www.elsevier.com/locate/brainres

Brain Research 1006 (2004) 100–106

Research report

Increased endogenous noradrenaline and neuropeptide Y release from the

hypothalamus of streptozotocin diabetic rats

Margaret J. Morris*, Jillian M. Pavia

Neuroendocrine Laboratory, Department of Pharmacology, University of Melbourne, Melbourne, Victoria 3010, Australia

Accepted 2 February 2004

Abstract

Noradrenaline and neuropeptide Y (NPY) in the hypothalamus regulate a number of important endocrine and autonomic functions.

Alterations in brain neurotransmitter content have been described in type 1 diabetes but there is little understanding of whether these changes

affect neurotransmitter release. This study examined for the first time, region-specific co-release of NPY and noradrenaline from the

hypothalamus of male Sprague–Dawley rats treated intravenously with 48 mg/kg streptozotocin (STZ) or vehicle. Five weeks later, the

release of endogenous noradrenaline and NPY was monitored by in vitro superfusion of ventral and dorsal hypothalamus slices under basal

and potassium-stimulated conditions. STZ-diabetes induced significant increases in basal noradrenaline and NPY overflow from the ventral

hypothalamus (P < 0.05); only NPY overflow was increased in the dorsal hypothalamus (P< 0.05). Noradrenaline overflow increased

similarly to potassium depolarisation in vehicle and STZ-diabetic rats, whereas diabetic rats showed a significantly increased NPY overflow

response to potassium depolarisation compared to vehicle rats. These region-specific increases in endogenous noradrenaline and NPY

overflow from the hypothalamus in diabetes suggest increased neuronal activity at rest and enhanced responses under some conditions.

Increased hypothalamic NPY and noradrenaline overflow most likely contributes to diabetic hyperphagia.

D 2004 Elsevier B.V. All rights reserved.

Theme: Endocrine and autonomic regulation

Topic: Neuroendocrine regulation: other

Keywords: Appetite; Hypothalamus; Neurotransmitter overflow; Type 1 diabetes

1. Introduction

Neuropeptide Y (NPY) is found in high concentrations in

the hypothalamus, where it is co-released with noradrena-

line. Marked increases in NPY mRNA and peptide content

have been described in streptozotocin (STZ)-induced dia-

betes, and it is likely that increases in this potent orexigenic

peptide contribute to the hyperphagia of uncontrolled dia-

betes [1,13,20,29]. NPY containing neurons of the arcuate

nucleus that project to the paraventricular nucleus (PVN) are

important in the feeding actions of NPY. Hypothalamic

NPY synthesis is regulated by both leptin and insulin, and

we have shown inhibitory effects of leptin on NPY release

in vitro [19,28,31], indicating acute effects on transmitter

0006-8993/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.brainres.2004.02.002

* Corresponding author. Tel.: +61-3-8344-5745; fax: +61-3-8344-

0241.

E-mail address: mjmorris@unimelb.edu.au (M.J. Morris).

release are possible in addition to regulation of gene

expression. As well as increases in NPY content and gene

expression in diabetes, increased peptide release from the

hypothalamus has been observed [18,26,27].

Diabetes is associated with marked changes in central

monoamine content and transport in both rodents and

humans [17], however conflicting results have been

reported. Within the hypothalamus, increases in noradrena-

line were observed following STZ treatment in the mouse

[6] and rat [3,4], while other workers have described no

change [34] or a decrease [23] in hypothalamic noradrena-

line. Region-specific alterations in monoamine transporter

gene and tyrosine hydroxylase activity have also been

described in diabetic animals. One week after STZ treat-

ment, increased noradrenaline transporter and tyrosine hy-

droxylase expression were reported in the locus coeruleus

[7], while a subsequent study [25] documented decreased

noradrenaline transporter mRNA in locus coeruleus, A1 and

A2 cell groups 4 to 8 weeks after STZ injection. There have

M.J. Morris, J.M. Pavia / Brain Re

been relatively few studies of the effect(s) of diabetes on

noradrenaline release. One in vitro study demonstrated

elevated 3H noradrenaline release from the hypothalamus

[15], while in vivo microdialysis of the ventromedial

hypothalamus revealed reduced noradrenaline release in

STZ-diabetic rats [23,33].

While altered noradrenaline and NPY production have

been reported in STZ-induced diabetes and most likely

contribute to the neurochemical sequelae of this disorder,

there is little understanding of the consequent effect of these

alterations on neurotransmitter release. We have developed

methods to simultaneously monitor release of endogenous

noradrenaline and NPY from discrete brain regions [10]. In

this study, we investigated the effects of diabetes on the co-

release of endogenous noradrenaline and NPY from hypo-

thalamic slices under basal and potassium-stimulated con-

ditions. Given the critical role of the hypothalamus not only

in appetite regulation, but also in glucose homeostasis, we

divided the hypothalamus into two regions; a dorsal seg-

ment containing the PVN, site of termination of brainstem

projecting catecholamine/NPY cell groups, as well as arcuo-

PVN projecting NPY cells, and a ventral segment contain-

ing the arcuate nucleus and the ventromedial hypothalamus,

regions that have been implicated in glucose-sensing [22].

2. Materials and methods

2.1. Animal preparation

Twenty-four adult male Sprague–Dawley rats (211F 3 g

body weight) obtained from the Pharmacology and Physi-

ology Animal Facility at the University of Melbourne were

used in this study. Animals were housed at a constant

temperature of 20F 2 jC with a 12-h light/dark cycle and

were fed standard rat chow and water ad libitum. To induce

diabetes, animals received one injection of STZ (48 mg/kg

in citrate buffer, pH 4.5) into the tail vein. Control animals

received an injection of buffer alone. Five weeks after STZ

injection, rats were anaesthetised by intraperitoneal injection

of pentobarbitone sodium (60 mg/kg body weight). A blood

sample was taken by cardiac puncture then rats were killed

by decapitation. The brain was rapidly removed and the

whole hypothalamus was dissected on ice by making two

coronal cuts along the hypothalamic sulcis. The hypothal-

amus was removed by making vertical incisions along the

lateral edge of the hypothalamus. The hypothalamus was

then hemisected into a dorsal segment containing the PVN,

dorsomedial nucleus and most of the lateral hypothalamic

area, and a ventral segment containing the arcuate, supra-

optic, ventromedial nuclei and median eminence. Urine was

taken by cystocentesis and liver and testicular and retroper-

itoneal fat masses were weighed. Experiments were per-

formed at approximately 10:00–11:00 h each day and all

procedures were approved by the Animal Experimentation

Ethics Committee of the University of Melbourne.

2.2. In vitro superfusion procedure

Dorsal and ventral hypothalamic segments were weighed,

diced into prisms using a McIllwain Tissue Chopper

(Mickle Laboratory Engineering, Guildford, Surrey, UK)

and then transferred to superfusion chambers (300

Al volume) within 10 min of sacrifice. Tissues were

continuously superfused at 40 Al/min with modified

Krebs–Henseleit buffer (composition in mmol/l: NaCl

108.6, KCl 4.3, MgSO4.7H20 1.1, KH2PO4 1.1,

CaCl2.2H2O 2.5, NaHCO3 25.0, glucose 8.0, bacitracin

0.1) and bovine serum albumin 0.1%, pH 7.4 which was

saturated with 95% O2:5% CO2 at 37 jC. Tissues were

allowed to equilibrate for 80 min, then samples were

collected on ice every 20 min until the end of the exper-

iment. To examine the effect of a depolarising stimulus,

high potassium Krebs–Henseleit buffer was perfused

through the system for one collection; NaCl concentration

was reduced to maintain isotonicity. Electrolyte concentra-

tions were monitored using a selective ion electrode (Beck-

man Synchron CX-5 Clinical System, USA); 33 mmol/

l potassium was achieved during this collection.

2.3. Sample preparation

Each 20 min superfusate sample (800 Al) was centrifugedat 12,300� g for 1 min to remove any cellular debris. For

noradrenaline measurement, 90 Al of superfusate was acid-

ified (final concentration 0.1 mol/l HCl), filtered through a

0.2-Am nylon syringe filter and frozen at � 80 jC until

HPLC analysis (within 1 week). The remaining sample was

stored at � 80 jC and NPY concentrations determined by

radioimmunoassay within 2 months.

2.4. HPLC measurement of noradrenaline overflow

Noradrenaline concentrations in the hypothalamic super-

fusates were determined by reverse phase HPLC using a

Rheodyne model 7125 syringe-loading sample injector, 50

Al loop (Alltech Associates, Australia), a phase-II narrow

bore column (100� 3.2 mm i.d., 3 Am ODS, Bioanalytical

Systems, West Lafayette, IA, USA) and an LC-4C electro-

chemical detector (ECD; Bioanalytical Systems) containing

a dual glassy-carbon working electrode versus a silver/silver

chloride reference electrode. A PM-80 solvent delivery

system was used to recirculate the following mobile phase

at 0.6 ml/min: disodium ethylenediaminetetraacetic acid, 0.5

mmol/l; mono-chloroacetic acid, 0.1 mol/l; sodium hydrox-

ide, 0.06 mol/l; 1-octane-sulfonate sodium, 2.40 mmol/l;

acetonitrile 2.4%; pH 3.25. All chemicals were of analytical

quality. Noradrenaline standard (Sigma, St. Louis, MO,

USA) was diluted in 0.1 mol/l HCl to yield a concentration

of 20 pg per 20 Al injection and was injected at the start,

during and end of each day. Noradrenaline had a retention

time of 5.0 min and a detection limit of 2–3 pg. Superfusate

samples (20 Al) were injected directly into the HPLC.

search 1006 (2004) 100–106 101

Table 1

Metabolic effects 5 weeks post-STZ treatment (48 mg/kg i.v.)

STZ (n= 12) Vehicle (n= 12)

Body weight (g) 247.3F 9.5a 384.7F 6.7

24-h food intake (g/rat) 43.4F 1.4a 26.9F 0.4

24-h water intake (ml/rat) 199.8F 12.9a 32.5F 1.0

Retroperitoneal WAT (g) 0.05F 0.02a 7.36F 0.68

Testicular WAT (g) 0.70F 0.11a 5.41F 0.45

Urine glucose (mmol/l) 547.1F13.7a 0.8F 0.2

Plasma glucose (mmol/l) 41.7F 1.0a 12.7F 0.4

Plasma cholesterol (mmol/l) 2.51F 0.15a 1.41F 0.05

Plasma HDL (mmol/l) 1.82F 0.10a 1.21F 0.05

Plasma triglycerides (mmol/l) 6.23F 0.80a 1.33F 0.09

Plasma leptin (ng/ml) 0.23F 0.04a 8.04F 1.27

Data expressed as meanF S.E.M.a Significantly different to vehicle, P< 0.001.

M.J. Morris, J.M. Pavia / Brain Research 1006 (2004) 100–106102

Noradrenaline overflow was calculated by comparing sam-

ple peak height to that of a known standard injection (20 pg)

and expressed as pg noradrenaline per 20 min collection per

mg wet weight of tissue.

2.5. Radioimmunoassay measurement of NPY

NPY-like immunoreactivity (NPY-LI) in the superfusates

was measured using a specific radioimmunoassay devel-

oped in the laboratory [21]. Standard curves were con-

structed in modified Krebs–Henseleit buffer. Duplicate or

triplicate 215 Al samples of superfusate solution or NPY

standards (2–600 fmol/tube; Auspep, Melbourne, Vic.,

Australia) were incubated overnight at 4 jC with an NPY

antibody raised in the rabbit (final dilution 1:170,000) in a

total volume of 365 Al. Radiolabelled NPY (125I-NPY,

Amersham, Buckinghamshire, UK, 2000 Ci/mmol, 5000

cpm/tube) was added and the incubation continued over-

night. Bound and free radioactivity was separated by incu-

bation with sheep anti-rabbit second antibody (Silenus

Laboratories, Melbourne, Vic., Australia) followed by cen-

trifugation. Zero binding was routinely 50%, the detection

limit of the assay was 2 pg/tube and the intra- and inter-

assay coefficients of variation were 6% and 13%, respec-

tively. Superfusate NPY overflow in each collection was

calculated as pg NPY-LI per 20 min collection per mg wet

weight of tissue.

2.6. Data analysis

Results are expressed as meanF S.E.M. and were eval-

uated using Statview statistical software. Noradrenaline and

NPY-LI overflow data were analysed by one-factor repeated

measures ANOVA followed by least significance difference

(LSD) tests to verify overall time and treatment-related

effects. Basal transmitter overflow was calculated as the

average of the two resting collections prior to potassium

(collections 2 and 3) for each individual rat and analysed

using two-way ANOVA. Each animal’s individual fold

increase in transmitter release following potassium depolar-

isation was also calculated and analysed using two-way

ANOVA. All other parameters such as tissue weights and

plasma glucose and lipids were analysed by one-factor

ANOVA. Differences were considered statistically signifi-

cant at P < 0.05.

3. Results

As shown in Table 1, STZ-treated animals consumed

significantly more food and water than the vehicle-treated

animals and their body weight was significantly reduced. At

sacrifice, 5 weeks after STZ or vehicle treatment, urine and

plasma glucose, and plasma cholesterol, HDL and trigly-

cerides were all significantly elevated in the STZ-treated rats

while plasma leptin and fat mass were significantly lower in

the STZ group compared to control animals (Table 1;

P < 0.001).

3.1. Noradrenaline overflow

In the ventral hypothalamus, basal noradrenaline over-

flow in the STZ-treated rats averaged 64.4F 3.1 pg/20 min/

mg tissue which was significantly elevated compared to

vehicle-treated animals (54.1F1.2 pg/20 min/mg tissue;

P < 0.05; Fig. 1A). In the dorsal hypothalamus, there was

no difference in basal noradrenaline overflow between STZ-

and vehicle-treated rats (55.1F 4.9 and 53.5F 3.5 pg/20

min/mg tissue, respectively; P>0.05; Fig. 1B).

Depolarisation with a high potassium stimulus resulted in

increased noradrenaline overflow in both STZ and vehicle-

treated rats in both tissue regions (P < 0.05; Fig. 1). Nor-

adrenaline returned towards pre-KCl values in the following

collection. When the individual fold increase in potassium

stimulated noradrenaline overflow was analysed, the re-

sponse in vehicle-treated rats was greater in the ventral

hypothalamus compared to the dorsal hypothalamus

(P < 0.01; Table 2). This increased regional response was

also present in the STZ-treated rats but appeared to be

blunted and failed to reach significance (P= 0.06).

3.2. NPY overflow

Increases were observed in NPY-LI overflow in both

the ventral and dorsal hypothalamus of STZ-treated rats

compared to vehicle-treated rats (Fig. 2). In the ventral

hypothalamus, average basal NPY-LI overflow in the

STZ-treated rats was 0.88F 0.1 vs. 0.48F 0.1 pg/20

min/mg tissue in vehicle-treated animals (P < 0.01). In

the dorsal hypothalamus, average basal NPY-LI overflow

in the STZ-treated rats was increased compared to the

vehicle-treated animals (0.57F 0.1 vs. 0.35F 0.1 pg/20

min/mg tissue, respectively; P < 0.05). NPY-LI overflow

from the ventral hypothalamus was significantly increased

relative to the dorsal hypothalamus in both groups of

animals (Fig. 2).

Fig. 2. Effect of high potassium stimulus on NPY-LI overflow, expressed as

pg/20 min/mg tissue in perfusate collections from the ventral hypothalamus

(panel A) and dorsal hypothalamus (panel B) of STZ-treated (closed

squares, n= 11) and vehicle-treated (open squares, n= 10) rats. Tissues were

exposed to 33 mmol/l K+ for one 20-min collection as indicated by solid

bar. Results are expressed as meanF S.E.M. and data were analysed by

repeated measures ANOVA and LSD tests. *Significantly different to pre-

KCl (collection 3), P< 0.05. ySignificantly different to vehicle-treated rats,

P < 0.05.

Fig. 1. Effect of high potassium stimulus on noradrenaline overflow,

expressed as pg/20 min/mg tissue in perfusate collections from the ventral

hypothalamus (panel A) and dorsal hypothalamus (panel B) of STZ-treated

(closed squares, n= 9–11) and vehicle-treated (open squares, n= 9) rats.

Tissues were exposed to 33 mmol/l K+ for one 20-min collection as

indicated by solid bar. Results are expressed as meanF S.E.M. and data

were analysed by repeated measures ANOVA and LSD tests. *Significantly

different to pre-KCl (collection 3), P < 0.05. ySignificantly different to

vehicle-treated rats, P < 0.05.

M.J. Morris, J.M. Pavia / Brain Research 1006 (2004) 100–106 103

The time-course of the potassium-stimulated response in

NPY-LI overflow was more delayed than that seen with

noradrenaline, with the maximum response sometimes

occurring in the collection following high KCl perfusion

(collection 5) especially with the STZ-treated animals (Fig.

2). The 33 mmol/l potassium stimulus resulted in a 35–40%

increase in NPY-LI overflow in the vehicle-treated animals

in ventral and dorsal hypothalamus, respectively, with more

marked responses occurring in the STZ-treated rats (Fig. 2).

Table 2

Fold increase in neurotransmitter overflow following 33 mmol/l potassium

depolarisation (n= 9–11)

Noradrenaline NPY Noradrenaline/

NPY

Ventral

hypothalamus

STZ

Vehicle

1.80F 0.09

1.71F 0.08b2.08F 0.18a

1.49F 0.12

0.94F 0.12

1.18F 0.06b

Dorsal

hypothalamus

STZ

Vehicle

1.50F 0.12

1.29F 0.06

1.58F 0.14

1.45F 0.12

1.01F 0.10

0.92F 0.05

Data are the average of maximal response in each individual rat.a Significantly different to vehicle, P < 0.05.b Significantly different to dorsal hypothalamus, P< 0.05.

The individual maximum fold increase in potassium-stimu-

lated NPY-LI overflow from the ventral hypothalamus of

STZ-treated rats was significantly higher than vehicle-trea-

ted rats (2.08F 0.18 vs. 1.49F 0.12, respectively; P < 0.05;

Table 2).

Due to the delayed NPY response, the net amount of

NPY released during collections 4 and 5 was also calculated

(as pg/20 min/mg tissue released in collection 4 + 5 minus

twice the basal value). In the ventral hypothalamus, the net

increase in NPY overflow was 1.65F 0.33 and 0.53F 0.30

pg/mg tissue in diabetic and vehicle rats respectively

(P < 0.05), while in the dorsal hypothalamus, values of

0.42F 0.13 and 0.22F 0.06 pg/mg tissue were obtained.

This analysis confirms that diabetic animals could release

more NPY to this stimulus, particularly in the ventral

hypothalamus. Moreover, using this analysis, net potassium

stimulated release of both noradrenaline and NPY was 2–4

fold greater in the ventral compared to dorsal hypothalamus.

When the individual fold increases in noradrenaline and

NPY were compared, the ratio of the change in noradren-

aline and NPY was close to unity across treatment groups

M.J. Morris, J.M. Pavia / Brain Research 1006 (2004) 100–106104

and regions (Table 2). Thus, overall the relationship be-

tween the two transmitters appeared to be preserved in

diabetes.

4. Discussion

Data from the present study demonstrate that after STZ

treatment, overflow of NPY was elevated in both ventral

and dorsal hypothalamic regions, while noradrenaline over-

flow was increased in the ventral, but not the dorsal

hypothalamus. The increased NPY overflow in STZ treated

rats is in keeping with earlier observations of increased NPY

release in the hypothalamus of diabetic rats [18,27] and

work from our laboratory [8]. Induction of diabetes resulted

in the expected changes in body weight and fat mass, and in

this study plasma leptin was reduced by over 95% in STZ-

treated rats. This dramatic decrease in leptin would be

expected to increase hypothalamic NPY production and

release [19], and contribute to the hyperphagia that we

observed. Recent work has suggested that hypoleptinemia

rather than hypoinsulinemia is responsible for the hyper-

phagia of diabetes [14]. Other workers have reported that

regional hypothalamic increases in noradrenaline content

were reversed by either leptin or insulin replacement [3].

Interestingly, in this study, more modest changes in nor-

adrenaline overflow were observed in diabetes, in line with

our report that leptin appears to have no effect on in vitro

basal hypothalamic noradrenaline release [12].

NPYand noradrenaline can modulate each other’s release

[9,11,24], so it is of interest to compare the effects of

diabetes on both transmitters. Few studies have examined

region-specific alterations in transmitter release in diabetes,

and none have examined the co-release of NPY and nor-

adrenaline from the hypothalamus. As reported previously,

lower quantities of NPY were released relative to noradren-

aline [10]. In this study, we investigated dorsal and ventral

segments of the hypothalamus. The observation of increased

NPY and noradrenaline overflow from the ventral hypothal-

amus of diabetic rats suggests STZ-diabetes may lead to

increased neuronal activity in ascending projections to this

region, although these observations do not allow us to

distinguish which pathways may be involved. It is probable

that the two pools of transmitters arise from different

sources in both the dorsal and ventral segments. The

hypothalamus receives direct ascending projections from

the noradrenergic (A1, A2 and A6) and adrenergic (C1, C2

and C3) cell groups in the medulla [30]. NPY, as well as

being co-localised in some of these catecholaminergic

projections, may also arise from a number of intra-hypotha-

lamic NPY-containing projections such as from the arcuate

nucleus to the PVN [2]. The increased NPY release from the

dorsal hypothalamus of diabetic rats is in keeping with

previous in vitro and in vivo studies centred on the PVN

[8,27]. In line with our observation of increased noradren-

aline, increased hypothalamic 3H noradrenaline efflux was

observed in diabetic ovariectomised female rats under basal

conditions [15].

The differential effects of diabetes on basal noradrenaline

overflow in dorsal versus ventral regions may be related to

prolonged elevation of NPY release from arcuo-PVN pro-

jecting NPY neurons (which would be disinhibited by the

dramatically lowered leptin levels), leading to some inhibi-

tion of noradrenaline release. This may explain the normal

basal noradrenaline overflow we observed in the dorsal

hypothalamus region, while in the ventral region, activation

of ascending NPY/catecholaminergic neurons led to similar

increases in both transmitters.

Release of both NPYand noradrenaline can be evoked by

activating voltage-dependent calcium channels. In the pres-

ent study, increasing potassium levels gradually via the

superfusion system to 33 mmol/l resulted in an immediate

increase in superfusate noradrenaline concentration, which

then decreased when potassium fell in the subsequent

collection. When the maximal potassium-induced increase

in noradrenaline was calculated, control and diabetic ani-

mals responded in a similar fashion, with slightly greater

responses in the ventral hypothalamus relative to the dorsal

region (Table 2). Overall, the depolarisation-induced in-

crease in noradrenaline overflow was not affected by

diabetes.

The changes in NPY overflow after potassium-induced

depolarisation were noticeably delayed relative to noradren-

aline release, and appeared to be blunted in the control

animals relative to the diabetic rats. Following potassium

stimulation, NPY overflow was sometimes maximal in the

collection following the high KCl stimulus, as has previ-

ously been reported for NPY overflow from the periphery

[9]. This may be due to prolonged release of this transmit-

ter, or related to its relative stability and lack of neuronal

uptake. When the maximal fold increase, or the net NPY

release after potassium were compared, similar changes

were observed in the dorsal hypothalamus in both control

and diabetic rats, but in the ventral hypothalamus STZ-

diabetic rats mounted a greater response than control

animals (Table 2). Little is known regarding the effects of

diabetes on hypothalamic responses to KCl stimulation,

although one study in chronic (5 months) STZ-diabetic rats

reported no effect of diabetes on basal hypothalamic NPY

release, but an elevation in KCl-induced release [26]. Other

work using a similar treatment interval to our study showed

increased sensitivity of hippocampal slices to increases in

the extracellular potassium concentration in diabetic, rela-

tive to control rats [5]. This suggested a diabetes-dependent

increase in sensitivity of central neurons to changes in

[K+]o that may be relevant to increased seizure suscepti-

bility. Our work provides evidence that under some con-

ditions, hypothalamic NPY release may be more easily

provoked by depolarisation in diabetic relative to control

rats. The results of this study do not allow speculation

regarding the underlying reasons for this, but the observed

elevation in both basal and stimulated NPY overflow may

M.J. Morris, J.M. Pavia / Brain Research 1006 (2004) 100–106 105

suggest an increase in the releasable pool of this transmitter

in diabetes.

Clearly, changes in other central transmitters occur after

STZ treatment, including corticotropin-releasing factor,

POMC and agouti-related peptide [13,16,32] and we have

only examined changes in two important regulators. We

cannot exclude the possibility that changes in another

transmitter in response to STZ may be influencing the

release of both noradrenaline and NPY. It is also possible

that diabetes-induced changes in the metabolism of the

transmitters may contribute.

In summary, we have shown elevated basal overflow of

both noradrenaline and NPY from the ventral hypothalamus,

and of NPY from the dorsal hypothalamus in STZ diabetes.

These selective increases may arise from differential acti-

vation of ascending brainstem catecholaminergic and intra-

hypothalamic NPY-ergic pathways. Potassium-induced

depolarisation led to similar increases in noradrenaline and

NPY overflow. Greater increases in NPY release were

observed after KCl in diabetic relative to vehicle-treated

rats, particularly in the ventral hypothalamus. This suggests

transmitter-specific changes can occur, particularly under

stimulated conditions.

Acknowledgements

This study was supported by grants from the Juvenile

Diabetes Research Foundation and Diabetes Australia

Research Trust. We are thankful to Angela Gibson for

conducting glucose, cholesterol, HDL and triglyceride

measurements and to Prof. Bevyn Jarrott for his gift of

NPY antibody.

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