the present study was to analyze further the information which leads them to respond, by measuring their responses to parametrically filtered stimuli. The responses of 32 such single neurons were measured to faces which were digitized, lowpass filtered at spatial frequencies of 2, 4, 8,...128 cycles/face, highpass filtered at frequencies of 4, 8,...64 cycles/face, and presented in random sequence using a video framestore. It was found that many of the neurons could respond to blurred images of faces, with a mean frequency at half-maximum amplitude of the neuronal response to the series of lowpass filtered images of faces of 3.3 cycles/face. Almost all the neurons had lowpass cutoff frequencies defined in this way below 8 cycles/face. Many of the neurons could also respond to images of faces in which the only information remaining was a limited amount of high spatial frequency edge information. The mean frequency at half-maximum amplitude of the neuronal response to the series of highpass filtered images of faces was 29.7 cycles/face. Almost all the neurons had highpass cutoff frequencies above 8 cycles/face. Thus, many of the neurons could respond to a lowpass and a highpass filtered image of a face even when these had no spatial frequencies in common. The mean separation between the lowpass and highpass cutoff frequencies was 3.2 octaves. For comparison, face recognition in man can be performed with images which contain only information up to 8 cycles/face, or with highpass filtered images which contain only information down to 8 cycles/face. The response of the neurons was not always a smooth function of frequency, but could decrease as higher frequencies were included in the lowpass filtered images of faces, or as low frequencies were included in the highpass filtered images of faces. This indicates that information in certain frequency bands was able to inhibit these neurons. This was particularly likely to occur for the non-optimal face stimulus for a given neuron, indicating that the selectivity of these neurons to different faces was a combination of the excitation produced by some information in faces and inhibition produced by other.

Action Potentials↗

PubMed1985

Neurons in the amygdala of the monkey with responses selective for faces.

To investigate the functions of the amygdala in visual information processing and in emotional and social responses, recordings were made from single neurons in the amygdala of the monkey. A population of neurons (40 of more than 1000 recorded in 4 monkeys) was investigated which responded primarily to faces. These neurons typically (1) responded to some human or monkey faces, which were presented to the monkey through a large aperture shutter so that response latencies could be measured, or were simply shown to the monkey, (2) responded to 2-dimensional representations of these faces, as well as to real 3-dimensional faces, (3) had no responses or only small (less than half maximum) responses to gratings, simple geometrical, other complex 3-D stimuli, or to arousing and aversive stimuli, (4) had response latencies of 110-200 ms, (5) were located in the basal accessory nucleus of the amygdala, (6) responded differently to different faces, as shown by measures of d', and could thus over a population of such neurons code information useful for making different responses to different individuals, (7) could in some cases (9/11 tested) respond to parts of faces, and (8) in a few cases (4/19 tested) responded more to a face which produced an emotional response. A comparison made in three monkeys of the responses of these neurons with the responses of 77 neurons with face-selective responses recorded in the cortex of the superior temporal sulcus (STS) showed that the amygdaloid neurons had longer response latencies (110-200 compared to 90-140 ms), and were in some respects more selective in their responses to different faces. It is suggested that the deficits in social and emotional behavior produced by amygdala lesions could be due in part to damage to a neuronal system specialized in utilizing information from faces so that appropriate social and emotional responses can be made to different individuals.

Amygdala↗

PubMed1985

Esophageal speech: double-contrast evaluation of the pharyngo-esophageal segment.

Alaryngeal voice is usually accompanied by esophageal speech; however, about 40% of laryngectomy patients are unable to achieve adequate esophageal speech and must rely on mechanical devices for communication. A technique was developed for performing double-contrast studies of the hypopharynx, cervical esophagus, and pharyngo-esophageal segment using thick barium and the air normally injected for speech. Simultaneous audio and video recordings obtained during esophageal speech allowed correlation of the quality of speech with the motion of the pharyngo-esophageal segment. In 35 patients with various degrees of fluency in esophageal speech, normal and abnormal function of the pharyngo-esophageal segment was documented. Inadequate esophageal speech can be related to abnormal motion of the pharyngo-esophageal segment.

Contrast Media↗

PubMed1983

Early recovery of function after olfactory tract section correlated with reinnervation of olfactory tubercle.

Behavioral recovery and cortical reinnervation after early olfactory tract section were assessed in the infant golden hamster (Mesocricetus auratus). Hamster pups show strong thermotaxis at birth which declines abruptly after postnatal day (P) 8 in normal pups. Unilateral olfactory bulbectomy on P5 causes persistent thermotaxis through the second postnatal week. In this study, the bulb's output pathway, the lateral olfactory tract, was unilaterally severed on P5 and pup thermotaxis was tested through P15. Complete tract section, like bulbectomy, prolonged thermal responding beyond P8. In contrast to bulbectomy, however, some tract-sectioned pups showed recovery before P15 while others continued to show persistent thermotaxis throughout testing. The olfactory bulb projection was examined 10 days after tract section in order to determine whether recovery and persistent thermotaxis were associated with different patterns of cortical innervation. Eleven pups with complete transections showed recovery during the second week. In 10 of these pups, olfactory bulb fibers had penetrated the damaged region after surgery to reinnervate the olfactory tubercle. Three of these pups also exhibited some reinnervation of piriform cortex. The lesions of pups showing persistent thermotaxis were more severe, extending bilaterally or into deep cortical layers, and olfactory fibers had failed to reinnervate caudal terminal fields. All pups with olfactory tract sections showed extensive sprouting rostral to the cut, regardless of their behavioral profile. In no case had postlesion growth innervated the entorhinal or amygdaloid areas. Inhibition of thermotaxis was associated with reinnervation of the olfactory tubercle rather than more rostral, lateral or caudal olfactory cortex. We conclude that regrowth of olfactory tract fibers caudal to early transection is rapid and has functional consequences for early behavioral development.

Animals↗